mikepukmel 6/16/2018 5:12 PM
LM7815 power supply question
Hi All!

I got some cheap regulated power supply boards: has 4 diodes LM7815, heat sink, and a couple of electrolytic capacitors.

I think I screwed up ordering the transformers.

The LM7815 data sheet specifies absolute max input 35v. I got a couple of Triad F229X 115V primary, 24v secondary. After rectification, about 24 * 1.414 = 33.94v almost right on the limit.

I hate to waste usable current, but should I put a dropping resistor to get the input to the LM7815 down 15% or so to give the LM7815 some breathing room?

Thanks
Mike
 
Jazz P Bass 6/16/2018 5:16 PM
Either way you have to 'dump' some 10 volts.

One or the other must do it.
The resistor or the device itself.
 
mikepukmel 6/16/2018 5:20 PM
Thanks Jazz. Wondering if I should exchange the transformers.
 
nickb 6/16/2018 5:36 PM
It's complicated. Hard to believe for so few components, I know

1) You mustn't have too many volts in i.e < 35V
2) You mustn't overheat it i.e voltage drop x current and is your heatsink big enough?
3) Oh.. but wait, you can't just lower the voltage as can't have too few either i.e >18V

It gets worse...
Under no load conditions expect about 10% more volts out of the secondary. Now add in say 5% for higher than usual line voltage.
Under load, the output will drop due to winding resistance. Naturally the drop will be more than you expect as the current flows in (very) big gulps to recharge the smoothing caps.
To add to it all, the voltage on the caps is not constant but a ripple that depends of the size of the cap and the current draw. You must allow for that too.
Finally allow for 5% line voltage drop.

All this is why we have simulation tools. Go and get Duncan's power supply designer and work it all out using that. Define your inputs i.e. min and max volts and output min & max volts and current.

You might want to consider sending the transformers back before it's too late. Dropping volts just wastes power.
 
mikepukmel 6/16/2018 5:58 PM
Thanks Nick. The calculation I should have done before (one of them anyway) but screwed up:

(35-17)/2 = about 26 -> 26/1.414 -> about 18.4ac. They sell a 20vac sec, similar price.

Thanks, I got a copy of Duncan's software, looking at it now...
 
Enzo 6/16/2018 6:03 PM
If that is a transformer rated for 24v, that will be at its rated current. Unloaded or lightly loaded, that 24v can rise too.
 
mikepukmel 6/16/2018 6:04 PM
Oh man, you flick that power switch on, and stuff really starts to happen before it settles down.
 
mikepukmel 6/16/2018 6:06 PM
Quote Originally Posted by Enzo View Post
If that is a transformer rated for 24v, that will be at its rated current. Unloaded or lightly loaded, that 24v can rise too.
Thanks Enzo. So, its important to have the post rectifier voltage right in the middle of the regulators min/max input range.
 
g1 6/16/2018 6:07 PM
Quote Originally Posted by nickb View Post
It gets worse...
And then it gets even worser!
In addition to the items nick mentioned, the data sheet says 115V primary. Do they mean it? How about at 120V, or 124V as I have?
 
mikepukmel 6/16/2018 8:16 PM
Quote Originally Posted by g1 View Post
And then it gets even worser!
In addition to the items nick mentioned, the data sheet says 115V primary. Do they mean it? How about at 120V, or 124V as I have?
Got me thinking, maybe I should give up this hobby and take up whittling. Ain't quite as fun, tho.
 
eschertron 6/16/2018 8:41 PM
At least I'm not the only one a-fussin' and a-frettin' over power trannys!
 
mikepukmel 6/18/2018 6:36 PM
Quote Originally Posted by g1 View Post
And then it gets even worser!
In addition to the items nick mentioned, the data sheet says 115V primary. Do they mean it? How about at 120V, or 124V as I have?
Guess I better break out the meter and measure that as well . . . Well, my 115vac is 122.4 to 122.6 at least at 8:36pm on Monday evening.

The secondary on these 24v transformers measures 27.4vac. Didn't hook up to rectifiers, but should be 38.8v or so. unloaded. Not the worstest, but definitely worser for the LM7815.

2 x 16vac sec transformers on the way. Also, bought some beefier heat sinks. Should I put that white heat sink grease on the connection?
 
nickb 6/19/2018 1:06 AM
Quote Originally Posted by mikepukmel View Post
Guess I better break out the meter and measure that as well . . . Well, my 115vac is 122.4 to 122.6 at least at 8:36pm on Monday evening.

The secondary on these 24v transformers measures 27.4vac. Didn't hook up to rectifiers, but should be 38.8v or so. unloaded. Not the worstest, but definitely worser for the LM7815.

2 x 16vac sec transformers on the way. Also, bought some beefier heat sinks. Should I put that white heat sink grease on the connection?
My gut tells be that might be too low in general. But we'll see. I can't answer the heatsink question w/o knowing a bunch of other things.
The first question is what is your required max load current?
Who is your preferred transformer vendor (so I can look up the specs)?
 
Mick Bailey 6/19/2018 5:53 AM
When I'm sizing up for small PSUs using 78XX regulators I get the closest VA rating (higher rather than lower) to my maximum load and the closest AC voltage to my output voltage. Assuming 10% regulation this usually works out fine for dropout voltage. So for a 15V regulator I'd go for a 16v transformer. Usually the rectified output is a little higher than calculated due to primaries being wound for 2x115v or 1x230v and the mains being higher (mine is 248v today).
 
nickb 6/20/2018 1:38 AM
The secondary current will be much higher (about 1.7x) than the output current plus the secondary voltage is higher than the output meaning the VA rating needs to be at least twice the output power (as a starting guess). For such a transformer the regulation is be around 25%.

Here are my estimates for a 16V 32VA transformer.

[ATTACH=CONFIG]49404[/ATTACH]

Plugging the numbers into a simulation to be more precise I get,
Vo min = 18.3V this is above the 17V 7815 requirement, OK
Vo max = 28.2V this is below the 35V 7815 requirement, OK
Pd = 7.9 Watts dissipated in 7815
=> Heatsink better than 7.8 C/W, so yes best use thermal compound.
Secondary current= 1.64A rms
Min VA rating - 1.64 x 21.5 = 35.3 VA ( very worst case of continuous max load and max input voltage).
 
jmaf 6/20/2018 3:22 AM
Why produce heat? Instead, add a switcher between the 24VAC output and the rectifier:

[ATTACH=CONFIG]49405[/ATTACH]

Adjust it to switch at around 20 VAC peak.
 
mikepukmel 6/20/2018 4:42 AM
Quote Originally Posted by nickb View Post
My gut tells be that might be too low in general. But we'll see. I can't answer the heatsink question w/o knowing a bunch of other things.
The first question is what is your required max load current?
Who is your preferred transformer vendor (so I can look up the specs)?
Thanks Nick. After some toil, I found these: https://www.mouser.com/ProductDetail/546-187E16 16v 56va, 3.5a, a little bigger than needed, I think, for a 1a PS. Allows for some voltage drop and still stay above 17v min input.
 
mikepukmel 6/20/2018 4:44 AM
Quote Originally Posted by Mick Bailey View Post
When I'm sizing up for small PSUs using 78XX regulators I get the closest VA rating (higher rather than lower) to my maximum load and the closest AC voltage to my output voltage. Assuming 10% regulation this usually works out fine for dropout voltage. So for a 15V regulator I'd go for a 16v transformer. Usually the rectified output is a little higher than calculated due to primaries being wound for 2x115v or 1x230v and the mains being higher (mine is 248v today).

Thanks Mick, that's what I did (more or less by accident or trial and error), 16v and a little higher VA than needed 56va. Mains are a little higher here but Im not quite sure what that means all the way at the input of the 7815, Id have to measure.
 
mikepukmel 6/20/2018 4:49 AM
Quote Originally Posted by nickb View Post
The secondary current will be much higher (about 1.7x) than the output current plus the secondary voltage is higher than the output meaning the VA rating needs to be at least twice the output power (as a starting guess). For such a transformer the regulation is be around 25%.

Here are my estimates for a 16V 32VA transformer.

[ATTACH=CONFIG]49404[/ATTACH]

Plugging the numbers into a simulation to be more precise I get,
Vo min = 18.3V this is above the 17V 7815 requirement, OK
Vo max = 28.2V this is below the 35V 7815 requirement, OK
Pd = 7.9 Watts dissipated in 7815
=> Heatsink better than 7.8 C/W, so yes best use thermal compound.
Secondary current= 1.64A rms
Min VA rating - 1.64 x 21.5 = 35.3 VA ( very worst case of continuous max load and max input voltage).
Cool, thanks for the calc's. As far as I can tell: the transformer should never go to full load, its a 3.5a rated, and the board should not ever draw more than about 1a. So, I don't think the supply will ever get to that point. The board manual only says "10 - 15V DC power supply, 500 mA min." I believe that is to program and run one chip, without having to drive any additional hardware, i.e. only a few LED's on board., outside the boards power supply.

I got the duncan software, but spending some effort to figure out how to use it.
 
mikepukmel 6/20/2018 4:50 AM
Quote Originally Posted by jmaf View Post
Why produce heat? Instead, add a switcher between the 24VAC output and the rectifier:

[ATTACH=CONFIG]49405[/ATTACH]

Adjust it to switch at around 20 VAC peak.
Thanks JMAF! Reading up . . .
 
mikepukmel 6/20/2018 4:53 AM
Quote Originally Posted by nickb View Post
My gut tells be that might be too low in general. But we'll see. I can't answer the heatsink question w/o knowing a bunch of other things.
The first question is what is your required max load current?
Who is your preferred transformer vendor (so I can look up the specs)?
Nick, sorry, missed your question on first read: The board manual says 10-15v DC min 500ma. I think it doesn't state a max since you could be programming a microcontroller chip to drives other stuff, so I think they assume the user knows something and will calculate that.
 
mikepukmel 6/20/2018 5:05 AM
A more general question about these small regulated power supplies: I searched and found a bunch of different but very similar circuits for LM7815 regulated power supplies. It looks like, or at least what I found, most have an electrolytic cap on either side of the regulator, one on the input side and one on the output side. Say 470uf on the input side, 100uf on the output side. A few had a much bigger cap on the input side, like 2200uf and none on the output side.

Do both of these caps serve the same purpose: if the current draw increases rapidly by the load, then the cap will make up the difference until either the LM7815 or the transformer + rectifiers, have time to compensate?

If we know the max output is, say 1a, it seems like we also need to know the rate at which the load could change current draw to know how big capacitors to use?
 
jmaf 6/20/2018 6:04 AM
Quote Originally Posted by mikepukmel View Post
A more general question about these small regulated power supplies: I searched and found a bunch of different but very similar circuits for LM7815 regulated power supplies. It looks like, or at least what I found, most have an electrolytic cap on either side of the regulator, one on the input side and one on the output side. Say 470uf on the input side, 100uf on the output side. A few had a much bigger cap on the input side, like 2200uf and none on the output side.

Do both of these caps serve the same purpose: if the current draw increases rapidly by the load, then the cap will make up the difference until either the LM7815 or the transformer + rectifiers, have time to compensate?

If we know the max output is, say 1a, it seems like we also need to know the rate at which the load could change current draw to know how big capacitors to use?
The regulators can oscillate in some circuits. These caps are mostly meant to clamp oscillation, in precision circuits you usually place the cap very near the regulator and very near the load, with short copper tracks from the cap to the regulator and to the load.

Your concern with the max current is not the caps, forget the capacitors, the regulator needs no capacitor to maintain constant voltage, ripple rejection is absurd as long as your source can keep a voltage above 15V RMS + a offset (see the datasheet).

The problem is power dissipation, this is a passive regulator, it turns excess power into heat.

The 7815 can source max 1A but not continuously, all the LM78xx's fry if you do 1A 100% duty cycle.

If you have too large a voltage offset like you do in your project you may be better off with the switching version of the LM regulators. You didn't say what your application is, so gotta observe that the switching ones are noisy and may require special shielding and extra filtering.
 
Mick Bailey 6/20/2018 7:12 AM
Quote Originally Posted by jmaf View Post
Why produce heat? Instead, add a switcher between the 24VAC output and the rectifier:

[ATTACH=CONFIG]49405[/ATTACH]

Adjust it to switch at around 20 VAC peak.
I may be wrong, but I would have though that an audio circuit powered this way would be subject to switching noise - like having a light dimmer in the same enclosure.
 
J M Fahey 6/20/2018 7:30 AM
Quote Originally Posted by jmaf View Post
Why produce heat? Instead, add a switcher between the 24VAC output and the rectifier:

[ATTACH=CONFIG]49405[/ATTACH]

Adjust it to switch at around 20 VAC peak.
The OP might need a switcher but *definitely* not that one, which can only handle *resistive* loads (itīs the classic cheap lamp dimmer) or universal series wound motors, both of which integrate that horrible output waveform (because of thermal or mechanical mass) into something useful.
--------------------------------
The board manual only says "10 - 15V DC power supply, 500 mA min."
Then it can be fed by a 7815.

You need at least 3V more than +15V feeding the 7815, including ripple, so aim at some 20/22V DC RAW to account both for ripple and drop under load.

If you can get a 15/16VAC transformer, rated 1 to 1.5A, it will be perfect, so you donīt need more than, say, 22/25VA .

All of this is very conservative, the board may not even take 500mA by a large margin, if a "500mA supply" was suggested.
 
jmaf 6/20/2018 7:48 AM
Quote Originally Posted by J M Fahey View Post
The OP might need a switcher but *definitely* not that one, which can only handle *resistive* loads (itīs the classic cheap lamp dimmer) or universal series wound motors, both of which integrate that horrible output waveform (because of thermal or mechanical mass) into something useful.
I wouldn't feed the output of that to motors or other inductors. It can definitely be rectified and regulated, no problem.
 
nickb 6/20/2018 11:49 AM
Quote Originally Posted by jmaf View Post
The 7815 can source max 1A but not continuously, all the LM78xx's fry if you do 1A 100% duty cycle.

If you have too large
I really don't think that is right. If the thermal issues are managed properly i.e. you don't hit the internal thermal or safe are operating limits limit then it will be fine. Some versions will even do 1.5A. The data sheet I'm looking at specifies a max operating junction temperature of 150C and a thermal resistance of 5C/W junction to case. In my calcs I used 125C as max and determined the heatsink size using that for continuous 1A. BTW I see I used 3.5C/W for chip plus interface - that should be 5.5C/W making the heatsink 7.2C/W.

All that will be conservative if the max load is 500mA anyway.

Mikep, the best resource for reference circuits is the data sheet. The National LM7815 shows 0.1uf on the output and 0.33uF on the input. It states the input one is only required if the regulator is located an "appreciable distance" (whatever that is) from the main filter cap and the the output one improves stability and transient response. Just use both and locate close to the regulator.
 
jmaf 6/20/2018 12:18 PM
Quote Originally Posted by nickb View Post
I really don't think that is right. If the thermal issues are managed properly i.e. you don't hit the internal thermal or safe are operating limits limit then it will be fine. Some versions will even do 1.5A. The data sheet I'm looking at specifies a max operating junction temperature of 150C and a thermal resistance of 5C/W junction to case. In my calcs I used 125C as max and determined the heatsink size using that for continuous 1A. BTW I see I used 3.5C/W for chip plus interface - that should be 5.5C/W making the heatsink 7.2C/W.
I'm not giving advice based on datasheets. In fact I haven't opened a single PDF today.
 
nickb 6/20/2018 3:41 PM
You may have experienced a non-representative sample at some point.

We can test the hypothesis easily enough. Here we have have a L7815CV with 25V in and 1A out. It's been running happily for hours.

I don't have an LM7815 here but I'm sure you'll agree it would dissipate the same amount of power so we should expect the same result.

I do have an LM7805 if you'd like me to test that.


[ATTACH=CONFIG]49416[/ATTACH]
 
jmaf 6/20/2018 3:58 PM
Quote Originally Posted by nickb View Post
Here we have have a L7815CV with 25V in and 1A out. It's been running happily for hours.

I don't have an LM7815 here but I'm sure you'll agree it would dissipate the same amount of power so we should expect the same result.
Since you're choosing more powerful components, why not go with one of these just to shoot the shit?

[ATTACH=CONFIG]49417[/ATTACH]

I'm sure you'll agree it would dissipate the same amount of power so we should expect the same result.
 
nickb 6/20/2018 4:36 PM
Quote Originally Posted by jmaf View Post
Since you're choosing more powerful components, why not go with one of these just to shoot the shit?

[ATTACH=CONFIG]49417[/ATTACH]

I'm sure you'll agree it would dissipate the same amount of power so we should expect the same result.
Still don't believe me huh? OK, here's a LM7805, 15V in well over 1A out. Also quite happy.

[ATTACH=CONFIG]49419[/ATTACH]
 
jmaf 6/20/2018 5:21 PM
Quote Originally Posted by nickb View Post
Still don't believe me huh? OK, here's a LM7805, 15V in well over 1A out. Also quite happy.

[ATTACH=CONFIG]49419[/ATTACH]
I've tested hundreds of LM regulators in real production settings and they're not reliable at 1A.

Not much else I can say except that it's getting really pedantic to try and share some experience here and be confronted by random experimenters all the time.
 
g1 6/20/2018 6:29 PM
jmaf, I have great respect for your posts, but nickb is hardly someone I would call a 'random experimenter'. Never mind the implication that the forum is full of them. That seems somewhat of a low blow to be honest.
 
jmaf 6/20/2018 8:00 PM
Quote Originally Posted by g1 View Post
jmaf, I have great respect for your posts, but nickb is hardly someone I would call a 'random experimenter'. Never mind the implication that the forum is full of them. That seems somewhat of a low blow to be honest.
I didn't imply the forum is full of them. I might have implied that I've been rebuffed by this kind of reply more than once where one thing is cherry picked out of a general post where you're trying to help.

nickb's entire point here is that a component survived some time running at max rated current on his rig. That's all. But if he ever builds anything like that professionally, it'll be back for repair in less than a month. My advice to the original poster is to not do that professionally, because I've seen these components break, for years, since they don't really stand their max rated current in continuous operation. I hope it helps the member who asked originally, that was the only point of me posting here, trying to help.
 
g1 6/20/2018 9:13 PM
Thanks for the clarification. I appreciate your sharing your practical experience.
I agree with not using a 1A regulator in a circuit that needs 1A most of the time. (In this case we are off on a bit of a tangent as the circuit requirement was stated as 500mA, but tangents are par for the course around here anyway. )
For a circuit that needed constant 1A, would you be comfortable with a 1.5A reg. or go with 2A ?
 
jmaf 6/20/2018 9:53 PM
Quote Originally Posted by g1 View Post
Thanks for the clarification. I appreciate your sharing your practical experience.
I agree with not using a 1A regulator in a circuit that needs 1A most of the time. (In this case we are off on a bit of a tangent as the circuit requirement was stated as 500mA, but tangents are par for the course around here anyway. )
For a circuit that needed constant 1A, would you be comfortable with a 1.5A reg. or go with 2A ?
It depends. Would it be mass produced and low cost device? If so, then I'd go the extra mile to make it work with a 1.5 amp regulator to save costs. If it were a boutique/custom or personal hobby project with just one unit, then I'd use 2A or more, or whatever I found in the drawer in the latter case. How will it be used? Is it critical? Will it run 24x7? Does someone die if it fails?

For guitar amps I used to use the LM350 (3 amp) @ 1 Amp draw for preamp tube heaters.
 
J M Fahey 6/20/2018 10:03 PM
Quote Originally Posted by jmaf View Post
I've tested hundreds of LM regulators in real production settings and they're not reliable at 1A.
If you chop your post down to the useful part, which is what I left above, Karma will be better for everybody

FWIW I implied something similar, based on roughly similar reasons, but didnīt turn it into a pissing contest, just restricted it to the OP apparent needs

self quoting:
The board manual only says "10 - 15V DC power supply, 500 mA min."
Then it can be fed by a 7815.

You need at least 3V more than +15V feeding the 7815, including ripple, so aim at some 20/22V DC RAW to account both for ripple and drop under load.

If you can get a 15/16VAC transformer, rated 1 to 1.5A, it will be perfect, so you donīt need more than, say, 22/25VA .

All of this is very conservative, the board may not even take 500mA by a large margin, if a "500mA supply" was suggested.
Didnīt even mention 1A but was happy that it would take 500mA or less

And on the other side suggested reducing Raw Voltage input to decrease dissipation .

On the other side, understand JMAFīs position very well, very often walk away in disgust from other Forums (wonīt mention names) when TV couch "designers" steer some poor OP straight into the quicksand pit and boo boo my efforts to save him ... oh well.

Just not here
 
Mick Bailey 6/21/2018 1:51 AM
It's interesting to see how components in mass-produced, commercial designs are run at or close to their maximum rating - including voltage regulators. So we see 15v supply rails with 16v caps, power amps with transistors run right to the edge of their SOA, 300v tubes run at over 400v, 3w resistors run at 2.7w. In many cases, this is all down to cost and the component manufacturer's device specification. Why install components in (say) a set-top box to ensure 25-year reliability when it only needs to last maybe 3 years? There also factors into this the predicted failure rate and warranty costs. Fitting higher spec components may give increased reliability but the cost may outweigh fitting cheaper components and taking a hit on the increased failures.

Think of all the Fender amps with cooked boards where the 16v zeners and dropper resistors are fitted. Fender have made them with that failure area from day one and they started to fail after about three years. They have to know after a short while that almost every Deville/Hotrod Deluxe would fail in that area. They just kept building them like that, year-in, year-out. They never relocated the resistors and stuck a couple of aluminium-clad 15W devices on a piece of angle bolted to the chassis. They never uprated the zeners and mounted them off the board surface, they never installed 'proper' regulators. They saved money instead. Perhaps they only need to last the warranty period - maybe 5 years design life but no more.

When it comes to 78xx regulators, I find these to be pretty robust. They're short-circuit and thermally protected. So what's the worst that can happen if it's over-current or thermally compromised? It just shuts down. I see them running so hot they'll sizzle spit and they run for years like that on tiny (or no) heatsinks. They must be right on the edge. Often, if the load is too high, they won't conduct in the first place. A ready-made 500mA board does not need over-thinking.
 
jmaf 6/21/2018 6:06 AM
Quote Originally Posted by Mick Bailey View Post
It's interesting to see how components in mass-produced, commercial designs are run at or close to their maximum rating - including voltage regulators. So we see 15v supply rails with 16v caps, power amps with transistors run right to the edge of their SOA, 300v tubes run at over 400v, 3w resistors run at 2.7w. In many cases, this is all down to cost and the component manufacturer's device specification. Why install components in (say) a set-top box to ensure 25-year reliability when it only needs to last maybe 3 years? There also factors into this the predicted failure rate and warranty costs. Fitting higher spec components may give increased reliability but the cost may outweigh fitting cheaper components and taking a hit on the increased failures.

Think of all the Fender amps with cooked boards where the 16v zeners and dropper resistors are fitted. Fender have made them with that failure area from day one and they started to fail after about three years. They have to know after a short while that almost every Deville/Hotrod Deluxe would fail in that area. They just kept building them like that, year-in, year-out. They never relocated the resistors and stuck a couple of aluminium-clad 15W devices on a piece of angle bolted to the chassis. They never uprated the zeners and mounted them off the board surface, they never installed 'proper' regulators. They saved money instead. Perhaps they only need to last the warranty period - maybe 5 years design life but no more.

When it comes to 78xx regulators, I find these to be pretty robust. They're short-circuit and thermally protected. So what's the worst that can happen if it's over-current or thermally compromised? It just shuts down. I see them running so hot they'll sizzle spit and they run for years like that on tiny (or no) heatsinks. They must be right on the edge. Often, if the load is too high, they won't conduct in the first place. A ready-made 500mA board does not need over-thinking.
You're right about everything working on the limit. It's all about planned obsolescence and it moves our markets ever since Edison and friends came up with the idea. But that's a market thing, not technical good practice, and it creates mountains of electronic junk in Africa.

Quoting myself:

Quote Originally Posted by jmaf View Post
Would it be mass produced and low cost device? If so, then I'd go the extra mile to make it work with a 1.5 amp regulator to save costs. If it were a boutique/custom or personal hobby project with just one unit, then I'd use 2A or more, or whatever I found in the drawer in the latter case. How will it be used? Is it critical? Will it run 24x7? Does someone die if it fails?
If a fellow member is building a circuit from zero, why give advice to work on the limit when they can buy regulators for 3X, 5X the rated current cheaply? What's the point of running a toaster in a circuit?

Was it really bad advice to tell OP to not use 78xx's @ 1A?

Fender tube abuse is part of Leo's magic. But tubes are different beasts. Silicon fails sharply, vacuum doesn't. Abused tubes can last for 5000 hours which is a lot for a musician's instrument. 5000 hours is not a lot for a set top box or a PC USB port. They're different applications. Leo didn't have the cheap readily available components we have today, he had to adapt. It's bad electronic design, but it's what he had back then. He ran tubes like that because he had to adapt but then it became part of his tone recipe. Today you have 100's of different regulator IC's you cab buy by clicking a mouse, why use anything at 100% rated current if you're building one piece for yourself?



Quote Originally Posted by J M Fahey View Post
Didnīt even mention 1A but was happy that it would take 500mA or less
If anyone is curious, test a LM7812 to regulate 3 x 12AX7 150mA heaters. 450mA total, right? Safely under 50% Imax? Then take a thermometer gun and measure temperature after 30 minutes. You'd need a truck sized heatsink. Can't even fit a heatsink that big into most projects which demand 500mA. (PS. I also picked the useful part of your reply .)
 
Mick Bailey 6/21/2018 6:40 AM
Quote Originally Posted by jmaf View Post
If a fellow member is building a circuit from zero, why give advice to work on the limit when they can buy regulators for 3X, 5X the rated current cheaply? What's the point of running a toaster in a circuit?
1. He isn't building a circuit from zero.
2. I have never, anywhere, advised him to work on the limit - those are your words, not mine. In fact, I advised him on sizing for a transformer that will reduce thermal dissipation.
3. The regulators are already fitted.
4. He was asking for advice on transformer sizing for the boards he already has
 
jmaf 6/21/2018 7:05 AM
Quote Originally Posted by Mick Bailey View Post
1. He isn't building a circuit from zero.
This is unnecessary pedantry. My point was clear, we're electronic hobbyists, you can employ components any way you want to.

Quote Originally Posted by Mick Bailey View Post
2. I have never, anywhere, advised him to work on the limit - those are your words, not mine. In fact, I advised him on sizing for a transformer that will reduce thermal dissipation.
You wrote a long post about how everything uses components on the limit. Pardon me if I understood your implication wrong. What was your point then?


Quote Originally Posted by Mick Bailey View Post
3. The regulators are already fitted.
I assume he has a soldering iron.

Quote Originally Posted by Mick Bailey View Post
4. He was asking for advice on transformer sizing for the boards he already has
Which he's going to use somewhere on his own projects. Right?
 
Mick Bailey 6/21/2018 10:55 AM
Quote Originally Posted by jmaf View Post
You wrote a long post about how everything uses components on the limit. Pardon me if I understood your implication wrong. What was your point then?
Just illustrating the commercial approach and wishing I'd never bothered to post anything on the subject.
 
nickb 6/21/2018 2:09 PM
Quote Originally Posted by mikepukmel View Post
Thanks Nick. After some toil, I found these: https://www.mouser.com/ProductDetail/546-187E16 16v 56va, 3.5a, a little bigger than needed, I think, for a 1a PS. Allows for some voltage drop and still stay above 17v min input.
For some reason Hammond haven't given the regulation for those. At 56VA I'll guess 15%.

With a 3300uF and taking the the worst case line voltage of 115V less 7.5% at the input to the regulator would be about 17.1V, only just enough. Given your wall voltage is higher and the current is 500mA you should be fine. The power dissipation at max line volts of 115 + 7.5% and 1A is 7.4W so you'd need a 7.8C/W heatsink or better. If you want to limit to 500mA then 20C/W should do. The cooler you keep it the more reliable it should be.
 
J M Fahey 6/21/2018 4:17 PM
Quote Originally Posted by nickb View Post
For some reason Hammond haven't given the regulation for those. At 56VA I'll guess 15%.
Take manufacturerīs regulation with a pinch of salt.

The "number" they quote is for AC regulation into resistive loads (and maybe it holds for choke input supplies) , but capacitor input ones get charged by narrow pulses with quite high peak current and narrow duty cycle.

Since loss is proportional to I *squared*, 1A 50% of the time requires 2A 25% of the time just to keep *average* current the same, but RMS current will be twice as high, with matching doubled loss.
And even worse with narrower pulses.

My point being that rectified voltage drop is higher than expected.
I have used overbuilt 5% regulation transformers where DC under full load dropped some 15%
 
mikepukmel 6/21/2018 8:16 PM
Quote Originally Posted by J M Fahey View Post
Take manufacturerīs regulation with a pinch of salt.

The "number" they quote is for AC regulation into resistive loads (and maybe it holds for choke input supplies) , but capacitor input ones get charged by narrow pulses with quite high peak current and narrow duty cycle.

Since loss is proportional to I *squared*, 1A 50% of the time requires 2A 25% of the time just to keep *average* current the same, but RMS current will be twice as high, with matching doubled loss.
And even worse with narrower pulses.

My point being that rectified voltage drop is higher than expected.
I have used overbuilt 5% regulation transformers where DC under full load dropped some 15%
Wow, didn't think it would drop 15%. Is that a smooth drop off, or a hockey stick thing that goes down quickly near the limit?
EDIT: Oops, sorry, you wrote clearly above "loss is proportional to I squared".
 
J M Fahey 6/21/2018 10:40 PM
Quote Originally Posted by mikepukmel View Post
Wow, didn't think it would drop 15%. Is that a smooth drop off, or a hockey stick thing that goes down quickly near the limit?
EDIT: Oops, sorry, you wrote clearly above "loss is proportional to I squared".
Yes, itīs a smooth drop.
Commercial Amp designers know this of course, since forever; Booteeq ones or homemakers often do not and either write crap about the transformers they get OR overrate specs 2x or 3x above whatīs actually needed.

Most ampmkanufacturers donīt write supply or rail voltages any more, just check it yourself ... except +/- 15V which is regulated, of course.

Tube amps often do not change that much, but only because at idle, no signal, they are *already* pulling a lot: filaments and too much idle current through power tubes, plus low efficiency all over the place, but SS amps which pull feeble current at idle, drop rails a lot when actually played loud.

VERY FEW Commercial amps tell the whole story on schematics, (which I find VERY annoying and unprofessional) , only Roland (and maybe scant others) tell all.

Just check this Roland KB100 posted here a couple days ago:
[ATTACH=CONFIG]49440[/ATTACH]

a) rail voltage: +47 to +54V , meaning: +54V at idle, dropping to +47V at full power.

b) something which causes MUCH confusion, it took me a long time to decode, and had to check a ton of Roland schematics to self confirm it was so after all: transformer primary rating is AC (mains) **BUT** in Rolandspeak secondary voltage is NOT RATED IN VAC but in "DC rectified voltage achieved with that transformer" .

A normal tech and even more a somewhat advanced end user will see that schematic and, if neded, will buy a 47VAC+47VAC transformer ... and blow everything in its path.

That label must be read as: "transformer whose rectified secondary gives you +/-49 Vdc under a 1.7A load" which "will swing from 54V at idle down to 47V under full load and still be under spec".

Which looks complex but in fact is a very accurate way to fully describe the transformer which will fit there.

LAB Series amps, "by Engineers for Engineers", usually stated transformer secondary VAC but stated two rail voltages, for example: "+54 (+49)V" meaning: "+54 at idle, +49 full load"

Others just post nominal rail voltage and "forget" to mention it will drop a lot.

And as I said before, MANY plain do not post any rail voltages, period.
 
nickb 6/22/2018 1:15 PM
Quote Originally Posted by J M Fahey View Post
Take manufacturerīs regulation with a pinch of salt.

The "number" they quote is for AC regulation into resistive loads (and maybe it holds for choke input supplies) , but capacitor input ones get charged by narrow pulses with quite high peak current and narrow duty cycle.

Since loss is proportional to I *squared*, 1A 50% of the time requires 2A 25% of the time just to keep *average* current the same, but RMS current will be twice as high, with matching doubled loss.
And even worse with narrower pulses.

My point being that rectified voltage drop is higher than expected.
I have used overbuilt 5% regulation transformers where DC under full load dropped some 15%
The point of knowing the regulation (and it's such a basic and important parameter that I can't believe they didn't include it) is I can calculate the effective resistance and from that I can accurately allow for the high current pulses and determine the min output voltage. It's a bit more complicated than that, but I think we said that way back...
 
mikepukmel 6/25/2018 8:05 PM
As an aside, how do you test a power supply: i.e. OK I know how to test no load, just ... don't hook it up to any load. But is there a reasonable way to test various current draws, then check the voltage? Some kind of resistor network?
 
nosaj 6/25/2018 8:18 PM
Quote Originally Posted by mikepukmel View Post
As an aside, how do you test a power supply: i.e. OK I know how to test no load, just ... don't hook it up to any load. But is there a reasonable way to test various current draws, then check the voltage? Some kind of resistor network?
Enzo was telling me he used to have a big (I think 1 ohm resistor) in his drawer and he would use that to figure current draw. Kinda of like the 1 ohm resistor people will use on power tubes.

nosaj
 
mikepukmel 6/25/2018 8:36 PM
This will probably be shocking to you all, and I hope I didn't ruin anyone's day/evening, but these little regulator board kits I got for 1.60 USD each, have the + and - outputs labelled reversed. And the heat sink looks, rather small. Will post photos. The sinks are about the height of the installed regulator.

I got these kits mainly for the boards, thinking some of the components might need to be updated.
 
Enzo 6/25/2018 9:43 PM
I used to repair piles of SMPS for the arcade video game industry. Black boxes with +5, +12, and -5 outputs +12 at an amp or two, +5 at anaything from 5A to 20A. -5 was usually an amp.

First test it unloaded, then indeed I had some resistors for loads. They were mostly ceramic cylindrical ones. I had a 5 ohm one - to draw 1A from 5v. I had a 1 ohm one to draw 5A from 5v. I had a 12 ohm one for.. oh you can guess.

Plus I had a whole selection of power resistors in my stock, I could grab.

Put an appropriate resistor across the output and see if the voltage holds up. If I were in a lab setting I could use manay load values and chart the complete performance, but that is rarely necessary here. If the thing works at essentially full out, and at a gentle load, chances are real good it will also work at points between.
 
mikepukmel 6/26/2018 3:52 AM
Quote Originally Posted by Enzo View Post
I used to repair piles of SMPS for the arcade video game industry. Black boxes with +5, +12, and -5 outputs +12 at an amp or two, +5 at anaything from 5A to 20A. -5 was usually an amp.

First test it unloaded, then indeed I had some resistors for loads. They were mostly ceramic cylindrical ones. I had a 5 ohm one - to draw 1A from 5v. I had a 1 ohm one to draw 5A from 5v. I had a 12 ohm one for.. oh you can guess.

Plus I had a whole selection of power resistors in my stock, I could grab.

Put an appropriate resistor across the output and see if the voltage holds up. If I were in a lab setting I could use manay load values and chart the complete performance, but that is rarely necessary here. If the thing works at essentially full out, and at a gentle load, chances are real good it will also work at points between.
Cool, thanks Enzo. I will give these cheapies a run at 1/2a and 3/4a before going full bore with the programming board.
 
jmaf 6/26/2018 4:06 PM
Quote Originally Posted by mikepukmel View Post
As an aside, how do you test a power supply: i.e. OK I know how to test no load, just ... don't hook it up to any load. But is there a reasonable way to test various current draws, then check the voltage? Some kind of resistor network?
Adding to what Enzo already replied, this guy has a cool Youtube channel and he's done a test on Chinese batteries: http://www.instructables.com/id/DIY-...-current-load/

Similar gadget can be used to test the power supply, just place it where the battery would be and build the test rig to match your supply voltage (15V?).
 
mikepukmel 6/27/2018 7:03 PM
Quote Originally Posted by jmaf View Post
Adding to what Enzo already replied, this guy has a cool Youtube channel and he's done a test on Chinese batteries: http://www.instructables.com/id/DIY-...-current-load/

Similar gadget can be used to test the power supply, just place it where the battery would be and build the test rig to match your supply voltage (15V?).
Thanks for the link Jmaf! (Just read the page, cool project, I could build that!)
 
mikepukmel 6/27/2018 7:13 PM
Best Epoxy to glue heat sink to circuit board
Hi All!

So I got these way cheap kits (very cheap), came with all the parts. The one on the left is almost done, but has the smallest heat sink I've ever seen. I dug around on Mouser, and found better ones that I thought would fit ok.


[ATTACH=CONFIG]49514[/ATTACH]

The pins on these bigger heat sinks don't line up with the holes that the board came with. No surprise there. An hour with my hand drill and I got the bigger sinks into the board reasonably well for stone knives and bear skin tools I have. One fits reasonably tight. One fits a little loose. Either way, Id like to put some epoxy on the pins under the board.

I started reading about epoxy, found some high rolling stuff, but the links only have "Get a quote" so they want me to buy gallons of the stuff. The opposite end of the spectrum is the cr@p available at the big box stores. <frown>.

Can anyone suggest some kind of epoxy I can use: put a drop on the pins on the bottom of the board, that won't emit something corrosive like the home fixit epoxy and silicone?

Its not going into a high vibration environment, but I will bolt the board and transformer into a box and move it around, so I'd hate to have the thing loosen up the solder connections on the LMXX.

Thanks!
 
jmaf 6/27/2018 9:01 PM
Quote Originally Posted by mikepukmel View Post
Hi All!

So I got these way cheap kits (very cheap), came with all the parts. The one on the left is almost done, but has the smallest heat sink I've ever seen. I dug around on Mouser, and found better ones that I thought would fit ok.


[ATTACH=CONFIG]49514[/ATTACH]

The pins on these bigger heat sinks don't line up with the holes that the board came with. No surprise there. An hour with my hand drill and I got the bigger sinks into the board reasonably well for stone knives and bear skin tools I have. One fits reasonably tight. One fits a little loose. Either way, Id like to put some epoxy on the pins under the board.

I started reading about epoxy, found some high rolling stuff, but the links only have "Get a quote" so they want me to buy gallons of the stuff. The opposite end of the spectrum is the cr@p available at the big box stores. <frown>.

Can anyone suggest some kind of epoxy I can use: put a drop on the pins on the bottom of the board, that won't emit something corrosive like the home fixit epoxy and silicone?

Its not going into a high vibration environment, but I will bolt the board and transformer into a box and move it around, so I'd hate to have the thing loosen up the solder connections on the LMXX.

Thanks!
IMO the best solution would not be epoxy or any kind of filler.

Maybe you could bore a hole into the heatsink and affix it with a screw or pop rivet through the board.
 
Enzo 6/27/2018 9:14 PM
Amen, I agree.
 
mikepukmel 6/27/2018 9:25 PM
Well, I got holes in the board that let the bigger pins come through. I gota few extra heat sinks, could pull off the pins from one and try to put a screw in the same place. The pins look like they're friction fit into the fins, so a similar size screw could work.

Thanks! !! I'll try that! And I was dreading fooling around with messy epoxy.
 
jmaf 6/29/2018 7:42 AM
Quote Originally Posted by mikepukmel View Post
Well, I got holes in the board that let the bigger pins come through. I gota few extra heat sinks, could pull off the pins from one and try to put a screw in the same place. The pins look like they're friction fit into the fins, so a similar size screw could work.

Thanks! !! I'll try that! And I was dreading fooling around with messy epoxy.
Those heatsinks are aluminum and the pins are tin, so they can't be soldered together. They're usually rivetted. To remove the pins just drill a hole into the pop rivet.
 
mikepukmel 6/30/2018 7:54 PM
Thanks Jmaf. I finally got some time today, and the pins are press fit into the bottom of the sink. its not a closed hole, but more than "U" shape, so that it fits around the screw or pin slightly so it won't slide out. So I could pill the pin out with a vice grip, (its got a little knurling to make it stick) and use a screw in place. I'll try to get a photo, its tough to focus in there. Pretty cool design, I think. Have to trek out to the hardware store tomorrow to see what screws I can find. Hope to get at least a couple of these running tomorrow.
 
mikepukmel 7/1/2018 2:27 PM
Good Lord. got the board soldered up except for the regulator. Got the screws into the het sinks, and heat sinks screwed onto the boards. I wanted to measure the resistance between the heat sink and each of the 3 pin pads to make sure I didn't create a short. One board measured fine (0 ohms) the other one kept reading 3 to 28 megohms. back and forth took apart, reassembled. FINGERS have 3 -30 megohm resistance. Cleaned the board off, used a piece of clean plastic to hold the board, 0 ohms. No load (no regulator) reading about 23.5 volts dc (that would go into the regulator). Next step, wrist band, put the regulators in, solder, and ... smoke test. (I love that phrase).
 
mikepukmel 7/1/2018 3:13 PM
Another hopefully not too annoying question for you all: I have both 12vdc and 5vdc rectifier/regulator boards built and tested. Managed not to smoke anything. The particular transformer I could find is 18vac secondary, but 3.5 amps, way larger than needed for one 1 amp or 1.5amp power supply. I did a lot of searching, but didn't find both the primary and secondary voltages and the current rating, could find 2 both not all 3. And this transformer was way less expensive than one closer to the specs for the power supply. So, I get a little extra unused current.

Anyway, if I use one 3.5A rated transformer to power both rectifier/regulator boards, (1 x 1.5a 5vdc, and 1 x 1A 12VDC) is this OK to use like this? Is there some reason I should use one transformer for each board?

The 12vdc will power the microncontroller dev/programming board (manual says 500ma min), and the 5v will be for some other stuff, e.g. one of those little 16 char 2 line LCD display, not sure what else.

Thanks.
Mike
 
J M Fahey 7/1/2018 5:03 PM
Quote Originally Posted by mikepukmel View Post
I'll try to get a photo, its tough to focus in there.
You can use a standard reading glass in front of cellphone camera as a close up lens.
A "+4" one lets you focus between 20/25cm (8/10") with very good sharpness.
Just remember to keep it parallel with cellphone front.
 
mikepukmel 7/1/2018 6:13 PM
Thanks Juan.
 
mikepukmel 7/1/2018 6:38 PM
The heat sink has fins. The fins have slots that hold a screw or pin in place. Can't describe it well, but its not a 180 degree slot, its a little more, I ground the screw into the end of teh sink, and it holds pretty well, I put some glue in there as well with a broken Q tip.

The transformer and heat sinks don't quite fit exactly into the little cheap plastic boxes I got. A few microns off.

[ATTACH=CONFIG]49580[/ATTACH]

[ATTACH=CONFIG]49581[/ATTACH]

[ATTACH=CONFIG]49579[/ATTACH]


Anyway, I have two rectifier/regulator boards (1 x 12v 1A, and 1 x 5 v 1.5A) hooked up to the same 18v sec 3.5A transformer. Fusing is the only issue I don't quite understand yet. I have a 1A on the primary. But, I think I should also fuse the secondary as well. Or maybe split it up into 2 separate power supplies (I did get another transformer).
 
J M Fahey 7/1/2018 9:56 PM
Hey, those look GOOD!!!

Just curious: is that some kind of double cabinet or you krazy glued 2 side by side?

In any case, if you are going to close those boxes with some kind of cover, I suggest you drill some ventilation holes.

PD: and your pictures came out very sharp
 
Enzo 7/1/2018 10:49 PM
Juan,, I think I see two screws holding the two boxes together.

A dab of Loctite on those nuts will keep them from coming loose. Or if you are cheap like I am, a bottle of cheap nail polish daubed on them will work too.

For cooling, remember, for warm air to leave there must be a way for cool air to enter. This applies to fan cooled as well as simple convection. So vent holes in the lid would be happy with some more vent holes in the bottom or around the bottom sides.
 
nickb 7/2/2018 12:54 AM
Quote Originally Posted by mikepukmel View Post
Another hopefully not too annoying question for you all: I have both 12vdc and 5vdc rectifier/regulator boards built and tested. Managed not to smoke anything. The particular transformer I could find is 18vac secondary, but 3.5 amps, way larger than needed for one 1 amp or 1.5amp power supply. I did a lot of searching, but didn't find both the primary and secondary voltages and the current rating, could find 2 both not all 3. And this transformer was way less expensive than one closer to the specs for the power supply. So, I get a little extra unused current.

Anyway, if I use one 3.5A rated transformer to power both rectifier/regulator boards, (1 x 1.5a 5vdc, and 1 x 1A 12VDC) is this OK to use like this? Is there some reason I should use one transformer for each board?

The 12vdc will power the microncontroller dev/programming board (manual says 500ma min), and the 5v will be for some other stuff, e.g. one of those little 16 char 2 line LCD display, not sure what else.

Thanks.
Mike
With 0.5A on 12V and 1.5A on 5V the RMS current in the transformer secondary will be about 3.5A ,just at it's limit. A bigger problem will be the 5V regulator will be dissipating 20W. That requires a massive heatsink of about 4C/W.
 
mikepukmel 7/2/2018 5:32 AM
Quote Originally Posted by J M Fahey View Post
Hey, those look GOOD!!!

Just curious: is that some kind of double cabinet or you krazy glued 2 side by side?

In any case, if you are going to close those boxes with some kind of cover, I suggest you drill some ventilation holes.

PD: and your pictures came out very sharp
Thanks Juan. its a "junker" project, i.e. put something I can use together for the lowest cost. Thanks for the tip on vents, but the top won't fit. The heat sinks and transformer stick up about 1 1/2" above the edges of those 2.00 boxes.
 
mikepukmel 7/2/2018 5:33 AM
Quote Originally Posted by Enzo View Post
Juan,, I think I see two screws holding the two boxes together.

A dab of Loctite on those nuts will keep them from coming loose. Or if you are cheap like I am, a bottle of cheap nail polish daubed on them will work too.

For cooling, remember, for warm air to leave there must be a way for cool air to enter. This applies to fan cooled as well as simple convection. So vent holes in the lid would be happy with some more vent holes in the bottom or around the bottom sides.
Thanks for the tips, yes cheap here too, like those experiment project dollars to go far. I don't think I'l be able to get the top on the boxes, but I will put them on a shelf out of fingers way.
 
mikepukmel 7/2/2018 5:40 AM
Quote Originally Posted by nickb View Post
With 0.5A on 12V and 1.5A on 5V the RMS current in the transformer secondary will be about 3.5A ,just at it's limit. A bigger problem will be the 5V regulator will be dissipating 20W. That requires a massive heatsink of about 4C/W.
Thanks Nick. I don't think I'll come anywhere close to 1.5a on the 5v. I can't quite understand the data sheet for the LCD display (16 x 2 OSEPP) cheapie. The data sheet has "input current low/input current high" columns +2ua -100ua, didn't understand waht the sign meant since they have separate output current section. I think its very low. Will be that, plus a few LED's and switches.

20W ouch, that's a good size guitar amp power. The regulator is a 1.5A unit, but I didnt plan to put more stuff on it than 1/3rd that or so. No where near 1a.

Reading what 4C/W heat sinks look like...
 
mikepukmel 7/2/2018 5:50 AM
Wow that's a big heat sink. I don't know what the rating is on the ones I got, but they look to be about 1/3rd the mass.
 
mikepukmel 7/11/2018 8:27 PM
Getting there. Got the jack wired up, worked up the nerve and started up the board. Powers up fine, everything seems to work. The LED's on the board do the right thing. And the kit comes with a MCU preprogrammed with a cheesey program that makes moving light patterns on LED's by button presses. So, at least I know the inputs and outputs work, the power supply on the board is OK. and the power supply I made at least works.

When I have the board powered for a long time (hour?) the heat sink does get hotter than I expected. Not too hot to touch, but ... hot. The manual said 10 to 15v, so I used a 12v regulator.

Still can't get the AVR studio to see the board. I got a few really cheap USB-To-RS232 cable/converters, that came with drivers. Ive been installing and uninstalling drivers for a few days now, and I think Windows XP sees the cable, but either the cable/converter is no good, or maybe the RS232 port on the board is burned out (I REALLY hope that's not the case)

The last stretch, I opened a RS232 communications program I downloaded, and could send characters in, and when I hit return I got some garbage back. So, I think that means data is going all the way into the cable and to the board, and the board is responding although the comm's might be all screwed up. When I disconnect the board end of the cable, I dont get any response when I send garbage char's in.

So far, haven't found any way to test the RS232 on the board other than get a good working connection. so stuck for now.
 
The Dude 7/11/2018 8:38 PM
You lost me, Mike. What is it you're building? I must have missed something. I see a thread about regulation and then the last post about RS232, etc. Curiosity is getting the best of me. Is there maybe an associated thread I missed?
 
Enzo 7/11/2018 8:41 PM
Without review, what I recalled was he wanted to build a basic power supply in a box for his bench. He wanted it to power small circuits he wanted to play with. I think those circuits are the USB and all we hear of now. I could be wrong.
 
nickb 7/12/2018 12:44 AM
Quote Originally Posted by mikepukmel View Post
Getting there. Got the jack wired up, worked up the nerve and started up the board. Powers up fine, everything seems to work. The LED's on the board do the right thing. And the kit comes with a MCU preprogrammed with a cheesey program that makes moving light patterns on LED's by button presses. So, at least I know the inputs and outputs work, the power supply on the board is OK. and the power supply I made at least works.

When I have the board powered for a long time (hour?) the heat sink does get hotter than I expected. Not too hot to touch, but ... hot. The manual said 10 to 15v, so I used a 12v regulator.

Still can't get the AVR studio to see the board. I got a few really cheap USB-To-RS232 cable/converters, that came with drivers. Ive been installing and uninstalling drivers for a few days now, and I think Windows XP sees the cable, but either the cable/converter is no good, or maybe the RS232 port on the board is burned out (I REALLY hope that's not the case)

The last stretch, I opened a RS232 communications program I downloaded, and could send characters in, and when I hit return I got some garbage back. So, I think that means data is going all the way into the cable and to the board, and the board is responding although the comm's might be all screwed up. When I disconnect the board end of the cable, I dont get any response when I send garbage char's in.

So far, haven't found any way to test the RS232 on the board other than get a good working connection. so stuck for now.
I don't think it's surprising at all that it gets hot. How much current does it actually draw?

If you can send data but get garbage back, check the RS232 settings in in the dumb terminal your are using. If you get over that hurdle you and connect using AVR Studio ( it's 20 years since I last used it but I don't recall RS232, just their own dedicated ISP ) look for the RS232 settings in there. If there are none you can set them in windows Device Manager -> Com ports -> Properties->Port Settings
 
mikepukmel 7/18/2018 5:11 PM
Quote Originally Posted by The Dude View Post
You lost me, Mike. What is it you're building? I must have missed something. I see a thread about regulation and then the last post about RS232, etc. Curiosity is getting the best of me. Is there maybe an associated thread I missed?
Sorry Dude, I forget that this is a blog thread, that has a question, or topic and when that's resolved I should start another thread. It was a ham klutzy segue into what should be another topic.

So, the power supply works fine. Thanks to everyone for the help. The PS is powering an Atmel STK500 dev board, for programming Atmel microcontrollers (goal is to learn something about programming digital signal processing for audio).

Board powers up, initializes, the LED's do the right thing. The board comes with a chip that has a cheesy program on it, that responds to button presses by making a moving light pattern on the on board LED's, so I know that the chip socket is powered, and the i/o work fine.

Next step was to hook up a RS-232 to USB connection to my old PC, fire up Atmel software studio and see if it can talk to the STK500 board.
That connection is the problem.

I'll stop posting stuff about the RS232 on this thread and wind up the power supply questions. Thanks.
 
mikepukmel 7/18/2018 5:16 PM
Quote Originally Posted by nickb View Post
I don't think it's surprising at all that it gets hot. How much current does it actually draw?

If you can send data but get garbage back, check the RS232 settings in in the dumb terminal your are using. If you get over that hurdle you and connect using AVR Studio ( it's 20 years since I last used it but I don't recall RS232, just their own dedicated ISP ) look for the RS232 settings in there. If there are none you can set them in windows Device Manager -> Com ports -> Properties->Port Settings
Thanks Nick. I have a pretty good Fluke (not high end) but should handle the current measurement. have to figure out how to wire that up. Im not sure, but the board folks said "min 500ma" so Im guessing around there. I will work up the courage to measure the current tonight.

Thanks for the tips on RS232, its been ages. Just hooked up a cable, shorted pins 2-3, and get a round trip. So I think (maybe) the cable is OK. Hoping not since if its good, that might mean the receiver chip on the board is toast. But I will try fiddling with the data settings. The Atmel software doesn't have any settings but I think there are all in windows.

The 'better' quality cable with driver came in today. Should pretty much tell me if the RS232 chip is toast. Even on this really old board, its all surface mount IC's so a bit beyond my skill set to replace any of it.
 
mikepukmel 7/27/2018 12:10 PM
Wahoo moment. Got the new cable, and 'better' driver, installed, didn't work. So I went on a long path of installing older and older versions of the AVR Studio software. Finally, one version installed, and when I tried to connect, got a message "The firmware is version 1.x, install version 2.x?" I almost fell over. Followed the instructions, the firmware upgrade succeeded, then the firmware validation. Then, went back and forth with newer version of AVR Studio. They all seem to connect and 'see' the board just fine now. So, it might have been that the firmware was very, very old, like experimental. I think the guy bought this dev kit, put it in a closet and never touched it. Also, I plugged in and unplugged ... repeatedly many times, so maybe the little sockets on the female DB9 on the board had some 'crud and corruption' in there (thanks to Mr Cassavant, my 11th grade metal shot teacher for the phrase) that worked its way out. Im a gonna be a DSP programming fool, until I fry the chip.
 
mikepukmel 7/27/2018 12:25 PM
Quote Originally Posted by The Dude View Post
You lost me, Mike. What is it you're building? I must have missed something. I see a thread about regulation and then the last post about RS232, etc. Curiosity is getting the best of me. Is there maybe an associated thread I missed?
Hi Dude, sorry, I missed your question. I got a Atmel STK500 development board. its got a programmer on the board for their microcontrollers. But its an ancient design, so the port to the programmer is RS232. The power supply is for the board, which has a power supply of sorts. I don't understand the details very well, but the board has diodes and a regulator, but the mfr says the board should be 10 - 15vdc. So, the power supply will power up the board, which has some chips used to program the actual microcontroller under test. The nice thing about this old board is that it has a whole bunch of different sockets for many of their chips that come in PDIP. The board also has io ports that you can connect up either off the dev board to a breadboard, or to onboard set of buttons and LEDs. The board kit comes with a really old (outdated) microprocessor that you can plug in, that has a cheesy program that lights the LED's on the board in some pattern, to verify that the board is running OK.

There are a bunch of lectures online from the EE department at Cornell, for a course that teaches microcontrollers. That's the only reason I got this kit, is that I can go through the lectures, and also the homeworks and lab projects and build the stuff and learn how it works. They have one lab project that is DSP audio synth. Im interested in the other stuff, but really interested in audio and DSP. Not like Im going to be designing any DSP/Guitar boxes, but its something ive always been interested in since one of teh kids in my grade school picked up a real Moog mini synth back in the 70's at an accidental garage sale.

So, wanted a couple of power supplies, one for the board and that could power the chip running whatever program, and another one or two to power other 'stuff'. One of the other lab projects uses a 2 x 16 (I think) LCD display, and a keypad. They go over how to debounce the key buttton presses and send text and numbers to the LCD.