PS linear regulator issues
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Posted by Jon Slaughter on May 11, 2007, 7:44 am
Please log in for more thread options A PS I build a while back was screwed up yesterday when I was messing around. Its a variable split PS using 317's with, I think, about +-35V that it handles(20 somethign for the regulators). I'm not exactly sure what happened(well, I think I know) but in any case what happened after was that the voltage would read either about 2 voltage when the turned down or around 25+ volts when up. I think I fixed it as I replaced one of the protection diodes(the one from that goes from output to input). (I figured it was the diode since thats what there for). In any case it seems to be working but I'm not sure if any other damage happened. When I built the circuit I didn't design it to be able to remove components easily(didn't have the room in the box). I thought that the protection diodes were there to protect the 317(even though it has its own protection) but I didn't know it would destroy the diodes in the process. Is this normal? (if it did I would have made it easier to replace them). Also, in the case that the protection diodes do go does that completely eliminate(99%) any other things in the regulator circuit from being ruined. It wouldn't be fun to check the other protection diode I have or the 317. (since I probably would have to take them out of circuit to be completely sure). I'm worried about the other diode but really don't want to try and take it out to check it and since the PS looks like its working. (BTW, I think I essentially shorted the negative supply to ground and that is what caused it... but on the positive side ;/) What do you guys think I should do? Thanks, Jon | ||||||||||||||||
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Posted by Chris on May 12, 2007, 11:14 am
Please log in for more thread options the D2s shown in the ASCII diagram below (view in fixed font or M$ Notepad): | | .---------|<-----------------. | | D1 | | | .-------------. | | | | | | | V+o----o---o o-----o----o | | | + Regulator | | | | + | | | + | | | C --- | | C --- D2- | --- | | --- ^ | | '------o------' | | | | | | | | GNDo----o----------o------------o----o | | | | | | + | .------o------. + | | | C --- | | C --- D2- | --- | | --- ^ | | | | | | | | | - Regulator | | | V-o----o---o o-----o----o | | | | | | | '-------------' | | | D1 | | '--------->|-----------------'
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)
A lot of funny things can happen with dual supplies on turn-on and short circuit conditions. Many of these have to do with wiring inductance causing unexpected things to happen, some with the transformer at the input. Just put a couple of 1N5402 6 amp barrel diodes across the outputs of your power supply (put 'em right at the banana jacks, inside the box), and this should keep your problem from recurring. If your D1s are 1N400X, you could also upgrade those to 1N540X, also. Just clip the plastic body of the diode, and solder the heavier 1N5402 diode lead to what remains of the 1N400X lead on the circuit board. Be sure to use a clip on the smaller lead to prevent the solder under the circuit board from melting and spoiling your quick fix. Remember, your output caps aren't current limited to 1.5A like the ICs. Your power supply will be a lot more loyal if it knows you've spared no expense to protect it from itself. Cheers Chris | ||||||||||||||||
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Posted by Jon Slaughter on May 12, 2007, 2:48 pm
Please log in for more thread options
>> A PS I build a while back was screwed up yesterday when I was messing
>> around. Its a variable split PS using 317's with, I think, about +-35V >> that >> it handles(20 somethign for the regulators). >> >> I'm not exactly sure what happened(well, I think I know) but in any case >> what happened after was that the voltage would read either about 2 >> voltage >> when the turned down or around 25+ volts when up. >> >> I think I fixed it as I replaced one of the protection diodes(the one >> from >> that goes from output to input). (I figured it was the diode since thats >> what there for). In any case it seems to be working but I'm not sure if >> any >> other damage happened. >> >> When I built the circuit I didn't design it to be able to remove >> components >> easily(didn't have the room in the box). I thought that the protection >> diodes were there to protect the 317(even though it has its own >> protection) >> but I didn't know it would destroy the diodes in the process. Is this >> normal? (if it did I would have made it easier to replace them). >> >> Also, in the case that the protection diodes do go does that completely >> eliminate(99%) any other things in the regulator circuit from being >> ruined. >> It wouldn't be fun to check the other protection diode I have or the 317. >> (since I probably would have to take them out of circuit to be completely >> sure). >> >> I'm worried about the other diode but really don't want to try and take >> it >> out to check it and since the PS looks like its working. >> >> (BTW, I think I essentially shorted the negative supply to ground and >> that >> is what caused it... but on the positive side ;/) >> >> What do you guys think I should do? >> >> Thanks, >> Jon > Hi, Jon. From what you're saying, I'll bet you've got the D1s but not
> the D2s shown in the ASCII diagram below (view in fixed font or M$ > Notepad): > > | > | .---------|<-----------------. > | | D1 | > | | .-------------. | > | | | | | > | V+o----o---o o-----o----o > | | | + Regulator | | | > | + | | | + | | > | C --- | | C --- D2- > | --- | | --- ^ > | | '------o------' | | > | | | | | > | GNDo----o----------o------------o----o > | | | | | > | + | .------o------. + | | > | C --- | | C --- D2- > | --- | | --- ^ > | | | | | | > | | | - Regulator | | > | V-o----o---o o-----o----o > | | | | | > | | '-------------' | > | | D1 | > | '--------->|-----------------' > (created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de) > No, I have both(which I mentioned but maybe wasn't clear). I haven't checked them both though. There are a total of 4 diodes but I was just refering to one side of the supply since the other seemed to work fine. > A lot of funny things can happen with dual supplies on turn-on and
> short circuit conditions. Many of these have to do with wiring > inductance causing unexpected things to happen, some with the > transformer at the input. > > Just put a couple of 1N5402 6 amp barrel diodes across the outputs of > your power supply (put 'em right at the banana jacks, inside the box), > and this should keep your problem from recurring. If your D1s are > 1N400X, you could also upgrade those to 1N540X, also. Just clip the > plastic body of the diode, and solder the heavier 1N5402 diode lead to > what remains of the 1N400X lead on the circuit board. Be sure to use > a clip on the smaller lead to prevent the solder under the circuit > board from melting and spoiling your quick fix. Remember, your output > caps aren't current limited to 1.5A like the ICs. Your power supply > will be a lot more loyal if it knows you've spared no expense to > protect it from itself. > Thanks, I'm designing another power supply that has a bit more current to it and I'll try to keep this stuff in mind next time I do it. Jon | ||||||||||||||||
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> around. Its a variable split PS using 317's with, I think, about +-35V that
> it handles(20 somethign for the regulators).
>
> I'm not exactly sure what happened(well, I think I know) but in any case
> what happened after was that the voltage would read either about 2 voltage
> when the turned down or around 25+ volts when up.
>
> I think I fixed it as I replaced one of the protection diodes(the one from
> that goes from output to input). (I figured it was the diode since thats
> what there for). In any case it seems to be working but I'm not sure if any
> other damage happened.
>
> When I built the circuit I didn't design it to be able to remove components
> easily(didn't have the room in the box). I thought that the protection
> diodes were there to protect the 317(even though it has its own protection)
> but I didn't know it would destroy the diodes in the process. Is this
> normal? (if it did I would have made it easier to replace them).
>
> Also, in the case that the protection diodes do go does that completely
> eliminate(99%) any other things in the regulator circuit from being ruined.
> It wouldn't be fun to check the other protection diode I have or the 317.
> (since I probably would have to take them out of circuit to be completely
> sure).
>
> I'm worried about the other diode but really don't want to try and take it
> out to check it and since the PS looks like its working.
>
> (BTW, I think I essentially shorted the negative supply to ground and that
> is what caused it... but on the positive side ;/)
>
> What do you guys think I should do?
>
> Thanks,
> Jon