I am going to try the following: put instead of D1 and D5 zener diodes. Their rating should be more than 22V (38-16) and less the maximum rating of the regulator. If this will not solve the problem I am going to move to a simple zener with emitter follower solution and to hell with noise. Now I am going to do some orders from ebay 
They will still do what they're intended to do as you describe, but they will also avoid to much voltage from input to output. If the reg will not climb fast enough, the zener will break and push it up faster until the output is high enough to so they get below their rated voltage.
I see now, yes. Not sure that will work, but I see it. What about a eg 5V 1W zener in series with the vreg input? Or 2 vregs stepping down the voltage? The latter is probably what I would try... maybe that's a good reason not to
I sure hope some solutions are forthcoming for these vreg issues. I buy them from everywhere, I scrounge them from old boards, and I've never had any problems except overheating shutdowns. I built one supply that uses that as a crude current-limiting "feature".
I sure hope some solutions are forthcoming for these vreg issues. I buy them from everywhere, I scrounge them from old boards, and I've never had any problems except overheating shutdowns. I built one supply that uses that as a crude current-limiting "feature".
A zener in series will limit the current the regulator can provide since all output voltage must go through it.I see now, yes. Not sure that will work, but I see it. What about a eg 5V 1W zener in series with the vreg input? Or 2 vregs stepping down the voltage? The latter is probably what I would try... maybe that's a good reason not to
I sure hope some solutions are forthcoming for these vreg issues. I buy them from everywhere, I scrounge them from old boards, and I've never had any problems except overheating shutdowns. I built one supply that uses that as a crude current-limiting "feature".
I see now, yes. Not sure that will work, but I see it. What about a eg 5V 1W zener in series with the vreg input? Or 2 vregs stepping down the voltage? The latter is probably what I would try... maybe that's a good reason not to
The latter I have seen in industrial designs before and works very well. You might adopt a two stage voltage regulator too. First stage drops +/-38 V to (e.g.) +/-27 V and the next to +/- 16 V.
It's just a matter of putting two regulator circuits in series. Drop R1/R4. The first stage doesn't need D2/D6 but keep them in the second stage. D1/D5 are across both regulators, i.e. kathode of D1 on the input of the first regulator and the anode on the output of the second regulator, vice versa for D5. With a lower Vin-Vout difference, the maximum rating cannot be exceeded.
You could also go for a simpler pre regulator in the first stage, as has already been mentioned. You should be able to find examples on this forum with a search.
The LM3x7s are near impossble to destroy if used correctly. I have a class A headphone amplifier that needs +/-25 V. I didn't bother with installing the protection diodes (D1/D2/D5/D6) but then the amp draws enough current to discharge the output of the psu quickly at power down. The heatsinks are barely adequate because of lack of space. Still, it has been working fine for the last 11 or 12 years... That's why I can only imagine you're destroying them by exceeding the max Vin-Vout voltage.
Last edited:
Putting a zener in series will not guarantee that vin - vout is kept bellow the max rating. As has been suggested in this forum, it could climb up to 76V. Putting the zeners from vin to vout (kathode to input and anode to output for lm317) will ensure that. I am going to try this now. I pray the the lm337 is still alive because I don't have any others. I will put 3x8.2V zeners in series and see what happens.
"The latter is probably what I would try... maybe that's a good reason not to"
Just some self-deprecating humor. I've used the dual reg method often and it's worked well so far. I also often put an LED indicator on the output as well as that seems to both satisfy the minimum current requirements and avoid the premature input voltage drop... Not so relevant with a split supply, but maybe useful.
Just some self-deprecating humor. I've used the dual reg method often and it's worked well so far. I also often put an LED indicator on the output as well as that seems to both satisfy the minimum current requirements and avoid the premature input voltage drop... Not so relevant with a split supply, but maybe useful.
In my experience with them, the reverse voltage thing is the most commonly encountered problem. They don't always blow up as a result, sometimes they just get stuck into a 'current limit' mode when there's no current coming out. Power cycling can sometimes (randomly) result in them coming up OK the next time.
problem found
Guys, I am ashamed. I screwed up. There was a disconnected wire that caused a short circuit to the ground. Mostly it shorted the + rail and once it shorted the - rail. So far things look good. I connected my bass guitar and saw a nice signal at the output of the pre amplifier.
Thank you all for taking the time and helping. I learned a lot.
I am uploading a picture of the project if you want to see what it's all about
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
software development for living, music for the soul
Guys, I am ashamed. I screwed up. There was a disconnected wire that caused a short circuit to the ground. Mostly it shorted the + rail and once it shorted the - rail. So far things look good. I connected my bass guitar and saw a nice signal at the output of the pre amplifier.
Thank you all for taking the time and helping. I learned a lot.
I am uploading a picture of the project if you want to see what it's all about
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
software development for living, music for the soul
Thanks for the update...
If you get stuck with the pictures see post #10
http://www.diyaudio.com/forums/digital-source/165754-sony-cd-player-cdp-102-a.html#post2171957
If you get stuck with the pictures see post #10
http://www.diyaudio.com/forums/digital-source/165754-sony-cd-player-cdp-102-a.html#post2171957
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.