Stacking power supplies

[carpenter]

The schematic: (It's worth mentioning, there's a slow climb to full power--ten seconds or so. It makes for a gentle power-up circuit.)

[Jason Hubbard]

Three terminal regulators like the LM317 can operate at high voltages (i've seen diagrams where they are used in 350v tube designs). The only restriction is that the difference between the input and output voltages must not exceed 40v.

The adj pin can be slugged with a capacitor to bring the rail up on the output slowly (but in doing so may cause that 40v difference to ocurr).

I don't know if this helps, but perhaps food for thought?

[carpenter]

Thank you!

[carpenter]

Jason, thanks to your suggestion, I found the solution:

[dave_gerecke]

Hello Carpenter, I understand now. You're not talking about the caps in the schematic shown, you're talking about large filter caps later in the chain. Yeah, I would agree they tend to get expensive very quickly once you break the 60-80 volt range and want large capacitance values. From your observation you found one with voltage capabilities, but a lower capacitance. Are you planning on paralleling a bunch of these for a larger value?

Peace,

Dave

[carpenter]

Hi Dave,

Actually, now that I've located a plausible schematic that allows the LM317 to achieve high voltage regulation, I'll probably go that route.

If it doesn't work, then I'll follow through on my thoughts with the dual stage version of Nelson's filter.

[Jason Hubbard]

Q1/Q2 weren't used on the schematics i saw, in fact there were very few differences compared to a fairly standard regulator setup, so it might be worth your while googling some more to find other schematics.

As i said before you can slug the adj pin with a cap to make the output voltage rise slowly (with the proviso that the i/p to o/p voltage difference remains less than 40v), there is an example of this in the power supplies section see http://www.diyaudio.com/forums/showt...hreadid=129687).

You might also want to consider an LM329 on the adjust pin to reduce noise further still.

LT317 is a better spec device than LM317. I believe LT1085 is better still but i'm less familiar with it.

[carpenter]

Again, thanks, Jason. I'll check out those links and ideas you presented.

[carpenter]

Something I just read on a Bay Linear datasheet:

"Since the LM317 is a floating regulator and "sees" only the input-to-output differential voltage, supplies of very high voltage with respect to ground can be regulated as long as the maximum input-to-output differential is not exceeded."


How about that?