Simple DIY buffer PSU

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#21
While I'm here, main PSU design.
 

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#22
you can't use two positive-side regulators to post-regulate your +/- 35 V supplies. There is no way to connect them so that the ground of the +/- 15 V will be common with the +/- 35 V supplies. Go ahead and think about that... you will find it is impossible. You can still use two positive side regs for the +/- 35 V supplies, but you will need to post-regulate using one positive and one negative (e.g. LM337). Same goes for -12 V, if you need that. You'll need to use a 7912.
 
#24
macboy said:
you can't use two positive-side regulators to post-regulate your +/- 35 V supplies. There is no way to connect them so that the ground of the +/- 15 V will be common with the +/- 35 V supplies. Go ahead and think about that... you will find it is impossible. You can still use two positive side regs for the +/- 35 V supplies, but you will need to post-regulate using one positive and one negative (e.g. LM337). Same goes for -12 V, if you need that. You'll need to use a 7912.
Click to expand...

I would agree if TS needed + and - 15V, but as far as I know, he only needs +15 V (and +12 V).
 
#25
macboy said:
you can't use two positive-side regulators to post-regulate your +/- 35 V supplies. There is no way to connect them so that the ground of the +/- 15 V will be common with the +/- 35 V supplies. Go ahead and think about that... you will find it is impossible. You can still use two positive side regs for the +/- 35 V supplies, but you will need to post-regulate using one positive and one negative (e.g. LM337). Same goes for -12 V, if you need that. You'll need to use a 7912.
Click to expand...

Foolish me! You're correct.

AndrewT said:
The way I looked at it he wanted two positive supplies from one higher positive supply.
What has changed?
Click to expand...

OP:
Drops +/-35V from the main regulated power supply (sill in development, nearly there) down to +/-15V and +/-12V. Two of these in series will be used rather than using symmetric regulators (easier to construct this way, for one thing).
Click to expand...
That could be ambiguous.

No problem. It's simple to change to a symmetrical supply. I don't expect additional caveats or pitfalls.
 
#26
OK, symmetric design.

Return to zener pre-regulator stage to minimise complexity and PCB space + random (TM) aesthetic whim. Added fuses - rating is somewhat arbitrary given uncertain load of circuit and ~200mA is probably closer to being useful.
 

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#27
random007 said:
OK, symmetric design.

Return to zener pre-regulator stage to minimise complexity and PCB space + random (TM) aesthetic whim. Added fuses - rating is somewhat arbitrary given uncertain load of circuit and ~200mA is probably closer to being useful.
Click to expand...

OK, my bad, you did need symmetrical supplies.
Design looks OK to me, but I don't understand the -12V circuit if you're only going to need to switch some relays. You might as well leave it out and save yourself some space.

EDIT: is it on purpose that R2 and R3 are different values?
 
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#28
jitter said:
OK, my bad, you did need symmetrical supplies.
Design looks OK to me, but I don't understand the -12V circuit if you're only going to need to switch some relays. You might as well leave it out and save yourself some space.

EDIT: is it on purpose that R2 and R3 are different values?
Click to expand...

Yeah, I'm thinking that dropping 12V is a good idea.

No, R3 is wrong. Well spotted. :xeye: :crazy: :crying:
 
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