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Groundloops 9th October 2007 07:28 PM

Please rate this psu design
Im about to build a preamp and want to start with the psu. I came about this design in; what do you think of it?

Is it suitable to feed various opamps (the common suspects), up to 6 pieces? Or is it simply overkill and a lm317/337 with rc filter after the diodes will do as well?

Khron 9th October 2007 07:57 PM

I'm no electronics expert, but i do have a couple of ideas/tips, whatever you want to call them:

1) I think that bypassing the adjustment pots with some caps may well help with bringing down the noise (as per the LM317/337 datasheet

2) Arent those 100V caps just a *bit* overkill, given that you have a maximum of 48V DC? I'm thinking that some 63V caps would work just fine before the regs, and some 35-50V ones after, and this would be based on bulk and cost.


Elvee 10th October 2007 07:57 AM


Have you checked that the OPA548 accepts a capacitive load? Only very few opamps do.

AndrewT 10th October 2007 08:06 AM

the voltage drop across all the regs/Vref are very high.
What about dissipation?

m-tech 10th October 2007 04:35 PM

48Vdc is too high input voltage for LM317. It's OK if ADJ pin floating above ground, but you are using pot on this pin. Be careful.
No need for big capacitor ( 1000u is too much ) at output of LM317.

nonoise 11th October 2007 05:36 PM

Perhaps Kevin (it looks like his design) used a LM317HV this
variation of the device could handle the 48V.

AndrewT 12th October 2007 06:49 AM

the floating three pin regs (317 etc) can work at much higher than 35V. That is the input to output pin limit.
The problem is at start up when the output is discharged (zero V) and the input suddenly rises to maximum in a few mS. A big cap on the output makes this worse.
Similarly, the adjustment could take the output pin very low and exceed the differential limit.

nonoise 12th October 2007 11:24 PM

Yes Andrew quite correct,
I also saw that they tend to specify a delta V different to a normal vin
Max. The 317HV will do 60V but the 337 will only do -50 V which is a bit close to the -48V input.
In short the design seems a bit stressed (also considering the not unsubstantial dissipation the pass elements are subjected to).

Gordy 15th October 2007 09:46 PM

I agree that it needs adjusting as has been stated above (... lower input voltage to regulator for lower volt drop across [and hence lower dissipation in] the regulator, adjust the cap values, add a cap across the adjustment resistor). Also the regulators and op-amps may need heat-sinks.

However, the overall concept is right.

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