LM317 Dual Shunt Regulator

[schmitt trigger]

I am going to bring, and perhaps kill, the elephant in the room: would you consider using a SMPS? And perhaps follow it with a linear regulator?

Well it is a PSU of a guitar amplifier, maybe it would bring noise and harmonic artifacts...

Again, not attempting to flog a dead horse, but that is the reason for the linear post regulator. Anyways, it was only an idea.

I DO GET your point. I started electronics almost 50 years ago by repairing guitar amps. Indeed the harmonic artifacts, can really mess up a guitar sound. The only acceptable noise in a guitar amp is 120 Hz hum.    It adds warmth to the sound.

[David Hess]

I understand the first LM317 is configured as a CCS to provide the source current for the zeners.
I don't understand why the zeners are not referred to the ground?
instead to the opposite rail.

The opposite rail is just used to provide the current to bias the zener diodes into conduction.  Ground could be used with a resistor but the voltage would be the 1.25 volt reference of the 317, which might be preferable.

In this circuit the zener diodes add to the 1.25 volt 317 reference to make a power shunt regulator.  The only advantage of this circuit that I see is that it is a simple way to provide a fast responding current limited precision voltage output without separate current and voltage control loops with operational amplifiers.  I would have done it with operational amplifiers and one 317 per side.

[thyself]

The only acceptable noise in a guitar amp is 120 Hz hum. It adds warmth to the sound...

I will try both approaches (SMPS->LinReg and RCRCRC->LinReg) and share the observations.

[thyself]

I would have done it with operational amplifiers and one 317 per side.

Can you please post/ref to a schematic?

[David Hess]

I would have done it with operational amplifiers and one 317 per side.

Can you please post/ref to a schematic?

It is a little tricky because the current shunt cannot be on the positive side, for a 317, without affecting the regulation, and if it is on the input side or ground side, then the 317's quiescent current affects the current regulation, but except in precision applications that does not matter.

I am in the middle of moving and do not have access to my application library and did not find any good examples online.  It comes down to using an operational amplifier to pull the adjust pin negative through a diode when the current limit is reached.




I do not currently have access to my application notes but I would do something like this, but a little simpler.

https://forum.allaboutcircuits.com/ubs/a-16-16v-1-67a-constant-voltage-constant-current-lab-psu.480/