Electronics > Beginners

TL431 linear power supply

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mike_mike:

--- Quote from: spec on December 14, 2018, 09:20:55 pm ---mike_mike

Current limiting added to PSU circuit version 3 of reply #45, as per attached schematic:

--- End quote ---
C2, C17 and C15 are 10uF non polarised capacitors ?
Does they really need to have such a big value and they really need to be non polarised ? 
R11, R16, R6, R13 could have a more usual value ?

not1xor1:

--- Quote from: spec on December 14, 2018, 09:20:55 pm ---mike_mike

Current limiting added to PSU circuit version 3 of reply #45, as per attached schematic:

--- End quote ---

some notes:
- The common emitter stage inverts the phase so you have to swap inverting and non-inverting inputs.
- I've not made any calculations yet, but I think it would be safer to replace some transistors with BD139/40.
- Probably it would be hard to compensate.
I'll see if I can simulate it.

xavier60:

--- Quote from: not1xor1 on December 15, 2018, 09:28:39 am ---
- The common emitter stage inverts the phase so you have to swap inverting and non-inverting inputs.
-
- Probably it would be hard to compensate.


--- End quote ---

When the op-amp's inputs are reversed, its minimum gain becomes unity.
This can be a problem if there is too much gain elsewhere in the loop.
I know from recent experience. 

not1xor1:

--- Quote from: xavier60 on December 15, 2018, 09:51:06 am ---
--- Quote from: not1xor1 on December 15, 2018, 09:28:39 am ---
- The common emitter stage inverts the phase so you have to swap inverting and non-inverting inputs.
-
- Probably it would be hard to compensate.


--- End quote ---

When the op-amp's inputs are reversed, its minimum gain becomes unity.
This can be a problem if there is too much gain elsewhere in the loop.
I know from recent experience.

--- End quote ---

What do you mean?
In the classical floating PSU design, where the opamp inputs are swapped, the overall gain can be set to 0.

xavier60:

--- Quote from: not1xor1 on December 15, 2018, 10:19:21 am ---
In the classical floating PSU design, where the opamp inputs are swapped, the overall gain can be set to 0.

--- End quote ---
With the floating type regulator I built recently, the reference ended up on the  CV op-amp's inverting input and the voltage feedback divider on the non-inverting input.
Even if a large capacitor is connected between its output and inverting input, the AC gain can never go below unity.
This isn't a problem in this situation because there is no extra gain between the CV op-amps output and the MOSFET's Gate.

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