Design review: PSU regulator

[dougy83]

Hi,

I was wanting to make a simple adjustable CC/CV lab power supply with linear regulator fed from a SMPS. The SMPS output voltage will be a few volts above the linear regulator output voltage. The maximum voltage and current will presumably be limited by the choice of MOSFET.

I've attached my circuit. I've never had to do stability analysis. Are there any glaring errors in this circuit?

I'm aware that having R6 and R7 as the adjustment component (i.e. rheostat) will cause the CC/CV to go to maximum value in case of a dodgy wiper, and may swap it for the upper resistor.

Thanks

 

[AnalogKid]

I don't see a DC feedback path from the output to U1 for voltage regulation. Is the intent of the circuit a constant voltage output, or a constant current output?

ak

 

[dougy83]

I don't see a DC feedback path from the output to U1 for voltage regulation. Is the intent of the circuit a constant voltage output, or a constant current output?

The output voltage is sensed through the voltage divider formed by R5/R6. The intent is both current and voltage regulation

 

[danadak]

U1 has a large Cload on its output due to gate of pass transistor, so you want
to make sure its comped for that or possibly add a series R in series with U1
output and M1 gate. Use your sim to look at U1 output, to see how much
ringing is present, an indication of reduced phase margin.

Discussion over here - https://www.eevblog.com/forum/beginners/mosfet-linear-regulator-circuit/'

https://www.edn.com/understand-linear-regulator-stability/

https://www.ti.com/lit/an/slyt194/slyt194.pdf?ts=1643921696570&ref_url=https%253A%252F%252Fwww.google.com%252F

LTSPICE linear regulator loop gain stability analysis - Page 2

LTSPICE linear regulator loop gain stability analysis - Page 2

www.eevblog.com

Regards, Dana.

 

[dougy83]

Thanks, Dana. There is not that much ringing, and it dies out rather quickly. Adding a gate resistor increases the ringing, but it's possible the opamp model is unrealistic. I guess I can just build it and tweak as necessary.

There is a short overshoot of the current, but that is due to the response time of the opamp

 

[eTech]

Hi,

I was wanting to make a simple adjustable CC/CV lab power supply with linear regulator fed from a SMPS. The SMPS output voltage will be a few volts above the linear regulator output voltage. The maximum voltage and current will presumably be limited by the choice of MOSFET.

I've attached my circuit. I've never had to do stability analysis. Are there any glaring errors in this circuit?

I'm aware that having R6 and R7 as the adjustment component (i.e. rheostat) will cause the CC/CV to go to maximum value in case of a dodgy wiper, and may swap it for the upper resistor.

Than

What type of smps?
What is the switching frequency?
What is Vout and max Iout?

 

[dougy83]

What type of smps?
What is the switching frequency?
What is Vout and max Iout?

I'll start with the following: Boost from 12V (input) to 12-40V (output). 200-400kHz. Vout max 35V, Iout max 3A.
I should be able to connect higher input voltages, provided that the MOSFET can handle it, and if I add protection to U1 +ve input.