Feedback loop in linear regulator..Error amplifier connection?

[treez]

Hello,
The inverting input of the error amplifier, U1, is connected to the reference voltage via resistor R9.
it seems to work OK, but is this ok?
I always thought it was more usual to connect the inverting input of the error amplifier to the fed back signal?

LTspice simulation and schematic attached.

 

[FvM]

I always thought it was more usual to connect the inverting input of the error amplifier to the fed back signal?

Not usual, strictly required. But you overlooked that M1 is inverting the overall gain.

 

[LvW]

Treez, a stable feedback loop must contain one (or 3, 5,..) signal inversions. As your path transistor operates inverting, the error amplifier is required to be non-inverting.

 

[alexan_e]

This is a nice handbook if you want to read about power supply operation

Linear & Switching Voltage Regulator Handbook - ON Semiconductors
https://www.onsemi.com/pub/Collateral/HB206-D.PDF