alternative to TL431 in isolated smps with Vout= 38v

[eem2am]

I do isolated smps with TL431 /OPTO feedback.

Vout is 38V and since TL431 is maximum of 36V so I cannot use it.

Any reader know of a nice cheap alternative……..for example an op amp with this supply capability

 

[IanP]

The TL431 can be replaced with a circuit based on discrete components such as Zener diode, opamp and BJT/MOSFET OC/OD transistor ..
Have a look at the attached picture ..

IanP
:|

 

[eem2am]

hello
-but problem is that op-amp in TL431 is of necessity , very "slow"...it's difficult to find op-amps which are slow enough for this purpose.

I have tried your circuit, but the transistor that you have shown just smashes between fully on and fully off....no matter what kind of feedback i put round the op-amp.

Do you have suggestions?

 

[FvM]

it's difficult to find op-amps which are slow enough for this purpose

I don't understand the problem, an OP circuit needs frequency compensation as well as a TL431. The part
count of the OP circuit is most likely higher, that's why most designers would use a TL431 with a simple
voltage divider or series zener diode to handle the supply voltage range. Respective circuits have been
discussed at edaboard before.