+/-33V outputs - What opamp could I use?

[atferrari]

I wonder if is it possible to do something similar to what is proposed here

https://www.electro-tech-online.com/threads/pwm-signal-to-lm317-to-adjust-voltage-output.125091/

but this time to get two control signals: one from 0 to +33V to control an LM317 and another from 0 to -33V to control an LM337.

I imagine two separate opamps, one powered between 0 and +38V and the other between -38V and 0V. (I have those +/-38V DC available from an old power supply).

What could be the most suitable opamps?

Searching through Farnell I can at least compare some but the prices of the suitable(?) ones is scary. To come to my hands I have to think of them multiplied around 4 times!!

Maybe I am overlooking something...

Any suggestions? Gracias

 

[MrAl]

Hi,


You think you could post a schematic rather than have us search through a bunch of posts to see what you actually want to do? I think this would help a lot for people reading this thread. I know it would help me to understand you better.

 

[alec_t]

If I understand you correctly you want one PWM signal to give two simultaneous outputs; one of them negative (0 to -33) and the other positive (0 to 33) ?

 

[atferrari]

Here it is

I believed it was better to read about the idea until reaching the circuit. But OK, that is me.

Here it is

https://www.electro-tech-online.com/threads/pwm-signal-to-lm317-to-adjust-voltage-output.125091/#post1036064

Two independent PWM signals; each one controlling one regulator. That is why I think of having them powered between common and its respective rail (single supply).

My concern is the type (and COST) of the opamps I could use.

 

[alec_t]

The op-amps themselves aren't critical as they don't have to withstand 33V. You could run them at, say, 12V and use them to drive BJTs or FETs switching loads operating from 33V.

 

[ronsimpson]

High voltage op amps are not so common but:
AD8274
ADA4004
LTC6104, LTC6103, LT1013
AD5749
OP4177
PA340CC
PA341CE

 

[alec_t]

Perhaps this? Almost any opamp (I used a LM324 model) with rail to rail input will do. Not having a LM317 or LM337 model I used LT1085 and LT3015 respectively. There are two 0V to +5V PWM inputs (from a micro). One opamp has a 5V supply, the other a -5V supply. The regulators have +33V and -33V supplies respectively.

 

[atferrari]

Will try it.

Busy with vessels right now but I will try it.

Gracias.