High voltage OPAMP / PREAMP

[hugeli60]

I am working on a high voltage opamp for the pre-amp to a MOSFET voltage follower. What do you guys think about this schematic?

I am planning on using SOT-223 ZETEX HIGH Voltage Devices for the diff amp stage and there High current devices in the output stage.

I want this thing to operate at +/-100v and drive a mosfet power follower. Caps are TBD values. I dont have a good spice program yet to simulate.

 

[sonnya]

Your currentmirror Q1 and Q2 need a connection from their base to Q1 collector.
Place a bias resistor over C9.

Try find BJT with a high "va" and run them at ~.5 - 1 mA.
FZX493 and FZX593 is a good device from Zetex.

The spice data says :

NF = .99
Va = 270

Sonny

 

[sonnya]

Now i have a little more time.

You do know that C1 does not have a function?.

Why do you have installed C2,C3,C4,C6,C7??? They are not necessary. C5 (compensation cap) is enough to control the opamp's freq. response/phase margin.

Sonny

 

[yeti]

Preamp

The 4 output Transistors will blow, the current mirror Q1,Q2 will need biasing.

Regards:

Arne

 

[hugeli60]

OOPS. I sent the old schematic. The base connection of the current mirrors should be there. I wanted to put spaces where I could put capacitors or other components to play with the circuit.


I Am not sure what output devices to use yet. I need to find something beefy.Thanks for the input

 

[Nelson Pass]

I doubt that you need this much output stage just
to drive the inputs of MOSFET followers. Maybe
you should dump the outputs and just use the drivers.

 

[hugeli60]

I just wanted to make sure I have enough kick for large banks of MOSFETS.

 

[Havoc]

For a free spice version: http://www.winspice.com/
No schematic entry, but fast.

Suggestions:
- 2 small resistors (50-300 Ohm) in series with the emitors of the curent mirror Q1 Q2
- 2 even smaller resistors (10-30 Ohm) in series with the input pairs emitor Q4 Q5
- use leds to bias the current sources, zeners can be very noisy
- take a look at transistors meant for video stages, plenty of gain and voltage.