| 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. |
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| 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 |
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| 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 |
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| yeti |
The 4 output Transistors will blow, the current mirror Q1,Q2 will need biasing.
Regards:
Arne |
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| 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 |
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| 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. |
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| hugeli60 |
| I just wanted to make sure I have enough kick for large banks of MOSFETS. |
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| 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. |
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