High voltage output stage design

[predator89]

I have a signal coming from opamp (0-3 V) and want a high voltage output upto 40 V using HV mos.
I have confusion of whether to use class AB or B push pull output. Also please help me with schematic if possible.

 

[Audioguru]

A Mosfet can easily amplify 0-3V up to 0-40V. You did not say how much current and did not say the waveform or is it DC?
Class-AB has very low distortion and is used in audio amplifiers. Class-B has crossover distortion and is used for switching something on and off.

 

[predator89]

It is a AC signal. But how can i use both low voltage and HV mosfets for Class AB configuration?

 

[chuckey]

What frequency AC? How much current does the 40V output have to deliver?
Frank

 

[predator89]

100Khz freq and have to drive load of 1M

 

[chuckey]

With such a high load impedance a class A should do. You still have not said if its a sine wave of 40V P-P, 40 V RMS or a pulse of 0 -> +40 V.
Frank

 

[D.A.(Tony)Stewart]

We have confusion what inputs and outputs you have.
Single Supply or Dual?
AC out or DC coupled?
rise time?
Load Capacitance?
Rail-Rail out from 3V? or 5V? @ 10k load or 100k?
40V? or +/-20V?
Voltage gain=? 10? 12? 13? 15?
Single supply is more complex with biasing, unless AC coupled.

 

[dick_freebird]

High DC impedance is one thing, but 100kHz with good
waveshape fidelity would need a fair bit of output current
if there's any significant load capacitance. This needs to
be expressed before you can say that a Class A output
will be acceptable power-wise.

Figuring that, say, I wanted a 1MHz 3dB full power
bandwidth to ensure 100kHz is clean, and I had a 50pF
load, something like 1E-6s/50E-12F=>Rout=20Kohms
(leading to a 2% DC amplitude error if outside the
feedback loop) and a Class A idle current of 2mA
or so (higher than the 40uA that the DC load and
supply voltage alone, suggest). What is real Cload,
though?

 

[predator89]

I am designing a high voltage amplifier for a DAC coverter. For this i have designed a opamp and now designing high voltage output stage which i would be connecting in negative feedback. to the opamp.
Requirment for my high voltage amplifier is:
Single input
Input: 0-3V AC
Output: 0-40V AC
Load: 1M
Freq: 100Khz

I am still confused with which design to go for high voltage output stage.
Please help me with the schematic if possible.

 

[dick_freebird]

If you have the supply headroom (like 42V) you might
think about a voltage-to-current converter like an
emitter-degenerated NPN, throwing an output proportional
current to the high side, = a PNP mirror sourcing to the
load (which you may want to make lower impedance
by some parallel element). Very simple * stable in itself,
and the voltage-current transform may help stability /
settling over a voltage buffer type approach.

Now, you can find "40V" op amps (some higher, some
single-supply) and rigging one of these in A=15 ought
to not be too tough, stabilization issues aside. I think
the first op amp would want to be left as-is and just
make the buffer amp external to that loop, depending
on its local feedback only.