I have done some research on a bias circuit in a quasi complimentary circuit with two output vertical MOSFET's.
The bias circuit works well so long as there is not too much bais current in which case thermal runaway occurrs.
With 20mA bias current it is very hard to get thermal runaway.
I tested the circuit using a household iron to heat up the heatsink to above 70 degrees C and had no problems.
However, with 90mA starting bias the bias current just kept on rising out of control.
I used a simple Vbe multiplier with no emitter degeneration glued to the heatsink.
The bias circuit works well so long as there is not too much bais current in which case thermal runaway occurrs.
With 20mA bias current it is very hard to get thermal runaway.
I tested the circuit using a household iron to heat up the heatsink to above 70 degrees C and had no problems.
However, with 90mA starting bias the bias current just kept on rising out of control.
I used a simple Vbe multiplier with no emitter degeneration glued to the heatsink.
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sounds interesting and I probably won't have a clue as to the issue but a diagram would help me follow along and contribute if possible.
Hopefully you'll have this ironed out soon
An externally hosted image should be here but it was not working when we last tested it.
The source resistor is in the wrong place on your lower mosfet, it should be between the output rail and point where your cfp transistor joins the mosfet. This will help thermal stability of the lower half.
What have you got mounted on your heatsink? Outputs and drivers and bias generator? Or just outputs and bias generator?
What have you got mounted on your heatsink? Outputs and drivers and bias generator? Or just outputs and bias generator?
Just the bias and output transistors.
The driver transistors just have small bolt on heatsinks on them.
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