Here is a simple audio amplifier with an npn transistor. What should be the value of voltage source V2? How can I calculte it?
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Simple (very crude) approach, say when collector resistor is given (not asking why is it 10k): Transistor power limit -> reduce to 1/10 for safety -> choose collector current limit -> divide power by current to validate to 1/4 of max collector voltage -> multiply by resistor value -> double it to keep output in the middle -> get voltage.
The datasheet says: ~625mW is a limit, then 62.5 mW is nominal. Then choose sensible collector's current. Looking at datasheet it is between 1..10mA. Looks like for ~50mW the CE should be around 5..50V. Validating the CE limit from datasheet 40V/4=10V. Deriving for 10K resistor and voltage of 10V getting 1 mA current. Doubling it -> 20V.
No matter how safe it all looks, the number looks too high and overall the cascade feels a bit fragile. I'd rather go with no more than 9-10V and reconsider output impedance and optimize on something like bandwidth or noise figure.