How do I derive the optimum load impedance for class A, class B, and class F power amplifiers? I know that B should be 4/pi and F is either short or open, but I am unsure how to derive these.
A: You need to define the 'load' first, and then design your output circuit.
As an example, if you 'need to' load your circuit with 4 ohms speakers and you do all your design for 16 ohms 'load'; it would not work properly.
You need to star from the end. Where will you use that circuit, whit which kind of load, and then start adjusting you design to that output.
Comments: 2
yes, the supplies could get shorted out, but a few diodes in the right place will protect that.
So a DPDT relay will do that, or you could do it with transistors. Difficult to do with words only... Draw a schematic with power transistors, 2 PNP, 2 NPN and diodes.
I try to find an online schematic to match...
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well not sure of the complete circuit you have but what about just using a double pole double throw relay (DPDT). Tie the output (the commons) of the relay to the motor itself. Them tie one pair of the relay contacts to + and -, and the other set to - and +, thus creating a reverse polarity effect. Then all you would need to do is trigger the relay. This would prevent the reversing issue you spoke of and isolate the two sets of contacts. Since it's a DPDT, you'll never have it forward...