Power converter symmetry correction circuit

Claim 1

For use in a power converter having a magnetic core transformer having a primary and a secondary winding, a pair of solid state power switches for push-pull drive of the transformer and an output circuit for providing an output voltage derived from the transformer, a circuit comprising: output voltage sense means for producing an output voltage sense signal from the secondary winding; a pulse width modulator coupled to the solid state power switches and operative to apply pulse width modulated pulses alternately to the power switches for push-pull drive of the transformer having pulse duration controlled according to said output voltage sense signal; a symmetry correction circuit operative in response to the output currents of the power switches to provide a single error signal being time-multiplexed to include a representative sample of the magnitude of each current, further including: first and second integrators each operative to provide a respective error voltage derived from and representing the output current of respective ones of the power switches; and means for actuating each of the first and second integrators in alternating sequence to alternately receive said error signal and provide the integrator error voltages; and means for selectively applying the single error signal to the pulse width modulator to cause adjustment of the duration of the modulated pulses to compensate for the difference in characteristics between the power switches.