Patent ID: 7529108

Claim:
A digital controller for use with a full-bridge power converter which includes an isolation transformer and a switching means operated by said controller, said controller arranged to operate said switching means so as conduct first and second currents of opposite polarity through said isolation transformer's primary windings during respective power-transfer phases, said first and second currents both returned to a common node, said controller comprising: a current sensing means which generates a non-zero voltage V in when either of said first or second currents is greater than zero; a sigma-delta modulator arranged to integrate a signal applied to its input and modulate the integrated signal to a bitstream, said modulator comprising: a first integrator; and a second integrator; a first decimation filter; a second decimation filter; and a switching network arranged such that a signal which varies with V in is integrated by said first integrator and said bitstream is decimated to a digital word by said first decimation filter during said first power-transfer phase, and such that said signal which varies with V in is integrated by said second integrator and said bitstream is decimated to a digital word by said second decimation filter during said second power-transfer phase, such that the difference between the values represented by said digital words increases with the magnitude of any imbalance between said first and second currents.