Online Degradation Detection/Prediction Method for Current Transfer Ratio of Photo-Coupler Installed in Digitally-Controlled Switching Mode Power Supply

摘要： The software-implemented degradation detection/prediction of the current transfer ratio (CTR) of a photo-coupler installed in a digitally-controlled switching mode power supply was studied. The photo-coupler is one of the key devices in an isolated power supply circuit, which transmits a voltage/current signal to a controller though the isolation gap. If the CTR of the photo-coupler degrades to halfway between the normal value and the threshold of the hardware protection circuit, overvoltage/current may be supplied continuously to the load circuit and possibly cause a severe failure. By comparing the theoretical pulse width modulation (PWM) duty, which is calculated from the input/output voltage and the pre-measured power supply circuit e?ciency, and the applied PWM duty, which is calculated via feedback control, CTR degradation is detectable online. In this paper, we describe the concept of this method and verify it using both simulation and prototyping circuits.