Flyback Converter Protection Scheme with a Selective Shutdown Delay Time

This paper presents simple and effective protection schemes for the off-line flyback converter. The proposed protection schemes can protect the power MOSFET from various abnormal conditions. In the proposed scheme, the output short condition can be discriminated from over load or load transient condition by monitoring the duty cycle and error amplifier output. With this technique, the power supply is allowed to be shutdown immediately without time delay at output short condition. Meanwhile, the power supply is shut down with some time delay in over load condition to prevent the premature shutdown during load transient. The validity and effectiveness of the proposed schemes are verified through experimental results