Design of a Miniature High-Gain Quasi-Resonant Flyback Converter

Following the rapid increasing adoption of wide band-gap power semiconductor devices, the corresponding high voltage test equipment becomes indispensable nowadays. As one of the most important power semiconductor devices test, HTRB (high temperature reverse bias) puts the power semiconductor devices under high temperature environment with reverse-bias voltage applied to evaluate their projected anticipated lifetime. In this paper, a microminiaturized high-gain quasi-resonance flyback converter based on GreenPAK programmable chip SLG46855 is designed for HTRB testing of kV-level SiC power semiconductor devices and other related high voltage test applications. The converter topology couples an flyback circuit with two transformers, forming a differential charge pump-based voltage-multiplier to convert 5V~12V input to 800V~1600V output with higher voltage gain, lower stress on transformer, less diodes and smaller output capacitors, correspondingly less pre-charge time considerably. Quasi-resonant soft switching is applied in steady state DCM to realize higher voltage gain and lower power loss drastically. A new quasi-resonant voltage valley detection circuit leveraging the input pin characteristic of SLG46855 is designed to capture the rising edge of drain voltage to trigger the turn-on signal of MOSFET switch, while magnetizing current detection triggers the turn-off signal. A secondary current cancellation circuit is designed to eliminate the reflected charge pump current, thus allowing accurate detection of the true magnetizing current. Meanwhile, to implement high-speed magnetizing current detection without the use of an expensive and power hungry high speed comparator, an self-calibrating biasing circuit is introduced to elevate the detection signal to near trigger threshold of the input port of SLG46855. The combination mimics the behavior of a mV-level comparator with ns-level response time. Smooth mode switching is realized during startup, balancing voltage rising ratio and power heat. In this paper, the converter operation principal and SPICE simulation will be demonstrated around its topology, related control and detection methods correspondingly. A 3.0x1.8 cm
²
miniature prototype is made and evaluated, seeing high performance and advantages in HTRB test application.