Drive circuit for 2-stage converter combined with coupling capacitor

The capacitor coupled 2-stage converter (CC2SC) has large voltage conversion ratio and high power efficiency. However, when the conventional drive circuit is used for the CC2SC, there is a problem that the magnitude of gate drive voltage for the high side switch in the first stage becomes lower and the high side switch cannot be switched on properly. Without modification, a floating power supply is needed for the CC2SC. This paper presents a new drive circuit for the CC2SC. The proposed circuit uses two MOS-FET drivers, two diodes and two capacitors in order to remove a floating power supply. The circuit operation is described in detail and steady state analysis is performed. From the analysis, the magnitude of the gate driving signal is almost constant independent of the input voltage and the duty cycle. The experiment is performed for the prototype converter, and experimental result agrees well with analytical one. The power efficiency of the CC2SC with the proposed drive circuit is superior to those of the single stage converter and the conventional 2-stage converter.