Sinrace Power Supply Technology (Shenzhen) Co., Ltd.

Switching power supply in the buffer circuit performance has a direct impact on the quality of the system. The paper gives a simple, easy to install RC snubber circuit design method can not only reduce the switch turn-off losses, but also reduce the transformer leakage inductance and peak voltage.

    Switching power supply with a transformer in the topology, switch off the voltage and current overlap is the switching power losses due to loss of the main part, and because the circuit stray inductance and stray capacitance, the power switch off off, the circuit will also appear over-voltage and oscillation. If the peak voltage is too high, it will damage the switch. Meanwhile, the existence of oscillation will increase output ripple. To reduce the turn-off loss and voltage spikes, you need to switch both ends of the parallel snubber circuit to improve the circuit performance.

    The main functions of the buffer circuit: one is to reduce turn-on or turn-off losses; the second is to reduce the voltage or current spikes; third is to reduce dV / dt or dI / dt. The MOSFET, the current rate of decline quickly, so it is very small turn-off losses. While still using the turn-off MOSFET, the buffer circuit, but its role is not to reduce the turn-off losses, but to reduce the transformer leakage inductance voltage spike. In this paper, for the MOSFET, the turn-off snubber circuit to be discussed. 

    RC snubber circuit design

    RC snubber circuit design must be familiar with the main circuit topology used in the situation. Figure l shows the composition of the RC snubber forward converter. Figure, when Q is off, the collector voltage starts to rise to 2Vdc, and capacitor C limits the collector voltage rise rate, while reducing the rise in voltage and decrease current overlap, thus reducing the loss Q switch. And before the next time the switch turns off, C must have full voltage 2Vdc is done and the discharge path for the C, Q, R. 

  Assuming no buffered switch circuit shown in Figure 1, the reset forward converter primary winding turns winding and the same. Thus, when Q off instantly, stored in the magnetizing inductance and leakage inductance of the energy release, the reverse polarity voltage across the primary winding, the switch forward converter collector voltage quickly rose to 2Vdc. Meanwhile, the excitation current flows through diode D reset winding, and finally reduced to zero, then the voltage drop across Q to Vdc. Figure 2 shows the switch collector current and voltage waveforms. Can be seen, the switch without snubber circuit, in the Q is off, the leakage inductance voltage spikes across the large turn-off loss is produced by large, severe burn switch is likely, therefore, must give the switch tube with buffer circuits.