Switching losses & S nubber circuit

1. Switching losses & Snubber circuit

2. Ideal switch vs practical switch

3. Ideal switch vs practical switch • In this course, we use ideal switch to describe the power electronic circuits operations – occasionally practical switches will be mentioned. • PE circuit design need to use actual device model in order to analyze power dissipation and efficiency

4. Switching losses Since voltage and current do not change instantaneously, there will be power losses during switching – ‘switching losses’ • Switching Power Loss is proportional to: • switching frequency • turn-on and turn-off times

5. Switching losses turn-off iT turn-on Io turn-off turn-on Vd vT The profile must contained within the safe operating area (SOA) of the device

6. Switching losses The profile becomes worse if the stray inductance is considered during the switching

7. Switching losses

8. Snubber circuit • In order to reduce the stress and over voltage of the device, a snubber circuit is used to alter the v-i profile of the device • There are various type of snubbers: we will only consider the turn-off and turn-on snubbers Turn-on snubber Turn-off snubber

9. Snubber circuit Turn-off snubber circuit operation • The switch current can fall immediately since there is a path provided by the capacitor Cs • The capacitor voltages increase and stop conducting when Cs=Vd at which diode Df start to conduct

10. Snubber circuit Turn-off snubber circuit operation • The switch current can fall immediately since there is a path provided by the capacitor Cs • The capacitor voltages increase and stop conducting when Cs=Vd at which diode Df start to conduct

11. Snubber circuit Turn-on snubber circuit operation • The stress is reduced by reducing the switch voltage when the switch current increases.

12. Snubber circuit Turn-on snubber circuit operation • The stress is reduced by reducing the switch voltage when the switch current increases.