Question

In a zero current switching resonant converter, the switching loss and noise are increased due to presence of capacitive coupling called
1. Miller capacitor 
2. Series-resonant capacitor 
3. Parallel resonant capacitor 
4. Switch capacitor

Answer 1

Correct Answer - Option 1 : Miller capacitor 

Limitations of ZCS resonant converter:

• ZCS (zero current switching) can eliminate switching losses at turnoff and reduce the switching losses at turn-on.
• As a relatively large capacitor is connected across the diode, the inverter operation becomes insensitive to the diode’s junction capacitance.
• When power MOSFETs are used for ZCS the energy stored in the device’s capacitance is dissipated during turn on.
• This capacitive turn on loss is proportional to the switching frequency.
• During turn on a high rate of change of voltage may appear in the gate drive circuit due to the coupling through the Miller capacitor, thus increasing switching loss and noise.
• The switches are under high current stress, resulting in higher conduction loss.
• By the nature of ZCS, the peak switch current is much higher. In addition, a high voltage becomes established across the switch in the off state after the resonant oscillation.
• When the switch is turned on again, the energy stored in the output capacitor becomes discharged
• through the switch, causing a significant power loss at high frequency and higher voltages.