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AC-DC Resonant Half-Bridge Power Supplies

Resonant half-bridge power supplies are suitable for relatively large-capacity power supply applications and ideal for applications with a wattage of 150 W to 1 kW.

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Half-Bridge Power Supplies

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Application Examples

  • FPD TVs
  • Desktop PCs
  • Uninterruptible power supplies (UPS)
  • Servers

Circuit Overview

Resonant half-bridge power supplies alternately turn on two transistors and exhibit a high transformer utilization factor. Additionally, resonance helps reduce switching loss, making it possible to deliver high power conversion efficiency.

Resonant half-bridge power supplies can be employed for high-capacity power supply applications and are commonly used for power supplies with a capacity of 150 W to 1 kW.

To prevent shoot-through current, resonant half-bridge power supplies require a dead time during which both Q1 and Q2 do not turn on simultaneously. Biased magnetization is unlikely to occur due to the circuit configuration.  


1.  Q1 turns on. As a result, a voltage is applied to the resonance circuit comprising Lr, L and Cr, charging Cr.
The charging current is transmitted to the secondary coil through L. This resonance current increases gradually up to the peak level. Since the voltage applied to L decreases as Cr is charged, the resonance current then begins to decrease.
However, the excitation current passing through Lm continues flowing.

2.  Q1 turns off. Excitation current charges the parasitic of Q1 (Cds1) and discharges the parasitic capacitance of Q2 (Cds2).
Then, a current flows via Dq2. Therefore, Vds1 does not increase immediately, and Vds2 does not decrease immediately.

3.  When Vds2 reaches zero, Q2 turns on, causing the charge stored in Cr at Step 1 to be discharged.
This current is transmitted to the secondary coil via L.
Since the voltage across Cr decreases, the voltage across L decreases, causing the current to decrease gradually.
However, the excitation current passing through Lm continues flowing.

4.  Q2 turns off. As is the case with Step 2, Cq1 is discharged, and Cq2 is charged.

1.  When Vds1 reaches zero, Q1 turns on.


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