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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 1.6 kW. Since resonant half-bridge power supplies operate with very high efficiency because of zero-voltage switching (ZVS), they provide very high efficiency. Typical MOSFETs with a VDSS of 500 V to 600 V can be used for resonant half-bridge supply applications. Toshiba also offer MOSFETs with a high-speed diode (HSD) having a short reverse recovery time (trr) for applications in which a regenerative current flowing through the body diode causes recovery losses.

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Describes the features of the DTMOSV series and the improvements from the previous series 9/2017

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Application Note

Application note
Name outline Date of issue
Describes planar, trench and super-junction power MOSFETs 11/2016
Describes the absolute maximum ratings, thermal impedance and safe operating area of power MOSFETs 11/2016
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  • 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.  

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  • Operation

    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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