New Twist On The Half-Bridge Converter Solves Subtle Failure Mode

Focus:

If you are familiar with the half-bridge converter (also known as an isolated common-passive (buck) converter), you may be aware of a failure mode that arises from a resonance on the primary side of the circuit. Capacitors on the primary side form a resonance with the primary inductance, resulting in flux and charge imbalance. But there is also a lesser-known, transformer-related failure mode that arises from a resonance on the secondary side. Here, the secondary leakage inductance resonates with the diodes’ parasitic capacitance, leading to excessive voltage overshoot and power dissipation. This article explains how this failure mode arises and how to avoid it through a reconfiguration of the secondary-side circuit into a new circuit called a half-bridge series-L (HBSL) converter, which features zero-current switching of the bridge diodes and zero-voltage switching turn-on of the MOSFETs. Operation of this circuit and its various advantages (and one disadvantage) are described. In addition, an alternative (but not recommended) fix for the secondary resonance problem in the standard half bridge is briefly discussed.

What you’ll learn:

• How to avoid the secondary resonance problem in half-bridge converters
• How to understand possible failure modes in half-bridge converters
• How to understand the benefits of a half-bridge series-L (HBSL) converter

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Author & Publication:

Dennis Feucht, Innovatia Laboratories, Cayo, Belize, How2Power Today, Jun 14 2013

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