How To Correct Voltage Imbalance In Half-Bridge Converters Under Current-Mode Control

Focus:

A half-bridge converter operating under current-mode control has inherent issues that lead to oscillations. These issues are the result of slight imbalances in duty cycle and volt drops in the circuits, which cause the capacitors that terminate the primary winding to move slightly off the mid-point voltage into the converter. Current-mode control then leads to what can best be described as positive feedback to the current signal. This article examines the mechanism that leads to current imbalances in the primary winding of this converter, resulting in increased voltage imbalance. This article further explains how to overcome these imbalances while retaining current-signal integrity. The solution described here adds one extra winding to both the power transformer and the current transformer, and an additional two diodes.

What you’ll learn:

• How to correct voltage imbalance in current-mode controlled half-bridge converters
• How to understand the source of current imbalances in the primary winding of a half-bridge converter topology operating under current-mode control

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Author & Publication:

John Bottrill, Texas Instruments, Dallas, TX, How2Power Today, Apr 30 2012

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