Control circuit, control method and resonant converter

Abstract

The invention discloses a control circuit, a control method and a resonant converter. The resonant converter comprises a first power switch and a second power switch, wherein the first power switch and the second power switch are sequentially connected in series and coupled between the high potential end of the input end of the resonant converter and a ground potential. The control circuit comprises a bridge midpoint voltage control circuit. In the starting process of the resonant converter, bridge midpoint voltage is controlled to prevent the voltage of a resonant capacitor from being too high during the conduction period of the second power switch, and the bridge midpoint voltage is configured to be the voltage of the common end of the first power switch and the second power switch.

Description

technical field [0001] The present invention relates to the technical field of power electronics, and more specifically, relates to a control circuit, a control method and a resonant converter. Background technique [0002] figure 1 It is a schematic circuit diagram of an LLC resonant converter in the prior art. exist figure 1 In the control scheme of the resonant converter shown, after the system is powered on, the capacitor C2 is charged; after the voltage VCC at the common terminal of the capacitor C2 and the diode D3 reaches the first voltage threshold, the lower transistor Q2 is turned on, and the capacitors C2 and C3 are charged ; When the voltage VB at the common terminal of the capacitor C3 and the diode D3 is charged to the second threshold voltage, the resonant converter starts to work normally. However, in this way, when the lower transistor Q2 is turned on, the resonant network composed of the inductor LR and the capacitor CR will have a large resonance energy...

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Problems solved by technology

However, in this way, when the lower transistor Q2 is turned on, the resonant network composed of the inductor LR and the capacitor CR will have a large resonance energy, especially the half-bridge midpoint HB of the half-bridge structure composed of the upper transistor Q1 and the lower transistor Q2. When the initial value of the voltage is close to the input voltage Vbus, the lower tube Q2 is always on, and the voltage of the capacitor CR will resonate to an excessive voltage

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