Soft-start for resonant converters

Abstract

An LLC converter includes a switching stage including primary transistors, a resonant stage connected to the switching stage, a transformer including a primary winding connected to the resonant stage and a secondary winding coupled with the primary winding, a rectifying stage connected to the secondary winding of the transformer and providing an output voltage of the LLC converter, and a controller configured and / or programmed to, during start-up, control the output voltage by switching the primary transistors based on a first reference voltage that exponentially increases during start-up and a second reference voltage that is based on a resonant current of the resonant stage.

Description

technical field [0001] The present invention relates to soft starting of resonant converters. More specifically, the present invention relates to soft starting of a resonant converter using a first reference voltage that increases exponentially during start-up and a second reference voltage that is based on the resonant current of the resonant stage. Background technique [0002] Figure 1 to Figure 3 A resonant converter is shown that can be used with known soft-start schemes or with the soft-start scheme of the preferred embodiment of the present invention. [0003] It is known to soft start the converter to prevent large inrush currents and large output voltage overshoots. Some known soft-start schemes for resonant converters use a linear or exponential reference voltage V ref , where Exponential is an exponential curve or an approximation to an exponential curve. Such known soft-start schemes may not be able to maintain the minimum resonant current required to achieve...

AI Technical Summary

Problems solved by technology

[0007] 4. The resonant current can be very low, which can cause the main power switching (e.g. figure 1 and figure 2 Switches Q1, Q2 in the image 3 The switches Q1, Q2, Q3, Q4) in the switch are hard switched, that is, switched with a non-zero voltage

Therefore, one disadvantage of the control scheme of Feng et al. is that a resonant current and resonant capacitor voltage measurement circuit is required to achieve an asymmetrical current limiting band, which increases the overall cost of the system including the control scheme of Feng et al.

Another disadvantage of the control scheme of Feng et al. is that it can be difficult (if not impossible) to implement using a fixed-point microcontroller

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