Hybrid Switch Turn-Off Control for Lower Switching Loss
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Solution Overview
Problem
Hybrid switches incur higher switching losses than power MOSFETs, negatively impacting the efficiency of power conversion systems.
Innovation Solution
A control scheme for hybrid switches that includes a delay generator to stagger the turn-off commands for MOSFET and IGBT, using different gate-to-source voltages during the transition from an on-state to an off-state to minimize switching losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a hybrid switch combining MOSFET and IGBT is used, then conduction losses are improved across a wide range of currents, but switching losses increase
Solution Approach 1:
The control scheme applies preliminary action by preparing the MOSFET for turn-off before the IGBT actually turns off. A turn-off command signal is generated for the MOSFET that includes a delay period relative to the IGBT turn-off, so the MOSFET is already in the process of turning off or has turned off by the time the IGBT turns off, minimizing the overlap period where both devices conduct and reducing switching losses
Solution Approach 2:
The control scheme implements dynamics by adjusting the gate-to-source voltage of the MOSFET during the transition from on-state to off-state. The voltage is dynamically changed from a first voltage level during the on-state to a second voltage level during the transition, optimizing the switching behavior and minimizing switching losses while maintaining the conduction benefits of the hybrid switch configuration
Data Source
AI summary
A switch system includes a hybrid switch and a control circuit. The hybrid switch includes an IGBT and a MOSFET. The control circuit includes an input terminal configured to receive a switch-off command. The control circuit further includes an IGBT drive circuit configured to switch off the IGBT in response to expiration of a first delay period that begins in response to the switch-off command. In addition, the control circuit includes a MOSFET drive circuit configured to increase a gate-to-source voltage of the MOSFET from a first voltage level to a second voltage level in response to the switch-off command, to drive the MOSFET at the second voltage level for a second delay period that begins in response to the switch-off command and is longer than the first delay period, and to switch the MOSFET off in response to the expiration of the second delay period.