MOSFET Dead-Time Control for Reverse Current Loss Reduction
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Solution Overview
Problem
Conventional power conversion systems experience energy loss due to reverse current flowing from the source to the drain of MOSFET during dead time, especially at high frequencies, leading to inefficiencies.
Innovation Solution
A power conversion system incorporating a voltage detection circuit and logic circuit that determines when the drain-source voltage of a MOSFET is less than zero, triggering the driving circuit to pull the gate-source voltage high, thereby preventing the MOSFET from operating in the third quadrant and reducing energy loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If dead time is introduced to avoid short circuit in half-bridge circuit, then switching safety is improved, but energy loss increases due to reverse current flowing through MOSFET
Solution Approach 1:
The patent applies preliminary action by detecting the drain-source voltage of the MOSFET before the dead time ends and advancing the turn-on signal to the complementary switch. The voltage detection circuit monitors Vds, and when Vds drops below a threshold (indicating reverse current flow), the logic circuit triggers an early turn-on signal, preventing the reverse current from flowing through the MOSFET body diode and reducing energy loss during dead time.
2Adaptability or versatility
If MOSFET operates in third quadrant with Vgs less than Vth, then the MOSFET cannot be turned on completely, but this operation mode generates extra drain-source voltage and energy loss
Solution Approach 1:
The patent implements feedback by using the voltage detection circuit to continuously monitor the drain-source voltage of the MOSFET and feed this information back to the logic circuit. Based on the detected Vds level, the logic circuit adjusts the gate-source voltage of the complementary switch in real-time, ensuring the MOSFET operates in the optimal region and preventing operation in the third quadrant that would cause energy loss.
Data Source
AI summary
A power conversion system includes a voltage detection circuit and a logic circuit. When the logic circuit determines that the drain-source voltage of the power switch is less than zero through the detecting terminal of the voltage detection circuit, the logic circuit outputs the first high-level voltage. Accordingly, the driving circuit outputs the second high-level voltage to the power switch according to the first high-level voltage. Consequently, the gate-source voltage of the power switch is pulled high. When the reverse current flows from the source to the drain of the power switch, the energy loss of the power switch due to the drain-source voltage of the power switch in power conversion system operated at high frequency is reduced.