MOSFET Gate Driver Shaping for Low-EMI DC Brushed Motor Drives
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Solution Overview
Problem
Current MOSFET drive technologies in the automotive industry face challenges in reducing electromagnetic interference (EMI) and switching losses, leading to increased heat dissipation and gas consumption, while existing solutions for high-frequency switching are complex and difficult to implement effectively.
Innovation Solution
A gate driving method that dynamically controls the di/dt and dv/dt of MOSFETs through internal management of gate voltage, using detection circuits and logic control to optimize gate shaping and reduce EMI, while also incorporating an Overpower Protection circuit to prevent excessive power dissipation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If 20 kHz switching drive is used to reduce heat dissipation and improve efficiency, then energy efficiency is improved, but electromagnetic interference (EMI) increases due to high frequency coupling
Solution Approach 1:
The patent applies preliminary action by pre-charging the MOSFET gate to the threshold voltage (Vth) before the main switching event. This preparatory gate shaping reduces the di/dt during switching transitions, thereby minimizing EMI while maintaining the high-frequency 20 kHz operation that improves energy efficiency. The detection circuit identifies Vth to enable this precise preliminary gate charging.
Solution Approach 2:
The patent changes the gate voltage parameters dynamically by detecting Vth and using it to control the gate charging profile. By adjusting the gate voltage slope and timing based on detected Vth, the circuit optimizes the switching characteristics to reduce EMI while maintaining high-frequency operation for improved energy efficiency.
2Object-generated harmful factors
If gate shaping is implemented to reduce EMI, then electromagnetic interference is reduced, but device complexity increases due to complicated detection loops and auto-adaptation circuits
Solution Approach 1:
The patent applies self-service by using the MOSFET's own threshold voltage (Vth) as the reference for gate shaping control. The detection circuit automatically identifies Vth during normal operation, and this detected Vth is fed back to control the gate charging profile. This self-referencing approach eliminates the need for external calibration loops and complex auto-adaptation circuits, reducing device complexity while maintaining EMI reduction benefits.
3Object-generated harmful factors
If resistor is placed at gate terminal to smooth current injection, then EMI is reduced, but switching losses increase causing transistor to heat up
Solution Approach 1:
The patent changes the gate voltage application parameters by using detected Vth to control the timing and slope of gate charging. Instead of using a fixed resistor that continuously limits current, the circuit dynamically adjusts the gate voltage profile to achieve smooth current injection only when needed, minimizing switching losses while reducing EMI.
Solution Approach 2:
The patent applies preliminary action by pre-charging the gate to Vth before the main switching event. This preparatory step establishes the optimal starting point for switching, allowing the MOSFET to transition more efficiently and reducing both EMI and switching losses compared to using a simple gate resistor.
Data Source
AI summary
A gate driver for performing gate shaping on a first transistor of having gate, source, and drain terminals, the first transistor being selected from a switching stage of a power switching circuit having high- and low-side transistors series connected at a switching node for driving a load. The gate driver includes the following steps: upon receipt of an ON pulse pre-charging the gate terminal until gate to source terminal voltage equals Vth, controlling the di/dt(ON) flowing in the first transistor while free wheeling current is flowing in a second transistor of the switching stage, and controlling the dv/dt(ON) of the first transistor while a charge on the gate terminal is present; and upon receipt of an OFF pulse controlling the dv/dt(OFF) of the first transistor until free wheeling current is flowing in the second transistor, and controlling the di/dt(OFF) flowing in the first transistor while the gate to source terminal voltage equals Vth.