Programmable Gate Drive Voltage Control for Power MOSFET EMI Reduction
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Solution Overview
Problem
Existing drive circuits for power MOSFETs in converters, such as flyback and LLC resonant converters, face challenges in controlling the switching operation effectively, leading to unwanted electromagnetic interference (EMI) due to fast rising edges in gate drive signals, particularly in the Miller plateau and linear regions of the gate charge curve.
Innovation Solution
A driver circuit with a high-side driver transistor that operates in multiple modes to control the gate drive voltage, providing a first charge current until a threshold is reached, then a second, reduced current to limit the voltage, and finally a programmable clamp voltage to optimize the gate drive signal characteristics, reducing EMI and improving switching efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a fast rising edge gate drive signal is applied to quickly charge the MOSFET gate, then the switching speed is improved, but unwanted electromagnetic interference (EMI) is generated
Solution Approach 1:
The gate charge process is segmented into three distinct regions (sub-threshold, Miller plateau, and linear regions), with different charge currents applied to each region. This segmentation allows optimized control of the gate drive signal to reduce EMI while maintaining switching speed.
Solution Approach 2:
The gate drive circuit dynamically adjusts the charge current based on the MOSFET's operating region. A first charge current is applied during sub-threshold and Miller plateau regions, then switched to a second charge current in the linear region, creating a dynamic response that reduces EMI.
2Loss of time
If a large current is supplied to charge the gate in the linear region, then the gate-to-source voltage reaches peak value quickly, but EMI is increased
Solution Approach 1:
The gate drive circuit dynamically switches between different charge currents based on the operating region. A first charge current is used during Miller plateau region, then transitions to a second charge current in the linear region, optimizing the balance between speed and EMI.
Solution Approach 2:
The charge current parameter is changed based on the MOSFET's operating region. The circuit transitions from a first charge current to a second charge current, adjusting the electrical parameter to reduce EMI while maintaining efficient switching.
Data Source
AI summary
A driver includes a high-side driver transistor coupled between supply voltage and the gate drive nodes and provides a first charge current to a high side gate node of the high-side driver transistor until the gate drive node reaches a first gate drive threshold. Then a second charge current is provided to the high side gate node that is less than the first charge current. The gate drive node is limited to a first clamped threshold for a delay time. A gate drive current rise signal sets the value of the second charge current that charges the high side gate node and after the delay time the gate drive voltage is limited to a second clamped threshold greater than the first clamped threshold but less than the supply voltage. A gate drive programmable control signal sets the value of the second clamped threshold.