Half-Bridge Gate Driver Precharge for Fast High-Side Switching
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Solution Overview
Problem
Switching circuits face challenges in preventing simultaneous conduction of high-side and low-side switches, leading to excessive power consumption and electromagnetic interference (EMI), while requiring fast switching of the high-side transistor after the low-side transistor is turned off, and efficient use of bootstrap capacitor charge.
Innovation Solution
A switching circuit with a high-side and low-side transistor configuration in a half-bridge setup, where the high-side transistor's gate is precharged to a threshold voltage using the power supply voltage before the low-side transistor turns off, allowing for faster switching and reduced EMI by ramping up the gate voltage from this precharge voltage, conserving bootstrap capacitor charge and minimizing voltage drop.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If tight timing control is used to switch high-side and low-side alternately, then power consumption is reduced, but switching speed is limited and inadvertent overlapping may occur in some process corners
Solution Approach 1:
The gate of the high-side transistor is precharged to a threshold voltage during the period when the low-side transistor is on, before the actual switching event occurs. This preliminary action prepares the high-side transistor for faster turn-on when needed, eliminating the need for tight timing control while maintaining safe operation and reducing power consumption.
2Speed
If the ramp up rate of the output voltage of the high-side switch is maximized, then switching speed is increased, but excessive electromagnetic interference (EMI) is generated
Solution Approach 1:
The gate voltage is precharged to a threshold voltage before the actual switching event, so that when the high-side transistor turns on, the voltage ramp-up starts from this precharged level rather than from ground. This reduces the rate of change of voltage (dv/dt) during switching, thereby reducing EMI while still achieving fast switching.
3Speed
If the bootstrap capacitor is used to charge the high-side gate, then switching is enabled, but charge is depleted and voltage drop occurs
Solution Approach 1:
The gate is precharged to a threshold voltage during the period when the low-side transistor is on, before the bootstrap capacitor charge is needed for the actual switching event. This preliminary charging reduces the charge demand on the bootstrap capacitor, conserving its charge and minimizing voltage drop during operation.
Data Source
AI summary
A switching circuit includes first and second transistors, and a driver circuit. The first transistor has a first current electrode coupled to a first power supply voltage terminal, a second current electrode, and a control electrode. The second transistor has a first current electrode coupled to the second current electrode of the first transistor, a second current electrode coupled to a second power supply voltage terminal, and a control electrode. The driver circuit has an input for receiving an input signal, and an output coupled to the control electrode of the first transistor. The driver circuit precharges the control electrode of the first transistor to a first predetermined voltage, and in response to the input signal transitioning from a first logic state to a second logic state, the driver circuit provides a second predetermined voltage to the control electrode of the first transistor to cause the first transistor to be conductive.