Power Switch Gate Drive Circuit for Stable Negative Turn-Off Voltage
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Solution Overview
Problem
Existing power semiconductor drive circuits face reliability issues due to insufficient negative gate voltage during PWM activation and prolonged idle periods, leading to unreliable shutdown of power switches, especially in silicon carbide MOSFETs, and require additional isolated bias voltages, increasing complexity and cost.
Innovation Solution
A drive circuit with a capacitance adjustment unit, including a negative voltage charge pump, positive voltage adjustment element, and over-voltage adjustment element, that maintains capacitor voltage during idle periods, charges the capacitor when necessary, and clamps voltage to prevent overcharging, ensuring stable negative voltage for power switch shutdown without additional power supplies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a simple capacitor circuit is used to generate negative voltage, then the circuit complexity is reduced, but the negative voltage becomes insufficient during PWM activation and idle periods
Solution Approach 1:
The charge pump circuit pre-charges the capacitor to a predetermined voltage level before PWM activation. This preliminary charging action ensures that when the PWM signal is activated, the capacitor can immediately provide sufficient negative voltage without delay, resolving the contradiction between circuit simplicity and voltage stability.
Solution Approach 2:
The circuit incorporates voltage detection that monitors the capacitor voltage level and provides feedback control. When the voltage drops below the predetermined level during idle periods or PWM activation, the feedback mechanism triggers the charge pump to recharge the capacitor, maintaining reliable negative voltage without requiring complex external bias supplies.
2Reliability
If the capacitor is allowed to charge during PWM activation, then the negative voltage can be maintained, but the positive gate voltage becomes too high causing reliability issues
Solution Approach 1:
The circuit uses an intermediary charge pump circuit that selectively charges the capacitor only during specific phases (not during PWM activation when the power switch is on). This intermediary mechanism mediates between the need for negative voltage maintenance and the risk of excessive positive gate voltage, allowing capacitor charging during safe periods while preventing harmful voltage levels during active switching.
Solution Approach 2:
The charge pump operates periodically rather than continuously, activating only when the voltage detection circuit determines the capacitor voltage has dropped below the predetermined level. This periodic charging action maintains negative voltage reliability while avoiding continuous charging that would cause excessive positive gate voltage during PWM activation.
3Reliability
If additional isolated bias voltages are used to generate negative voltage, then the negative voltage stability is improved, but the device complexity and cost increase
Solution Approach 1:
The invention merges the functions of separate bias voltage supplies into a single integrated charge pump circuit that generates the negative voltage on-demand. Instead of requiring multiple isolated bias voltages (+V and -V), the charge pump consolidates these functions into one circuit block, reducing device complexity and pin count while maintaining reliable negative voltage for power switch shutdown.
Solution Approach 2:
The charge pump circuit is self-regulating, using voltage detection to automatically determine when charging is needed and executing the charging operation autonomously. This self-service capability eliminates the need for external control circuits or complex bias voltage management, allowing the circuit to maintain reliable negative voltage using only simple external capacitors and resistors.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution provides a stable turn-off negative voltage for power switches, reduces circuit complexity and cost, and improves charging efficiency by grounding electrodes during charging, ensuring reliable operation and avoiding excessive voltages.
Implementation Method 1
Cn is a capacitor
Implementation Method 2
a negative voltage charge pump, which is used to charge the capacitor whose voltage is lower than the predetermined voltage
Implementation Method 3
Dc is a diode
Implementation Method 4
Dz is a Zener diode
Data Source
AI summary
An apparatus includes a capacitor coupled to a gate of a power switch, and a negative voltage adjustment device connected to a common node of the capacitor and the gate of the power switch, wherein the negative voltage adjustment device is configured such that after a turn-off signal is applied to the gate of the power switch, a voltage across the capacitor is maintained at a predetermined voltage level through a negative current provided by the negative voltage adjustment device.