Power Switch Drive Circuit Negative Voltage Charge Pump
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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 long pulse signal off periods, charges the capacitor when necessary, and grounds electrodes for efficient charging, eliminating the need for additional power supplies and reducing circuit complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a simple capacitor-based negative voltage generation circuit is used, then the circuit structure is simplified, but the negative voltage becomes insufficient during PWM activation and idle periods, causing unreliable power switch shutdown
Solution Approach 1:
The circuit performs preliminary charging of the capacitor during PWM on-periods before the off-period begins. The charge pump circuit accumulates sufficient negative voltage in advance during the high-level PWM signal period, ensuring that when the PWM signal goes low, the capacitor already has adequate voltage to maintain reliable power switch shutdown throughout the entire off-period and idle periods.
Solution Approach 2:
The circuit ensures continuous maintenance of negative voltage through a combination of capacitor discharge during off-periods and recharge during on-periods. The charge pump circuit continuously operates during PWM on-periods to replenish the capacitor, creating a continuous cycle of charge and discharge that maintains reliable negative voltage throughout all operating phases including idle periods.
2Device complexity
If the capacitor is charged only during high-level PWM signals, then the charging circuit is simple, but the capacitor voltage drops during long idle periods, causing insufficient negative voltage
Solution Approach 1:
The circuit charges the capacitor in advance during PWM on-periods before idle periods begin. By accumulating sufficient charge during the high-level signal period, the capacitor is prepared to maintain negative voltage throughout subsequent long idle periods without requiring additional charging circuitry during idle states.
Solution Approach 2:
The circuit uses periodic charging during PWM on-periods to replenish the capacitor. The charge pump operates periodically synchronized with the PWM signal, charging the capacitor during on-periods and allowing it to discharge during off-periods and idle periods, creating a periodic charge-discharge cycle that maintains adequate voltage levels.
3Reliability
If additional isolated bias voltages are used to generate negative voltage, then the negative voltage is sufficient for reliable shutdown, but the system complexity and cost increase significantly
Solution Approach 1:
The circuit merges the negative voltage generation function with the existing PWM drive circuitry. The charge pump circuit is integrated into the drive circuit, using the same control signals and power supply rails already present in the system. This eliminates the need for separate isolated bias voltage sources while maintaining sufficient negative voltage for reliable power switch shutdown.
Solution Approach 2:
The circuit uses its own operating conditions to generate the required negative voltage. The charge pump circuit leverages the PWM signal already present in the system and the existing power supply voltage to generate the negative bias voltage needed for shutdown. The circuit serves itself by using its operational phases (on-periods) to charge the capacitor for its shutdown function (off-periods), eliminating external dependencies.
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 stable negative voltage for reliable power switch shutdown, reduces circuit complexity and cost, and ensures efficient capacitor charging, avoiding high positive or insufficient gate voltages, thereby enhancing the reliability and efficiency of the power switch drive circuit.
Implementation Method 1
a negative voltage charge pump, used to charge a capacitor whose voltage is lower than a predetermined voltage when the drive circuit receives the turn-off signal
Implementation Method 2
Cn is a capacitor... the capacitor can be charged only when the PWM signal (e.g., pulse signals) is a high-level signal
Implementation Method 3
Dc is a diode... the capacitor can be charged only when the PWM signal (e.g., pulse signals) is a high-level signal
Data Source
AI summary
The invention relates to the field of power semiconductor devices. This invention discloses a drive circuit and device of a power switch. The input terminal of the drive circuit receives a pulse signal; the output terminal of the drive circuit is connected to a capacitor circuit. The capacitor circuit is used to provide a negative voltage for a first electrode of the power switch to turn off the power switch when the pulse signal is a turn-off signal; the drive circuit includes a capacitance adjustment unit. The capacitance adjustment unit includes a negative voltage adjustment element that can charge a capacitor whose voltage is lower than a predetermined voltage when the pulse signal is the turn-off signal.