Bootstrap Gate Drive Path for Leakage and Rise-Time Control
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Solution Overview
Problem
The use of a single fixed-value resistor between a bootstrap capacitor and the gate of a high-side switch in an inverter compromises the performance by creating a design contradiction between reducing leakage current and improving rise time of the gate drive signal.
Innovation Solution
Implementing a variable-resistive gate drive path using a depletion mode transistor and a resistor, or a controllable switch in series or parallel configuration, to dynamically adjust resistance based on logic signals, thereby controlling leakage current and optimizing rise time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a large resistance value is used for the resistor connected to the bootstrap capacitor, then the leakage current is reduced, but the rise time of the gate drive signal increases
Solution Approach 1:
The patent applies the dynamics principle by making the resistance value variable rather than fixed. A control switch is introduced that dynamically changes the resistance value between a first value (during switching transitions) and a second value (during steady state). This allows the system to optimize both leakage current reduction and rise time performance at different operational moments, resolving the contradiction between these two parameters.
2Speed
If a small resistance value is used for the resistor connected to the bootstrap capacitor, then the rise time of the gate drive signal is improved, but the leakage current increases
Solution Approach 1:
The control switch dynamically adjusts the resistance value based on operational requirements. During switching transitions when fast rise time is needed, the switch connects the smaller resistance value. During steady state when leakage current reduction is prioritized, the switch connects the larger resistance value. This dynamic adjustment resolves the contradiction by allowing both small and large resistance values to be utilized at appropriate times.
Solution Approach 2:
The resistance value is periodically switched between two states: a low-resistance state during the brief period when fast charging is needed, and a high-resistance state during the extended period when leakage current reduction is important. This periodic action pattern allows the system to achieve both fast rise time and low leakage current by applying the appropriate resistance value at the right moment in the operational cycle.
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 reduces leakage current while enhancing the rise time of the gate drive signal, improving the efficiency and switching performance of the inverter.
Implementation Method 1
the gate drive path comprises a depletion mode transistor and a resistor. The depletion mode transistor is implemented with a GaN transistor in a GaN IC chip
Implementation Method 2
A high-side drive circuit and a low-side drive circuit are employed to control the gates of the high-side switch and the low-side switch respectively. In order to turn on the high-side switch, the high-side drive circuit may need a gate voltage higher than the voltage of the power source. This may be accomplished with a bootstrap capacitor circuit.
Data Source
AI summary
An apparatus includes a capacitive device configured to provide bias power for a high-side switch, a gate drive path connected between the capacitive device and a gate of the high-side switch, wherein the gate drive path comprises a controllable switch and a first resistive device connected in series between the capacitive device and the gate of the high-side switch, and a control switch connected between the gate of the high-side switch and ground.