Staged Gate Driver Current Control for Reverse Recovery Ringing
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Solution Overview
Problem
In bridge circuits, the transition from a high-impedance state to a high-output state leads to unstable output voltage due to through currents caused by reverse recovery currents of flywheel diodes, resulting in ringing and unnecessary radiation.
Innovation Solution
A gate driver circuit is designed to drive N-type power transistors, featuring a turn-on circuit with a first current source, a first current mirror circuit, and an on-fixing switch. The control circuit manages these components to adjust the drive current in stages, suppressing through currents and ringing during reverse recovery periods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the high-side transistor is turned on immediately after the low-side transistor turns off, then the switching speed is improved, but through current flows due to reverse recovery current of the flywheel diode, causing output voltage instability and ringing
Solution Approach 1:
The gate driver circuit performs preliminary action by pre-charging the gate capacitor before the high-side transistor is fully turned on. This is achieved by controlling the turn-on switch to charge the gate capacitor through a current source in advance, so that when the high-side transistor is activated, the gate voltage is already at an optimal level, reducing the risk of through current and output voltage instability
Solution Approach 2:
The gate driver circuit implements dynamic control by adjusting the charging current to the gate capacitor based on the switching state. The current source provides variable current control during the turn-on process, allowing the gate voltage to rise at an optimized rate that prevents through current while maintaining fast switching speed
2Speed
If a large drive current is applied to the power transistor gate, then the transistor turns on faster, but power consumption increases
Solution Approach 1:
The gate driver circuit uses periodic action by controlling the turn-on switch to operate in specific time intervals. The switch is activated only during the turn-on period to charge the gate capacitor, and then turned off. This periodic switching allows fast turn-on when needed while minimizing power consumption during steady-state operation
Solution Approach 2:
The gate driver circuit applies partial action by providing just enough drive current to achieve the required turn-on speed. The current source is controlled to supply adequate current during the critical turn-on phase, then is reduced or turned off, avoiding excessive current that would increase power consumption unnecessarily
Data Source
AI summary
A first current source is configured to generate a first current switchable between a first current amount and a second current amount less than the first current amount. A first current mirror circuit has an input node to which the first current source is connected and is configured to fold and supply the first current to a gate of a power transistor. An on-fixing switch is connected between the gate of the power transistor and a high-level line in which a high voltage equivalent to a high level of a gate voltage of the power transistor is generated. A control circuit is configured to control the on-fixing switch and the first current source.