Gate Driver Soft-Start Current Mirror for Spike Prevention
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Solution Overview
Problem
Existing gate driver circuits experience spikes in current due to large size ratios between transistors, counteracting the soft-start current limitation, leading to a too-short rise time of the power switch control signal.
Innovation Solution
A gate driver circuit with a first current mirror circuit that adjusts its mirror ratio during a predetermined period to prevent spikes by incorporating a path switch and additional current mirror and amplifiers to regulate transistor voltages, ensuring a stable soft-start current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a current mirror with large transistor size ratio is used to limit initial gate driving current, then soft-start effect is achieved, but voltage fluctuation at node A causes mirror output current to surge tens of times
Solution Approach 1:
The patent applies preliminary action by pre-charging node A through switch Sp1 before the main path switch Sp turns on. This preliminary charging prevents voltage fluctuation at node A when Sp turns on, thereby preventing the current mirror output current from surging. The switch Sp1 is controlled to conduct during a predetermined period to establish the necessary voltage condition before the main switching event.
Solution Approach 2:
The patent introduces switch Sp1 as an intermediary element between the power supply and node A. This intermediary switch controls the charging of node A independently from the main path switch Sp, allowing the system to prepare the voltage condition at node A without directly affecting the main current path. The intermediary switch mediates the interaction between the power supply and the current mirror circuit.
2Productivity
If path switch is turned on during soft-start period, then circuit operation is enabled, but mirror ratio amplification causes soft-start current to surge
Solution Approach 1:
The patent performs preliminary action by charging node A through switch Sp1 before the main path switch Sp turns on during the soft-start period. This preliminary voltage establishment prevents the voltage fluctuation that would otherwise be amplified by the current mirror, ensuring current stability when the circuit operation is enabled.
Solution Approach 2:
The patent applies preliminary anti-action by using switch Sp1 to prevent the voltage drop at node A before the main switch Sp turns on. This preliminary counter-measure offsets the potential harmful effect of voltage fluctuation that would occur when Sp turns on, thereby preventing the current surge that would result from the large mirror ratio amplification.
Data Source
AI summary
A gate driver circuit provides a soft-start current to a gate of a power switch during a soft-start period to soft-start the power switch. The gate driver circuit includes: a first current mirror circuit, configured to mirror a reference current according to a mirror ratio to generate a mirror output current; and a path switch coupled on a signal path between the mirror output current and the soft-start current. The soft-start current is generated according to the mirror output current. The path switch is configured to turn off the signal path when the power switch is off. The mirror ratio of the first current mirror circuit is reduced during a predetermined period in the soft-start period to compensate for a spike caused by the path switch being turned on during the soft-start period, such that the soft-start current is prevented from surging during the soft-start period.