Gate Drive Circuit Constant Current Control
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Solution Overview
Problem
Existing gate drive circuits face challenges in maintaining constant output current for switching elements across varying temperatures and supply voltages, leading to potential delays and increased complexity, especially when using multiple output transistors in parallel.
Innovation Solution
A gate drive circuit design featuring a reference current source with an error amplifier and a buffer amplifier to maintain constant current through a constant current transistor, with pre-drivers corresponding to each output transistor, and a capacitor to hold gate voltage for stable operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional gate drive circuit uses an error amplifier to control the output transistor, then the output current can be regulated, but response time delays occur due to the error amplifier's response delay
Solution Approach 1:
The patent extracts the error amplifier from the critical current control path and relocates it to only the reference current generation section. The main output transistor current is controlled directly by the reference current through a current mirror configuration, eliminating the error amplifier's response delay from the primary control loop while retaining its regulation function in the reference current path.
Solution Approach 2:
The control circuit is segmented into two independent parts: (1) a reference current generation section with the error amplifier that sets the control current, and (2) a current mirror section that directly replicates this reference current to the output transistor. This segmentation isolates the error amplifier's delay to only the reference generation phase, not the critical switching response phase.
2Adaptability or versatility
If multiple output transistors are provided in parallel to change gate resistance, then the switching element can be driven with different gate resistances, but the circuit scale increases
Solution Approach 1:
The patent implements a universal current mirror configuration where a single reference current source can control multiple output transistors in parallel. By adjusting the transistor width ratios in the current mirror, different current division ratios are achieved, providing multiple effective gate resistance values without adding separate control circuits for each transistor.
Solution Approach 2:
The patent changes the electrical parameters (transistor width ratios) of the existing current mirror configuration to achieve different current division ratios. This allows the same circuit structure to provide multiple gate resistance effects by simply adjusting the transistor dimensions, avoiding circuit scale expansion.
3Adaptability or versatility
If the supply voltage or temperature fluctuates, then the operating conditions change, but the output current becomes unstable
Solution Approach 1:
The patent implements a feedback mechanism where the error amplifier continuously monitors the reference current and adjusts the control transistor gate voltage to maintain a stable reference current. This stable reference current is then mirrored to the output transistor, ensuring that the output current remains stable despite supply voltage or temperature fluctuations.
Solution Approach 2:
The error amplifier acts as a counterweight to external disturbances by generating a compensating control signal. When supply voltage or temperature changes affect the reference current, the error amplifier detects this deviation and adjusts the control transistor to counterbalance the disturbance, maintaining constant reference current that is then reflected in the stable output current.
Data Source
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AI summary
A gate drive circuit includes an output transistor which supplies a constant current to the gate of a switching element and drives the switching element on; a pre-driver of a CMOS configuration, formed of a p-channel MOS-FET and n-channel MOS-FET, to which a gate control signal is inputted and which drives the output transistor on/off; a reference current source which controls the gate voltage of a constant current transistor and makes constant a current flowing through the constant current transistor; and a buffer amplifier which applies the gate voltage of the constant current transistor as the operating reference voltage of the pre-driver.