Drive Device Gate Current Control via Sense MOS Transistor
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Solution Overview
Problem
Existing drive devices for power switching elements face challenges in reducing switching loss and circuit scale, with large numbers of components leading to variations in switching speed and loss, and requiring discrete resistors for accurate gate current control.
Innovation Solution
A drive device configuration that includes a main MOS transistor, a sense MOS transistor with a current mirror, and a sense current control circuit with a reference power supply, reference resistor, and operational amplifier to control the gate current accurately, reducing the need for discrete resistors and minimizing layout area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a large number of MOSFETs and resistors are used to control gate current, then the power switching element can be protected from excessive current, but the circuit scale and layout area become large
Solution Approach 1:
The patent merges multiple protection functions into a single integrated circuit block. The off-side circuit integrates the sense MOS transistor, main MOS transistor, and control logic into one compact unit, eliminating the need for separate discrete resistors and MOSFETs scattered across the layout, thus reducing overall layout area while maintaining protection capability
Solution Approach 2:
The sense MOS transistor serves multiple functions: it senses the gate current, generates the mirrored current signal, and participates in the feedback control loop. This multi-functional design reduces the total component count and layout area compared to using separate dedicated components for each function
2Device complexity
If the gate current is controlled based on resistor resistance value, then the circuit can be simplified, but variations in threshold voltage cause variations in switching speed and switching loss
Solution Approach 1:
The patent implements a feedback control mechanism where the sense MOS transistor continuously monitors the gate current and adjusts its resistance dynamically to maintain constant gate current. The operational amplifier compares the sensed voltage with a reference and adjusts the sense MOS transistor's gate voltage to compensate for threshold voltage variations, ensuring consistent switching performance
Solution Approach 2:
The sense MOS transistor's resistance is made dynamic rather than fixed. By controlling the gate voltage of the sense MOS transistor through the feedback loop, its resistance can adapt in real-time to compensate for manufacturing variations in threshold voltage, maintaining consistent switching speed and loss across different devices
3Measurement precision
If discrete resistors are used for accurate gate current control, then the gate current precision can be improved, but the number of discrete parts increases
Solution Approach 1:
The patent extracts the resistor function from discrete components and integrates it into the MOS transistor structure. The sense MOS transistor's channel resistance replaces the need for external discrete resistors, and this resistance is precisely controlled through the feedback mechanism, achieving accurate gate current control without additional discrete parts
Solution Approach 2:
The operational amplifier acts as an intermediary that enables precise current control without requiring precise discrete resistors. It continuously adjusts the sense MOS transistor's gate voltage to maintain the desired current, compensating for any resistance variations and achieving high precision control through active feedback rather than passive component precision
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
This configuration allows for high-accuracy control of output current, reducing switching loss and variations, and enabling integration of the drive device and power switching element on the same package, while minimizing the number of passive components.
Implementation Method 1
a sense MOS transistor that includes a gate in common with the main MOS transistor, and provides a current mirror with respect to the main MOS transistor to define a drain current of the main MOS transistor
Implementation Method 2
an operational amplifier that generates an output at the gate of the sense MOS transistor so that a potential between the reference resistor and the sense MOS transistor approaches the reference potential
Data Source
AI summary
A drive device includes an off-side circuit controlling a gate current of a power switching element to perform an off operation. The off-side circuit includes: a main MOS transistor; a sense MOS transistor defining a drain current of the main MOS transistor; and a sense current control circuit controlling a drain current of the sense MOS transistor to be constant. The sense current control circuit includes: a reference power supply; a reference resistor; and an operational amplifier generating an output at the gate of the sense MOS transistor so that a potential between the reference resistor and the sense MOS transistor approaches the reference potential. The sense current control circuit flows a current, determined by a resistance value of the reference resistor and the reference potential, as the drain current of the sense MOS transistor.