Gate Driver Coupling Structure for Power Supply Current Sensing
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Solution Overview
Problem
In switched-mode power supplies, the sink current flowing through the low-side switch causes distortion in sensing the primary-side switch current, leading to inaccurate prediction of the secondary-side output, as the sink current influences the sense voltage and results in sensing errors.
Innovation Solution
A power supply device with a gate driver circuit that includes a first transistor connected between the power switch gate and a node, and a second transistor with a different channel type, which prevents the sink current from affecting the sense resistor, allowing precise detection of the peak current by a peak detector and generation of a control signal for accurate output prediction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a low-side switch is connected to the same ground as the power switch for gate driving, then the gate driver can be simplified and operated, but the sink current from the low-side switch causes distortion in sensing the switch current through the sense resistor
Solution Approach 1:
The patent divides the gate driver into two independent parts: a high-side switch for charging the gate and a low-side switch for discharging the gate. This segmentation allows the low-side switch to be isolated from the sense resistor connection, preventing sink current distortion while maintaining gate driving functionality.
Solution Approach 2:
The patent introduces a coupling capacitor as an intermediary element between the low-side switch and the sense resistor. This capacitor blocks the DC sink current from affecting the sense resistor while allowing AC gate drive signals to pass through, thus eliminating sensing distortion without compromising gate driver operation.
2Productivity
If the low-side switch is used to sink gate current, then the power switch can be turned off efficiently, but the sink current distorts the sense voltage and causes sensing errors
Solution Approach 1:
The coupling capacitor serves as a mediator that allows the low-side switch to efficiently sink gate current for turning off the power switch, while simultaneously blocking this sink current from reaching the sense resistor and distorting the sense voltage, thus preserving sensing accuracy.
Solution Approach 2:
The patent segments the gate discharge path from the sense resistor path by introducing the coupling capacitor. This allows the low-side switch to perform its switching function independently without interfering with the current sensing path, maintaining both switching efficiency and sensing reliability.
3Device complexity
If the sense resistor is directly connected to the power switch for current sensing, then the sensing circuit is simplified, but the sink current from the gate driver flows through the sense resistor causing distortion
Solution Approach 1:
The coupling capacitor is inserted as an intermediary between the sense resistor and the gate driver's low-side switch. This maintains a relatively simple sensing circuit structure while effectively blocking the sink current from distorting the sense voltage, thus preserving measurement precision without significantly increasing complexity.
Data Source
AI summary
A power supply device includes a power switch that is switched according to a gate voltage. A sense resistor receives a switch current that flows through the power switch to develop a sense voltage. A peak of a primary-side current is detected from the sense voltage. The gate driver has a pair of switches for generating the gate voltage in accordance with a control signal. When a low-side switch of the gate driver is turned on according to the control signal, the gate voltage of the power switch decreases as a sink current flows from the gate of the power switch via the transistor.