Sense Transistor Current Sensing With Feedback Voltage Matching
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Solution Overview
Problem
Existing methods for measuring current in power transistors are inaccurate and inefficient, often requiring sense resistors in series, which increase power consumption and heat generation.
Innovation Solution
A circuit using multiple sense transistors, a voltage divider, and a negative feedback circuit to measure power current without a sense resistor, ensuring a stable voltage drop ratio and accurate current determination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a sense resistor is used in series with the power transistor to measure current, then current measurement can be achieved, but power consumption increases and heat generation occurs
Solution Approach 1:
The patent uses sense transistors that are scaled-down copies of the power transistor to measure current. By creating a proportional copy with known scaling factors, the measurement can be performed without inserting a sense resistor in the main current path, thereby avoiding the power loss and heat generation associated with resistive sensing while maintaining measurement accuracy through the proportional relationship between the sense and power transistors.
2Measurement precision
If a sense resistor is used in series with the power transistor to measure current, then current measurement can be achieved, but heat generation increases
Solution Approach 1:
The patent uses sense transistors that are scaled-down copies of the power transistor to measure current. By creating a proportional copy with known scaling factors, the measurement can be performed without inserting a sense resistor in the main current path, thereby avoiding the power loss and heat generation associated with resistive sensing while maintaining measurement accuracy through the proportional relationship between the sense and power transistors.
3Measurement precision
If multiple sense transistors and feedback circuits are used to improve measurement accuracy, then current measurement precision increases, but device complexity increases
Solution Approach 1:
The patent employs feedback circuits that monitor the voltages at the drains of the sense transistors and adjust the gate voltages accordingly to maintain equal drain voltages. This feedback mechanism ensures accurate current measurement by compensating for variations in transistor parameters and loading conditions, while the systematic feedback architecture provides a structured approach to managing circuit complexity.
Solution Approach 2:
The sense transistors serve multiple functions: they act as current sensors, voltage references, and part of the feedback control system. By making the sense transistors multi-functional, the patent reduces the need for separate dedicated components for each function, thereby managing overall circuit complexity while achieving high measurement precision.
Data Source
AI summary
A power transistor current sense circuit. The control nodes of each of a power transistor and sense transistors are connected. The input nodes of the power transistor and each of the sense transistors are also connected. A voltage divider is connected between a reference voltage source and the output node of a second sense transistor. A negative feedback circuit is connected between the output of the voltage divider and the output node of the first sense transistor. The negative feedback circuit forces a voltage at the output node of the first sense transistor to be approximately equal to the divided voltage. A power transistor current determination component measures a sense current that passes through the first sense transistor, and from that detects the current passing through the power transistor.