MOSFET Switch Array Configuration for Stable On-Resistance Sensing
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Solution Overview
Problem
The on resistance of transistors used as power switches is susceptible to variations due to voltage, temperature, and manufacturing processes, making them unsuitable for precise current sensing, which affects the efficiency and accuracy of power conversion systems.
Innovation Solution
A switching circuit with a switch array and control circuitry that adjusts the configuration states of MOSFET switches based on stored configuration data, allowing for a controlled on resistance that is less susceptible to variations, using a memory element to set the configuration states and a current sensor to measure currents through the switch array.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a sense resistor is added to measure current, then current measurement capability is improved, but power loss and heat generation increase
Solution Approach 1:
The patent combines the power switch and sense resistor into a single integrated device. The power switch contains multiple parallel switch elements, and a sense resistor is integrated within the same device structure, allowing current sensing without requiring an external sense resistor. This integration eliminates the need for additional current sensing components while maintaining power loss characteristics of the original power switch.
2Loss of energy
If the resistance of the sense resistor is reduced to improve efficiency, then power loss is reduced, but voltage drop measurement accuracy deteriorates
Solution Approach 1:
The patent employs different switch element configurations within the same device to achieve different resistance characteristics for different functions. Some switch elements are configured to provide low resistance for power conduction (reducing power loss), while the integrated sense resistor provides a known, stable resistance value specifically for accurate current measurement. This local differentiation of resistance properties allows simultaneous optimization of both efficiency and measurement accuracy.
Solution Approach 2:
The patent incorporates feedback circuitry that uses the voltage drop across the integrated sense resistor to control the switching operation. The control circuit monitors the voltage drop and adjusts the switching duty cycle or frequency to maintain desired output characteristics, thereby using the inherently present voltage drop for both measurement and control purposes, eliminating the trade-off between reducing resistance for efficiency and maintaining measurement accuracy.
3Loss of energy
If multiple switches are used in parallel to reduce on resistance, then power loss is reduced, but manufacturing variation impact increases
Solution Approach 1:
The patent divides the power switch into multiple discrete switch elements connected in parallel within the same device. Each switch element can be independently controlled or grouped, allowing the system to achieve lower effective on-resistance through parallel combination while maintaining manufacturing tolerances. The segmentation allows for modular construction where each element meets specified parameters, and their parallel combination provides the desired low resistance without amplifying individual manufacturing variations.
Data Source
AI summary
A switching circuit and a method for providing a switch array having an on resistance is presented. The switch array has a plurality of switches, where each switch is arranged to be in different configuration states. The states include an enabled configuration and a disabled configuration. The switching states include an on state and an off state. Each switch is held in the off state when in the disabled configuration. Control circuitry sets the switches to either the enabled configuration or the disabled configuration, and a memory element coupled to the control circuitry and arranged to store configuration data for setting the configuration state of each of the switches. The control circuitry sets the configuration state of the switches based on a signal received from the memory element. The on resistance of the switch array depends on the switching state of the switches and their individual on resistances.