Voltage Converter RDSon Current Sensing Circuit
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Solution Overview
Problem
Conventional switched-mode power converters using low value ohmic resistors for current sensing result in significant power losses and increased system cost and size, especially in applications with high currents, due to the need for additional components and heat management.
Innovation Solution
A gate drive powered current sense circuit that utilizes the on-resistance (RDSon) of the power switch to sense current, eliminating the need for a conventional current sense element connected in series with the power switch and a dedicated VCC input.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a low value ohmic resistor is used as current sense element, then current sensing is achieved, but power losses increase significantly
Solution Approach 1:
The patent extracts the current sensing function from a separate resistive element and integrates it into the power switch itself by utilizing the switch's inherent on-resistance (RDSon). This eliminates the need for an external current sense resistor, thereby removing the source of significant power losses while maintaining current sensing capability.
Solution Approach 2:
The power switch is made multi-functional by using its on-resistance for both switching operation and current sensing purposes. The same component (power switch) serves dual functions: controlling power flow and providing current measurement, thereby eliminating the need for a dedicated sense resistor and reducing overall system power losses.
2Measurement precision
If conventional resistive current sense element is used, then current monitoring is achieved, but system cost and size increase
Solution Approach 1:
The patent removes the external current sense resistor from the system and extracts the sensing function into the power switch's inherent resistance. This elimination of separate components directly reduces system cost, board space requirements, and complexity while maintaining the essential current monitoring capability.
Solution Approach 2:
The current sensing function is merged with the power switch by utilizing the switch's on-resistance. This consolidation combines two previously separate functions (power switching and current sensing) into a single component, thereby reducing the number of parts, lowering cost, and decreasing system size.
3Measurement precision
If multiple sensing resistors are used for high current applications, then current sensing is achieved, but heat management becomes difficult
Solution Approach 1:
The patent extracts the sensing function from separate resistive elements that generate heat and integrates it into the power switch's inherent resistance. Since the sensing is done through the switch's normal operating resistance rather than dedicated sense resistors carrying high current, the heat management problem is significantly reduced or eliminated.
4Reliability
If conventional current sensing circuitry is used, then current protection is achieved, but additional components are required
Solution Approach 1:
The patent merges the current sensing function with the power switch's inherent resistance, eliminating the need for separate sense resistors and reducing the component count. The protection function is maintained through the same integrated approach, where the switch's on-resistance provides both the sensing mechanism and the basis for over-current protection.
Solution Approach 2:
The power switch is made multi-functional by using its on-resistance for both switching operation and current sensing/protection purposes. This eliminates the need for dedicated sense resistors and additional protection components, thereby reducing system complexity while maintaining reliable current protection.
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 solution reduces power losses associated with conventional current sense elements and eliminates the need for a dedicated VCC input, improving efficiency and reducing system size and cost by leveraging the power switch's on-resistance for current sensing.
Implementation Method 1
A gate drive powered current sense circuit is configured with a sense input, a sense output, and a gate drive input. The sense input is coupled to a voltage converter power switch, the gate drive input is coupled to receive a gate drive signal for the power switch, and the sense output provides a current sense output corresponding to a current through the power switch.
Data Source
AI summary
In one implementation, a voltage converter includes a driver providing a gate drive for a power switch and a sense circuit coupled across the power switch. The gate drive provides power to the sense circuit, and the sense circuit provides a sense output to the driver corresponding to a current through the power switch. In one implementation, the sense circuit includes a high voltage (HV) sense transistor coupled between a first sense input and a sense output, a delay circuit configured to be coupled to the gate drive to provide power to the HV sense transistor when the gate drive is high, and a pull-down transistor configured to couple the sense output to a second sense input when the gate drive is low.