Switch Mode Power Converter Current Sensing via Rds-on
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional switch mode power converters face challenges in measuring current through an inductive element efficiently, particularly at low power outputs, due to resistive losses associated with sense resistors, and high-voltage operation complications when positioning resistors on the input side or measuring voltage drops across power switches.
Innovation Solution
Sensing the voltage across the switch in its on-state, using knowledge of the switch's on-resistance (Rds-on), allows direct determination of current through the switch, potentially eliminating the need for a separate sense resistor and associated losses, with an amplifier connected across the switch's main terminals to determine current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a sense resistor is used to measure current through the inductive element, then current measurement is achieved, but resistive losses increase
Solution Approach 1:
The patent extracts the current sensing function from a separate sense resistor and integrates it into the existing power switch. By utilizing the switch's inherent on-resistance (Rds(on)) for current sensing, the separate sense resistor is eliminated, thereby removing its associated resistive losses while maintaining current measurement capability.
Solution Approach 2:
The power switch is given a dual function: it serves both as the power switching element and as the current sensing element. The switch's Rds(on) is utilized for current measurement purposes, eliminating the need for a dedicated sense resistor and reducing overall system losses.
2Loss of energy
If the sense resistor is positioned on the input side in series with the power switch, then resistive losses are reduced, but high-voltage operation complications arise
Solution Approach 1:
The power switch serves itself by utilizing its own Rds(on) for current sensing. This self-service approach eliminates the need for external sense resistors and their associated high-voltage handling requirements, simplifying the overall system while maintaining low losses.
3Measurement precision
If a separate sense resistor is used, then current measurement is achieved, but device complexity increases
Solution Approach 1:
The patent merges the current sensing function with the power switch by utilizing the switch's Rds(on)). This integration eliminates the separate sense resistor component and reduces the overall device complexity while maintaining accurate current measurement capability.
Solution Approach 2:
The power switch performs multiple functions: power switching and current sensing. By making the switch universal, the patent eliminates the need for separate sense resistor components, thereby reducing device complexity.
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 approach reduces ohmic losses and avoids high-voltage demands on current sense amplifiers, enhancing efficiency and reducing costs by eliminating the need for separate sense resistors, while maintaining accuracy across varying operating conditions.
Implementation Method 1
Sensing the voltage across the switch in its on-state, and with knowledge of the switch's 'on-resistance' Rds-on, the current through the switch may be directly determined
Data Source
Figure 1~2
Figure 3~5
Figure 6~7
AI summary
A switch mode power converter is disclosed, being configured for operation with a plurality of outputs and comprising an inductive element and a resistance in series with the inductive element and being for determining a current through the inductive element, wherein the resistance is a resistance between the main terminals of a switch in an on-state, the switch having two main terminals and a control terminal and being arranged for directing current through the inductive element to a one of the plurality of outputs.