Chopper Circuit Current Measurement Offset Cancellation
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Solution Overview
Problem
Switched-mode power supply circuits face measurement errors due to operational amplifier offset voltage, which are amplified and costly to mitigate with low-offset amplifiers or high-value measurement resistors, leading to inefficiency and increased costs.
Innovation Solution
A method and device that measure the output current or voltage of a chopper circuit by calculating the difference between 'on' and 'off' phases, canceling out offset voltage errors, and optionally using a correction voltage to compensate for amplification defects, allowing for reliable measurements without low-offset amplifiers or high-value resistors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a measurement resistor of high value is used to reduce the relative error from offset voltage, then measurement precision is improved, but heat dissipation increases and efficiency decreases
Solution Approach 1:
The patent applies periodic action by measuring the voltage across the measurement resistor during both the ON phase and OFF phase of the chopper circuit. By periodically switching between these two measurement states and calculating the difference, the system achieves accurate current measurement without requiring a high-value measurement resistor, thus avoiding excessive heat dissipation.
Solution Approach 2:
The patent converts the harmful effect of offset voltage into a beneficial measurement method. Instead of trying to eliminate or compensate for the offset voltage through expensive low-offset amplifiers or high-value resistors, the invention uses the offset voltage as a reference by measuring it during the OFF phase, then subtracts it from the ON phase measurement. This transforms the offset voltage from a source of error into a useful reference signal for achieving accurate measurements with standard components.
2Measurement precision
If an operational amplifier with low offset voltage is used, then measurement precision is improved, but device cost increases
Solution Approach 1:
The patent converts the harmful effect of offset voltage into a beneficial measurement method. Instead of trying to eliminate or compensate for the offset voltage through expensive low-offset amplifiers or high-value resistors, the invention uses the offset voltage as a reference by measuring it during the OFF phase, then subtracts it from the ON phase measurement. This transforms the offset voltage from a source of error into a useful reference signal for achieving accurate measurements with standard components.
Solution Approach 2:
The system performs self-calibration by automatically measuring the offset voltage during the OFF phase and using it to correct the ON phase measurement. This self-service approach eliminates the need for external calibration procedures or expensive precision components, allowing the system to maintain high measurement precision using standard, cost-effective operational amplifiers.
3Measurement precision
If a measurement resistor of high value is used, then measurement precision is improved, but device complexity increases due to heat dissipation systems
Solution Approach 1:
The patent applies periodic action by measuring the voltage across the measurement resistor during both the ON phase and OFF phase of the chopper circuit. By periodically switching between these two measurement states and calculating the difference, the system achieves accurate current measurement without requiring a high-value measurement resistor, thus avoiding excessive heat dissipation.
Data Source
AI summary
The invention relates to a method for measuring a current or voltage output quantity of a switched-mode power supply circuit (H), referred to as a chopper circuit, of period T and of cyclic ratio α, belonging to the interval]0; 1[, such that, at each period, the supply current is non-zero during an “ON” phase of duration αT, and zero during an “OFF” phase of duration (1−α)T. The measurement method includes the following steps: measuring the value Gon of an image of the output quantity during an “ON” phase; measuring the value Goff of an image of the output quantity during an “OFF” phase; calculating the difference ΔG=Gon−Goff; and using the difference ΔG for evaluating the output quantity.