Current Sense Circuit Input Voltage Dependence Suppression
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Solution Overview
Problem
Conventional current sense circuits are inadequate in suppressing input voltage dependence of effective threshold values, leading to inefficiencies and inaccurate overcurrent detection.
Innovation Solution
A current sense circuit incorporating a comparator and a variable retarder that delays the comparison signal by a time proportional to the square of the initial time, using timers and capacitors to generate a current sense signal, effectively reducing input voltage dependence by canceling out current components related to the delay and input voltage variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional current sense circuit is used, then the circuit structure is simple, but the input voltage dependence of the effective threshold value cannot be suppressed
Solution Approach 1:
The current sense circuit is segmented into distinct functional modules: a comparator for generating the comparison signal, a first timer for measuring the time interval, and a second timer for generating the delayed current sense signal. This segmentation allows each component to perform its specific function independently, achieving effective suppression of input voltage dependence while maintaining clear functional separation.
Solution Approach 2:
The comparison signal acts as an intermediary between the voltage drop signal and the current sense signal. The first timer measures the time from output switch turn-on to comparison signal transition, and the second timer uses this measurement to generate a delayed current sense signal. This intermediary mechanism enables accurate overcurrent detection that is independent of input voltage variations.
2Reliability
If the delay time is not proportional to the square of the first time, then the circuit is simpler, but the input voltage dependence cannot be effectively suppressed
Solution Approach 1:
The delay time parameter is changed to be proportional to the square of the first time interval. This parameter relationship is achieved through the coordinated operation of the first timer (measuring the initial time) and the second timer (generating delay proportional to the square of that time). This specific parameter relationship effectively suppresses input voltage dependence in the current sense circuit.
3Measurement precision
If conventional timing methods are used, then the timing circuit is simpler, but the overcurrent detection accuracy deteriorates under varying input voltage
Solution Approach 1:
The first timer measures the actual time interval from output switch turn-on to comparison signal transition, and this measured time is fed back to control the delay time of the second timer. This feedback mechanism ensures that the current sense signal timing accurately reflects the actual circuit conditions, maintaining high overcurrent detection accuracy regardless of input voltage variations.
Solution Approach 2:
The timing circuit operates dynamically by continuously measuring the first time interval and adjusting the second delay time accordingly. The delay time is not fixed but varies dynamically based on the measured first time, allowing the circuit to adapt to different operating conditions and maintain accurate overcurrent detection across varying input voltages.
Data Source
AI summary
A current limiter 200 (corresponding to an example of a current detection circuit) has a comparator 210 and a variable delay unit 220. The comparator 210 switches a comparison signal OCP from a low level to a high level when the current to be monitored, which flows through an output switch, reaches a predetermined threshold value (in the present figure, when a sense voltage Vcs reaches an overcurrent detection voltage Vocp). The variable delay unit 220 measures a first time T1 from when the output switch turns on by SET=H until when the comparison signal OCP switches to the high level and delays the comparison signal OCP by a second time T2 (=K·T12) proportional to the square of the first time T1 to generate an overcurrent detection signal Sc. The variable delay unit 220 includes a first timer 223 for measuring the first time T1 and a second timer 224 for generating the overcurrent detection signal Sc by delaying the comparison signal OCP by the second time T2.