Buck Converter Current Sensing With PWM Blanking Control
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Solution Overview
Problem
Existing DC/DC buck converter circuits struggle to accurately regulate average current to LED lighting systems due to non-ideal device behavior and transient fluctuations, which can be costly and complex to measure directly.
Innovation Solution
A DC/DC buck converter circuit that estimates average current by measuring high-side and low-side currents, using blanking circuits to ignore transient periods and adjust peak and valley thresholds for improved accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If direct current sensing is used at the output to accurately regulate average current, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent uses indirect current sensing by measuring the voltage across a known resistor in the high-side circuit and calculating the average current through integration and computation, rather than directly sensing the output current. This creates a computational model that copies the effect of direct sensing without the associated complexity and cost.
Solution Approach 2:
The patent introduces an intermediary resistor and voltage measurement system as a mediator between the power circuit and the control system. By measuring the voltage across this resistor and computing the average current from that measurement, the system achieves accurate current regulation without requiring direct output current sensing.
2Measurement precision
If transient current fluctuations are measured to improve accuracy, then measurement precision is improved, but reliability deteriorates due to noise and instability
Solution Approach 1:
The patent applies preliminary action by pre-establishing blanking periods during which transient current fluctuations are intentionally ignored. The integration circuit is configured to exclude measurements during switch transitions and transient periods, preventing these unstable measurements from affecting the average current calculation. This proactive filtering ensures that only stable, reliable current measurements contribute to the regulation decision.
3Device complexity
If simple averaging of current measurements is used, then device complexity is reduced, but manufacturing precision deteriorates due to transient errors
Solution Approach 1:
The patent applies preliminary action by pre-configuring the integration circuit to automatically exclude transient periods through blanking intervals. The circuit is designed to begin integration only after transients have settled and to stop before the next transient occurs, ensuring that the simple averaging operation produces accurate results without requiring complex preprocessing or postprocessing.
Solution Approach 2:
The patent uses feedback by continuously monitoring the current measurements and using the computed average current to adjust the PWM duty cycle. This closed-loop feedback ensures that despite the simplicity of the averaging circuit, the system achieves precise current regulation by constantly correcting for any deviations from the target current.
Data Source
AI summary
A converter circuit may require sensing an average current as feedback for regulating the average current supplied to a load. Sensing the average current may be inaccurate due to the non-ideal behavior of devices in the converter circuit. The disclosed circuits and methods help to improve the accuracy of the sensed average current by ignoring portions of a PWM cycle. Some of the ignored portions are based on a peak threshold for a rising current of a PWM cycle and a valley threshold for a falling current of a PWM cycle. The peak threshold and the valley threshold may be adjusted to control the average current and the switching frequency of the converter circuit.