LED Driver Circuit PWM Current Distortion Compensation
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Solution Overview
Problem
LED driver circuits using pulse width modulation (PWM) for dimming LED filament lamps face challenges in synchronizing the rectified mains signal with the PWM control signal, leading to uncontrolled phase angle of input current peaks, which fails to meet regulatory requirements due to high frequency distortion.
Innovation Solution
A compensating arrangement is introduced in the LED driver circuit, comprising a first current source for PWM control and a second current source for charging the storage capacitor, with a coupling mechanism that adjusts the charging current during off periods of PWM, ensuring current peaks occur at fixed timing, thus reducing input current distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If PWM dimming control is used for LED current control, then dimming accuracy and color point control are improved, but mains input current distortion increases and regulatory requirements are not met
Solution Approach 1:
A compensating current source is introduced as an intermediary element that generates a compensating current signal to counteract the distortion caused by PWM switching. This compensating current is injected into the mains input current path, effectively canceling out the high-frequency distortion components and harmonics, thereby reducing total harmonic distortion (THD) while preserving PWM dimming accuracy
Solution Approach 2:
The invention changes the current parameters by dynamically adjusting the compensating current magnitude and phase based on the PWM switching state. The compensating current source modifies its output current waveform parameters (amplitude, frequency content) in real-time to counterbalance the distortion introduced by PWM switching, achieving compliance with regulatory current quality requirements
2Use of energy by stationary object
If a fixed current source is used to control storage capacitor charging, then power factor is improved, but current distortion remains due to fast PWM switching frequency
Solution Approach 1:
The invention transitions from a static fixed current source to a dynamic compensating current source that actively responds to PWM switching events. The compensating current source dynamically adjusts its output based on real-time detection of PWM switching states and resulting current distortion, enabling it to effectively counteract distortion across varying operating conditions while maintaining improved power factor
3Measurement precision
If PWM control signal operates at high frequency (e.g., 1 kHz), then dimming control resolution is improved, but the phase angle of input current relative to rectified mains cannot be well controlled
Solution Approach 1:
The invention implements a feedback mechanism where the compensating current source continuously monitors the phase relationship between input current and rectified mains voltage. Based on this feedback, the compensating current is adjusted in real-time to maintain proper phase alignment, ensuring that high-frequency PWM dimming control does not compromise phase angle control and regulatory compliance
Data Source
AI summary
A LED driver circuit uses a first current source circuit to set an output current, controlled by pulse width modulation and a second current source circuit for charging a storage capacitor. A compensating arrangement is used for increasing the current delivered by the second current source circuit during off period times of the pulse width modulation. This compensates the current drawn from the input and enables better timing control of the input current pulses.