Dimmable LED Drive Circuit with Adaptive Bleeder Current Control
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Solution Overview
Problem
Linear LED drivers coupled with thyristor dimmers experience inefficiencies due to the need for a bleeder current circuit, leading to increased system loss and potential LED lamp flashing caused by asymmetrical chopping of the thyristor dimmer.
Innovation Solution
A dimmable LED drive circuit with a thyristor dimmer, bleeder current circuit, thyristor chopping angle detection circuit, and bleeder current control circuit that dynamically controls the bleeder current based on detected chopping angles and current parameters to minimize power loss and prevent flashing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a bleeder current circuit is equipped to maintain thyristor conduction, then the thyristor dimmer can maintain conduction state, but system loss increases and system efficiency decreases
Solution Approach 1:
The patent applies dynamics by making the bleeder current controllable and adaptive rather than fixed. The control circuit dynamically adjusts the bleeder current magnitude based on real-time detection of LED string breakdown voltage and thyristor holding current requirements, enabling the system to maintain thyristor conduction with minimal necessary current, thus reducing energy loss while ensuring reliable operation
Solution Approach 2:
The patent changes the parameter of bleeder current from a constant value to a variable parameter that adapts to different operating conditions. By detecting the breakdown voltage of LED strings and adjusting the bleeder current accordingly, the system optimizes the balance between maintaining thyristor conduction and minimizing energy consumption, directly addressing the contradiction between reliability and energy loss
2Ease of operation
If conduction angle chopping is performed by thyristor dimmer, then dimming function is achieved, but asymmetrical chopping causes LED lamp flashing
Solution Approach 1:
The patent implements feedback by detecting the actual output voltage waveform characteristics and LED current status, then using this information to adjust the thyristor firing angle and bleeder current in real-time. This closed-loop control compensates for asymmetrical chopping effects, preventing LED flashing while maintaining the dimming function, thus resolving the contradiction between ease of operation and waveform stability
Solution Approach 2:
The patent applies preliminary anti-action by proactively detecting potential asymmetrical chopping conditions and adjusting operating parameters before flashing occurs. The control circuit monitors the conduction angle and voltage waveform, and preemptively modifies the bleeder current and firing angle to prevent the development of asymmetrical conditions that would cause LED flashing, thereby maintaining waveform stability while preserving dimming capability
Data Source
AI summary
A dimmable LED drive circuit and a control method is provided in the present disclosure. The dimmable LED drive circuit may include a thyristor dimmer, a bleeder current circuit, and an LED circuit. The bleeder current circuit may provide a current required by the thyristor dimmer when an input voltage does not reach a forward voltage of the LED circuit. The dimmable LED drive circuit may further include a thyristor chopping angle detection circuit and a bleeder current control circuit. The thyristor chopping angle detection circuit may obtain a first electrical parameter signal characterizing a thyristor chopping angle when the thyristor dimmer is in a conducting state. The bleeder current control circuit may compare the first electrical parameter signal with a first threshold, and control the bleeder current circuit according to a comparison result. Moreover, an output current compensation circuit may also be included, which may be configured to compare the first electrical parameter signal with a second threshold to control a current flowing through the LED circuit.