LED Driver Circuit for Triac Dimmer Compatibility
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Solution Overview
Problem
LED light bulbs are not compatible with triac dimmer switches due to the triac's requirement for a charge current when off and a minimum load current when conducting, leading to flickering or non-linear dimming effects, and their non-linear light output makes it difficult to achieve smooth dimming control.
Innovation Solution
A non-linear electrical circuit comprising a current sense circuit, PNP transistor current amplifier, NPN transistor controller, and N-channel MOSFET circuit that senses input current and adjusts resistance to maintain consistent conduction, combined with a non-linear OPAMP circuit to mimic incandescent dimming characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If LED light bulbs are used with triac dimmer switches, then energy efficiency is improved, but compatibility and dimming performance deteriorate due to triac charge current requirements and minimum load current requirements
Solution Approach 1:
A dummy load circuit is introduced as an intermediary component between the LED driver and the triac dimmer switch. This dummy load provides the necessary charge current when the triac is off and maintains minimum load current during conduction, enabling the LED bulb to work seamlessly with triac dimmers without modifying the LED driver's core functionality.
Solution Approach 2:
The invention dynamically adjusts the dummy load resistance based on the triac's conduction state. When the triac is off, the dummy load provides higher resistance to supply charge current; during conduction, it adjusts to maintain minimum load current. This parameter change enables compatibility across different dimming levels and triac states.
2Device complexity
If LED drivers linearly scale LED current to AC input voltage, then control simplicity is improved, but dimming linearity deteriorates due to LED's non-linear light output characteristics
Solution Approach 1:
The invention implements a feedback mechanism where the actual LED current is sensed and compared with the desired current. The error signal is then used to adjust the PWM duty cycle, compensating for the LED's non-linear characteristics. This closed-loop control ensures linear dimming perception while maintaining relatively simple driver architecture.
Solution Approach 2:
The invention dynamically adjusts the PWM duty cycle based on the desired dimming level and LED current characteristics. Rather than using a fixed linear relationship between AC voltage and LED current, the system adapts the duty cycle in real-time to achieve perceptually linear dimming across the entire brightness range.
Data Source
AI summary
An electrical circuit for providing led light bulb drivers with the necessary electrical load for most triac and digital dimmer switches and provide dimming control to mimic incandescent light bulbs is described herein. The electrical circuit includes a non-linear electrical load circuit that is electrically coupled to a rectified alternating current (AC) input power source and providing the necessary load current to initiate and maintain activation of triac and digital dimmer switches. A phase sense and amplifier circuit is also coupled to the rectified AC input power source and it senses the AC input voltage phase, then transmits a control signal to the light emitting diode (LED) driver to adjust the current level of the power being delivered to the LEDs in a manner to mimic the dimming of incandescent light bulbs.