LED Driver Dimming Control Using Pulse Extension and Reference Shaping
Solution Overview
Problem
Conventional LED dimming circuits face issues with power loss and low dimming accuracy due to analog circuitry and conventional DC-DC converter methods, which limit the range and accuracy of illumination control.
Innovation Solution
The proposed LED dimming circuit incorporates an amplifier, a pulse extension circuit, and a reference shaping circuit to extend the sampling interval and shape the reference voltage, enabling more accurate current sensing and higher frequency PWM dimming by delaying the trailing edge of PWM pulses and synchronizing the reference voltage with PWM signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional PWM dimming control is used, then the circuit is simple, but dimming accuracy is low
Solution Approach 1:
The pulse extension circuit extends the PWM pulse width before it reaches the switch control input, ensuring that the switch remains on for a longer, more precisely controlled duration. This preliminary extension of the pulse allows for more accurate dimming control by compensating for timing delays in the control circuitry.
Solution Approach 2:
The pulse extension circuit acts as an intermediary between the PWM terminal and the switch control input. It receives the PWM signal, extends its duration through RC timing circuits, and provides the extended pulse to the switch control, thereby improving dimming accuracy without requiring changes to the basic PWM control architecture.
2Measurement precision
If sampling interval is short, then response speed is fast, but measurement accuracy is insufficient
Solution Approach 1:
The reference shaping circuit performs preliminary shaping of the reference voltage waveform to anticipate the timing requirements of current sensing. By pre-conditioning the reference voltage to lead or synchronize with the extended PWM pulse, the circuit ensures accurate current measurement during the entire on-time of the switch without requiring extended sampling intervals.
Solution Approach 2:
The amplifier compares the voltage across the sense resistor with the shaped reference voltage in real-time during the extended PWM pulse duration. This feedback mechanism continuously monitors the LED current and provides accurate measurement throughout the extended on-time, maintaining both speed and accuracy.
3Measurement precision
If PWM frequency is increased, then dimming accuracy improves, but audible noise increases
Solution Approach 1:
The pulse extension circuit extends the PWM pulse duration to include the entire inductor current decay period. This ensures that the switch remains on long enough for complete current transfer, eliminating residual current that would cause audible noise at high frequencies, while maintaining accurate dimming control through the extended pulse width.
Data Source
AI summary
A light emitting diode (LED) dimming circuit includes an amplifier, a switch, a pulse extension circuit, and a reference shaping circuit. The amplifier has an amplifier output, a first amplifier input, and a second amplifier input. The first amplifier input is coupled to a current sense terminal. The switch has a first switch terminal, a second switch terminal, and a switch control input. The first switch terminal is coupled to the amplifier output. The pulse extension circuit has an extended pulse output and a pulse input. The extended pulse output is coupled to the switch control input. The pulse input is coupled to a pulse width modulation (PWM) terminal. The reference shaping circuit has a reference input and reference control input. The reference input is coupled to the second amplifier input. The reference control input is coupled to the PWM terminal.