Multi-Channel Driver Equalizer for LED Current Matching
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Solution Overview
Problem
Conventional LED driver circuits face challenges in maintaining accurate current matching across multiple LED strings at low intensity levels, leading to power supply burdens and susceptibility to offset voltages, which affects the matching of LED string currents.
Innovation Solution
A multi-channel driver equalizer circuit is introduced, utilizing an analog equalizer to sequentially couple the output of a reference amplifier with each current source amplifier in a current limit loop, correcting offsets and ensuring average current matching across LED strings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If conventional LED driver circuits use duty cycle control to adjust brightness, then the circuit can achieve dimming and brightness adjustment, but the power supply must respond to fast load changes causing transient response burden
Solution Approach 1:
The circuit performs preliminary action by setting the reference voltage Vref to the desired level before the LED string current needs to be adjusted. This allows the power supply to anticipate load changes rather than reacting to them, reducing transient response burden. The reference voltage is established in advance based on the desired brightness level, enabling smoother power supply operation.
2Ease of operation
If conventional circuits modify Vref directly to set brightness level, then brightness can be controlled, but the circuit becomes susceptible to offset voltages at low currents
Solution Approach 1:
The circuit introduces an intermediary mechanism by using a separate reference voltage generation path that is independent of the LED string current path. The reference voltage Vref is generated through a dedicated path involving a reference current source and resistors, rather than being directly modified by the LED current. This intermediary approach isolates the brightness control from the current measurement path, preventing offset voltage contamination at low current levels.
3Device complexity
If conventional circuits use single reference voltage for all LED strings, then the circuit structure is simple, but currents in multiple LED strings have poor matching at low current levels
Solution Approach 1:
The circuit applies segmentation by dividing the reference voltage distribution into separate paths for each LED string. Instead of using a single reference voltage for all strings, each LED string has its own reference voltage generated through independent current source amplifiers. This segmentation allows each string to have its offset independently corrected while maintaining overall simplicity through the use of identical modular circuit blocks.
4Reliability
If conventional circuits use high voltage switching transistors for current sources, then the transistors can handle the required voltage range, but the circuit cost increases
Solution Approach 1:
The circuit applies parameter changes by operating switching transistors at lower voltages through the use of multiple series string configurations. Instead of requiring single high-voltage transistors, the circuit divides the voltage stress across multiple transistor switches arranged in series strings. Each transistor operates at a lower voltage level, reducing the need for expensive high-voltage devices while maintaining the required overall voltage handling capability through the series arrangement.
Data Source
AI summary
The disclosed multi-channel driver equalizer circuit matches currents in multiple strings of illumination devices at low current levels by using an analog equalizer to sequentially couple the output of a reference amplifier in series with each current source amplifier in a current limit loop of the driver equalizer circuit to correct the offsets of the current source amplifiers, resulting in the matching of string currents on average.