Linear Constant Current Controller for Ultra-Fast LED Dimming
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Solution Overview
Problem
Existing LED dimming systems face limitations in achieving ultra-fast rise and fall times for pulsating current outputs, with prior art circuits typically providing rise and fall times ranging from tens of microseconds to hundreds of microseconds, which is not sufficient for high dimming ratio applications.
Innovation Solution
A linear constant current controller is designed with an operational amplifier and a VC switch circuit that charges a compensation capacitor initially and then isolates it, allowing the compensation capacitor to maintain a voltage without recharging for each subsequent cycle, enabling output current rise and fall times in the tens of nanoseconds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a DC-DC power converter circuit is used to provide pulsating current output, then power efficiency is improved, but output current rise time and fall time are limited to tens of microseconds to hundreds of microseconds
Solution Approach 1:
The invention separates the power conversion function (DC-DC converter) from the current control function (linear constant current controller). The DC-DC converter provides efficient power conversion while the linear constant current controller handles precise current regulation with ultra-fast response. This functional segmentation allows each subsystem to be optimized for its specific purpose, resolving the contradiction between power efficiency and speed.
Solution Approach 2:
The linear constant current controller acts as an intermediary between the DC-DC power converter and the LED load. It receives the converted power from the DC-DC converter and transforms it into precisely controlled pulsating current with ultra-fast rise and fall times. This intermediary component enables the system to achieve both high power efficiency (from the DC-DC converter) and ultra-fast current switching (from the linear controller).
2Measurement precision
If a linear constant current controller is used with PWM input signal, then output current precision is improved, but output current rise time is limited by compensation capacitor charging time
Solution Approach 1:
The compensation capacitor is pre-charged to a specific voltage level before the PWM dimming cycle begins. This preliminary charging action ensures that when the PWM signal transitions to change the output current, the capacitor is already in the optimal state to enable ultra-fast response. By performing the charging action in advance rather than during each current transition, the system achieves both precise current control and minimal rise time.
Solution Approach 2:
The invention dynamically controls the charging and discharging of the compensation capacitor based on the PWM input signal. The capacitor is charged to a specific voltage level in response to the PWM signal, and this dynamic voltage adjustment enables the operational amplifier to rapidly respond to current control requirements. The dynamic behavior of the capacitor, rather than a fixed state, allows the system to achieve both precision and speed.
Data Source
AI summary
A system and method are disclosed for providing a pulsating current output having ultra fast rise and fall times. A linear constant current controller is provided that comprises an operational amplifier. A compensation capacitor is connected to an output of the operational amplifier through a switch circuit. The switch circuit closes to initially charge up the compensation capacitor. The switch circuit then opens to isolate the compensation capacitor when the output of the operational amplifier is connected to ground. A value of voltage is maintained on the compensation capacitor so that the compensation capacitor does not need to be recharged for each subsequent cycle of the pulsating current output. The linear constant current controller is capable of generating a pulsating output current that has rise and fall times in the tens of nanoseconds.