Sample and Hold Circuit for LED Driver Voltage Stability
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Solution Overview
Problem
Existing LED driver circuits face challenges in maintaining a constant output voltage for constant current source circuits, especially when the feedback loop is disconnected, leading to issues like color shift, slow PWM dimming frequency, and noise due to residual voltage and overshoot.
Innovation Solution
A system and method utilizing a sample and hold circuit in conjunction with a second feedback loop to regulate the output voltage, sampling and holding a feedback voltage signal when the feedback loop is connected and using it to maintain a constant voltage when disconnected, preventing overshoot and allowing for higher PWM dimming frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a feedback loop is disconnected to enable rapid turn-on and turn-off of LED driving current, then the turn-on and turn-off speed is improved, but the output voltage becomes unstable and causes overshoot
Solution Approach 1:
The sample and hold circuit performs preliminary action by sampling the output voltage before the feedback loop is disconnected and holding this sampled voltage value. This pre-captured voltage information is then used to maintain stable output voltage during the disconnection period, preventing overshoot while enabling rapid turn-on and turn-off of the LED driving current.
2Productivity
If PWM dimming frequency is increased to improve dimming performance, then the dimming responsiveness is improved, but residual voltage and overshoot cause noise and distortion
Solution Approach 1:
The invention implements a feedback mechanism where the output voltage is continuously sampled and fed back to the sample and hold circuit. This feedback loop ensures that any residual voltage or overshoot conditions are detected and corrected by adjusting the held voltage value, thereby reducing noise and distortion even at high PWM dimming frequencies.
3Device complexity
If a single feedback loop is used to simplify the circuit, then the circuit complexity is reduced, but the ability to maintain constant voltage during feedback disconnection is lost
Solution Approach 1:
The feedback function is segmented into two independent loops: a first feedback loop for normal operation and a second feedback loop specifically for sampling and holding the output voltage. This segmentation allows the second loop to maintain voltage regulation reliability during feedback disconnection without significantly increasing overall circuit complexity, as each loop has a dedicated function.
Data Source
AI summary
A system and method are disclosed for maintaining an output voltage of a constant current source circuit. A constant current source circuit is provided that comprises a voltage regulator, a first feedback loop and a second feedback loop that are connected to the voltage regulator, and a sample and hold circuit that is connected to the second feedback loop. The voltage regulator regulates an output voltage VOUT to a reference voltage VREF using a first feedback voltage signal FB on the first feedback loop. The sample and hold circuit samples and holds a second feedback voltage signal VFB from the second feedback loop while the first feedback loop is connected. The voltage regulator regulates an output voltage VOUT to the second feedback reference voltage signal VFB when the first feedback loop is disconnected.