Constant-On-Time LED Driver Circuit for Fast Dimming
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Solution Overview
Problem
Current control systems for electronic devices, such as illumination devices, face challenges in independently regulating average and instantaneous currents to achieve desired intensity and color spectrum, particularly in efficiently managing the transition between different illumination levels and maintaining stable current regulation.
Innovation Solution
A method and apparatus utilizing a constant-on-time switching regulator that pulse modulates the output current, employing a converter circuitry with a control signal to maintain output voltage at a defined level during both on-time and off-time, enabling quick resumption of current regulation and reducing start-up time, which includes components like a sense resistor, amplifier, control signal switch, and capacitor to buffer the voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If conventional current regulators are used to provide constant average current, then illumination intensity can be controlled, but the transition between different illumination levels is slow and start-up time is long
Solution Approach 1:
The patent employs pulse-width modulation (PWM) to periodically switch the LED driver on and off at high frequency. By varying the duty cycle of these periodic pulses, the circuit achieves different average current levels while maintaining fast response capability. The periodic switching action enables rapid transition between illumination levels without the slow ramp-up characteristic of conventional linear regulators.
Solution Approach 2:
The patent uses dynamic control of the switching regulator to adaptively adjust the output current. The control circuit dynamically modifies the switching parameters based on the desired illumination level, enabling fast transitions between different operating states. This dynamic approach replaces static regulation with adaptive control, significantly reducing start-up time and transition delays.
2Speed
If pulse modulation is used to control average current, then transition speed improves, but maintaining stable current regulation during off-time becomes difficult
Solution Approach 1:
The patent incorporates feedback control through sense resistors that monitor the output current and feed this information back to the control circuit. During both on-time and off-time periods, the feedback mechanism continuously adjusts the switching parameters to maintain the desired average current level. This closed-loop feedback ensures stable current regulation despite the periodic discontinuity introduced by pulse modulation.
Solution Approach 2:
The control circuit prepares the switching regulator in advance for the next switching cycle by pre-charging capacitors and setting appropriate gate drive voltages during the off-time period. This preliminary action ensures that when the next on-time period begins, the circuit can immediately establish the correct current level without instability or delay, maintaining continuous stable regulation throughout the PWM cycle.
Data Source
AI summary
The invention relates to a method and an apparatus for controlling average current by pulse modulating an output current. The apparatus includes a constant-on-time switching regulator. During the pulse modulation on-time, an output voltage is regulated at a level corresponding to a defined value of a corresponding output current. A control signal is provided to indicate an adjustment to the output voltage that enables regulation of the output current to the defined value. During the pulse modulation off-time, the output voltage is maintained at the level that substantially corresponds to the defined value of the output current during the pulse-modulation on-time.