LED Driver Circuit Shunt Path PWM Brightness Control
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Solution Overview
Problem
Conventional LED driver circuits face challenges in controlling brightness while maintaining a fixed color, as high PWM frequency and low duty cycle require fast response times, leading to flicker and instability in light output.
Innovation Solution
A LED driver circuit that generates a constant current and switches it between an external LED and a shunt path, using a PWM circuit to control the shunt transistor's operation, allowing for brightness adjustment through duty cycle changes without affecting the color, thus eliminating the need for high-speed control loops.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If high PWM frequency and low duty cycle are used to achieve brightness control, then brightness adjustment range is improved, but the circuit response time becomes insufficient leading to flicker and instability
Solution Approach 1:
Instead of switching the LED on and off rapidly to control brightness (conventional approach), the patent inverts the approach by keeping the LED continuously on and switching a shunt path across it. This allows the LED to remain in a stable state while brightness is controlled by duty cycle of the shunt switching, eliminating the response time issues associated with high-frequency LED switching.
Solution Approach 2:
The patent introduces a shunt transistor as an intermediary element between the LED and ground. This shunt transistor acts as a mediator that can be switched on and off to divert current away from the LED, thereby controlling brightness without directly switching the LED itself. This intermediary approach eliminates the need for the LED to respond to high-frequency switching signals.
2Stability of the object's composition
If constant current is maintained through LED to keep color fixed, then color stability is improved, but brightness control becomes difficult due to PWM switching requirements
Solution Approach 1:
The patent segments the current path into two separate paths: one through the LED and one through the shunt transistor. By controlling the shunt transistor's switching state, the circuit can independently control brightness without affecting the constant current through the LED. This segmentation allows color (determined by constant LED current) and brightness (determined by shunt switching duty cycle) to be controlled independently.
Solution Approach 2:
The shunt transistor serves as an intermediary that controls brightness by diverting current away from the LED without directly controlling the LED's forward current. This allows the LED to maintain a constant current (and thus stable color) while the shunt transistor's duty cycle controls the overall brightness by controlling how much current reaches the LED on average.
Data Source
AI summary
A Light-Emitting Diode (LED) driver circuit is disclosed that controls the brightness of light generated by a LED that is coupled between a first terminal and a second terminal in response to a user supplied brightness control signal. A constant current source generates a constant current that is supplied to the LED and to a shunt circuit, which his connected in parallel with the LED. A brightness control circuit generates a pulse signal having a duty cycle that is proportional to the brightness control signal, and controls the shunt circuit such that, when said pulse signal is high, the constant current is passed through the shunt circuit and the LED is turned off, and when the pulse signal is low, the constant current is passed through the LED. The duty cycle of the brightness control signal is adjusted to adjust the LED's brightness, while the LED color remains constant.