LED Channel Current Control Using PWM Switching
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Solution Overview
Problem
Existing LED driving apparatuses face challenges in maintaining constant average current across LED channels due to manufacturing errors causing voltage differences, leading to heat generation and inefficiencies in controlling channel currents.
Innovation Solution
A light emitting device (LED) driving apparatus that uses a PWM scheme to control average current by comparing detected currents with a reference wave, employing a channel current controller and switching element to adjust duty ratios and generate driving voltage, allowing operation in a saturation region to reduce heat and maintain constant current across LED channels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a linear control method is used to control average current through a transistor operated in an active region, then the average current flowing on the channels can be controlled, but heat generation occurs due to the voltage applied across the transistor multiplied by the current
Solution Approach 1:
The patent replaces the linear control method using a transistor in an active region with a PWM (Pulse Width Modulation) control method using a switching element. This substitution changes the control mechanism from continuous linear adjustment to periodic switching, eliminating the heat generation problem associated with voltage drops across the transistor while maintaining constant current control capability
Solution Approach 2:
The patent implements PWM control where the switching element is periodically switched on and off according to a reference wave signal. This periodic switching action allows the average current to be controlled by adjusting the duty cycle (ratio of on-time to total period) rather than using continuous linear control, thereby eliminating heat generation while maintaining reliable current control
2Reliability
If voltage control methods are used to adjust channel voltages by comparing detected voltages with reference potential, then voltage values can be constantly adjusted, but this does not directly address current variations due to manufacturing errors
Solution Approach 1:
The patent implements a feedback control system where the actual current flowing through each LED channel is detected and compared with a reference wave signal. The detected current feedback is used to generate PWM control signals that adjust the switching element duty cycle, thereby compensating for manufacturing variations in forward voltage and ensuring uniform current distribution across all channels
Solution Approach 2:
The patent changes the control parameter from voltage control to current control. By directly controlling the current through PWM modulation of the switching element based on detected current feedback, the system compensates for forward voltage deviations caused by manufacturing errors, ensuring that each channel receives the appropriate current regardless of its specific forward voltage characteristics
Data Source
AI summary
The present invention relates to a light emitting device (LED) driving apparatus that constantly maintains the average current flowing onto a plurality of channels. The light emitting device (LED) driving apparatus includes: a LED light source unit in which at least one LED channel is connected in parallel; at least one current detector that is disposed on a low end of a LED channel of the LED light source unit to detect the current flowing onto respective LED channels; at least one channel current controller that generates control signal controlling the average current of the channels by comparing current detected from the channels with reference wave; and a switching element that controls the average current of the LED channels in a PWM scheme according to the control signals.