LED Driver Pulse Narrowing via Sub-Transistor Current Stabilization
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Solution Overview
Problem
Existing light-emitting element driving devices face limitations in narrowing light emission pulses due to unstable current stabilization and overshoots, especially when driving multiple LEDs in series, which restricts the range of light control and brightness adjustment.
Innovation Solution
A light-emitting element driving device with a constant current circuit and a main switching element, where a sub switching element is used to pass current before the main switching element turns on, allowing for controlled pulse width modulation and enabling the main switching element to be turned on when the current circuit is stable, thereby reducing overshoots and allowing for narrower light emission pulses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the light emission pulse width is narrowed to achieve better light control, then the light control range is improved, but the current becomes unstable with blunt edges and overshoots
Solution Approach 1:
The constant current circuit is activated before the main switching element turns on, allowing the circuit to stabilize and establish proper current conditions in advance. This preliminary current establishment ensures that when the switching element activates, the current is already stable and ready for precise pulse control without overshoots or blunt edges.
2Duration of action of moving object
If the pulse width is excessively narrowed, then the light emission duration is reduced, but the constant current cannot be maintained throughout the pulse width
Solution Approach 1:
By establishing the constant current before the pulse begins, the system ensures that current stability is already in place before the light emission duration starts. This allows the pulse to be narrowed without compromising constant current maintenance, as the current foundation is laid in advance.
Solution Approach 2:
The constant current circuit acts as an intermediary that prepares and stabilizes the current flow before the main switching element operates. This intermediary preparation ensures that even when pulse widths are narrow, the constant current can be reliably maintained throughout the emission duration.
3Device complexity
If a single switching element is used, then the device complexity is reduced, but the ability to control current stabilization is limited
Solution Approach 1:
The switching function is segmented into two distinct elements: a main switching element for controlling light emission pulses and a constant current circuit with its own switching mechanism for current stabilization. This segmentation allows each element to specialize in its function, with the main switch handling pulse timing and the constant current circuit handling current stability, thereby improving overall control capability.
Data Source
AI summary
An LED driver includes a constant current circuit for supplying a constant current to a light-emitting portion composed of LEDs, a main transistor inserted serially between the light-emitting portion and the constant current circuit, a sub transistor connected to the node between the constant current circuit and the main transistor, and a control circuit. The LED driver drives the main transistor with pulses to make the light-emitting portion emit light in pulses. The control circuit, before turning on the main transistor, turns on the sub transistor to pass the constant current in the constant current circuit via the sub transistor, and, when turning on the main transistor, turns off the sub transistor.