LED Driving Device Resolving PWM Control Contradictions

A resistor is inserted between the transistor and LED to act as an intermediary element. This resistor speeds up the transistor's rising time by providing a discharge path for the gate capacitance, thereby extending the controllable duty-ratio range at the leading edge of the PWM signal without being limited by the transistor's inherent switching characteristics.

The circuit changes the voltage parameter at the transistor gate by maintaining one terminal at a constant voltage level. This parameter change improves the accuracy of control current by stabilizing the transistor's operating point, making the LED driving less sensitive to element characteristic variations.

One terminal of the transistor is maintained at a constant voltage level, creating an equipotential reference point. This stabilizes the voltage across the LED and transistor, improving control current accuracy by reducing voltage fluctuations that would otherwise occur due to element characteristic changes.

The resistor serves as a mediator that decouples the transistor's switching behavior from the LED's current control. By providing a controlled discharge path, it allows the transistor to switch faster while maintaining accurate current control through the resistor's stabilizing effect on the gate voltage.