That is, there’s no fading required, so a static voltage with current limiting circuit would power the LED perfectly fine.. Is it to increase the already long life of the LED’s? Is it to reduce power consumption?
The same thing happens with DRL’s on a car, they’re fed a PWM signal rather than just static 12V from the car’s battery
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PWM has several advantages, two of them just off the top of my head being:
1. LED brightness can be regulated with a digital input, by invreasing the on/off ratio
2. Less/no heat dissipation required in the power supply as opposed to a current-limiting resistor
Yes, primarily to reduce power consumption, in turn reducing heat, which greatly extends the life of the LEDs, and allows the lamp package to be smaller because it doesn’t require as large a heatsink.
Brightness of LED can be controlled by adjusting DC voltage. But doing it this way is hard. LEDs are very sensitive to voltage changes. Small change in voltage causes large change in current. Too high current burns the LED.
And car electric system has varying voltages. The voltage on “12 V” wire can be as high as 14 V.
Without current controlling circuit the LED will burn when the voltage changes.
So the LED can’t be reliably powered directly from it. There must be some control circuit.
There are two most common ways to control LEDs: PWM and constant current circuit.
* PWM has the advantage that it allows finer control on the brighness of the LED.
* Constant current circuit can behave a bit weird when the LED starts to fail. PWM fails more gracefully.
* Cheap PWM with too low frequency can have visible flickering (especially noticeable in move).
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