Quote:
Originally Posted by BWinmill
I wonder why they haven't solved the problem of flicker with front/backlights. If I recall correctly, the intensity of an LED is related to the current passing through it. A simple approach involves using a potentiometer, which I understand isn't popular because it isn't software controlled. (Again if I recall correctly,) transistors can use voltage to control current as well, so it should be easy to design a software controlled way to control the intensity of a backlight using transistors.
Is there something that I'm missing?
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PWM has the advantage of being very power efficient. The PWM waveform can be driven in many ways, but they mostly come down to some sort of transistor-based "switch" controlling the current. This switch is either open (zero current through it) or closed (zero voltage across it, for an ideal switch). In either case, given that power is current multiplied by voltage, the power dissipated in the switch (and hence wasted) is zero (or negligibly small, in the case of real-world switches with finite on-resistance).
A design which controls brightness by modulating the current in an analogue way, for example by controlling it with a transistor or variable resistor of some kind, will dissipate power in the controlling element (i.e. it will have non-zero voltage across it and non-zero current through it). For low brightness settings this can typically result in more power being wasted in the controlling load than is used by the LED.
The wasted power is lost as heat, which may also cause thermal issues in some applications.
For mains-powered devices like TVs this may not matter, but it may be significant for low-power devices.
/JB