8

Brightness-control circuits

In most applications, simple light-generating devices such as filament lamps and LEDs are used in the basic ON/OFF mode, in which they are always either at full brilliance or are fully off. In fact, however, the brightness of these devices is fully variable between these two extremes; this chapter presents a variety of practical brightness-control circuits.

Lamp-control basics

Ordinary filament lamps can be powered from AC or DC supplies and consist of a coil of tungsten wire (the filament) suspended within a vacuum-filled glass envelope and connected to the outside world via a pair of metal terminals; the filament runs white hot when connected to a suitable external voltage, thus generating a bright white light. ...

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