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A light dimmer is a means of controlling the "brightness" level of a lamp, in this application we will use a 555 timer to control the brightness level of a low voltage incandescent bulb of up to 60 watts. Do not confuse that with a fluorescent lamp where it will not work.
The 555 timer "light dimmer" schematic circuit is shown in figure 1 below. For the light dimmer to work the 555 timer is configured as a "variable cycle", astable oscillator running some where around 300 Hz.
Figure 1 - "light dimmer" schematic circuit
The power mosfet used here would be a TO-220 type such as MTP3055E or similar. Note the need for a TO-220 type heat sink for full rated loads.
If you look back at the tutorial on 555 timers (figure 2a - modified duty cycle in astable operation) you will note the need for Ra and Rb. Cunningly this is provided for in our light dimmer circuit by using a 47K potentiometer (often marked 50K).
In our light dimmer circuit, if the potentiometer were set around mid way the Ra and Rb would be something like 25K each. Moving our potentiometer from minimum to maximum varies the values of both Ra and Rb simultaneously and accordingly the duty cycle of the 555 timer controlling our light dimmer circuit.
I am particularly indebted to Philips Components and Semiconductors Australia for their most generous assistance in giving me access to material presented on this page.
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Bibliography: - Philips Semiconductors - Data Handbook IC11
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Updated 17th May, 2001