Light Dimmers

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. 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...

This reference design is a high efficiency, high power factor, digital dimming electronic ballast designed to drive rapid start fluorescent lamp types. The design contains an active power factor correction circuit for universal voltage input as well as a ballast control circuit using the IR21592. The design also includes a PIC16F628 microcontroller and an isolation circuit for connecting to a Digitally Addressable Lighting Interface (DALI). Other features include EMI filtering, transient protection and lamp fault protection...

Figures 1 and 2 show a schematic diagram of the ML4831EVAL-220V ballast and control interface circuit. An additional secondary winding of 25 turns is wound on T1 (see figure 2) to obtain the bias voltage for circuit operation and the required safety isolation. Components D17, C26, R37, C29 and D18 rectify, filter and regulate this voltage to 18VDC. Components R36, R35, R34, C27 and the Programmable Unijunction Transistor, Q4, form an astable sawtooth oscillator...