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Saturday, October 10, 2009

A Phase Control Circuit

This is a phase control circuit that can be used to control the power delivered to an AC load. The phase control circuit can control the AC waveform, cutting the cycle to give full cycle, half cycle, zero cycle, or somewhere in between. You can say this circuit is similar to a dimmer circuit, but the switching is synchronized with the zero crossing of the waveform. This circuit is works using based on IC U208B. This is the figure of the circuit.

The benefit of switching the power in zero crossing condition is that the triacs doesn’t suffer power dissipation, thus increasing the overall efficiency. This phase control circuit is suitable for brushed AC motor, heater filament, or incandescent lamps. The IC U208B is designed as a phase control circuit in bipolar technology with internal supply-voltage monitoring. As the voltage is built up, uncontrolled output pulses are avoided by internal monitoring. Furthermore, it has internal-current and voltage synchronization. It is recommended as a low cost open-loop control.
[Circuit's schematic diagram source: TEMIC TELEFUNKEN Microelectronic Application Notes]

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