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Silicon-controlled rectifiers (SCR) are solidstate semiconductor devices that are usually used in power switching circuits. SCR controls the output signal by switching it ‘on’ or ‘off,’ thereby controlling the power to the load in context. The two primary modes of SCR control are phase-angle fired—where a partial waveform is passed every half cycle—and zerocrossing fired—where a portion of the complete waveforms is passed to regulate the power. In the phase-angle controller, the firing pulse is delayed to turn on the SCR in the middle of every half cycle. This means that every time a part of an AC cycle is cut, the power to the load also gets cut. To deliver more or less power to the load, the phase angle is increased or decreased, thereby controlling the throughput power. There are several ways to control the firing angle of SCR. This article describes a microcontroller AT89C51-based phase-angle controller. A microcontroller can be programmed to fire SCR over the full range of half cy...

A phase-controlled dimmer delays the triac turn-on to a selected point in each successive ac half cycle. Use this circuit only for incandescent lamps, heaters, soldering irons, or universal motors that have brushes. Phase Controlled Dimmer Circuit Diagram

Simple phase shift measurement can be done by squaring both the measured and the reference, then compute the difference of the two signals. The accuracy of the circuit shown in the schematic d iagram  below is 1% UP to 2000 cps. This circuit is used in computers and for high speed analog instrumentation. Negative value for zero phase shift is indicated by the zero center DC ammeter, zero for 90′ phase shift and some maximum value for 180′ phase shift.  Phase-Shift Meter for Audio Frequency Signal Circuit Diagram