Projector lamp AC automatic voltage regulation circuit circuit diagram

 　　In order to stabilize the brightness of the projection lamp L, a thyristor AC automatic voltage regulation circuit is used in the circuit . For this reason, the thyristor T5 is connected from a diagonal line of the AC bridge. Its trigger pulse is equivalent to the equivalent resistance of the unijunction transistor VT1, VT2 and the photosensitive three-pole VT3. When the light of the projection lamp changes due to changes in the power supply voltage, the resistance of the phototransistor changes, and the voltage phase of the control single-junction transistor also changes, thereby causing the pulse phase of the triggering thyristor to move and increase or decrease the thyristor conduction time. The voltage on L is kept approximately constant, and the brightness of the projection lamp is also kept approximately constant, making the light stable.