Oppptiittttiiiicalllllllaally operated thyristor current controller - with current varying according to the amount of light allowed to fall on a photocell

摘要

The amount of light incident of the photocell (5) can be varied, for example, by the pedal-controlled shutter (8). The photocell functioning as a variable resistance is connected in series with the capacitor (12). This capacitor charges up to a certain threshold voltage and then discharges into the diode thyristor (13) which in turn switches on the reversible thyristor (3). Thus the proportion of each cycle of the alternating supply (1) for which the reversible thyristor is conducting and hence the supply of current to the load (2), for example a sewing machine motor, is determined by the amount of light allowed to fall on the photocell.