PHOTOSENSOR CIRCUITS INCLUDING A CURRENT AMPLIFIER

摘要

Photosensor circuits include a relay coil configured to control application of an alternating current (AC) power source to a load. The circuit includes a pulse width modulator circuit configured to generate a pulse width modulated signal having a pulse width that varies responsive to an average voltage across the relay coil, including a capacitor of an averaging circuit coupled in parallel with the relay coil. A drive transistor is coupled between the relay coil and a neutral bus that controls the average voltage across the relay coil responsive to the pulse width modulated signal. A photo control circuit, including a select transistor, is configured to control application of the pulse width modulated signal to the drive transistor responsive to a detected light level. The pulse width modulator circuit further includes a current amplifier coupled between the voltage averaging circuit and the select transistor. The current amplifier may amplify a current discharged from the capacitor of the voltage averaging circuit to a base of the drive transistor during the negative half of the AC power source to reduce an amount of current discharged from the capacitor of the voltage circuit.during the negative half of the AC power source.