Patent ID: 8890050

Claim:
A photosensor circuit, comprising: a relay coil configured to control application of an alternating current (AC) power source having a negative half and a positive half of a line cycle to a load; 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, the pulse width modulator circuit including a comparator; a drive transistor coupled to the relay coil that controls the average voltage across the relay coil responsive to the pulse width modulated signal; a photo control circuit configured to control application of the pulse width modulated signal to the drive transistor responsive to a detected light level; and a power circuit, coupled to the power source, that is configured to provide a regulated power signal to the comparator of the pulse width modulator circuit, wherein the power circuit includes the drive transistor coupled between the relay coil and the regulated power signal and a second transistor coupled between a base of the drive transistor and the regulated power signal and wherein the drive transistor conducts current passing through the relay coil to the regulated power signal when the drive transistor is on and the second transistor conducts current not passing through the relay coil to the regulated power signal when the drive transistor is turned off.