Fiber optic/solid-state switch system designed for switching 20-amp inductive and resistive loads

A high-power microelectronic switching circuit is interfaced with a fiber optic data link, whereby inductive or resistive loads up to 20 amperes are switched, with a forward voltage drop of less than one volt. An input signal of one-half milliwatt is passed to the gate of a VMOS FET power device, which drives P-N-P output transistor to switch power supply to load circuits such as a window lift motor, a seat lift motor, a windshield wiper motor, headlights, and turn indicators. Also the switch is useful in nonautomotive control applications. For the purpose of achieving remote switching, the automotive manufacturer has used mechanical relays. Until recently the power required to activate an electromechanical relay was not itself recognized as a problem. Moreover, the electromechanical interference generated by mechanical relays was not particularly objectionable. However, today there is a clear incentive to reduce the power requirement to drive remote switching devices; and moreover, electromechanical interference can be extremely troublesome because, for example, it may cause other sensitive electronic controls to function erractically. The power switch of this design helps to solve these problems because it permits a direct interface with a very low input power command signal, such as is typical of a low-power microprocessor-fiber optic output and the electromechanical interference is eliminated.