An apparatus in an electronic control system allows two or three wire operation. A power supply can supply power to the enclosed circuitry in both two and three wire installations. Two separate zero cross detectors are used such that timing information can be collected in both two and three wire installations. Both zero cross detectors are monitored and are used to automatically configure the electronic control. Over voltage circuitry senses an over voltage condition across a MOSFET which is in the off state and turns the MOSFET on so that it desirably will not reach the avalanche region. Over current circuitry senses when the current through the MOSFETs has exceeded a predetermined current threshold and then turns the MOSFETs off so they do not exceed the MOSFETs' safe operating area (SOA) curve. Latching circuitry is employed to keep the protection circuitry in effect even after a fault condition has cleared. Lockout circuitry is used to prevent one protection circuit from tripping after the other circuit has already tripped from a fault condition. The protection circuitry output is desirably configured such that it can bypass and override the normal turn on and turn off impedance and act virtually directly on the gates of the MOSFETs. Preferably, the system has a high efficiency switching type power supply in parallel with a low frequency controllably conductive device.
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a Divisional of U.S. application Ser. No. 10/409,228 filed Apr. 8, 2003, which is a Divisional of U.S. application Ser. No. 10/013,746, filed Dec. 10, 2001, now U.S. Pat. No. 6,969,959, which claimed the benefit of U.S. Provisional Application No. 60/303,508, filed Jul. 6, 2001, the entire disclosures of which are hereby incorporated by reference.
