Abstract: A wide input voltage range relay drive circuit allowing a more than 2:1 input voltage variation is provided. The circuit utilizes a scaled and rectified bulk voltage to drive the relay coil. As the monitored bulk voltage increases beyond the relay coil rated voltage, the circuit pulse width multiplexes this bulk voltage to protect the relay coil. The bulk voltage switching does not begin, however, until the relay energizes. To reduce the power dissipation during the PWM switching, of the relay coil, a power dissipating switch is included and held on during the PWM switching events. To further increase relay life, the circuit controls the energizing of the relay coil to actuate the contacts of the relay at or near a zero cross of the power switched thereby.

Abstract: An electronic universal defrost timer (UDT) utilizes an electronic microprocessor controlled timer that is capable of operating over a supply voltage range of 120 Volt AC to 240 Volt AC (nominal) with no customer configuration or moving of wires, jumpers, etc. is provided. The UDT provides the ability for a user to initiate a non-scheduled defrost interval at any time. Further, the UDT provides diagnostic capability to indicate miswiring or an internal fault during detected failure conditions. The UDT provides variable defrost duration times for each scheduled defrost period. The setting and indication of these defrost intervals are provided on an LCD display styled to resemble current mechanical dial faces with customer installed trippers. The UDT also resumes operation at the correct time after a power outage without requiring a user to reset the timing mechanism.