Introduction
The HV9901 is a universal relay driver employing PWM switching techniques utilizing the relay coils inductance to provide efficient operation over a wide supply voltage range. Relay drive is constant-current.  Pull-in current, pull-in time, and hold current are all programmable via 2 resistors and a capacitor.  An adjustable regulator provides 1mA for external circuitry.

The HV9901DB1 demo board contains all the circuitry necessary to demonstrate the operation of the HV9901. Included on-board are a full-wave input rectifier, fuse, the HV9901, and a 10A relay.  Provisions for connecting an external relay are available.  The circuit may be modified to accomodate the drive requirements of other relays.