HV9901

LEDs have been around for years now but it’s only recently that things have started to get interesting with white and superbright versions appearing at reasonable cost. LEDs of course require some form of driving circuit and there is a lot of interest in more efficient or versatile techniques for driving them. This circuit isn’t fussy; it outputs a constant current suitable for high power LEDs and it doesn’t care whether the input is 12 V or 230 V! It sometimes happens that a chip manufacturercomes up with an IC to perform a specific function and later the chip is found to be useful in a different application, not anticipated by the original designer. The HV9901 Universal Relay Driver from Supertex Inc. is just such a device. It was originally designed to provide a constant current output drive for a relay coil from a very wide range of supply voltages from 10 V up to 450 V DC without the need to alter any of the circuit components. This device offers a number of benefits both to the designers of white goods where the variety of relays used in equipment can be reduced (optimising quantity discounts) and also to the maintenance engineer who does not need to check coil ratings of a replacement relay. The HV9901 operates at DC voltages only so for AC operation a bridge rectifier is also needed (but no reservoir capacitor is usually necessary).