Out in Front: July 4, 1996

For trickle-charging low-power products such as shavers, yard and power tools, and flashlights, the Unitrode UCC3890 off-line, battery-charger IC provides 1 to 2W of constant-current or -voltage charge from 100 to 400V dc. The device charges single-cell rechargeable batteries and directly drives small motors in constant-current mode. The IC uses an internal topology similar to two cascaded flyback converters driven from a single external power switch. This technique controls switch on-time inversely proportional to the input line voltage and switch off-time in-versely proportional to the output voltage. This ap-proach allows a large voltage-conversion ratio with a reasonable range of switch on/off duty cycle and low-cost, transformerless operation from a rectified ac line. The UCC3890 is available in eight-pin DIPs and SOICs and costs $1.22 (1000).

—by Bill Schweber

Unitrode Corp, Merrimack, NH. (603) 424-2410, fax (603) 429-8963.