Two new monolithic, very high voltage, off-line switching regulators unveiled by Motorola today combine a powerful MOSFET, which drives the transformer primary, on the same chip with the supply controller circuit. This single chip solution makes possible a reduction in the overall component count for power supplies, which reduces PC board area and total system cost for power supplies - as well as lowers manufacturing placement and inventory costs.

Employing a very high voltage SMARTMOS process, the two new off-line switching regulators, types MC33363B and MC33365, are specifically designed to operate from a rectified 240 or 120 Vac line source. They are highly integrated for use in off-line AC-DC and high voltage DC-DC applications such as office automation, consumer and industrial products.

The MC33363B features an on-chip 700 V/1.0A SENSEFETTM power switch, a 450V active off-line startup FET, a duty cycle controlled oscillator, a current limiting comparator with a programmable threshold and leading edge blanking, latching pulse width modulator for double pulse suppression, high gain error amplifier and a trimmed internal bandgap reference. Protective features include cycle-by-cycle current limiting, input undervoltage lockout with hysteresis, output overvoltage protection and thermal shutdown.

The MC33365 contains the same features except that the overvoltage protection is replaced by a comparator to sense the line voltage of the bulk capacitor and detect any brown-out condition (drop of AC line voltage).

"The MC33363B and MC33365 series give designers flexibility to optimize their power supply solutions" commented Scott Delaney, Marketing Director of Motorola's Semiconductor Components Group. "At the same time, they will lead to smaller form factors for their designs.".

A pair of logical parts when you have the high-voltage process technology to build them. It's almost like going full circle in that Motorola can now achieve performances in single components that were dreamed of by tube designers -- but never achieved -- and now implemented with solid-state. Both parts remove some much other circuitry from around the power supply design that they will inevitably achieve a large number of design wins, and rightly so. The large number of protection features will attract itself to the higher-end power supply designs but the parts are also priced to be used across the board, including cost-sensitive consumer equipment.

I also like the surface-mount heat tab package that is available only for the MC33363B; which is a pity because although both are great parts that will be highly successful, I would guess that the MC33365 -- with brownout protection -- will greatly outsell the MC33363B -- with overvoltage protection -- particularly outside North America.

The MC33365 is available only in a 16-pin plastic DIP while the MC33363B is also available in the surface mount packages. Both are in production and are priced at $0.80 in 10,000-piece lots.