Browse Prior Art Database

AUTO SWITCHING POWER SUPPLY

IP.com Disclosure Number: IPCOM000005930D
Original Publication Date: 1990-Mar-01
Included in the Prior Art Database: 2001-Nov-16
Document File: 1 page(s) / 49K

Publishing Venue

Motorola

Related People

James Wiggenhorn: AUTHOR [+2]

Abstract

Power supplies used in chargers are normally designed for 110 VAC or 220 VAC operation. They can be designed with either a different line transformer for 110 VAC or 220 VAC or a configuration with a split winding on the transformer with user selectable jumpers or a switch. The first approach requires the manufacturer to build and inventory two separate models which adds cost. The second requires the customer to either change jumpers or change the position of a switch. If this is done incorrectly by the user, damage will result to the unit.

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MOlVROLA Technical Developments Volume 10 March 1990

AUTO SWITCHING POWER SUPPLY

by James Wiggenhorn and Junious Wilson III

   Power supplies used in chargers are normally designed for 110 VAC or 220 VAC operation. They can be designed with either a different line transformer for 110 VAC or 220 VAC or a configuration with a split winding on the transformer with user selectable jumpers or a switch. The first approach requires the manufacturer to build and inventory two separate models which adds cost. The second requires the customer to either change jumpers or change the position of a switch. If this is done incorrectly by the user, damage will result to the unit.

A better method would be to have a circuit designed that could sense the line voltage and automahcally switch. The circuit described below fulfills this need.

   Transformer Tl is connected to 110 VAC or 220 VAC and provides 12 volts or 24 volts AC. When the supply is con- nected to 110 VAC the relay Kl, is not energized allowing the diodes D3, D4, D5, D6 to operate in a bridge configuration providing about 18 volts D.C. When 220 VAC is applied the transformer's voltage output is doubled providing about 24 VAC. When this occurs the zener diodes Dl and D2 conduct and pull-in relay Kl causing the transformer center tap to be grounded and the opening of D3 and D5. This again results in about 18 volts D.C.

The thermistor Rt is used to minimize in-rush currents and to provide an R-C time constant to allow ampl...