Off-line dc power supply

Abstract

A method and apparatus are disclosed for controlling an off-line dc power supply circuit including a printed circuit board. The power supply circuit comprises a source of unregulated dc input power and a power transformer which separates the circuit into a primary side and a secondary side. An error amplifier compares an output dc voltage generated at a secondary winding of the power transformer to a reference voltage to generate an error signal representative of the difference error therebetween. The error signal is coupled from the secondary side of the power supply circuit to the primary side of the power supply circuit by means of a capacitor formed from traces on opposite sides of the printed circuit board. A solid state switch selectively connects the unregulated dc input power to a primary winding of the power transformer to regulate the power supply circuit in the primary side of the circuit in response to the error signal which is generated in the secondary side of the circuit. The error signal is converted to a frequency signal for coupling from the secondary to the primary sides where it controls a one shot circuit, the output of which is filtered to generate a control signal corresponding to the error signal for regulation of the off-line dc power supply.