Patent ID: 6087782
Filing Date: 2000-07-11
Classification: H02M,H05B,Y02B

Abstract:
A resonant mode power supply comprising:means for generating a d.c. supply voltage having a first terminal and a second terminal;a first switching element having a first terminal coupled to said first terminal of said generating means, and a second terminal connected to a supply node;a second switching element having a first terminal coupled to said supply node and a second terminal coupled to said second terminal of said generating means;a transformer comprising a primary winding having a first end, and a second end connected to the second terminal of said second switching element, and a secondary winding having a first end, a second end and a central tap connected to ground;a capacitor for coupling the first end of the primary winding to the supply node;a sensing resistor for connecting the second end of the primary winding to said second terminal of said generating means;a first diode for connecting the first end of said secondary winding to an output node;a second diode for connecting the second end of said secondary winding to said output node; anda controller connected to control inputs of said first and second switching elements for alternatively turning on and off said first and second switching elements for inducing an oscillation in an oscillating circuit including at least said capacitor and said primary winding of said transformer, wherein a frequency of said oscillation is inversely proportional to an amount of power being delivered by said resonant mode power supply, characterized in that said resonant power supply further comprises an over-power protection circuit for protecting the resonant mode power supply against a fault in a load that draws a power larger than normal operating power limits, wherein said over-power protection circuit performs a true measurement of real primary side power, said over-power protection circuit comprising:means for determining an amount of said real power being delivered to said resonant mode power supply;means for comparing said real power with a predetermined threshold value; andmeans for generating a control signal for said controller when said real power exceeds said threshold value, whereby said controller initially increases said frequency of oscillation to reduce the power being delivered, and then stops the switching of the first and second switching elements if an over-power condition persists.