Patent ID: 9263954
Filing Date: 2016-02-16
CPC Classification: H02M

Claim Text:
1. A switched mode power supply comprising: an input for connection to a rectified mains supply, a transformer having a primary winding on a mains side and a secondary winding on a dc output side; a switching element for controlling current flow in the primary winding of the transformer; a sense resistor in series with the switching element; a feedback control system for controlling the switching element dependent on a sense voltage, which is dependent on the sense resistor, wherein the feedback control system is part of an integrated circuit, and the transformer is outside the integrated circuit, and wherein the integrated circuit further comprises a detection arrangement for converting a rate of change of the sense voltage into a constant current using a capacitor and converting the constant current into a constant voltage level using a resistor, thereby deriving a voltage signal representing the mains voltage, wherein the feedback control system comprises a first comparator and a second comparator, wherein the first comparator and the second comparator are for comparing the sense voltage with respective reference voltages to generate two comparator outputs, wherein the first comparator is for comparing the sense voltage with a first reference voltage to generate a first comparator output signal and inputting the first comparator output signal into a reset input of a first set-reset latch to control the first set-reset latch, wherein a second set-reset latch is provided which receives the two comparator outputs generated by the first and second comparators and which generates a sample signal for a sample and hold circuit.