Universal input voltage detection system for a flyback converter

A universal input voltage detection system for a flyback converter comprising:

• a first comparator configured to assert a first comparator output signal responsive to a sense resistor voltage being greater than an adaptive threshold voltage, wherein the sense resistor voltage is produced by a primary current through a sense resistor;
• a second comparator configured to assert a second comparator output signal responsive to the sense resistor voltage being greater than a peak primary current threshold voltage, wherein the adaptive threshold voltage equals the peak primary current threshold voltage minus an offset;
• a voltage threshold time detector configured to time a threshold time starting from the assertion of the first comparator output signal and ending at the assertion of the second comparator output signal;
• and
• a controller for controlling a cycling of a power switch to regulate an output voltage of the flyback converter, wherein the controller is configured to cycle off the power switch responsive to the assertion of the second comparator output signal;
• and wherein the controller is further configured during a continuous conduction mode to:
• determine a voltage gradient over time of the sense resistor voltage from the threshold time, and
• determine an input voltage to the flyback converter from the voltage gradient over time and a magnetizing inductance of a transformer for the flyback converter.