Lighting circuit and method for negative feedback control recovery in overload conditions

A method to regain negative feedback control from an overload condition in a resonant power converter, the method comprising:

• (a) regulating a switch operating frequency of the resonant power converter to provide output power to an LED load;
• (b) generating an error signal corresponding to a difference between the provided output power and a reference value;
• (c) generating a reference control signal based at least in part on the error signal;
• and
• (d) automatically controlling the reference value when the reference value is greater than the generated reference control signal.

An LED driver comprising:

• a DC-DC converter comprising a plurality of switching elements configured to produce an output voltage across first and second output terminals and an output current through an LED load coupled thereto, based on a DC input and an operating frequency;
• a current sensor coupled in series with the LED load;
• a control means for regulating the operating frequency based on an error signal derived at least in part from output signals from the current sensor relative to a reference value;
• and
• a reference control means for controlling the error signal in response to the error signal exceeding a reference error signal for regaining negative feedback control of the control means, wherein the reference control means includes:
• a quick discharge means for quickly reducing the error signal in response to the error signal exceeding the reference error signal;
• and
• a slow charge means slowly increasing the error signal in response the error signal being reduced.

A power converter, comprising:

• first and second switching elements coupled across a direct current (DC) power source;
• a resonant circuit coupled between an isolation transformer primary winding and an output node between the first and second switching elements;
• a current sensing circuit coupled between an output load and a secondary winding of the isolation transformer, and configured to provide a sensor output signal representative of an output current through the load;
• a feedback circuit configured to generate an error signal corresponding to a difference between the sensor output signal and a reference signal;
• a controller comprising a frequency control input terminal, and configured to generate drive signals to the first and second switching elements at a determined operating frequency;
• a frequency control circuit coupled between the feedback circuit and the frequency control input terminal of the controller, and configured, responsive to the error signal, to determine the operating frequency of the controller with respect to defined minimum and maximum frequencies;
• a current reference control circuit configured to control the error signal of the feedback circuit when the error signal is greater than a reference error signal of the current reference control circuit;
• wherein the feedback circuit includes a buffer resistor coupled between the reference signal and the first input terminal, and a buffer capacitor coupled between the first input terminal and a secondary side ground reference;
• and
• wherein the current reference control circuit is configured to control a voltage across the buffer capacitor when a reference control signal generated by the current reference control circuit is less than the reference signal.