Multi zone secondary burst modulation for resonant converters

A power converter, comprising:

• an energy transfer element coupled between an input of the power converter and an input of the power converter;
• a switching circuit coupled to energy transfer element and the input of the power converter;
• and
• a controller coupled to control switching of the switching circuit to control a transfer of energy from an input of the power converter to the output of the power converter, wherein the controller includes:
• a control loop clock generator coupled to generate a switching frequency signal in response to a burst load threshold, a power signal, and a load signal responsive to the output load of the power converter, a switching frequency of the switching frequency signal is greater than a mechanical audio resonance range of the energy transfer element and above an audible noise frequency;
• a burst control circuit coupled to generate a burst on signal, and a burst off signal in response to a feedback signal representative of the output of the power converter and a burst enable signal responsive to the burst load threshold and the load signal to operate the controller in a plurality of burst modes, wherein a burst frequency of the burst on signal or the burst off signal is less than the mechanical audio resonance range of the energy transfer element and less than an audible noise frequency;
• and
• a request transmitter circuit coupled to generate a request signal in response to the switching frequency signal, the burst on signal, and the burst off signal to control switching of the switching circuit.

A method of controlling a power converter having a plurality of burst modes, comprising:

• operating the power converter in a first state with a burst on signal asserted and with a switching frequency signal responsive to a value of a load signal;
• operating the power converter in a second state with a burst off signal asserted, a fixed burst period substantially fixed to a second threshold period, and a burst on period is equal to a difference between the second threshold period and a burst off period;
• operating the power converter in a third state with the burst on signal asserted and with the switching frequency signal responsive to a value of the burst load threshold;
• operating the power converter in a fourth state with the burst off signal asserted;
• operating the power converter in a fifth state with the burst on signal asserted, the fixed burst period substantially fixed to a sum of a third threshold period and a fourth threshold period, and the switching frequency signal is substantially equal to either a fixed burst load threshold value or a maximum switching frequency;
• and
• operating the power converter in a sixth state with the burst off signal asserted, and the fixed burst period substantially fixed to the sum of the third threshold period and the fourth threshold period.