A power-supply circuit includes a transformer with primary and secondary windings, and an energy accumulator on the secondary winding. A circuit monitors the secondary winding and generates a feedback signal that is transferred by a transmission circuit through the secondary winding by selectively transferring energy from the energy accumulator. The transmission circuit includes: a) an electronic switch having a control terminal; and b) a driver circuit for driving the electronic switch. The driver circuit includes a charge-accumulation capacitor connected to the control terminal, and a charge circuit configured to draw energy from the secondary winding and charge the charge-accumulation capacitor.

A boost converter receives an input voltage and provides an output voltage and includes a power switch and a voltage control circuit configured to drive the power switch as a function of the output voltage. A voltage sensing circuit in the form of a voltage divider is coupled to sense the output voltage and provide a feedback voltage. The voltage control circuit drives the power switch. An electronic control switch is configured to selectively connect the voltage divider to sense the output voltage as a function of an enable signal generated by a timer circuit. The enable signal is pulsed such that the voltage divider is periodically connected to sense the output voltage during a first time and is disconnected from sensing during a second time.

A power converter has a power transistor and inductor coupled in a conduction path with the power transistor. A switching frequency of the power transistor is reduced during a light load condition. A pulse width of a drive signal to the power transistor is controlled to select a current through the inductor and power transistor corresponding to the switching frequency to maintain a fixed output power of the power converter, and further to vary the current through the inductor and power transistor to maintain the fixed output power of the power converter over a range of switching frequencies. A first number of pulses of the drive signal to the power transistor during a first time period sets the fixed output power of the power converter. No pulses of the drive signal are provided during a second time period after the first time period.

A synchronous rectification controller is arranged on the secondary side of an insulated synchronous rectification DC/DC converter. The synchronous rectification controller controls a synchronous rectification transistor M. An automatic shutdown circuit judges, based on the voltage V.sub.DS across the synchronous rectification transistor, whether the operation mode of a primary-side controller is a burst mode or a non-burst mode. When judgment has been made that the operation mode is the burst mode, the automatic shutdown circuit instructs a driver to suspend the switching of the synchronous rectification transistor M.

A power supply apparatus (10) includes a voltage input side (102), a power switch circuit (104), a voltage output side (106), a pulse width modulation signal generating circuit (108) and a burst frequency detection circuit (110). According to a pulse width modulation signal (114), the pulse width modulation signal generating circuit (108) controls the power switch circuit (104), so that the power supply apparatus (10) enters a burst mode. The burst frequency detection circuit (110) detects a burst frequency of the power switch circuit (104). The burst frequency detection circuit (110) informs the pulse width modulation signal generating circuit (108) that the burst frequency is in an audio frequency range if the burst frequency is in the audio frequency range. The power supply apparatus (10) leaves from the burst mode to avoid audio noise.

A switching power supply apparatus, including serially-connected first and second switching elements, a series circuit of a resonant inductance and a resonant capacitor connected in parallel to the first or second switching element, first and second capacitors respectively connected in parallel to the first and second switching elements, and a switching control circuit that alternately turns on the first and second switching elements. The switching control circuit includes a load detection circuit detecting a load state, a burst control circuit that switches to a burst control mode when the load detection circuit detects a light load, and a detection circuit that detects a timing at which a high-side reference voltage at a connection point between the first and second switching elements has a lowest value. The burst control circuit switches from switching stop to switching operation of the first and second switching elements at the detected timing.

In accordance with an embodiment, a method of driving a switching element in a switching converter includes generating a feedback signal that is dependent on the output voltage, driving the switching element in a plurality of subsequent burst cycles, determining a burst frequency, and adjusting an effective switching frequency in at least one burst cycle dependent on the determined burst frequency. Each burst cycle includes a burst-on period and a subsequent burst-off period, and determining the burst frequency includes evaluating a duration of at least one burst cycle.

A power converter and a method of operation thereof is disclosed including an input, an output, a sensor unit, a switched power converter, and a processor module. The power converter may convert an input power into an output power. The power converter may sense real-time measurements of the input power and the output power to determine a real-time calculated efficiency. The power converter may chop the input power into sized and positioned portions of the input power based on a plurality of determined operating parameters. The power converter may determine the operating parameters based on the real-time calculated efficiency and on a plurality of other operating factors/conditions.

A switching power supply device includes a first converter of boost type to which a full-wave rectified AC power supply is input, and a second converter of current resonant type to which an output of the first converter is supplied as an input voltage. The second converter has a normal mode for performing power supply control by continuously outputting an output of an oscillator to a switching element of the second converter and a standby mode for performing power supply control by intermittently outputting the output of the oscillator thereto under light load by comparing a feedback voltage from a secondary side of an isolation transformer with a threshold voltage. The second converter corrects the threshold voltage according to an output voltage of the first converter.

A method for controlling an output of a power converter includes switching a switching element with drive signals that are generated for switching a switching element during normal operation when an energy requirement of one or more loads at the output are above a low-load threshold. A non-regulated dormant mode of operation is entered when the flow of energy to the output is detected to be less than the low-load threshold value for more than a first period of time. The control circuit is powered down when in the non-regulated dormant mode of operation the control circuit is unresponsive to stop regulating the flow of energy to the output of the power converter. The control circuit remains in the non-regulated dormant mode of operation for a second period of time before powering up again to resume generating the drive signal and regulating the flow of energy.