Abstract: In an embodiment, a USB interface includes a transformer, a primary winding of the transformer, and a first switch in series between a first and a second node, a secondary winding of the transformer and a component in series between a third and a fourth node, the fourth node configured to be set a first reference potential, a second switch connected between the third node and a first terminal, the first terminal configured to provide an output voltage of the USB interface; wherein the component is configured to avoid a current circulation in the secondary winding when the first switch is closed and a control circuit configured to compare a first voltage of an interconnection node between the secondary winding and the component to a first threshold and compare the first voltage to a second threshold when the first voltage is, in absolute values, above the first threshold.

Abstract: A power converter including a controller to control a synchronous rectifier (SR) switch. The controller includes a request control circuit and a discharge prevention circuit. The request control circuit is configured to generate a request signal in response to an output of the power converter. The request control circuit generates a secondary control signal to control the SR switch. The discharge prevention circuit is configured to prevent a parasitic capacitance discharge of a power switch caused by a turn on of the SR switch. The discharge prevention circuit is further generates a prevent signal to disable the secondary control signal from control of the synchronous rectifier switch when a period of the request signal is greater than a first time threshold, and enable the secondary control signal to control the synchronous rectifier switch when the period of the request signal is less than a second time threshold.

Abstract: A zero-voltage-switching control circuit for a switching power supply having a main power switch and a synchronous rectifier switch, is configured to: control the synchronous rectifier switch to be turned on for a first time period before the main power switch is turned on and after a current flowing through the synchronous rectifier switch is decreased to zero according to a switching operation of the main power switch in a previous switching period of the main power switch; and where a drain-source voltage of the main power switch is decreased when the main power switch is turned on, in order to reduce conduction loss.

Abstract: Disclosed examples include flyback converters, control circuits and methods to facilitate secondary side regulation of the output voltage. A primary side control circuit operates a primary side switch to independently initiate power transfer cycles to deliver power to a transformer secondary winding in a first mode. A secondary side control circuit operates a synchronous rectifier or secondary side switch to generate a predetermined cycle start request signal via a transformer auxiliary winding to assume secondary side regulation and to cause the primary side controller to initiate new power transfer cycles.

Abstract: Operation of a switching power converter, such as to reduce voltage spikes on the secondary side of switching power converters. One example is a method of operating a switching power converter, the method comprising: sensing, by a controller of a switching power converter, a strength-selection signal; and driving, by the controller within a plurality of switching cycles, a control input of a primary electrically-controlled switch, the driving in each switching cycle at a drive strength based on the strength-selection signal.

Abstract: The invention relates to a circuit apparatus (10) for controlling the current flow of the secondary side (20) of a direct voltage converter, comprising: a controllable switch element (1) having a first connection (1a), a second connection (1c) and a control connection (1b); a snubber circuit, which is electrically coupled to the source connection (1a) and the second connection (1c); and a control circuit (5), which is designed to control a deactivation time of the controllable switch element (1) via the control connection (1b); wherein the control circuit (5) is electrically coupled to the snubber circuit and is designed to control the deactivation time according to an electrical parameter of the coupling.

Abstract: The synchronous rectifier controller includes a voltage regulator to provide a control voltage to the control terminal of the rectifier switch. The synchronous rectifier controller compares the channel voltage of the rectifier switch with a threshold voltage to generate a comparison result signal. When the channel voltage is greater than the threshold voltage, the comparison result signal has a first logic value, and when the channel voltage is less than the threshold voltage, the comparison result signal has a second logic value. An inverted comparison result signal is generated according to the comparison result signal. When the channel voltage is less than the threshold voltage, the inverted comparison result signal enables a pull-up power supply to pull up the control voltage; and when the channel voltage is greater than the threshold voltage, the comparison result signal enables a pull-down power supply to pull down the control voltage.

Abstract: A secondary controller applied to a secondary side of a power converter includes a control signal generation circuit and a gate control signal generation circuit. The gate control signal generation circuit generates a gate control signal, and generates an injection signal according to the gate control signal. When a superposition voltage is less than a reference voltage, the control signal generation circuit generates a gate pulse control signal, wherein the gate pulse control signal corresponds to an output voltage of the power converter and the injection signal, the gate control signal generation circuit is further used for generating a gate pulse signal according to the gate pulse control signal, and the gate pulse signal is used for making a primary side of the power converter turned on.

Abstract: Isolated power supply control circuits, isolated power supply and control method thereof are disclosed, the control circuit for controlling an isolated power supply includes a secondary-side control signal generator and a primary-side control signal generator. The secondary-side control signal generator produces a secondary-side transistor switch control signal containing information about a turn-off instant of a secondary-side synchronous rectification transistor, which serves as a second turn-on instant. The primary-side control signal generator derives, from a feedback signal, a supposed turn-on instant for a primary-side transistor switch, which serves as a first turn-on instant. The primary side turn-on signal generator further derives a turn-on instant for the primary-side transistor switch from the second or first turn-on instant whichever is later and responsively generates a primary-side transistor switch control signal.

Abstract: A flyback converter with secondary-side control includes a secondary-side controller configured to emulate a primary-winding current. Based upon the emulated primary-winding current, the secondary-side controller signals a primary-side controller through at least one isolation capacitor to switch off a power switch transistor.

Abstract: A switching control circuit for a power supply circuit that generates an output voltage from an AC voltage. The power supply circuit includes a rectifier circuit rectifying the AC voltage, an inductor receiving the rectified AC voltage, and a transistor controlling an inductor current flowing through the inductor. The switching control circuit controls switching of the transistor, based on the inductor current and the output voltage. The switching control circuit includes a target value output circuit that outputs a target value of a peak value of the inductor current for shaping a waveform of the peak value so as to be similar to a waveform of the rectified voltage, and a drive signal output circuit that outputs a drive signal to turn on the transistor upon the inductor current falling below a predetermined value and turn off the transistor upon the peak value of the inductor current reaching the target value.

Abstract: An electronics (100) configured to determine an input voltage to a galvanic isolation point of the electronics (100) is provided. The electronics (100) comprises an isolation transformer (120) configured to conduct a primary current (Ip) provided by an input voltage source (110), and provide a secondary voltage (Vs), the secondary voltage (Vs) being proportional to a primary voltage (Vp) induced by the primary current (Ip). The electronics (100) also comprises a peak detection circuit (130) coupled to the isolation transformer (120), the peak detection circuit (130) being configured to receive the secondary voltage (Vs) and, based on the secondary voltage (Vs), provide a signal that is proportional to the primary voltage (Vp).

Abstract: A flux-corrected switching power converter includes a first transformer, a first switching stage, a controller, and a flux correction current source. The first transformer includes a first magnetic core, a first primary winding, and a first secondary winding, and the first switching stage is electrically coupled to the first secondary winding. The controller is configured to control switching of at least the first switching stage. The flux correction current source is electrically coupled to the first primary winding, and the flux correction current source is configured to inject current into the first primary winding to at least partially cancel magnetic flux in the first magnetic core that is generated by current flowing through the first secondary winding.

Abstract: The present disclosure relates to an adapter. The adapter includes an input port, a first output port and a second output port, and the adapter further includes: a rectifier circuit having an input terminal being connected to the input port of the adapter; a bus capacitor connected to an output terminal of the rectifier circuit in parallel; a first flyback converter having an input terminal connected to the bus capacitor and an output terminal coupled to the first output port; and a second flyback converter having an input terminal connected to the bus capacitor and an output terminal coupled to the second output port.

Abstract: A high-voltage semiconductor device integrates a MOS transistor with a Schottky barrier diode. The MOS transistor has a semiconductor substrate of a first conduction type, a well of a second conduction, a body of the first conduction type, and a doped source of the second type. A control gate formed above the body controls electric connection between the doped source and the well. The Schottky barrier diode has a metal, functioning to be an anode of the Schottky barrier diode and contacting the well to form a Schottky barrier junction therebetween.

Abstract: A flyback converter is provided that dynamically adjusts a drain threshold voltage for a current cycle of a synchronous rectifier switch transistor based upon operating conditions in a previous cycle of the synchronous rectifier switch transistor. A differential amplifier drives a gate voltage of the synchronous rectifier switch transistor during an on-time of the current cycle so that a drain voltage of the synchronous rectifier switch transistor equals the drain threshold voltage during a regulated portion of the current cycle.

Abstract: Pulse sharing control to enhance performance in multiple output power converters is described herein. During a switching cycle, an energy pulse is provided to more than one port (i.e., output) using pulse sharing transfer. Pulse sharing transfer may enhance performance by reducing audible noise due to subharmonics and by reducing a root mean square current of one or more secondary currents. A primary switch is closed to energize an energy transfer element via a primary current. Energy may be shared among a first load port on a first circuit path via a first secondary current and among a second load port on a second circuit path via a second secondary current.

Abstract: A flyback converter includes a power transformer, a primary side switch, a secondary side switch and a controller. A secondary side switching signal has an SR pulse for achieving synchronous rectification, and a ZVS pulse for achieving zero voltage switching. The ZVS pulse is enabled according to a first characteristic of a resonance waveform, whereas, a primary side switching signal is enabled according to a second characteristic of resonance waveform. When an output current increases, the primary side switching signal is disabled during an inhibition interval, such that primary side switching signal does not overlap with the ZVS pulse, thereby preventing the primary and secondary side switches from being both conductive simultaneously. The inhibition interval is correlated with a rising edge of the primary side switching signal in a previous switching period and a resonance period of the resonance waveform.

Abstract: A switching control circuit for a flyback converter having a main switch coupled to a primary winding of a transformer and a rectifier switch coupled to a secondary winding of the transformer, can include: a first voltage generating circuit configured to generate a first voltage sampling signal representing information of an input voltage; a synchronous rectification control circuit configured to adjust an on-time of the rectifier switch according to the first voltage sampling signal in order to adjust an absolute value of a negative current flowing through the secondary winding; and where the negative current is configured to discharge a parasitic capacitor of the main switch in order to reduce a drain-source voltage of the main switch.

Abstract: A switching power supply circuit with synchronous rectification has an energy storage component, a SR switch coupled to a secondary side of the energy storage component, and a secondary control circuit. The secondary control circuit has a turning-ON control circuit for providing a turning-ON control signal based on a comparison of a drain to source sensing voltage of the SR switch and a turn ON threshold, a mode determination circuit for providing a mode signal to determine a turn ON delay based on a detection to a transient event or the drain to source sensing voltage ringing of the SR switch, and a gate driver circuit for driving the SR switch. When the turning-ON control signal is asserted, the gate driver circuit charges a gate voltage of the SR switch after the turn ON delay based on the mode signal, to turn ON the SR switch.

Abstract: A controller to regulate a power converter includes a terminal that receives an enable signal including enable events representative of an output of the power converter. A drive circuit generates a drive signal to control switching of a power switch to control an energy transfer from an input to an output of the power converter. The drive circuit turns on the power switch when an enable event is received in the enable signal. A current limit threshold generator is coupled to the drive circuit to generate a threshold signal. The threshold signal increases in response to the power switch turning off and subsequently decreases. The threshold signal and a time between consecutive enable events are used to modulate the drive signal to regulate the output of the power converter.

Abstract: A synchronous rectification controller that controls driving a synchronous rectification transistor arranged on secondary side, includes: a gate terminal being electrically connectable to a gate of the synchronous rectification transistor; a drain terminal being electrically connectable to a drain of the synchronous rectification transistor via a first resistor; a first comparator comparing a drain terminal voltage generated at the drain terminal with negative first threshold voltage; a second comparator comparing the drain terminal voltage with negative second threshold voltage higher than the first threshold voltage; and a driver performing on/off control of the synchronous rectification transistor based on result of the comparison by the first comparator and result of the comparison by the second comparator, wherein when the synchronous rectification transistor is turned on, voltage is added to the drain terminal voltage by current flowing through the first resistor according to a second resistor.

Abstract: A flyback converter is provided that dynamically adjusts a drain threshold voltage for a current cycle of a synchronous rectifier switch transistor based upon operating conditions in a previous cycle of the synchronous rectifier switch transistor. A differential amplifier drives a gate voltage of the synchronous rectifier switch transistor during an on-time of the current cycle so that a drain voltage of the synchronous rectifier switch transistor equals the drain threshold voltage during a regulated portion of the current cycle.

Abstract: Disclosed is a system for determining a primary switching event in an isolated converter having a primary-side and a secondary-side. The system includes a primary-switch (PS) on the primary-side, a synchronous rectifier (SR) on the secondary-side, an integration circuit, and a SR controller. The integration circuit is in signal communication with the SR on the secondary-side and the SR controller is in signal communication with the SR and the integration circuit. The SR is configured to produce a drain-to-source voltage (VDS) and the integration circuit is configured to integrate a difference between the VDS and a output voltage (VOut) (produced by the secondary-side) over time to produce a VDS over time value (VTime). The SR controller is configured to determine if the VDS is greater than a first threshold voltage (VTH) and determine the primary switching event when the VTime is greater than a second threshold voltage (VSTH).

Abstract: A ZVS (zero voltage switching) control circuit for controlling a flyback power converter includes: a primary side controller circuit, for generating a switching signal to control a primary side switch; and a secondary side controller circuit, for generating a synchronous rectifier (SR) control signal to control a synchronous rectifier switch. The SR control signal includes an SR-control pulse and a ZVS pulse. The primary side controller circuit determines a trigger timing point of the switching signal according to a first waveform characteristic of a ringing signal, to control the primary side switch to be ON. The secondary side controller circuit determines a trigger timing point of the ZVS pulse according to a second waveform characteristic of the ringing signal, to control the synchronous rectifier switch to be ON for a predetermined ZVS time period, thereby achieving zero voltage switching of the primary side switch.

Abstract: A synchronous rectification control circuit for controlling a switching circuit comprising a synchronous rectifier switch, can include: a drive circuit configured to generate a drive signal to control switching states of the synchronous rectifier switch; and a voltage regulation circuit configured to control the drive circuit to adjust an amplitude of the drive signal to decrease to a preset threshold in an adjustment state when a drain-source voltage of the synchronous rectifier switch is greater than an adjustment threshold before the synchronous rectifier switch is turned off, where a time that the voltage regulation circuit is in the adjustment state is an adjustment time.

Abstract: The power supply apparatus of a synchronous rectification systems includes a current detection unit configured to detect a current for charging a secondary-side smoothing element, and a driving unit configured to drive a rectification unit based on a detection result by the current detection unit.

Abstract: A secondary controller for use in a power converter includes a drive circuit coupled to a secondary side of the power converter. The drive circuit is coupled to generate a first signal to enable a first switch coupled to a primary side of the primary converter. The first signal is generated in response to a feedback signal representative of an output of the power converter. A control circuit is coupled to receive the first signal and an input signal representative of a secondary winding voltage of the power converter. The control circuit is coupled to generate a second signal to control a second switch coupled to the secondary side of the power converter in response to the first signal and the input signal.

Abstract: A wireless power transmitting device for wirelessly transmitting power to an electronic device is provided. The wireless power transmitting device includes a first coil configured to have a first number of windings and to receive power to be transmitted to the electronic device, thereby generating a magnetic field; and a second coil configured to have a second number of windings, which is different from the first number of windings, wherein an induced electromotive force generated, based on the magnetic field generated from the first coil, in the second coil is used for operation of at least one hardware component of the wireless power transmitting device, and wherein a ratio of a voltage applied to the first coil to a voltage applied to the second coil is determined by a ratio of the first number of windings to the second number of windings.

Abstract: A charge/discharge switch control circuit for a battery pack includes a set of driving terminals and detection circuitry coupled to the driving terminals. The driving terminals provide driving signals to control a status of a switch circuit to enable charging or discharging of the battery pack. The detection circuitry receives voltages at multiple terminals of the switch circuit, and detects a status of an interface of the battery pack according to the status of the switch circuit and a difference between the voltages. The interface can receive power to charge the battery pack and provide power from the battery pack to a load.

Abstract: A switched-mode power supply includes an input, an output, and a transformer including primary and secondary windings. The power supply also includes a synchronous rectifier coupled to selectively conduct current through the secondary winding of the transformer. The synchronous rectifier includes a source, a gate and a drain terminal. The power supply further includes a controller having a supply voltage terminal and a gate terminal to supply a control signal to the gate of the synchronous rectifier, and a circuit coupled between the supply voltage terminal of the controller and at least one of the gate terminal of the controller and the drain terminal of the synchronous rectifier to supply power from the gate terminal of the controller or the drain terminal of the synchronous rectifier to the supply voltage terminal of the controller. Methods of supplying power in switched-mode power supplies are also disclosed.

Abstract: Techniques for avoiding false negative sense (NSN) detection in a flyback AC-DC converter are described herein. In an example embodiment, a secondary side controller of the AC-DC converter comprises a frequency detector, a negative sense detector, and control logic. The frequency detector is configured to determine a frequency of an input signal from the drain node of a synchronous rectifier (SR) circuit on the secondary side of the AC-DC converter. The negative sense detector is configured to determine a negative voltage of the input signal. The control logic is configured to: enable the negative sense detector, when the frequency of the input signal rises above a frequency threshold value; and turn on the SR circuit to transfer power to the secondary side of the AC-DC converter, when the negative voltage of the input signal falls below a voltage threshold value.

Abstract: Communicating fault indications between primary and secondary controller in a secondary-controlled flyback converter is described. In one embodiment, an apparatus includes a primary-side field effect transistor (FET) coupled to a flyback transformer coupled to the primary-side FET, and a primary-side controller coupled to the flyback transformer. The primary-side controller is configured to receive a signal from a secondary-side controller across a galvanic isolation barrier, apply a pulse signal to the primary-side FET in response to the signal to turn-on and turn-off the primary-side FET, communicate information to the secondary-side controller across the flyback transformer by varying a first pulse width of the pulse signal to a second pulse width and applying the pulse signal with the second pulse width to the primary-side FET.

Abstract: A switching power supply circuit has an energy storage component, a synchronous rectifier switch and a synchronous rectifier control circuit. The synchronous rectifier switch is coupled to a secondary side of the energy storage component, and the synchronous rectifier control circuit turns ON the synchronous rectifier switch based on a drain-source voltage across the synchronous rectifier switch when a primary switch is judged as turned ON. When the switching power supply circuit is not operating in a preset mode, the primary switch is judged as turned ON when the drain-source voltage remains larger than a dynamic reference voltage during a preset window time period, and when the switching power supply circuit is operating in the preset mode, the primary switch is judged as turned ON once the drain-source voltage is larger than the dynamic reference voltage.

Abstract: An in-vehicle power supply device includes a first voltage conversion unit for performing at least a step-down operation to lower a voltage applied to a first conductive path electrically connected to an in-vehicle power storage unit, and apply the lowered voltage to a second conductive path; a second voltage conversion unit for performing at least the step-down operation to lower a voltage applied to a first conductive path and apply the lowered voltage to a second conductive path, a second voltage conversion unit having a smaller power capacity than the first voltage conversion unit; a driving unit that drives the first voltage conversion unit and the second voltage conversion unit, and a capacitor that is electrically connected to the second conductive path and is charged with a current flowing through the second conductive path.

Abstract: A secondary side controlled control circuit for power converter with synchronous rectifier is provided. The secondary side controlled control circuit comprises a primary side controller and a secondary side controller. The primary side controller generates a primary side switching signal for switching a primary side switch of the power converter. The secondary side controller generates a secondary side switching signal for switching a switch of the synchronous rectifier of the power converter. The secondary side controller generates a primary side control signal to control the primary side controller for controlling the primary side switching signal.

Abstract: Synchronous rectification in active clamp flyback power converters. At least some example embodiments are methods including: sensing, based on a rate of change of voltage on a drain of a synchronous rectifier field effect transistor (SR FET), that the power converter has entered a charge mode of a transformer arranged for flyback operation; changing, responsive the sensing, a parameter within a SR driver from an original state to a modified state, the SR driver coupled to the SR FET; making the SR FET conductive during a discharge mode of the transformer; sensing, based on a voltage at the drain of the SR FET, that the discharge mode of the converter has ended; returning, responsive to sensing that the discharge mode has ended, the parameter to the original state.

Abstract: Disclosed is an electronic apparatus including a connector configured to connect the electronic device to an external apparatus; and a power circuit configured to supply power to the connected external apparatus, the power circuit including: a transformer configured to output an output voltage by varying a level of an input voltage; a switching unit comprising a switch configured to perform switching operation for the transformer; a controller configured to control the switching unit to match a level of the output voltage with the external apparatus; and an auxiliary power circuit including an auxiliary winding, and configured to supply power to the controller based on a voltage induced in the auxiliary winding by the output voltage and to decrease the number of turns of the auxiliary winding based on the output voltage having a level greater than or equal to a predetermined value.

Abstract: A power converter includes a primary side with switch devices that form a power transfer stage, and a secondary side with switch devices that form a rectification stage and an output filter coupled to the rectification stage and including an output inductor and output capacitor. A transformer couples the primary and secondary sides. The switch devices are controlled in DCM (discontinuous conduction mode) to transfer energy from the primary side to the secondary side during a power transfer interval in which one branch of the power transfer stage is conducting, one branch of the rectification stage is conducting and another branch of the rectification stage is blocking. As a voltage of the transformer first begins to rise at the start of a new power transfer interval in DCM, the branch of the rectification stage that is to be conducting during the new power transfer interval is hard switched on.

Abstract: A method of controlling a secondary-side rectifier switch of a flyback converter, can include: detecting a slope parameter of a secondary-side detection voltage along a predetermined direction, where the secondary-side detection voltage is configured to represent a voltage across a secondary winding of the flyback converter; and controlling the secondary-side rectifier switch to turn on when the slope parameter is greater than a slope parameter threshold, and a relationship between the secondary-side detection voltage and the ON threshold meets a predetermined requirement.

Abstract: An adaptive pulse width modulation threshold is provided for a flyback converter that controls the transition between the pulse frequency mode of operation and the pulse width modulation mode of operation. The adaptive pulse width modulation mode is adapted responsive to an output voltage for the flyback converter.

Abstract: A driving device for driving a light-emitting element includes a bridge rectifier, a first capacitor, an inductive control circuit, a transformer, a power switch element, an output stage circuit, and a controller. The bridge rectifier generates a rectified voltage. The inductive control circuit includes an inductor, and adjusts an inductive current through the inductor according to the rectified voltage and a first control voltage. The first control voltage is selectively used to perform a PFM (Pulse Frequency Modulation) operation. The transformer generates a transformation voltage according to the inductive voltage of the inductor. The output stage circuit generates an output voltage according to the transformation voltage. The light-emitting element determines whether to generate light according to the output voltage. The controller detects the rectified voltage, and determines the first control voltage according to the rectified voltage.

Abstract: A power converter includes a primary side with switch devices that form a power transfer stage, and a secondary side with switch devices that form a rectification stage and an output filter coupled to the rectification stage and including an output inductor and output capacitor. A transformer couples the primary and secondary sides. The switch devices are controlled in DCM (discontinuous conduction mode) to transfer energy from the primary side to the secondary side during a power transfer interval in which one branch of the power transfer stage is conducting, one branch of the rectification stage is conducting and another branch of the rectification stage is blocking. As a voltage of the transformer first begins to rise at the start of a new power transfer interval in DCM, the branch of the rectification stage that is to be conducting during the new power transfer interval is hard switched on.

Abstract: An active clamp circuit includes an active clamp capacitor coupled in series with an active clamp switch and an active clamp controller circuit to receive an active clamp switch current that passes through the active clamp switch and to control the active clamp switch based on the received active clamp switch current. The active clamp controller circuit is configured to enable the active clamp switch based on a first amplitude comparison, the first amplitude comparison being based on the active clamp switch current. The active clamp controller circuit is configured to disable the active clamp switch based on a second amplitude comparison and a third amplitude comparison, the second amplitude comparison and the third amplitude comparison being based on the active clamp switch current.

Abstract: Disclosed examples include battery apparatus and balancing circuits for transferring charge between one or more of a plurality of battery cells and a second battery, in which a battery is coupled with a first winding of a transformer, and the second battery is coupled with a second transformer winding. A first transistor is turned on to allow current flow in the first winding to discharge the first battery, and then the first transistor is turned off. The resulting induced voltage in the second winding turns on a second transistor to provide flyback active charge balancing to charge the second battery. A signal from the third winding allows detection of low or zero current flow in the second winding for a controller to begin subsequent charge transfer cycles for full isolation between the first and second batteries.

Abstract: Methods, apparatus, systems, and articles of manufacture for zero voltage switching of flyback converters are disclosed. An example apparatus includes a first driver to operate a first switch to direct a first current to flow to a first winding of a transformer, and a second driver to operate a second switch to direct a second current to flow to a second winding of the transformer and operate the second switch to cause the second current to discharge a voltage of the first switch.

Abstract: A ZVS (zero voltage switching) control circuit for use in a flyback power converter includes a primary side controller circuit, a secondary side controller circuit, and a pulse transformer. In one switching cycle, a synchronous rectifier transistor is turned ON twice to generate a circulation current at the primary side winding, and after the synchronous rectifier transistor is turned OFF, the power transistor is turned ON for zero voltage switching. A synchronous signal coupled between the primary side and the secondary side is employed to synchronize the power transistor and the synchronous transistor. The synchronous signal also triggers an SR-ZVS pulse to turn ON the synchronous rectifier transistor for achieving the zero voltage switching when the power transistor is turned ON.

Abstract: A ZVS (zero voltage switching) control circuit for use in a flyback power converter includes a primary side controller and a secondary side controller. The primary side controller generates a switching signal to control a power transformer through a power transistor to generate an output voltage. The secondary side controller generates an SR (synchronous rectifier) signal to control an SR transistor at a secondary side of the power transformer. The SR signal includes an SR-control pulse and a ZVS pulse. The SR-control pulse controls the SR transistor according to a demagnetizing period of the power transformer. The ZVS pulse determines the starting timing of the switching signal to achieve zero voltage switching for the power transistor. The secondary side controller generates the ZVS pulse after a delay time from when the power transformer is demagnetized. The delay time is determined according to an output load of the output voltage.

Abstract: A flyback converter includes a primary-side switch connected to a primary-side winding of a transformer and a secondary-side switch connected to a secondary-side winding of the transformer. The flyback converter is operated by controlling the primary-side switch to store energy in the transformer during ON periods of the primary-side switch, switching on the secondary-side switch synchronously with switching off the primary-side switch to transfer energy from the transformer to the secondary side, determining an off time of the secondary-side switch based on a reflected input voltage measured at the secondary-side winding when the primary-side switch is on, accounting for a settling time of the reflected input voltage when determining the off time of the secondary-side switch so that the settling time has little or no effect on the off time, and switching off the secondary-side switch based on the off time.

Abstract: Synchronous rectifier gate voltage boost method and system. At least some of the example embodiments are methods of operating a power converter to create an output voltage, including storing energy in a field of a main transformer arranged for flyback operation, the storing during periods of time when a primary switch is conductive and current flows through a primary winding of the transformer; and then transferring energy from the field of the main transformer to the output voltage on a secondary side of the power converter; activating a secondary rectifier (SR) switch on the secondary side of the power converter during periods of time when the primary switch is non-conductive, the activating by: driving a gate of the SR switch without boost if the output voltage is above a first threshold; and driving the gate of the SR switch with boost if the output voltage is below the first threshold.