Abstract: Improving start-up time of a light emitting diode (led) driver at lower input voltage is accomplished with a quick start circuit comprising a constant current source that replaces the traditional trickle charge start-up path for charging of a Vcc capacitor supplying operating voltage to an SMPS controller. Also the constant current source will only be operational during SMPS start-up, then will turn off after the SMPS is capable of producing its own regulated power supply to the Vcc terminal of the SMPS controller, thereby minimizing E2/R power losses in the SMPS.

Abstract: A power converter includes a current controller coupled to an energy transfer element to selectively enable a first, second or third current in the current controller. The first current is substantially zero, the second current is greater than the third current, and the third current is greater than the first current. The third current only partially discharges a capacitance coupled to the energy transfer element and the current controller. A control circuit is to be coupled to the current controller to selectively enable the first, second or third current in the current controller. A first feedback circuit is coupled to generate a first feedback signal while the first current is enabled by the current controller after a full discharge pulse. A second feedback circuit is coupled to generate a second feedback signal while the first current is enabled in the controller after a partial discharge pulse.

Abstract: AC-DC converter is provided which comprises an auxiliary winding 8c in a transformer 8, a voltage detector 21 for detecting a voltage VN appearing on auxiliary winding 8c of transformer 8 by on-off operation of a main switching element 9 in a DC-DC converter 10 to produce an output signal VCP1 when voltage VN on auxiliary winding 8c has a negative polarity, a waveform shaper 23 for generating chopping signals VRC from output signal VCP1 of voltage detector 21, and a PWM circuit 27 for comparing output voltage VRC from waveform shaper 23 and output voltage VCH from a boosting chopper 3 to supply drive signals VG1 to step-up switching element 5 in boosting chopper 3 when output voltage VRC from waveform shaper 23 exceeds output voltage VCH from boosting chopper 3. While controlling fluctuation in output voltage from boosting chopper with respect to fluctuation in AC input voltage, the converter can improve input power factor relative to AC voltage and also reduce consumption power during light load period.

Abstract: A power supply device for driving a light emitting diode (LED) capable of controlling the switching of multiple output powers, in synchronization with the frequency of one of the multiple output powers and simplifying a power conversion stage in supplying power for driving an LED.

Abstract: A switching control circuit for a switching power converter is provided. The switching control circuit is coupled to a switching device and an auxiliary winding of a transformer. The switching control circuit includes a valley detecting circuit, a valley lock circuit, and a PWM circuit. The valley detecting circuit is coupled to receive a reflected voltage signal from the auxiliary winding of the transformer for outputting a control signal in response to the reflected voltage signal. The valley lock circuit is coupled to receive the control signal for outputting a judging signal in response to the control signal during a first period and a second period following the first period. The PWM circuit outputs a switching signal in response to the judging signal.

Abstract: The present invention relates to a trigger circuit for a switch in a switching power supply, especially in a primary-side, triggered switching power supply. The trigger circuit here comprises a feedback signal terminal for detecting an auxiliary voltage induced on a primary-side auxiliary winding of a transformer of the switching power supply, a supply voltage terminal for supplying the trigger circuit with a supply voltage, and a ground terminal for connecting the trigger circuit to a ground potential, wherein the feedback signal terminal is formed by the supply voltage terminal and the auxiliary voltage is superimposed on the supply voltage. Alternatively, the voltage of the auxiliary winding could be superimposed on the voltage on an additional pin that is used for detecting the primary peak current.

Abstract: Methods, systems, and devices are described for both power and control signal transmission through a single coupled inductor. A current driver generates a cyclical current signal on a primary winding of a coupled inductor, to induce a voltage signal at the secondary winding corresponding to the cyclical current signal. A rectifier module is coupled with the secondary winding and configured to rectify the signal induced at the secondary winding. A control timing signal module is coupled with the primary winding and configured to induce voltage pulses on the secondary winding, the induced voltage pulses having an insubstantial impact on the output of the rectifier module. A switching module coupled with the secondary winding is configured to receive the voltage pulses and control a switching signal for a power switch coupled with the output of the rectifier and provide power to a load coupled with the output of the rectifier.

Abstract: The switching power supply device includes: an input unit which receives an input voltage; a transformer which includes a primary winding and a secondary winding; an output unit which provides an output voltage; a switching element; and a control circuit. The control circuit includes: a T2on measuring unit which measures a secondary-side conduction time period; a frequency control circuit which provides a second signal used for changing an on-frequency of the switching element in order to narrow a difference between the measured secondary-side conduction time period and a reference value; a primary current detecting circuit which detects a primary current; a current comparing circuit which provides a third signal used for turning the switching element off when the detected primary current becomes equal to a threshold value; and an oscillation control circuit which controls on-off switching of the switching element according to the second signal and the third signal.

Abstract: This invention relates to SMPS controllers employing primary side sensing. We describe a system for identifying a knee point in a sensing waveform, at which the output voltage of the SMPS may be sampled accurately on the primary side. The system identifies the knee point, broadly speaking, by tracking a portion of a power transformer voltage waveform, and samples the voltage waveform at the knee point to determine the SMPS output voltage. In preferred embodiments this technique is implemented using a circuit akin to a decaying peak detector, providing a timing signal indicating detection of the knee point. Sample/hold and error amplifier circuits may be employed to achieve output voltage regulation.

Abstract: Switch mode power converter system and method thereof. The system includes one or more isolation boxes including at least a first isolation box, an input primary winding for receiving an input signal for the switch mode power converter system, and an output secondary winding for generating an output signal for the switch mode power converter system. The switch mode power converter system is configured to convert the input signal to the output signal. One of the input primary winding and the output secondary winding is substantially enclosed in the first isolation box, and the other of the input primary winding and the output secondary winding is not enclosed in the first isolation box. The first isolation box is conductively connected to a constant-voltage source.

Abstract: An LCD backlight driving device with an isolating transformer comprises a DC power supply, a square wave generator, a square wave controller, said isolating transformer and a driver transformer; wherein said isolating transformer has a primary side connected to said square wave generator and a secondary side connected to said driver transformer, since said isolating transformer is placed between said square wave generator and said driver transformer, it helps to effectively shorten a safety distance required for setting up said driver transformer; the present invention uses said isolating transformer to shorten the safety distance required than that of using said driver transformer directly and to decrease an area in implementing a circuit board and to cut cost of said device.

Abstract: A control IC including a full-bridge circuit is disposed on a primary side and a secondary side. Bidirectional communication is performed between the primary side and the secondary side in a state in which they are isolated. A control signal output from the primary side or the secondary side earlier is preferentially processed. As a result, the authority to control a switching element can be freely given to a primary-side control IC or a secondary-side control IC, and any control processing can be performed with software.

Abstract: An isolated switching power supply apparatus includes a direct-current input power supply, a power transmission transformer including a primary winding and a secondary winding, at least one main switching element configured to perform switching control on a direct-current voltage applied to the primary winding of the power transmission transformer, a rectification circuit that includes at least one rectification switching element and is connected to the secondary winding of the power transmission transformer, a smoothing circuit connected to the secondary winding of the power transmission transformer, a power conversion circuit configured to obtain an output voltage from the smoothing circuit, and a control circuit configured to control an operation of the power conversion circuit.

Abstract: A DC/DC converter has three half-bridge-type current resonant DC/DC converters that are connected in parallel, have a phase difference of 120 degrees, and are operated at a frequency higher than a resonant frequency. Each of the three half-bridge-type current resonant DC/DC converters includes a transformer having a primary winding, a secondary winding, and a tertiary winding, a series circuit connected to both ends of a DC power source and including first and second switching elements, a series circuit connected to both ends of the first or second switching element and including a resonant reactor, the primary winding of the transformer, and a resonant capacitor, and a rectifying circuit to rectify a voltage generated by the secondary winding and output the rectified voltage to a smoothing capacitor. The tertiary windings are annularly connected to a reactor.

Abstract: A controller for use in a power converter includes a control circuit to be coupled to a current controller coupled to an energy transfer element. A first, second or third current is enabled in the current controller in response to the control circuit. The first current is substantially zero, the second current is greater than the third current, and the third current is greater than the first current. The third current only partially discharges a capacitance coupled to a terminal coupled between the energy transfer element and the current controller. A first feedback circuit coupled to the control circuit generates a first feedback signal after a full discharge pulse of current through the current controller. A second feedback circuit coupled to the control circuit generates a second feedback signal after a partial discharge pulse of current through the current controller.

Abstract: An embodiment of a self-supply circuit, for a voltage converter that converts an input voltage into an output voltage and has a main switch and a controller, designed to control switching of the main switch for controlling the output voltage; the self-supply circuit is provided with: a charge accumulator, which is connected to the controller and supplies a self-supply voltage to the same controller; a generator, which supplies a charge current to the charge accumulator; and an auxiliary switch, which has a first conduction terminal in common with a respective conduction terminal of the main switch and is operable so as to control transfer of the charge current to the charge accumulator. In particular, the self-supply circuit is provided with a precharge stage, connected to the auxiliary switch, which carries out a precharging of an intrinsic capacitance of the auxiliary switch before a turning-off transient of the main switch ends.

Abstract: The configurations of a compensation device configured in a circuit having a synchronous rectifier (SR), a controller and a load, and a compensation method thereof are provided in the present invention. In the proposed circuit, the SR includes a first terminal, a first inductor electrically connected to the first terminal in series, a second terminal and a second inductor electrically connected to the second terminal in series, the controller is coupled to the first and the second inductors, and the device includes a voltage source having a positive terminal coupled to the controller and a negative terminal coupled to the second inductor and providing a compensation voltage to reduce or eliminate the influence of the first and the second inductors towards a voltage value across the first and the second terminals.

Abstract: An output regulation circuit of a power converter without current sensing loss includes a transforming circuit to receive a proportional voltage from the primary winding of the power converter during the on-time period of the power switch. The first proportional voltage is transformed to a charging current signal to charge an energy storage device. Thus, the circuit controls the power switch according to a voltage limited signal of the energy storage device.

Abstract: Dual-mode AC/DC power converters and associated methods of operation are disclosed herein. In one embodiment, the AC/DC converter includes a primary winding, a switching transistor coupled to the primary winding, the switching transistor configured to carry a drain-source current, and a feedback voltage port configured to carry a feedback voltage. The feedback voltage port is coupled to the switching transistor to switch off the switching transistor when the drain-source current reaches a peak current limit. The peak current limit increases with increasing feedback voltage if and only if the feedback voltage satisfies an ordered relationship with a threshold.

Abstract: A single-stage AC to DC conversion device includes an energy storage unit, a magnetic unit, and a switch unit. The magnetic unit electrically connects the energy storage unit with the switch unit, and has a core, a first winding, a second winding, a third winding, and at least one output winding. The first winding couples with the core and transfers a first electric energy to the core. The second winding couples with the core and stores a second electric energy in the energy storage unit. The third winding couples with the core and transfers the second electric energy to the core. The output winding couples with the core that transfers the first electric energy and the second electric energy, and outputs a third electric energy through the output winding.

Abstract: A controller for providing a constant output current control signal in a switched mode power supply (SMPS) includes a conduction time compensation circuit that is configured to produce a compensated conduction time interval signal that includes compensation for a ringing waveform of a feedback signal. The compensated signal reflects more accurately the actual conductive time of a rectifying diode in a secondary winding of the switched mode power supply. In one embodiment, the compensated conduction time interval signal is used to generate a fixed ratio between the conduction time and the non-conduction time of the rectifying diode. In another embodiment, the controller also provides a constant voltage control signal.

Abstract: A device generates a signal representative of a current flowing through a load inductor of a converter, the converter having a first transformer including a primary winding driven with a pulse width modulated (PWM) voltage signal. The device may include a sense inductor magnetically coupled to the load inductor, and an integrator configured to integrate a voltage drop on the sense inductor and to generate a first signal representative of the current flowing through the load inductor with an offset. The device may further include a second transformer to be magnetically coupled to the primary winding of the first transformer and generating a second signal representative of a current flowing through the primary winding, and a peak detector configured to sample and hold a peak value of the second signal at every cycle of the PWM voltage signal.

Abstract: A control circuit includes a switch coupled to a transformer of a power converter for switching the transformer. A sampling circuit is coupled to the transformer to sample a reflected voltage of the transformer to generate a voltage signal. A switching circuit generates a switching signal to control the switch in response to the voltage signal. The minimum on time of the switching signal is changed in response to the change of an input voltage of the power converter. Because the pulse width of the reflected voltage is narrower at light load, the minimum on time of the switching signal helps the reflected voltage detection.

Abstract: A controller for use in a power converter providing sensing of an isolated output is disclosed. An example controller includes a current controller to be coupled to an energy transfer element and an input of the power converter. A control circuit is included that generates a mode select signal coupled to be received by the current controller. A first, second or third current is enabled in the current controller in response to a selection of a first, second or third mode of operation, respectively, of the current controller by the control circuit. The first current is substantially zero, the second current is greater than the third current and the third current is greater than the first current. A first feedback circuit is coupled to the control circuit and is coupled to generate a first feedback signal representative of an output of the power converter during the first mode of operation after a period of operation of the second mode of operation of the current controller.

Abstract: A reverse energy recovery circuit is located on a power conversion circuit equipped with a transformer which has a primary winding side connected to a power switch driven by a control unit. The primary winding side has a first end and a second end bridged by the reverse energy recovery circuit which comprises a first capacitor, a second capacitor, an ancillary winding and a diode. The first and second capacitors are coupled in series. The second capacitor has one end connected to the first end of the primary winding side. The ancillary winding has a first end connected to the first end of the primary winding side. The diode has a cathode connected to a second end of the ancillary winding and an anode bridged the first and second capacitors so that the diode and ancillary winding form a one way path between the first and second capacitors.

Abstract: Disclosed a switching power supply apparatus which includes a voltage converting transformer including an auxiliary winding on a primary side and a switching control circuit, wherein the switching control circuit includes a detection circuit to detect a falling edge of a terminal voltage of the auxiliary winding, and controls a switching transistor connected to a primary winding of the transformer based on the terminal voltage of the auxiliary winding at the time immediately before current flowing through a secondary rectifier diode of the switching power supply apparatus becomes zero, which terminal voltage is obtained based on a detection timing of the detection circuit.

Abstract: Switch mode power converter system and method thereof. The system includes one or more isolation boxes including at least a first isolation box, an input primary winding for receiving an input signal for the switch mode power converter system, and an output secondary winding for generating an output signal for the switch mode power converter system. The switch mode power converter system is configured to convert the input signal to the output signal. One of the input primary winding and the output secondary winding is substantially enclosed in the first isolation box, and the other of the input primary winding and the output secondary winding is not enclosed in the first isolation box. The first isolation box is conductively connected to a constant-voltage source.

Abstract: A converter is disclosed for using at least one switch to convert an input signal to a square wave signal, and using the square wave signal to generate an output voltage. The converter converts the square wave signal by a switching operation of a switch and generates the output voltage, and includes a switch controller for controlling the switching operation. The switch controller generates a first signal VCT having a first period that varies according to an output voltage, controls the switching operation of the switch by using the first signal, detects the output voltage, a first current Ids2 flowing through the switch, and a level of the first signal, and controls a burst mode according to the detection results.

Abstract: A high-voltage discharge lamp lighting device provides a starting pulse voltage sufficient to turn on a high-voltage discharge lamp having terminal wire connections of variable length. A power conversion circuit is coupled to a commercial AC power source input and rectifies the AC input into a predetermined DC voltage output. A charging capacitor is coupled to the power conversion circuit. A full bridge circuit is coupled to the power conversion circuit and the charging capacitor and provides a rectangular wave AC output signal to a transformer primary winding circuit of at least a capacitor, a single switching element and a primary winding of a transformer. A low pulse voltage is induced in the primary winding and a transformer secondary winding is connected on one end to the high-voltage discharge lamp, wherein the low pulse voltage is stepped up to a high pulse voltage and applied to the high-voltage discharge lamp.

Abstract: A voltage regulator is provided that includes a plurality of buck-boost transformers each having primary and secondary windings. The secondary windings of the transformers are electrically disposed in series between a source and a load. Each transformer is controlled by a plurality of control switches configured to control the voltage across the primary winding of a corresponding transformer. A controller monitors the output voltage and generates control signals for the switches. The transformers generate different voltage level changes in between the source and load and the voltages across the primary windings are capable of assuming opposite polarities to enable scaling of resolution and range. The voltage regulator efficiently regulates power with relatively few or no moving parts and also partially protects the power switching components by removing them from the path of the load current thereby producing a device that is smaller in size, costs less and is more reliable.

Abstract: The invention relates to a switch-mode power converter including a bias circuit. A power converter power transformer includes a magnetic core. The switch-mode power converter power transformer also includes an initial bias primary winding and an initial bias secondary winding, both wound on the magnetic core, wherein the initial bias secondary winding shares at least one magnetic path in common with the initial bias primary winding. A driver is configured to drive the initial bias primary winding with high frequency pulses when enabled by an enable signal. A rectifier and capacitor are configured to provide a voltage to power a control circuit during a power converter start-up. A method provides an initial bias power for a power converter output side referenced controller, powering the output side referenced controller from the initial bias windings.

Abstract: A hybrid constant current control system that uses both pulse width modulation (PWM) and pulse frequency modulation (PFM) control. When transitioning from constant voltage mode to constant current mode the present invention can continue to control using PWM. Thereafter, when the voltage has dropped, the present invention smoothly transitions to PFM mode. The point of transition is based upon the switching frequency and the lowest rated voltage of operation. The system and method avoids very short (narrow) Ton times which ensures accurate constant current (CC) control with bipolar junction transistor (BJT) devices. The present invention also avoids acoustic noise because the switching frequency is maintained at a high enough level to avoid such acoustic noise even when the energy transferred through the transformer is still substantial and the output voltage is not too low.

Abstract: A semiconductor device for switching power supply control limits the startup current supplied from a high-voltage input terminal, and prevents heat generation and combustion in case of an anomaly. A high-voltage input terminal is connected to the main winding of a transformer, and is supplied with a startup voltage upon input of a power supply to the switching power supply device. A power supply terminal is connected to a capacitor, and outputs a startup current to charge the capacitor after input of the power supply input. A startup circuit is connected between the high-voltage input terminal and the power supply terminal, and charges the capacitor while increasing the startup current with magnitude proportional to the voltage value of the power supply terminal, and after startup, turns off the startup current and supplies the power supply voltage only from the auxiliary winding of the transformer.

Abstract: A power converter includes at least one electric control switch, an electric current detecting and converting unit, a power controller, and a voltage detecting and controlling unit at the primary side; and a synchronous rectifying circuit, two MOSFETs, and an oscillating loop. During the actual operation, electric current detecting and converting unit outputs an AC voltage signal to the power controller and outputs a DC voltage signal to the voltage detecting and controlling unit, and then voltage detecting and controlling unit compares with a reference voltage to turn off the synchronous rectifying circuit at the no-load mode and to rectify via a body diodes of the MOSFETs. Accordingly, the power converter can reduce the power wastage at the no-load mode to be energy-saving.

Abstract: An exemplary DC to DC converter includes a first transistor, a second transistor, a transformer, and a pulse generating circuit having a first capacitor, a sampling resistor, a zener diode, and a first diode. A DC voltage input terminal is configured for receiving a first DC voltage and is grounded via the primary winding of the transformer, a collector electrode and an emitter electrode of the first transistor in series. A terminal of the auxiliary winding of the transformer is grounded via the inverted first diode, the non-inverted zener diode, the sampling resistor, and the first capacitor. The other terminal of the auxiliary winding is grounded. A first transistor having a base electrode connected to the DC voltage input terminal. A second transistor includes an emitter electrode a cathode of the zener diode, a collector electrode connected to a base electrode of the first transistor, and a grounded base electrode.

Abstract: A switch control device, a switch control method, and a converter using the same are disclosed. The converter includes: a switch; an energy transfer element that converts input energy into output energy according to a switching operation of the switch; and a switch control device that generates a first signal, which is maintained at a first level during a first interval starting from a first time at which the switch is turned on by using a feedback signal corresponding to the output energy and is then gradually lowered from the first level to the feedback signal during a second interval, and controls the switching operation of the switch by using a second signal corresponding to a current flowing at the switch and the first signal. A malfunction due to an LEC can be effectively prevented, and the converter and the converter controller can be implemented to be compact and low-priced.

Abstract: A switch mode power supply according to the invention that can improve the reliability thereof includes a series circuit connected between the positive and negative electrodes of a DC power supply 3, the series circuit including a capacitor 4, a main switching device 1, and a subsidiary switching device 2; a main control circuit 13; a subsidiary control circuit 10; control circuits 13 and 10 turning main switching device 1 and subsidiary switching device 2 alternately ON and OFF to obtain a DC output via a transformer 6; and subsidiary control circuit 10 preventing a voltage exceeding the gate breakdown voltage of subsidiary switching device 2 from being applied to the gate electrode of subsidiary switching device 2.

Abstract: A circuit for reducing the variations of auto-supply voltage of a control circuit of a switching power supply, where the control circuit supplies an activation or deactivation signal of a power transistor, includes an auto-supply voltage generator, a controlled switch capable of selectively connecting the generator to the control circuit, and a driving circuit of the controlled switch that supplies a closing signal of the controlled switch after a predefined delay of time starting from the deactivation command.

Abstract: Provided is a power supply circuit that supplies an electronic device with a supply power, including a voltage control section that outputs a control voltage that tracks an input voltage with a prescribed frequency characteristic and applies a voltage corresponding to the control voltage to the electronic device, a voltage adjusting section that detects the voltage applied to the electronic device and adjusts the input voltage based on the detected voltage, a current adjusting section that detects a current applied to the electronic device and adjusts the input voltage when the detected current is outside of a prescribed limit range, and a frequency characteristic adjusting section that increases a speed at which the control voltage tracks the input voltage by adjusting the frequency characteristic of the voltage control section when the applied current is outside of the limit range.

Abstract: A circuit includes a pulse transformer having primary and secondary windings. An oscillating waveform is applied to the primary winding to induce an oscillating waveform at the secondary winding. A transistor in series with a first resistor is coupled between the secondary winding and the ground. An R-C network formed by a second and a third resistor and a capacitor is coupled to a base junction of the transistor. The R-C network causes a slow, tapered linear pinch off of the transistor's conductance to enable the circuit to output a triangular waveform, which is characterized by a relatively short linear rise time followed by a substantially long linear fall time. The R-C network is coupled to the secondary winding via a first and a second diode, respectively.

Abstract: A primary side is provided with an oscillation circuit arranged to turn on a power switch at a constant cycle. The secondary side is provided with an on period control circuit arranged to output an off signal for turning the power switch off by detecting output voltage and comparing with a reference triangle wave signal. An isolated signal transfer circuit is provided between the primary side and secondary side to transfer an on signal. The primary side is provided with a power switch off circuit arranged to turn off the power switch based on the on signal.

Abstract: An electronic ballast including a rectifying circuit to provide a signal representative of the current signal associated with a buck inductor, a monitoring circuit to provide a monitoring circuit signal when the signal representative of the buck inductor is within a specified range, and a comparing circuit coupled to the rectifying circuit and the monitoring circuit and operable to alter the output of the power converter circuit driving the lamps in response to comparisons between the signals from the rectifying circuit and the monitoring circuit to control power conditions in the ballasts.

Abstract: Detection and control circuitry are added to a conventional power supply to detect when a load, such as a portable electronic device, has been disconnected from the power supply and, when disconnected, interrupt a current path to the primary windings of a transformer within the power supply to substantially reduce the amount of reactive power that is consumed by the power supply.

Abstract: A switching power supply apparatus which includes a DC power supply, an isolation transformer having primary, secondary and tertiary windings, and a switching element, and in which, by turning the switching element on and off, the high-frequency voltage appearing in the secondary windings of the isolation transformer is rectified to obtain a DC output, power consumption can be decreased during standby (in burst mode) in particular by means of a control circuit which controls the turn-on and turn-off of the element and similar.

Abstract: In an isolated DC-DC converter, an on-period control circuit generates an off-timing signal when the output voltage of an isolated DC-DC converter exceeds a reference voltage. A signal reception/power switch driving circuit causes a first switching device to be turned on based on a pulse signal for switching that is output from a PWM control circuit, and causes the first switching device to be turned off based on an off-timing signal transmitted by an off-timing signal transmission unit. A bootstrap circuit boosts a control voltage of the first switching device with the pulse signal for switching that is output from the PWM control circuit.

Abstract: In one embodiment, a control circuit for a series resonant switching power supply control system is configured to disable a power switch of secondary side of the system in response to a polarity reversal of the voltage across a primary side winding of the system.

Abstract: An amplifier is driven by DC voltage from a switchmode power supply, whereby the switchmode power supply includes on the primary side a primary winding and bias supply winding. The bias supply winding supplies a reflected voltage from a secondary winding to a bias supply capacitor. The bias supply capacitor drives the control circuit and provides a sensing to the control circuit. The power supply further includes an active clamp circuit for controlling the voltage stress on a main switch. In another embodiment, boost inductors and a balancing transformer are added on the primary side of the transformer to prevent overvoltage conditions at light loads.

Abstract: A circuit and a method for detecting a voltage of a transformer are provided. The circuit includes a current output circuit coupled to a winding of a transformer to generate a current signal. A current-to-voltage circuit is coupled to the current output circuit to generate a voltage signal in response to the current signal. A sample-and-hold circuit generates an output signal by sampling the voltage signal. An input voltage is applied to the transformer. The output signal is correlated to the input voltage of the transformer.

Abstract: A power supply (V1) for an electrical device comprising a transformer (X1) having primary and secondary windings. The primary winding is connectable to an AC voltage supply and circuitry on the secondary side is arranged to provide a DC output voltage for the electrical device. The power supply also comprises a switch (111—transistors Q1 & Q2) between the primary winding of the transformer and the AC supply, and a rectifier (Diode D6) for rectifying the AC voltage. The switch is arranged to switch on at some point as the rectified AC voltage increases, once it has reached a non-zero value, thereby providing a current flow through the primary winding and hence through the secondary winding when the switch (111—transistors Q1 & Q2) is switched off. The switch is further arranged to switch off before the rectified AC voltage starts to increase again.

Abstract: The present invention discloses an active peak voltage-limiting clamp circuit, which comprises a primary switch unit and a secondary switch unit that are used to control the coil current of a transformer, wherein a signal acquisition unit, a zero-point decision unit, a feedback unit and a pulse control unit are used to control the turn-on periods of the primary switch unit and the secondary switch unit; thus, the turn-on period of the primary switch unit is separated from the turn-on period of the secondary switch unit, and a buffer interval for the transient voltage variation is formed therebetween.