Abstract: This invention relates to methods and apparatus for sensing the output current in a switch mode power supply (SMPS) using primary side sensing. We describe a module which senses a current in a primary winding of a transformer and a voltage on a primary or auxiliary winding of the transformer, and which includes a multiplier coupled to an output of a signal averager averaging a primary winding current and to an output of a timing signal generator using the sensed voltage to signal when a secondary winding is powering an output of the SMPS, to multiply an averaged current sense signal by a fraction of a total cycle period of said SMPS during which the secondary winding is providing power to provide a signal estimating an output current of the SMPS.

Abstract: A charging device with boundary mode control is disclosed. The charging device includes a transformer, a power switch, a detection circuit and a pulse-width modulation (PWM) controller. The power switch is electrically connected to one end of a primary-side winding of the transformer. The detection circuit is electrically connected to the primary-side winding and the power switch. The detection circuit detects the resonance of the parasitic capacitance of the power switch, thereby generating a detection signal for boundary mode control. The PWM controller generates a pulse-width modulation signal for driving the power switch, and turns on the power switch according to the detection signal.

Abstract: A method and apparatus of sampling reflected voltage signal of a transformer is proposed. Sampling signals are used for generating hold voltages by sequentially sampling the reflected voltage from the transformer. A buffer circuit generates a buffer signal from the higher voltage of hold voltages. A sampling switch periodically conducts the buffer signal to produce a feedback signal according to an output of the buffer circuit. The feedback signal is proportional to output voltage of the transformer. A threshold signal added by the reflected voltage signal produces a level-shift signal. A discharge-time signal is enabled once the switching signal is disabled. The discharge-time signal is disabled once the level-shift signal is lower than output of the buffer circuit. The pulse width of the discharge-time signal is correlated to the discharge time of the transformer. The sampling signals are enabled to generate hold voltages when discharge-time signal is enabled.

Abstract: A power converter includes a switch controller generating a pulse signal controlling a switch to emulate peak current mode control. The switch controller generates a control voltage from a representation of an output voltage of the power converter and a reference voltage. Based on the control voltage and a representation of an input voltage of the power converter, the switch controller determines a peak current in that switching cycle. If the peak current detected exceeds a maximum peak current, an on-time of the pulse signal in the next switching cycle is decreased. The power converter also provides short circuit or overload protection by increasing an off-time of the pulse signal until the off-time exceeds a transformer reset time of a transformer. If the switch period increased to prevent short circuit or overload exceeds a limit, the pulse signal is shut off immediately.

Abstract: The present invention discloses an integrated voltage regulator comprising a switching regulation and an additional regulation mechanism. The additional regulation mechanism permits better control of the voltage regulator to enable improved performance. The present invention integrated voltage regulator provides an output voltage Vout in the form Vout=(Vin?Vamp)*(Duty Cycle)?Vslew where the additional regulation mechanism comprises an amplitude modulation Vamp to modulate the input voltage Vin, a slew rate modulation Vslew to modulate the output voltage Vout, or a combination of amplitude modulation and slew rate modulation.

Abstract: A control circuit for adjusting leading edge blanking time is disclosed. The control circuit is applied to a power converting system. The control circuit adjusts a leading edge blanking time according to a feedback signal relative to a load connected to the output terminal of the power converting system. An over-current protection mechanism of the power converting system is disabled within the leading edge blanking time.

Abstract: A DC-DC converter is provided with a control circuit 6 which comprises a drive signal generator 11 for producing on-off signals to a control terminal of a MOS-FET 3 in synchronization with pulse signals VOSC from an oscillator 10; an intermittent controller 12 for producing a control signal VC1 to drive signal generator 11 in response to the level of detection signal from an output voltage detector 5 to convert MOS-FET 3 to the intermittent operation during the light load period; and a power control circuit 16 for ceasing power supply VCC to oscillator 10 in response to control signal VC1 from intermittent controller 12 to stop production of pulse signal VOSC from oscillator 10 for the cessation term of MOS-FET 3 during the intermittent operation.

Abstract: A high voltage power supply apparatus and a method of correcting current output from the high voltage power supply apparatus. The high voltage power supply apparatus includes a switching unit; a transformer; a pulse width modulation signal processing unit, which receives a pulse width modulation signal changed for environmental conditions, converts the received pulse width modulation signal into a direct current (DC) voltage, and outputs the converted signal as a reference signal; a drive control signal generating unit, which compares an output current signal output from the transformer with the reference signal, and outputs a drive control signal to drive the switching unit; and an output current detecting unit, which detects the output current signal. Accordingly, the magnitude of current output from the high voltage power supply apparatus can vary according to environmental conditions and the current can be uniformly output without an output error.

Abstract: In one embodiment, a method is provided for a power converter system. The method includes: automatically configuring the power converter system to operate with burst mode functionality if a control module of the power converter system is coupled in a first arrangement; and automatically configuring the power converter system to operate without burst mode functionality if the control module of the power converter system is coupled in a second arrangement.

Abstract: Methods and apparatus for sensing the output current in a switch mode power supply (SMPS) using primary side sensing are described. A system includes a primary current sense input, a charge input to sense a charging time of an SMPS transformer; a discharge input to sense a discharging time of the transformer; at least one averager; and a calculator. The primary current is averaged by the averager over at least a switching cycle of the SMPS and the calculator estimates the output current of the SMPS using the averaged primary current, the charge signal and the discharge signal.

Abstract: A flyback converter with a leakage-inductance energy recycling circuit includes a transformer and a leakage-inductance energy recycling circuit. The leakage-inductance energy recycling circuit includes a clamping circuit, an energy storage circuit, and a switch connected between the clamping circuit and the energy storage circuit. A power transistor is electrically connected to a primary winding of the transformer. The clamping circuit clamps the voltage of the power transistor at a predetermined voltage. The energy storage circuit stores the leakage-inductance energy of the primary winding. When the switch is turned off, the clamping circuit receives and stores the leakage-inductance energy of the primary winding, so as to clamp the voltage of the power transistor to a predetermined voltage; when the switch is turned on, the energy stored in the clamping circuit is stored in the energy storage circuit through the switch.

Abstract: A switching mode power supply and a corresponding method of protection operation is presented. A switching controller of the switching mode power supply receives current sensing information corresponding to the current flowing through a main switch and feedback information corresponding to an output voltage through a single terminal, and performs a protection operation when the voltage at the terminal is maintained to be lower than a reference voltage for more than a predetermined time frame. The power supply requires a low number of terminals, while preserving the protection operation function.

Abstract: According to one embodiment, a voltage regulator includes a switch configured to selectively conduct electrical energy according to a signal, and circuitry configured to provide the signal to implement a soft start procedure comprising varying frequency and duty cycle of the signal.

Abstract: In one embodiment, a secondary side power supply controller is configured to enable a secondary side power switch independently of a state of a drive signal used to control a primary side of the power supply.

Abstract: A DC converter comprises a single primary circuit which is coupled to each of a plurality of output circuits in respective time periods, the coupling being provided by switching in the output circuits. Each output circuit produces a respective output voltage and a respective feedback signal which is coupled as a control signal to the primary circuit during the respective time periods, so that each output voltage is regulated substantially independently of each other output voltage. The time periods for the different output circuits can be equal or different, and can be dynamically changed depending on error voltages of the output circuits.

Abstract: There is provided a power supply for AC/DC and DC/DC conversion which receives the DC power supplied from airplanes, vehicles and vessels as well as normal AC power, and converts the power to DC power and supplies it to portable electronic products. The power supply for AC/DC and DC/DC conversion includes an AC input 10, a DC input 20, a switch 30 for selecting AC input power or DC input power, a DC output 40, and a circuit used for AC/DC and DC/DC conversion 100 which converts the power input from the AC input or the DC input to DC power having predetermined values of current and voltage, and a secondary side of a transformer (TL) for AC/DC conversion inside the circuit for conversion serves as an inductor for performing DC/DC conversion.

Abstract: This invention generally relates to discontinuous conduction mode switch mode power supply (SMPS) controllers employing primary side sensing. We describe an SMPS controller which integrates a feedback signal from a point determined by a target operating voltage to a peak or trough of an oscillatory or resonant portion of the feedback signal when substantially no energy is being transferred to the SMPS output. When regulation is achieved this value should be zero; the difference from zero can be used to regulate the output voltage of the SMPS.

Abstract: System and method for providing control for switch-mode power supply. According to an embodiment, the present invention provides a system for regulating a power converter. The system comprises a signal processing component that is configured to receive a first voltage and a second voltage, to process information associated with the first voltage and the second voltage, to determine a signal based on at least information associated with the first voltage and the second voltage, and to send the signal to a switch for a power converter. The switch is regulated based on at least information associated with the signal. The signal processing component is further configured to determine the signal to be associated a first mode, if the first voltage is higher than a first threshold.

Abstract: A linear-predict sampling circuit is developed to generate a feedback signal by detecting a demagnetized voltage of the transformer. A switching signal is generated in response to the feedback signal for regulating the output of the power converter. A signal-generation circuit is used to generate a sample signal in response to a first signal, a second signal, and the switching signal. The first signal is correlated to a magnetized voltage of the transformer. The second signal is correlated to the demagnetized voltage of the transformer. A sample-and-hold circuit is coupled to the transformer to generate the feedback signal by sampling the demagnetized voltage of the transformer in response to the sample signal. The feedback signal is correlated to the output voltage of the power converter.

Abstract: A pulse-width-modulation control circuit of a switching-mode power converter with a primary-side feedback control is disclosed. The switching-mode power converter includes a transformer, a power switch, a current sensing resistor and the pulse-width-modulation control circuit. The transformer includes a primary-side winding, a secondary-side winding and an auxiliary winding. The pulse-width-modulation control circuit includes a sample and hold circuit, a transconductor circuit, an error amplifier and a pulse-width-modulation generator.

Abstract: A radiation tolerant high-power DC/DC converter is disclosed. The converter does not incorporate radiation-hardened parts, but instead uses p-channel FET switches that have a negative gate threshold voltage. With exposure to radiation, the gate threshold voltage decreases, becoming more negative. Thus, the gate is still controllable.

Abstract: A discharging device capable of realizing a proper PWM drive by accurately reflecting, as a strobe device, the secondary-side condition of a separately-excited strobe charging circuit being charged. A charging device which charges a main capacitor (2) via a separately-excited DC/DC converter and discharges the energy of the main capacitor, wherein a pulse width control circuit (1) for controlling a conduction pulse width on the primary side of the separately-excited DC/DC converter is provided, and this pulse width control circuit is configured such that a PWM soft start drive is performed that expands a conduction pulse width on the primary side of the separately-excited DC/DC converter stepwise up to a maximum pulse width.

Abstract: A detection circuit for detecting the demagnetizing time of a magnetic device is provided. An input circuit is coupled to the magnetic device for detecting a magnetizing voltage and a demagnetizing voltage of the magnetic device. A control circuit is coupled to the input circuit for generating a demagnetizing-time signal in response to the magnetizing voltage, the demagnetizing voltage, and a magnetizing time. The magnetizing time is correlated to the enable period of the magnetizing voltage. The demagnetizing time of the magnetic device is represented by the demagnetizing-time signal.

Abstract: A switch power supply with standby function is disclosed. The power supply can satisfy the need of the green environment protection. And a single ended green switch power supply IC or thick film or modular circuit design with standby function is disclosed, too. It comprises a standby power supply, a main power supply, a PFC device, and a supplemental circuit, wherein a remote control signal is transmitted to main control circuit in response to a main error signal to control main power supply. A method for preventing switch power current from overload and saturation is disclosed too. Finally, the present invention also provides a green power supply with standby function as well as its IC associated with digital processing highly qualified PFC, and a PC standard (such as ATX, ATX12, SSI) computer switch power supply.

Abstract: A PWM controller having an oscillator, a control circuit and a two-level limiter is provided. The oscillator generates a pulse signal. The control circuit couples to the oscillator for generating a PWM signal in response to the pulse signal, wherein the PWM signal controls a power switch. The two-level limiter couples to the control circuit for generating a two-level limit signal in response to an on-time of the PWM signal, wherein the two-level limit signal is formed by a first-level signal and a second-level signal during a switching period of the PWM signal, and the first-level signal is used to limit the maximum output power of the power converter under a high-line input voltage with a heavy-load condition, and the second-level signal is used to limit the maximum output power of the power converter under a low-line input voltage with the heavy-load condition.

Abstract: A method and apparatus are provided for a switching mode converter to improve the light load efficiency thereof. The converter is thus operated with three modes by monitoring a feedback signal and a supply voltage. When the feedback signal indicates that loading gets light enough, the converter is switched from the first mode to the second mode, and during the second mode some cycles are skipped. If loading is too light, the converter is switched from the second mode to the third mode, and during the third mode more cycles will be skipped.

Abstract: In a feedback circuit of a power supply, an electrical level of an output voltage is stabilized corresponding to changes of an electrical level of a pulse width modulation signal, and effects, which are caused by spikes, on passive elements are decreased to a lowest degree. The electrical level of the output voltage is stabilized by storing a voltage corresponding to a low-to-high electrical level of the PWM signal with a capacitor, by discharging the stored voltage with a high-to-low electrical level of said PWM signal, and by regulating a discharging path of the stored voltage with a diode, which is not conducted. The abovementioned disposition may be utilized on various power-consuming devices, a duty cycle of each of which is controlled with a PWM signal, for stabilizing output voltages of said power-consuming devices, and for reducing effects, which are caused by spikes, on passive elements inside said power-consuming devices.

Abstract: This invention discloses a power converter with a secondary-side control, including an input circuit with one or more switches, an output circuit with an output end and a controller, and a transformer with a primary-side coil assembly connecting the switch(es) and a secondary-side coil assembly connecting the output circuit. The on/off state of the switch(es) is controlled by variations in voltage of primary-side coil assembly. The controller in the output circuit detects an output voltage and sends detected results to the primary-side coil assembly as a feedback for primary-side coil assembly to regulate the PWM or PFM action of the switch in a specific way to maintain voltage stability.

Abstract: A driver for a DC-to-DC converter that may utilize a flyback or buck-boost converter circuit. The driver includes a driver circuit and an interface circuit. The interface circuit has a sensor sensing an input voltage from a DC supply and generating a sensor signal to a driver selector. The driver selector compares the sensor signal to a comparison voltage to determine the type of converter circuit and then transmits a selector signal to a driver circuit where it is used to control one or more of the components of the driver circuit, such as the logic circuit which is used for driving the converter to regulate the converter output. The sensor includes a sense resistor along with a current-sense amplifier, which is adapted for connection to a high side or a low side of a power supply while still producing a substantially equivalent output voltage or sensor signal.

Abstract: In one embodiment, a multi-function signal sensor is configured to receive a signal having a plurality of states and to offset the input signal by a first amount for values of the input signal that are greater than a first value.

Abstract: The invention relates to a switched mode power converter and a method of operating such a converter A switched mode power converter according to the invention includes a transformer (2) having a primary winding (2a) and at least one secondary winding (2b) and a secondary side rectifier circuit including an output filter (6, 10) coupled to the at least one secondary winding (2b), and a secondary side active switch device (S3) coupled between the at least one secondary winding and the output filter. The converter further includes primary side and secondary side control means (12, 16, 18) for regulating the switching of the primary side and secondary side switches, respectively, and configured so as to reduce the duty cycle of the primary side switch device (S1) during a lower power mode of operation of the converter, the reduction of the duty cycle of the primary side switch being determined with reference to the duty cycle of the secondary side switch (S3).

Abstract: Disclosed is a switching converter without an auxiliary winding. The switching converter has a transformer, a switching transistor, a coupling circuit and a regulating circuit. The transformer has a primary winding and a secondary winding, and is for transforming an input voltage into an output voltage; a first end of the switching transistor is coupled to the primary winding of the transformer, and the switching transistor is for controlling an operation of the transformer according to a control signal; the coupling circuit is for coupling a signal at the first end of the switching transistor to generate a coupled signal; and the regulating circuit is for detecting the coupled signal to generate the control signal according to the detecting result.

Abstract: An inductor current flows through an inductor of a flyback converter. In a constant voltage mode, the pulse width of an inductor switch control signal is adjusted to maintain a constant output voltage of the flyback converter. The inductor switch control signal controls a switch through which the inductor current flows. In a constant current mode, a comparing circuit, a control loop and a clamp generator circuit are used to maintain the peak level of inductor current. The comparing circuit generates a timing signal based on the ramp-up rate of the inductor current. The control loop uses the timing signal and a feedback signal to generate a time error signal. The clamp generator circuit uses the time error signal to generate a clamp signal that adjusts the pulse width of the inductor switch control signal to clamp the peak current output by the flyback converter in the constant current mode.

Abstract: A pulse-width-modulation control circuit of a switching-mode power converter with a primary-side feedback control is disclosed. The switching-mode power converter includes a transformer, a power switch, a current sensing resistor and the pulse-width-modulation control circuit. The transformer includes a primary-side winding, a secondary-side winding and an auxiliary winding. The pulse-width-modulation control circuit includes a sample and hold circuit, a transconductor circuit, an error amplifier and a pulse-width-modulation generator.

Abstract: The switched-mode power supply has a transformer which contains a primary winding and at least one secondary winding, a switching transistor in series with the primary winding, a driver stage for controlling the switching transistor, and a control circuit for controlling an output voltage. The control circuit in this case contains an oscillator which can be adjusted via a connection and is coupled to a secondary winding in order to determine the time at which the switching transistor is switched on. A switching stage is, in particular, arranged between the connection and the secondary winding and passes on a supply voltage to the connection when a sudden voltage change occurs on the secondary winding at the time of an oscillation. In consequence, the switching transistor is switched on at a time at which the losses when switched on are low, thus considerably reducing the losses which occur in the switching transistor.

Abstract: A method is disclosed for generating pulse width modulated pulse control signals for controlling switches in a switching power supply. First, a count value is determined of a master clock within a switching cycle of the power supply from beginning to end thereof. A separate state machine providing for each edge in each of pulse control signals and each is operated to generate the associated edge as a function of the sum of a fixed reference count value from the beginning of the switching cycle and a determined count value when the sum is determined to equal the actual count value.

Abstract: A switching regulation system and control scheme efficiently enables driving multiple loads from a common energy storage element, such as an inductor. The control scheme operates to store energy in the energy storage element over a first portion of a cycle, such as by ramping up current through an inductor, according to energy requirements of the multiple loads. After storing the energy in the storage element during the first portion of the cycle, the stored energy is delivered consecutively to each of the multiple loads over a subsequent portion of the cycle.

Abstract: An object of the present invention is to lower the voltage applied to the starting resistor of the starting circuit in a switching power supply circuit to reduce the power loss especially when the receiving voltage is high and thereby provide a small and inexpensive switching power supply circuit. According to the present invention, a switching power supply circuit comprises: a DC voltage section having two or more capacitors connected in series; and a PWM control circuit for receiving DC power supply from the DC voltage section and performing switching control on a primary side of a transformer in order for the switching power supply circuit to output a DC voltage of different voltage specifications; wherein the starting resistor for the PWM control circuit is connected to a connection point of the capacitors.

Abstract: A control circuit 8 of a switching power source comprises a voltage detector 31 for detecting a voltage VDC of a DC power supply 1 to produce a detection voltage VDT; a comparator 41 for producing an output signal VCP when detection voltage VDT from voltage detector 31 exceeds a reference voltage VR2; a bottom voltage detector 51 for detecting a bottom point of voltage VDS across a MOS-FET 3 after energy has been discharged from transformer 2; and a switching controller 61 for selectively turning MOS-FET 3 on depending on existence or absence of the output signal VCP from comparator 41. When the input voltage VDC from DC power supply 1 so rises that detection voltage VDT of voltage detector 31 is above the reference voltage VR2, switching controller 61 serves to late turn MOS-FET 3 on at the time bottom voltage detector 51 detects the second or later bottom point of the voltage VDS across MOS-FET 3, extending the off period of MOS-FET 3 to reduce switching frequency of MOS-FET 3.

Abstract: In a switching mode power supply, an input received from the secondary side of the transformer 7 and indicative of the power being drawn by the loads is used to control the timing of bursts. The input is compared with two threshold different threshold values V2, V3, and switching is enabled if the input rises above a first higher threshold value V2, and disabled if it falls below a second lower threshold value V3. A memory device FF1 controls a current limitation circuit which limits currents in the primary of the transformer when the switching mode power supply is operating in the burst mode.

Abstract: Disclosed is an SMPS for preventing abnormal overcurrents. A circuit having a short circuit delay is used to generate a control signal for turning off a main switch (i.e., a switching MOS transistor) when the overcurrent occurs, that is, in an initial startup or when a protection circuit is operated. Accordingly, a drain-source voltage of the main switch is reduced when the main switch is turned off, and a switching MOS transistor with a low withstanding voltage can be used.

Abstract: A switching power supply of the present invention comprises: a switching element through which a DC voltage is supplied via a primary winding; an output voltage detection circuit detecting a voltage of a secondary winding to generate an error signal; a regulator generating a predetermined voltage based on a voltage generated at a node between the switching element and the primary winding; a photocoupler through which a feedback current signal corresponding to the error signal passes; a feedback current detection circuit detecting a feedback current signal; a feedback voltage generation circuit generating a feedback voltage according to the current of the feedback current detection circuit when the switching element is OFF and holding the generated feedback voltage when the switching element is ON; and a control circuit controlling ON/OFF duty of the switching element according to an increase or decrease of the feedback voltage.

Abstract: In one embodiment, a secondary-side controller is configured to detect a burst-mode of operation and responsively block or prevent sending drive pulses to a power transistor that is coupled in the secondary side.

Abstract: The present invention discloses a switching control circuit for a primary-side controlled power converter. A voltage-waveform detector produces a voltage-feedback signal and a discharge-time signal. A current-waveform detector generates a current-waveform signal by measuring a primary-side switching current. An integrator generates a current-feedback signal by integrating the current-waveform signal with the discharge time. A time constant of the integrator is correlated with the switching frequency, thus the current-feedback signal is proportional to an output current of the power converter. A PWM circuit controls the pulse width of the switching signal in response to the outputs of a voltage-loop error amplifier and a current-loop error amplifier. The output voltage and the maximum output current of the power converter are therefore regulated.

Abstract: A resonant switching power system operates with two resonant frequencies. A first frequency depends on the secondary leakage inductance of an output transformer and capacitor. The first frequency varies with changes in the load because load changes alter the leakage inductance. A second resonant frequency depends on the gate source capacitance of two MOSFET power devices in the circuit and the leakage inductance of the circuit's driving transformer. Power is thereby supplied that is always in phase with the load so that switching in the power supply occurs when current is near zero. High thermal efficiency is thereby achieved.

Abstract: Techniques are disclosed to adjust a current limit in a switching regulator. One example switching regulator includes a switch to be coupled to an energy transfer element of a power supply. A controller to generate a drive signal is coupled to control switching of the switch to regulate an output of the power supply. A current limiter is included in the controller to adjust the drive signal to limit a current though the switch to a variable current limit value. The variable current limit value is set by the current limiter in response to an input line voltage to be coupled to the energy transfer element.

Abstract: A switching regulator has an input voltage detection circuit which inputs a voltage applied to a rectifier diode 7 connected in series with the secondary side of a transformer and generates a voltage signal Vvp corresponding to the voltage, and a calculation unit which calculates a voltage value Vin inputted to the primary side of the transformer based on a voltage value of the voltage signal generated by the input voltage detection circuit.

Abstract: A switching power supply is disclosed for improving the no-load power drain of low-power mains operated supplies. The power converter utilizes a cascoded switch arrangement with a conventional high voltage power MOSFET and a low voltage, low gate charge MOSFET. Driving only the small low voltage device reduces the power required for gate drive. The disclosed configuration is also capable of generating a non-isolated auxiliary rail for powering its control circuitry utilizing the parasitic capacitance of the high voltage power devices as an element in a charge pump. The resulting power supply requires significantly fewer components.

Abstract: The present invention is associated with a power adapter capable of simultaneously providing a low-level DC voltage and a high-level DC voltage. The power adapter includes a transformer having a primary winding for storing energy when a main switch coupled therewith is turned on and transferring the stored energy to the secondary side of the transformer when the main switch is turned off. The transformer includes a first secondary winding and a second secondary winding connected in series with each other. A first rectifier/filter circuit is connected across the first secondary winding for generating a low-level DC voltage by rectifying and filtering the energy received by the first secondary winding, and a second rectifier/filter circuit is connected across the first secondary winding and the second secondary winding for generating a high-level DC voltage by rectifying and filtering the energy received by the first secondary winding and the second secondary winding.

Abstract: The present invention provides a primary-side flyback power converter that supplies a constant voltage output and a constant current output. To generate a well-regulated output voltage under varying load conditions, a PWM controller is included in the power converter in order to generate a PWM signal controlling a switching transistor in response to a flyback voltage sampled from a first primary winding of the power supply transformer. Several improvements are included in this present invention to overcome the disadvantages of prior-art flyback power converters. Firstly, the flyback energy of the first primary winding is used as a DC power source for the PWM controller in order to reduce power consumption. A double sample amplifier samples the flyback voltage just before the transformer current drops to zero. Moreover, an offset current is pulled from a detection input of the double sample amplifier in order to generate a more accurate DC output voltage.