An AC-DC converter of a type having an improved power factor having an arrangement that enlargements of loads to be borne by circuit components due to AC input voltage is prevented so that the size and cost of the AC-DC converter are reduced. A constant-current circuit is, in parallel, connected to a voltage dividing point of charge voltage of an output capacitor to be connected to an input terminal of an error amplifier of a booster converter circuit and realized by a plurality of resistors so that control of a constant-current value of the constant-current circuit is performed with the rectified output from the rectifying circuit. As a result, the loads to be borne by the circuit components of the AC-DC converter can be made constant regardless of the supplied AC voltage level so that the size and cost of the AC-DC converter are reduced.
A device for power factor correction in a forced switching power supply unit is provided. The device includes a converter and a control device coupled to the converter so as to obtain from an input alternating mains voltage a direct regulated voltage on the output terminal. The converter includes a power transistor, and the control device includes an error amplifier having its inverting terminal coupled to a first signal that is proportional to the regulated voltage and its non-inverting terminal coupled to a reference voltage. A drive circuit of the power transistor is coupled to the output terminal of the error amplifier. The control device also includes a circuit for generating a current signal that is representative of the effective input voltage. The current signal is coupled to the inverting terminal of the error amplifier to vary the regulated voltage in reply to variations in the effective input voltage.
A converter for enhancing power factor utilizes a line sense winding magnetically coupled to sense a voltage across a line inductor in the input of a high power factor power converter. This winding in the illustrative embodiment is typically a single turn. This winding provides a measurement of the derivative (with respect to time) of the line current, and a specially designed integrator connected to the winding provides the estimate of the line current. An integrator is operative to accurately estimate the current by using known properties of this current to prevent mismeasurement due to reconstructing the "constant of integration" and any small biases in the integrator which normally cause errors.
A power supply circuit for a video display appliance capable of reducing even the unnecessary power consumption caused by a power factor correction circuit when a display control for power saving is performed. The power supply circuit includes a rectifying section, a power factor correction section, an SMPS, a control section for determining whether to perform a display control for power saving of the video display appliance to provide a control signal, and a switching section for controlling the operation of the power factor correction section according to the control signal provided from the control section.
A secondary active clamp for a power converter, a method of actively clamping energy of the power converter and a power converter employing the clamp or the method. The power converter has a primary switching circuit coupled to a primary winding of an isolation transformer and a rectifier coupled to a secondary winding of the isolation transformer. In one embodiment, the clamp includes (1) an inductor coupled in series with a freewheeling diode of the rectifier and (2) a series-coupled capacitor and clamping switch coupled in parallel with the inductor. The series-coupled capacitor and clamping switch cooperate with the inductor to mitigate adverse effects of a reverse recovery phenomenon associated with the rectifier and to effect substantially zero voltage switching of a power switch of the primary switching circuit.
A converter includes a rectifier 1 of the diode bridge connected across the alternating current power supply via an input filter F; a circuit 2 having an reactor L.sub.1, switching element Tr1, and the reverse current flow blocking diode D.sub.1 connected across output terminals of the diode bridge; a smoothing capacitor Cd charged according to an energy stored in the reactor L.sub.1 ; and a controller 3 arranged having a comparator 36 for comparing a signal of circuits 31 through 34 which detects a difference between the direct current output voltage Vd and the set (reference) voltage Vs and amplifies thereof with a triangular carrier wave 36 so as to control the transistor Tr1, the transistor Tr1 being controlled to be turned on or off according to the carrier wave frequency. When the transistor Tr1 is turned to ON, the energy is stored in the reactor L1 via the rectifier of the diode bridge 1. When the transistor Tr1 is turned to OFF, the capacitor Cd is charged according to the energy stored in the reactor L.sub.1. The current in the element Tr1 flows therethrough when the input voltage is low irrespective of the voltage across the capacitor Cd so that the input current provides the sinusoidal wave.
