A high power factor AC/DC converter is disclosed. In the AC/DC converter in which a rectifying circuit RC1 rectifies a commercially available AC power supply Ei, a switching device turns on and off so that the rectified voltage is applied across the primary winding n1 of the transformer Tr1 to provide a high frequency voltage across the secondary winding n2, and the high frequency voltage is rectified by means of a rectifying circuit connected across the secondary winding so as to generate a predetermined DC output, a choke coil (L1) and a diode (D1) are interposed between the rectifying circuit (RC1) and a smoothing capacitor (C1) and a capacitor (C3) is interposed between a first junction and a second junction. The first junction connects the choke coil (L1) to the diode (D1) and the second junction connected the switching device (Q1) to the primary winding (n1) of the transformer (Tr1).
In order to prevent malfunction resulting from the variation of the output of a boosting converter in a boosting two-converter type dc power unit, a dc power unit includes a boosting converter composed of a control circuit and a rectifying diode connected to an ac input through a switch and an insulating dc-to-dc converter connected at a later stage of the boosting converter. Between the boosting converter and the insulating dc-to-dc converter, there is provided a first control circuit composed of a shunt regulator, a voltage dividing resistor for producing a control voltage for the shunt regulator, a photocoupler to be turned on and off by the shunt regulator, and a resistor. When the dc output voltage Vo of the boosting converter reaches a predetermined value, the photocoupler is enabled to handle a REMOTE.sub.-- ON/OFF signal through a remote control terminal for starting the insulating dc-to-dc converter.
In an AC-powered power supply with a bipolar controller V controlling the instantaneous value of a control quantity measured by a sensor F.sub.1 to a predetermined setting within a deviation of less than 0.1% at 1 Hz via the output DC current I.sub.o, and with an adjustable rectifier EQ followed by a charging inductance L.sub.1 and a filter capacitor C.sub.1, whereby the output of controller V is electrically connected to the output line of the power supply, the output of controller V is AC-decoupled from filter capacitor C.sub.1 by a decoupling inductance L.sub.2, two potentials V.sub.o +V.sub.1 and V.sub.o -V.sub.2 are supplied to controller V, and a sensor F.sub.2 is provided for the output current I.sub.2 of controller V, which feeds an output signal to a control unit CTR which controls rectifier EQ in such a way that the mean value of output current I.sub.2 of controller V is regulated to a minimum value. In this way, a stable and high precision control over the full frequency bandwidth is possible with high efficiency.
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 built-in input filter forward converter performs to shape an input current to a non-pulsating fashion. Shaping action is obtained by placing two cross-coupled capacitors to a plurality of splitting windings of a power transformer such that the input current will not be interrupted. The cross-coupled capacitors also operate as a lossless snubber by allowing the leakage inductance energy to be stored and recovered during normal operation. Thus significant improvements of reducing harmonic of the input current, input current ripple, and increasing the converter's efficiency are achieved.
Switch mode power supplies produce a brief pulse-like load on the mains and have a high harmonic content. Such a high harmonic load on the mains is undesirable. There are increasingly strict regulations for the level of harmonic loads connected to the mains. The present switch mode power supply includes a series circuit formed by an inductor and a diode connected between a charge capacitor, which is dimensioned to be relatively small, and a pickoff of a primary winding of a transformer of the switch mode power supply. A relatively large energy storage capacitor connected to the primary winding is decoupled from the charge capacitor by a second diode. The series circuit produces an additional charging current, which extends the current which is drawn from the mains during one half cycle of the mains voltage, and reduces the amplitude of the current.
