JP2001136747A - Ac-dc power supply - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an AC-DC power supply which saves space and cost to improve efficiency and noise level. SOLUTION: In a switching power supply having a voltage-boosting type power factor improving circuit, a flyback converter is structured by winding a second winding 3b around a voltage-boosting reactor 3 and then connecting in series a second switch element 16 to such a reactor, connecting a series power supply 17 to both ends of a serial circuit which consists of a second winding 3b and a second switching element 16 and using in common the first winding 3a, a first diode 6 and a first capacitor 7 of the reactor 3 used in the voltage-boosting type power factor improving circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching power supply, and more particularly to an AC / DC power supply.

[0002]

2. Description of the Related Art In a switching power supply for producing a DC voltage from a DC voltage obtained by rectifying and smoothing an AC voltage of an AC power supply through a DC-DC converter, a DC power supply can be used in addition to the AC power supply. Several methods have been used for this. The circuit shown in FIG.
This is an example, and employs a method of sharing the transformer 10 of the DC-DC converter. In FIG.
The secondary winding and switch element are provided separately for the AC power supply and the DC power supply.However, compared to the method using separate transformers for the AC power supply and the DC power supply, the space is saved by sharing the transformer. An advantage is that costs can be reduced.

[0003]

Since the conventional system shown in FIG. 3 shares the transformer 10 of the DC-DC converter, the conventional system shown in FIG. 3 can be supplied with power from an AC power supply or DC power supply. The same power conversion scheme must be used. In the example shown in FIG. 3, since a circuit form called a forward converter is used, both the AC power supply and the DC power supply need to operate as a forward converter. The winding 10a through which the primary current flows when the power is supplied from the AC power supply and the winding 10c through which the primary current flows when the power is supplied from the DC power supply are electromagnetically coupled. When a voltage is applied to one, an induced voltage proportional to the winding is generated on the other. Therefore, the diode 104 and the diode 105 are inserted in series with the switch element 8 and the switch element 102, respectively.
Mutual interference between the two windings is prevented.

If the two diodes are not inserted, the following problem occurs. In the circuit shown in FIG. 3, when the power supply from the AC power supply 1 is stopped and the power supply from the DC power supply 101 is operating, the voltage of the DC power supply 101 is applied to the winding 10c during the ON period of the switch element 102. However, an induced voltage proportional to the number of turns is generated in the winding 10a, and this voltage charges the first capacitor 7.
The direction of the current is such that the switch element 8 easily flows regardless of the on / off state of the switch element whether the switch element 8 is a MOSFET or a bipolar transistor. If the switch element is a MOSFET, the current flows through the body diode, and if the switch element is a bipolar transistor, the current flows through an effect called an inverse transistor. When the current for charging the first capacitor 7 has almost no impedance on the line, the waveform of the current becomes a pulse having a high peak value, and the overcurrent protection is not activated. However, a large power loss occurs. Therefore, the diode 104 is connected to the switch element 8.
Are inserted in series to block the current for charging the first capacitor 7.

The switching element 102 also has a diode 105
Are inserted in series in order to prevent the DC power supply 101 from being charged by the induced voltage generated in the winding 10c when operating with the power supplied by the AC power supply 1. The diode 105 is connected to the winding 1 with respect to the winding 10a.
It is possible to omit by reducing the number of turns of 0c, but the operating conditions are different between when the secondary circuit operates with the power of the AC power supply 1 and when it operates with the power of the DC power supply 101. Another problem arises.

[0006] The diode 104 and the diode 105
A power loss corresponding to the drop voltage of the diode is caused. Furthermore, these diodes generate noise called reverse recovery noise at the moment when each switching element turns off and then becomes reverse biased, that is, at the moment when it changes from the forward direction to the reverse direction, increasing the switching noise of the entire power supply device. ing.

Accordingly, the present invention provides a switching power supply device having a boost type power factor correction circuit, which uses a system in which a boosting reactor is shared, thereby saving space and cost and reducing power loss and switching noise. The purpose is to provide a better system.

[0008]

In order to achieve the above object, an invention according to claim 1 comprises an AC power supply, a full-wave rectifier, a first winding of a reactor, a first switch element, a first diode, and a first diode. In a step-up power factor correction circuit including a first capacitor and a first oscillation control circuit connected to a control electrode of a first switch element, a second winding is wound around a step-up reactor, A second switch element is connected in series to the winding of the second switch element, a DC power supply is connected to both ends of a series circuit composed of the second winding element and the second switch element, and a second switch element is connected to the control electrode of the second switch element. The oscillation control circuit was connected to form a one-stone converter.

According to a second aspect of the present invention, the converter of the first aspect is replaced with a bridge type converter.
A second capacitor was inserted in series between the output terminal of the bridge converter and the second winding. Further, a second diode and a third diode are connected to charge a first capacitor with a bidirectional current generated in the first winding.
The second diode and the third diode do not affect the operation of the boost power factor correction circuit. According to a third aspect of the present invention, the bridge type converter according to the second aspect is replaced with a half bridge type converter.

The first winding, the first diode, and the first capacitor of the reactor, which are the main components of the power factor correction circuit, are used as the main components of the single converter or the main components of the bridge converter. Space and cost can be reduced because they are shared. Although a diode inserted in series with the switch element used in the conventional method can be omitted, power loss and noise are improved, but the reason why the diode can be omitted can be explained as follows.

In the first aspect of the present invention, consider the case where the second oscillation control circuit stops operating, the second switch element is turned off, and only the first switch element is operating. The maximum value of the voltage applied to the first winding during the ON period of the first switch element is a peak value of a full-wave rectified sine wave. When the AC effective voltage is 100V, the peak value is 141V. In the second winding, a voltage proportional to the number of turns is generated in a direction in which a current flows toward the DC power supply.
The current in this direction cannot be prevented by the second switch element alone for the same reason as described in the problem to be solved by the invention, but the turn ratio of the first winding to the second winding is reduced. It can be made to not flow by choosing properly. For example, if an AC power supply with an effective value of 100 V and a DC power supply with a 24 V power supply are connected, and the first winding is wound 100 times and the second winding is wound 10 times, the first switch The voltage generated in the second winding during the ON period of the element is 1
Never exceed 5V. This voltage is lower than the voltage of the DC power supply, and therefore does not flow toward the DC power supply,
The current flowing through the first winding is stored in the reactor as excitation energy.

During the off period of the first switch element, the exciting energy of the reactor is discharged through the AC power supply, the full-wave rectifier, and the diode via the first winding, and is stored as electric charge in the first capacitor. A voltage is generated in the second winding in a direction opposite to the voltage generated during the ON period of the first switch element, but does not flow because the second switch element is in the OFF state.

Next, consider a case where the first oscillation control circuit stops operating, the first switch element is turned off, and only the second switch element is operating. Normally, in the case of an AC / DC power supply, a sequence is set so that the DC power supply operates when the AC power supply fails, so it is assumed here that the power supply from the AC power supply is stopped.

When the ratio of the voltage of the DC power supply to the turns of the reactor winding is the same as in the above-described example, a voltage of 24 V is applied to the second winding during the ON period of the second switch element. A voltage of 240 V is generated on the line. This voltage tends to flow toward the AC power supply, but does not flow because it is blocked by the full-wave rectifier, and the current flowing through the second winding is stored in the reactor as exciting energy. This excitation energy is applied to the first switching element during the off period of the second switching element.
Through the full-wave rectifier and the first diode, and is accumulated as electric charge in the first capacitor.

According to the second and third aspects of the present invention, the second oscillation control circuit stops operating, the bridge circuit or the half bridge circuit is off, and only the first switch element operates. In the case, the above claim 1
As in the case of the described invention, by appropriately selecting the turns ratio of the first winding and the second winding, it is possible to prevent a current from flowing toward the DC power supply. However, for the following reasons, the influence of the current flowing toward the DC power supply can be neglected without considering the turns ratio.

The second capacitor inserted between the output terminal of the bridge circuit and the second winding may have such a small capacity as to be charged in one ON period of the second switch element. On the other hand, there is leakage inductance between the first and second windings, which together with the second capacitor creates a suitable series resonance impedance and suppresses the peak value of the current.

When the power supply from the AC power supply is stopped, the first oscillation control circuit stops operating, and only the bridge circuit or the half bridge circuit is operating, the bidirectional current of the first winding is generated. The first diode and the full-wave rectifier conduct for current in one direction, and the second and third diodes conduct for current in the opposite direction.

[0018]

FIG. 1 is a circuit diagram of an AC / DC power supply device according to an embodiment of the present invention. In FIG. 1, a sine-wave-shaped voltage of an AC power supply 1 is applied to a full-wave rectifier 2.
The sine wave is converted into an absolute value and output. The voltage of the absolute value of the sine wave is converted into a stable DC voltage by a boost converter constituted by the first winding 3a of the reactor 3, the first switch element 4, the first diode 6, and the first capacitor 7. . The first purpose of this boost converter is not to produce a stable DC voltage, but to make the current supplied by the AC power supply 1 similar to the waveform of the AC voltage. That is, it works as a power factor improving circuit. The DC voltage generated by the power factor correction circuit is charged in the first capacitor 7, but is set to a voltage higher than the peak value of the AC voltage because a boost converter is used. Therefore, the voltage charged in the first capacitor 7 is converted into power by another converter drawn on the right side of the first capacitor 7 to generate various voltages required by the load.

The DC power supply 17 shown in FIG. 1 includes the second winding 3b and the second switch element 16 of the reactor 3 and the components of the boost converter when the AC power supply 1 loses power. Power is supplied to a flyback converter including a first winding 3a, a full-wave rectifier 2, a first diode 6, and a first capacitor 7 of a certain reactor 3. The diode 22 attached to the output terminal of the full-wave rectifier 2 is not indispensable for the operation of the flyback converter, but the current flowing through the full-wave rectifier 2 is bypassed by the diode 22 to reduce the drop voltage. Can be.

When the circuit of FIG. 1 operates as a boost converter by the power supplied from the AC power supply 1, an induced voltage is generated in the second winding 3b of the reactor 3, but this will be described in the section for solving the problem. As described above, by appropriately selecting the turns ratio with respect to the first winding 3a, the current for charging the DC power supply 17 can be prevented from flowing. When operating as a flyback converter with the power supplied by the DC power supply 17, when the AC power supply 1 is in a power outage state and the first switch element 4 is kept in the off state, the circuit is connected to the boost converter circuit. To prevent interference.

FIG. 2 is a circuit diagram of an AC / DC power supply according to an embodiment of the present invention. FIG. 2 is different from the circuit diagram of FIG. 1 showing the embodiment of the first aspect of the present invention in that a portion corresponding to the flyback converter of FIG. 1 is replaced with a bridge type current resonance converter.
Adding a second diode 19 and a third diode 20 so that bidirectional current can be extracted from the first winding 3a of the reactor 3;
This is the point to which 1 is added. The second capacitor 21 works as a resonance capacitor, but the resonance reactor is the reactor 3
The leakage inductance existing between the first winding 3a and the second winding 3b is used. If this leakage inductance is insufficient to obtain the required resonance period, a new reactor can be inserted in series with the capacitor 21.

In FIG. 2, a set consisting of a switch element 16a and a switch element 16d repeatedly turns on and off simultaneously, and a set consisting of a switch element 16c and a switch element 16b repeats on and off at the same time. The second oscillation control circuit 18 sends a signal to each control electrode of the four switch elements so that if one set is on, the other set is off.

[0023]

As described above, there is an uninterruptible power supply as a device for protecting the memory of a personal computer against an instantaneous power failure of an AC power supply. However, as the cost of the personal computer itself decreases, the cost becomes more expensive. Is coming. On the other hand, as the use time of a personal computer increases, the probability of encountering an instantaneous power outage increases, and the demand for an uninterruptible power supply is also increasing. There is an increasing need for circuit technology that can be incorporated in According to the present invention, the circuit for securing the output voltage of the power supply device by the DC power of the battery when the AC power supply fails can be easily incorporated into the conventional personal computer power supply device, so that the economic effect is large. .

[Brief description of the drawings]

FIG. 1 is a circuit diagram of an AC / DC power supply device according to an embodiment of the present invention.

FIG. 2 is a circuit diagram of an AC / DC power supply device according to an embodiment of the present invention.

FIG. 3 is a circuit diagram of an AC / DC power supply device showing an example of a conventional system.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 AC power supply 2 Full-wave rectifier 3 Reactor 4 First switch element 5 First oscillation control circuit 6 First diode 7 First capacitor 8 MOSFET 9 Oscillation control circuit 10 Transformer 11, 12 Diode 13 Reactor 14 Capacitor 15 Load 16 Second switch element 17 DC power supply 18 Second oscillation control circuit 19 Second diode 20 Third diode 21 Second capacitor 22 Diode 3a First winding 3b Second winding 10a Primary winding 10b Secondary winding 10c Primary winding 16a, 16b, 16c, 16d Switch element 101 DC power supply 102 Switch element 103 Oscillation control circuit 104, 105 Diode

Claims (3)

[Claims] 1. An AC power supply, a full-wave rectifier, a first winding of a reactor, a first switch element connected in series to the first winding, and a parallel connection to the first switch element. Having a series circuit composed of a first diode and a first capacitor connected to the first switching element, and a step-up power factor correction circuit including a first oscillation control circuit connected to a control electrode of the first switching element. In a power supply device, a second winding electromagnetically coupled to the first winding is wound, and a second switch element is connected in series to the second winding. And a DC power supply is connected to both ends of a series circuit including the second switch element, and a second oscillation control circuit is connected to a control electrode of the second switch element, thereby connecting the AC power supply and the DC power supply. The feature is that any power can be used AC / DC power supply. 2. An AC power supply, a full-wave rectifier, a first winding of a reactor, a first switch element connected in series to the first winding, and a parallel connection to the first switch element. Having a series circuit composed of a first diode and a first capacitor connected to the first switching element, and a step-up power factor correction circuit including a first oscillation control circuit connected to a control electrode of the first switching element. In the power supply device, a second terminal between a terminal of the first winding opposite to a terminal to which the first switch element is connected and a terminal of the first capacitor to which the first diode is connected. Connect a diode,
A third diode is connected in parallel to the first switch element, a second winding electromagnetically coupled to the first winding is wound, and a bidirectional current flows through the second winding. An output terminal of a bridge circuit composed of four switch elements that can be connected, a DC power supply is connected to an input terminal of the bridge circuit, and a second oscillation control circuit is connected to control electrodes of the four switch elements of the bridge circuit. Connected, and a second capacitor is inserted in series between the output terminal of the bridge circuit and the second winding, so that both the AC power supply and the DC power supply can be used. AC / DC power supply. 3. An AC / DC power supply according to claim 2, wherein the bridge circuit composed of the four switch elements is a half bridge circuit composed of two switch elements.