JPH1169823A - Switching power source - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a switching power source capable of improving conversion efficiency. SOLUTION: This power unit 1 is equipped with a transformer 4, which has primary windings 4a and 4b and a secondary winding 4c, input parts 3a and 3b each side of which is connected to one end 4d each of the primary windings 4a and 4b and which receive the input of AC which is applied between the one hand each and the other hand each, a switching element 6a which is connected between the other end of the primary winding 4a and the input part 3b, a unidirectional element 5a which is connected in series to the switching element 6a and through which a current can be conducted from the other end of the primary winding 4a to the input part 3b, a switching element 6b which is connected between the other end of the primary winding 4b and the input part 3b, a unidirectional element 5b which is connected in series to the switching element 6b and through which a current can be applied from the input part 3b to the other end of the primary winding 4b, and a switching control circuit 7 which controls the switching of the switching elements 6a and 6b. In this case, a DC power is generated by rectifying the induced voltage of the primary winding 4c at a switching control.

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 for generating a DC power by applying a pulsating voltage to a primary winding of a switching transformer and rectifying an induced voltage of a secondary winding. .

[0002]

2. Description of the Related Art As a switching power supply of this type, a power supply 21 shown in FIG. 4 is conventionally known.
The power supply device 21 shown in FIG. 1 includes a pair of input terminals 3 a and 3 b for inputting AC of the AC power supply 2 and both input terminals 3 a and 3 b.
a and a switching transformer 24 having one end of a primary winding 24a connected to the cathode of the diode 22a in the diode bridge 23; An FET 25 as a switching element disposed between the other end of the winding 24a and the anode of the diode 22d in the diode bridge 23, a switching control circuit 26 for controlling the switching of the FET 25, and a secondary winding 24b side of the transformer 24 And a rectifying diode 8 and a smoothing capacitor 9 which are disposed at the same time.

In the power supply device 21, when switching is performed by the switching control circuit 26, the AC current output from the AC power supply 2 has a positive AC voltage at the input terminal 3a and a negative AC voltage at the input terminal 3b. when the voltage input terminal 3a, the diode 22a, the primary winding 24a, FET 25, a current path I ₁₁ consisting of diode 22c and the input terminal 3b flows, the input terminal 3b
When the AC voltage on the input terminal 3ab side is a positive voltage and the AC voltage on the input terminal 3ab side is a negative voltage, the input terminal 3b,
A current path I ₁₂ composed of a diode 22b, a primary winding 24a, an FET 25, a diode 22d, and an input terminal 3a.
Flows through. As a result, the output AC of the AC power supply 2 is rectified into a pulsating flow by the diode bridge 23, and the pulsating current becomes F
By causing the primary winding 24a to intermittently flow according to the switching of the ET 25, an induced voltage is induced in the secondary winding 24b. Next, the diode 8 rectifies the induced voltage,
By the condenser 9 smoothing the rectified pulsating flow,
DC power is being generated. In this case, the switching control circuit 26 controls the duty ratio of the switching signal so that the positive voltage of the capacitor 9 becomes a predetermined voltage, so that the stabilized DC is output to the outside as a DC output.

[0004]

However, the conventional power supply 21 has the following problems. That is, in the power supply device 21, when the output AC of the AC power source 2 flows through the current path I _11, the diode 22a, the power loss caused by the 22c and FET 25, when flowing through the current path I ₁₂ includes a diode 22b, 22d and FET25
Causes power loss. In this case, for example, if the forward voltage of the diodes 22a to 22d is 1V and the input current value of the alternating current is 10A, two diodes 2
20W by 2a, 22c (or 22b, 22d)
However, there is a problem that the conversion efficiency of the entire device is reduced due to the loss of the power.

[0005] The present invention has been made to solve such a problem, and has as its main object to provide a switching power supply device capable of improving the conversion efficiency of the entire device.

[0006]

According to a first aspect of the present invention, there is provided a switching power supply device comprising:
A switching transformer having a primary winding and a secondary winding, one of which is connected to one end of each of the two primary windings, and an input unit for inputting an alternating current applied between the one and the other. A first switching element connected between the other end of the first primary winding and the other input portion, and another input from the other end of the first primary winding connected in series to the first switching element. A first unidirectional element capable of conducting current toward the second switching element, a second switching element connected between the other end of the second primary winding and the other input section, and a second switching element. A second unidirectional element connected in series and capable of conducting a current from the other input section toward the other end of the second primary winding; and a switching control circuit for controlling switching of both switching elements; Switch by control circuit An induced voltage induced in the secondary winding when a controlled rectifier to and generates DC power.

In this switching power supply, the bidirectional elements are turned on in accordance with the phase of the input alternating current.
That is, in a positive cycle in which the AC voltage applied to one input unit is a positive voltage, the first switching element and the first
During the negative cycle in which the AC voltage applied to one input is a negative voltage, the pair of the second switching element and the second unidirectional element is turned on. Operate on. Thereby, the rectification and the switching operation of the AC are performed simultaneously. Specifically, the alternating current flows through the following path. That is, at the time of the above-described positive cycle, the switching control circuit causes the first switching element to perform switching, so that the AC current is supplied to the one input section, the first primary winding, the first
Flows through a current path including a series circuit of the switching element and the first unidirectional element and the other input part. Conversely, at the time of the negative cycle described above, the switching control circuit causes the second switching element to perform switching, so that the alternating current flows through the other input portion, the second switching element, and the second one-way. Flows through a current path consisting of a series circuit with a conductive element, a second primary winding, and one input. As a result, rectification of alternating current for generating a pulsating flow and switching operation for applying a pulsating voltage to the primary winding are performed simultaneously. In these cases, a unidirectional element and a switching element are each provided in the path through which the alternating current flows.
Intervene one by one. Therefore, to rectify the alternating current,
In the conventional power supply device 21, power is lost by two rectifying diodes, whereas in this switching power supply device, power is only lost by one unidirectional element. Can be reduced. As a result, it is possible to improve the power efficiency of the entire device.

The switching power supply according to claim 2 is
2. The switching power supply according to claim 1, wherein each of the two unidirectional elements is formed of a diode.

Various semiconductor elements can be used as the unidirectional element. On the other hand, when a diode is used as in this switching power supply device, the diode as the first unidirectional element conducts during the above-described positive cycle, and the second diode as a first unidirectional element during the negative cycle. The diode as the directional element conducts. Therefore, only one of the diodes conducts according to the AC cycle, so that complicated control can be omitted.

The switching power supply according to claim 3 is
2. The switching power supply device according to claim 1, wherein the bidirectional elements are each formed of a field effect transistor, and only one of the unidirectional elements is turned on in accordance with the phase of the alternating current.

In this switching power supply, rectification of alternating current is performed by a field effect transistor. Therefore, compared to the case where rectification is performed using a diode, power loss can be reduced by a smaller forward voltage of the field-effect transistor.

The switching power supply according to claim 4 is
The switching power supply device according to any one of claims 1 to 3, wherein the switching control circuit switches both switching elements synchronously.

For the switching operation, it is sufficient if only the switching elements in the path through which the alternating current flows are turned on. On the other hand, in this switching power supply, since both switching elements are switched in synchronization,
Compared to the case where both switching elements are controlled individually,
The switching control circuit can be easily configured.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of a switching power supply according to the present invention will be described below with reference to the accompanying drawings. Note that the same components as those of the power supply device 21 are denoted by the same reference numerals, and redundant description will be omitted.

First, the configuration of a power supply 1 to which a switching power supply according to the present invention is applied will be described with reference to FIG. As shown in the figure, the power supply device 1 is a flyback type switching power supply device, and has two primary windings 4a and 4b and a secondary winding 4c each having one end commonly connected as an intermediate tap 4d. And a switching transformer 4 having the following. Further, input terminals 3a and 3b to which an AC voltage from the AC power supply 2 is applied are provided on the primary circuit side of the transformer 4, and the input terminal 3a is connected to the intermediate tap 4d. On the other hand, the primary winding 4a
Between the other end of the first terminal and the input terminal 3b.
The diode 5a as a unidirectional element and the FET 6a as a first switching element in the present invention are connected in series. Further, a diode 5b as a second unidirectional element according to the present invention and an FET 6b as a second switching element according to the present invention are connected in series between the other end of the primary winding 4b and the input terminal 3b. Have been. On the primary circuit side, a switching control circuit 7 for controlling the switching of both FETs 6a and 6b is provided. The switching control circuit 7 rectifies and smoothes in the secondary circuit on the secondary winding 4c side. The input DC voltage is input, and the feedback control is performed so as to maintain the DC voltage at a predetermined voltage by controlling the switching duty ratio of both FETs 6a and 6b based on the DC voltage.

Next, the overall operation of the power supply device 1 will be described.

After the start of the switching operation, the switching control circuit 7 outputs a switching signal S _S to both FETs 6a and 6b, so that both FETs 6a and 6b are switched.
a, 6b continues the switching operation in accordance with the switching signal S _S. In this state, the input terminals 3a, 3
During a positive cycle in which the AC voltage applied to b is a positive voltage, the diode 5a is turned on and the diode 5b is turned off. Thereby, the alternating current is applied to the input terminal 3
a, an intermediate tap 4d, a primary winding 4a, a diode 5a,
FET6a and flows a current path I _1a consisting of an input terminal 3b, and the input terminal 3a, an AC voltage applied to 3b During some negative cycles in the negative voltage, it does not flow a current path I _1a. As a result, the alternating current is rectified by the diode 5a. At the same time, FET 6a is, to switch the pulsating accordance switching signal S _S outputted from the switching control circuit 7. At this time, FET
Energy is stored in the transformer 4 by the switching of 6a, and an induced voltage based on the stored energy is induced in the secondary winding 4c. Next, the induced voltage is rectified by the diode 8, and the rectified DC is smoothed by the capacitor 9 and output to the outside of the apparatus as a DC output. In this case, the switching control circuit 7
Inputs a smoothed DC and controls the duty ratio of the switching signal S _S so that the DC voltage becomes a predetermined voltage. Incidentally, both FET 6a, 6b are brought into ON operated together in synchronism with the switching signal S _S outputted from the switching control circuit 7, when the switching signal S _S is a low level signal (hereinafter, also referred to as L signals ") of, As a result, the two current paths I _1a and I _1a are cut off by controlling both FETs 6a and 6b to be in a non-conductive state, so that the alternating current is maintained in a non-conductive state.

Conversely, at the time of the negative cycle, the diode 5b is turned on and the diode 5a is turned off. As a result, the alternating current flows through the above-described current path I _1b , and at the time of the above-described positive cycle, the current path I _1b
Never flow. As a result, the AC is applied to the diode 5b.
Rectified by At the same time, the FET 6b
Switches the pulsating flow according to the switching signal S _S output from the switching control circuit 7. Also at this time, energy is accumulated in the transformer 4 by switching of the FET 6b, and an induced voltage based on the accumulated energy is induced in the secondary winding 4c. Next, the induced voltage is rectified by the diode 8, and the rectified DC is smoothed by the capacitor 9 and output to the outside of the apparatus as a DC output. Also in this case, the duty ratio control of the switching signal S _S by the switching control circuit 7 is performed in the same manner.

As described above, in this power supply device 1, the diode 5a and the FET 6 are connected to the input terminal 3a, 3b in accordance with the phase of the alternating current applied to the input terminals 3a, 3b, ie, the positive and negative cycles of the alternating current.
By turning on the set a or the set of the diode 5b and the FET 6b, AC rectification and switching operations are performed simultaneously. In these cases, since only one diode and one FET are interposed in each of the AC current paths I _1a and I _1b , power loss during rectification can be reduced. Specifically, assuming that the forward voltages of the diodes 5a and 5b are 1V and the input current value of the AC current is 10A, the power loss accompanying the rectification of the AC is 10W, and the power loss (20W) in the power supply device 21 is In comparison, it can be reduced to half.
As a result, the conversion efficiency of the entire device can be improved. Further, both the FET 6a, by synchronizing to the on operation of 6b, both FET 6a, separately compared with the case of outputting a switching signal S _S with respect 6b, it is possible to configure the switching control circuit 7 simply.

Next, a power supply device 11 according to another embodiment will be described with reference to FIG. The power supply 1
In the configuration 1 as well, the same components as those of the power supply device 1 are denoted by the same reference numerals, and redundant description will be omitted.

As shown in FIG. 1, a power supply device 11 includes an FET 1 instead of the diodes 5a and 5b in the power supply device 1.
It differs from the power supply device 1 in that 2a and 12b are used. In the power supply device 11, after the start of the switching operation, the switching control circuit 13 outputs the switching S _S shown in FIG. 3D to the FETs 6a and 6b, so that the FETs 6a and 6b switch the switching signal. and a switching operation is performed in accordance with _S S. In this state, when the AC voltage V _AC shown in the diagram (a) is at a positive cycle described above, the switching control circuit 13 is a high level signal in the diagram (hereinafter, also referred to as "H signal") (b) By outputting the control signal Sa shown in FIG.
T12a is turned on. Thus, the alternating current is
Input terminal 3a, middle tap 4d, primary winding 4a, FET
12a, flows through the current path I _2a consisting FET6a and the input terminal 3b, and, at the time of the negative cycle as described above, it does not flow through the current path I _2a. As a result, the AC
It is rectified by 12a. At the same time, FE
T6a is, to switch the pulsating accordance switching signal S _S outputted from the switching control circuit 13.

Conversely, at the time of the above-described negative cycle, the switching control circuit 13 outputs the control signal Sb shown in FIG. 3C, which is an H signal, to turn on the FET 12b. As a result, the alternating current is applied to the input terminal 3b,
Flows through a current path I _2b composed of an FET 12b, an FET 6b, a primary winding 4b, an intermediate tap 4d, and an input terminal 3a;
In the above-described normal cycle, the current does not flow through the current path _I2b . As a result, the alternating current is rectified by the FET 12b. At the same time, FET 6b is, to switch the pulsating accordance switching signal S _S outputted from the switching control circuit 13. In this power supply device 11 as well, energy is stored in transformer 4 and rectification and smoothing of the induced voltage output from secondary winding 4c, and non-conduction to AC current when switching signal _SS is L signal. The control of the state is performed in the same manner as in the power supply device 1.

As described above, in the power supply device 11, the FET 12a and the FET 6 are controlled in accordance with the phase of the AC applied to the input terminals 3a and 3b, ie, the positive and negative cycles of the AC.
By turning on the set a or the set of the FET 12b and the FET 6b, AC rectification and switching operations are performed simultaneously. In these cases, since only two FETs are interposed in each of the AC current paths I _2a and I _2b , power loss during rectification can be reduced. Specifically, the FETs 12a and 12b
Is 0.2 V and the input current value of the AC current is 10 A, the power loss accompanying the rectification of the AC is 2 W, which is 1/10 of the power loss (20 W) in the power supply device 21. Can be reduced. As a result, the conversion efficiency of the entire device can be further improved. In this power supply device 11, both FETs 6
a and 6b are turned on in synchronization with each other so that both FEs
The switching control circuit 13 can be easily configured as compared with the case where the switching signal S _S is separately output to T6a and 6b.

The power supply device 1 uses FETs as switching elements, and the power supply device 11 uses FETs as switching elements and one-way elements. However, the present invention is not limited to this. In the power supply device, a transistor can be used instead of the FET as the switching element. In the above embodiments, the configuration of the flyback type switching power supply has been described. However, the present invention is not limited to this, and the present invention can be applied to a forward type switching power supply.

In this embodiment, the example in which the transformer 4 is provided with the intermediate tap 4d is described. However, one end of each of the primary winding 4a and the primary winding 4b may be provided without the intermediate tap 4d. Can be connected in common. Further, the diode 5a and the FET 6
Also, the connection between a and the diode 5b and the FET 6b may be appropriately changed as long as they form a series circuit. For example, an FET 6a is connected to one end of the primary winding 4a.
May be connected, the source of the FET 6a is connected to the anode of the diode 5a, and the cathode of the diode 5a is connected to the input terminal 3b.

[0026]

As described above, according to the switching power supply device of the first aspect, the two-way elements are turned on in accordance with the phase of the input alternating current to rectify the alternating current. In the conventional power supply device 21, power is lost by two rectifying diodes, whereas in this switching power supply device, power is only lost by one unidirectional element. The loss can be reduced, thereby improving the power efficiency of the entire device.

According to the switching power supply device of the second aspect, since the bidirectional elements are each constituted by a diode, the power efficiency of the entire device can be improved without performing complicated control. it can.

Further, according to the switching power supply device of the third aspect, since the bidirectional elements are each constituted by a field effect transistor, the switching power supply apparatus is compared with the case where rectification is performed using a diode as a unidirectional element. Thus, power loss can be further reduced.

According to the switching power supply device of the fourth aspect, by switching both switching elements synchronously, a switching control circuit can be easily configured and the power efficiency of the entire device is improved. be able to.

[Brief description of the drawings]

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

FIG. 2 is a circuit diagram of a power supply device according to another embodiment of the present invention.

3A and 3B are signal waveform diagrams of various parts in a power supply device according to another embodiment of the present invention, wherein FIG. 3A is a voltage waveform diagram of an _AC voltage VAC, and FIG. 3B is a signal waveform diagram of a control signal Sa. ,
(C) is a signal waveform diagram of the control signal Sb, and (d) is a signal waveform diagram of the switching signal S _S.

FIG. 4 is a circuit diagram of a conventional power supply device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Power supply 3a Input terminal 3b Input terminal 4 Transformer 4a Primary winding 4b Primary winding 4c Secondary winding 5a Diode 5b Diode 6a FET 6b FET 7 Switching control circuit 11 Power supply 12a FET 12b FET 13 Switching control circuit

Claims (4)

[Claims] 1. A switching transformer having first and second primary windings and a secondary winding, one of which is connected to one end of each of the two primary windings, and a voltage applied between the one and the other. An input unit for inputting an alternating current to be input, a first switching element connected between the other end of the first primary winding and the other input section, and a series connection to the first switching element. A first unidirectional element capable of conducting a current from the other end of the first primary winding toward the other input portion, between the other end of the second primary winding and the other input portion; A second switching element connected to the second switching element, and a second one direction connected in series with the second switching element and capable of conducting a current from the other input portion to the other end of the second primary winding. Switching element and the switching element. And a switching control circuit for controlling the switching control circuit to rectify an induced voltage induced in the secondary winding during switching control by the switching control circuit to generate DC power. 2. The switching power supply device according to claim 1, wherein said bidirectional elements are each formed of a diode. 3. The switching power supply according to claim 1, wherein the bidirectional elements are each formed of a field-effect transistor, and only one of them is turned on in accordance with the phase of the alternating current. apparatus. 4. The switching power supply according to claim 1, wherein the switching control circuit switches the two switching elements synchronously.