JP2012182932A - Switching power supply device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a switching power supply device which can ensure high efficiency without increasing the cost.SOLUTION: The switching power supply device 1A comprises a main transformer 3 and a switching element 4 connected in series with a DC power supply 2, a control circuit 5A which controls the switching element 4, a capacitor 10 which is charged when the switching element 4 is turned off and discharged when the switching element 4 is turned on, and an auxiliary transformer 14 consisting of a primary winding 14a through which the discharge current from the capacitor 10 flows, and a secondary winding 14b generating a secondary current corresponding to the discharge current. The switching power supply device 1A is further provided with a first diode 11 provided between the primary winding 3a of the main transformer 3 and the switching element 4 and connected forward in the direction from the primary winding 3a of the main transformer 3 toward the switching element 4, and the discharge current flows into the joint of the first diode 11 and the switching element 4 and then flows to the switching element 4 side.

Description

  The present invention relates to a switching power supply device, and more particularly, to a switching power supply device including a snubber circuit for reducing a loss caused by a switching operation.

As a conventional switching power supply device, for example, the one described in Patent Document 1 is known. As shown in FIG. 3, the conventional switching power supply device 1B includes a transformer 3 in which one end of a primary side winding 3a is connected to one end of a DC power supply 2 that supplies a DC voltage. The other end (the end of winding), the same applies hereinafter) and the other end of the primary winding 3a of the transformer 3 are connected in series. A transistor 4 as a switching element, a control circuit 5B for controlling the switching operation of the transistor 4, a rectifying and smoothing circuit including a diode 6 and a capacitor 7 connected in parallel to the secondary winding 3b of the transformer 3, and a snubber circuit a 9B, the control circuit output voltage V ₀ which under the control transistor 4 is formed by the step-up or step down the DC voltage by operating switching 5B are the output of the rectifying and smoothing circuit It is supplied in parallel connected load 8.

  Further, the snubber circuit 9B includes a diode 12 having an anode connected to a connection portion between the primary winding 3a of the transformer 3 and the transistor 4, a resonance capacitor 10 connected in series to the cathode of the diode 12, and a diode 12 An auxiliary transformer 14 composed of a primary side winding 14a having one end connected to the cathode and a secondary side winding 14b having one end connected to one end of the DC power source 2 via a diode 13, and a primary side winding of the auxiliary transformer 14. And an auxiliary transistor 15 connected to the other end of the line 14a.

  The auxiliary transistor 15 basically performs a switching operation based on a control signal output from the control circuit 5B so as to be turned on (or turned off) simultaneously with the transistor 4.

According to this switching power supply device 1B, when the transistor 4 and the auxiliary transistor 15 are turned off, the current I ₀ flowing through the primary winding 3a of the transformer 3 flows into the capacitor 10 via the diode 12 and the capacitor 10 is charged. Therefore, the rising speed of the collector-emitter voltage of the transistor 4 and the auxiliary transistor 15 can be delayed, and the turn-off loss of the transistor 4 and the auxiliary transistor 15 can be reduced.

  In addition, according to the switching power supply device 1B, when the transistor 4 and the auxiliary transistor 15 are turned on, the capacitor 10 is discharged and a discharge current flows through the primary winding 14a of the auxiliary transformer 14, and according to the discharge current. Since the secondary current generated in the secondary winding 14b of the auxiliary transformer 14 flows toward the primary winding 3a of the transformer 3 through the diode 13, the discharge energy of the capacitor 10 can be regenerated, and the high current Efficiency can be realized.

Japanese Patent Laid-Open No. 11-318075

  However, since the conventional switching power supply 1B shown in FIG. 3 requires the auxiliary transistor 15 to flow the discharge current of the capacitor 10 to the primary winding 14a of the auxiliary transformer 14, a total of two transistors as the entire device. In addition, a control circuit 5B for controlling these two transistors is required, resulting in an increase in cost due to an increase in the number of components.

  In the conventional switching power supply device 1B, since the collector current of the auxiliary transistor 15 is smaller than the collector current of the transistor 4, a transistor having a smaller capacity and a faster switching speed than the transistor 4 is often used as the auxiliary transistor 15. Therefore, in the conventional switching power supply device 1B, in order to turn on the auxiliary transistor 15 and the transistor 4 at the same time (or off), a delay circuit such as a CR circuit (not connected) is provided between the auxiliary transistor 15 and the control circuit 5B. It is necessary to delay the control signal of the auxiliary transistor 15 output from the control circuit 5B.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a switching power supply device that can achieve high efficiency relatively easily without increasing the cost.

  In order to solve the above-described problems, a switching power supply according to the present invention includes a main transformer in which a primary winding is connected in series to a DC power supply that supplies a DC voltage, and a primary transformer in which a primary winding is connected in series. A switching element, a control circuit that controls the switching operation of the switching element, a capacitor that is charged through the primary winding of the main transformer when the switching element is turned off, and that is discharged when the switching element is turned on, and a capacitor A secondary winding that generates a secondary current corresponding to the discharge current, and a secondary current that flows through the primary winding of the main transformer. A switching power supply device used as a main part, provided between the primary side winding of the main transformer and the switching element, A first diode connected in a forward direction from the primary winding to the switching element, and a discharge current is connected to the connection between the first diode and the switching element via the primary winding of the auxiliary transistor. After flowing in, it flows to the switching element side.

  According to this configuration, control of the current flowing through the primary side winding of the main transformer and control of the discharge current flowing through the primary side winding of the auxiliary transformer are performed by one switching element (for example, a transistor). That is, when the switching element is turned on, the discharge current from the capacitor flows into the connection portion between the first diode and the switching element through the primary side winding of the auxiliary transformer and then flows to the switching element side. When the discharge current from the capacitor flows in the primary winding of the auxiliary transformer, a voltage is generated in the secondary winding of the auxiliary transformer, and the secondary current based on the voltage is the current flowing in the primary winding of the main transformer. Used as part. Therefore, it is possible to obtain the same loss reduction effect as before without adding a new transistor. Further, according to this configuration, the control circuit can be made simpler, and a delay circuit such as a CR circuit is not necessary, so that the cost can be reduced.

The switching power supply according to the present invention further includes a second diode having an anode connected to a connection portion between the first diode and the primary side winding of the main transformer, and a cathode connected to the capacitor. The anode is connected to the primary side winding of the main transformer, and the cathode is connected to the switching element. The primary side winding of the auxiliary transformer has one end connected to the connection part of the second diode and the capacitor, And it can be set as the structure by which the other end was connected to the connection part of a 1st diode and a switching element.
According to this configuration, even if the discharge from the capacitor is finished and the voltage generated in the primary winding of the auxiliary transformer is inverted, both ends of the primary winding of the auxiliary transformer are It is possible to prevent a loss caused by a short circuit with the second diode.

  In order to use the secondary current based on the voltage generated in the secondary side winding of the auxiliary transformer as a part of the current flowing in the primary side winding of the main transformer, an anode is provided on the secondary side winding of the auxiliary transformer. It is preferable to further include a third diode connected and having a cathode conductively connected to the primary winding of the main transformer.

  Furthermore, the switching power supply according to the present invention preferably further includes a smoothing capacitor connected in parallel to the DC power supply.

  According to this configuration, even if the secondary current generated in the secondary winding of the auxiliary transformer according to the discharge current cannot be consumed as the current flowing in the primary winding of the main transformer, Since the secondary current can be regenerated in the smoothing capacitor, further higher efficiency can be realized.

  ADVANTAGE OF THE INVENTION According to this invention, the switching power supply device which can implement | achieve efficiency improvement comparatively easily can be provided, without increasing cost.

1 is a circuit diagram of a switching power supply device according to the present invention. It is a voltage and current waveform diagram of each part of the switching power supply according to the present invention. It is a circuit diagram of the conventional switching power supply device.

  Hereinafter, preferred embodiments of a switching power supply according to the present invention will be described with reference to the accompanying drawings. 1 that are the same as those used in the description of FIG. 3 are denoted by the same reference numerals.

FIG. 1 shows a forward switching power supply device 1A according to the present embodiment. As shown in the figure, a switching power supply 1A includes a transformer 3 (corresponding to a “main transformer” of the present invention) in which a primary winding 3a is connected in series to one end of a DC power supply 2 that supplies a DC voltage, An NPN transistor (hereinafter simply referred to as “transistor”) 4 corresponding to the “switching element” of the present invention connected in series to the primary side winding 3a of FIG. 3, and a control circuit 5A for controlling the switching operation of the transistor 4; A rectifying / smoothing circuit comprising a diode 6 and a capacitor 7 connected in parallel to the secondary winding 3b of the transformer 3, and a snubber circuit 9A provided between the DC power source 2 and the primary winding 3a of the transformer 3. It has. This switching power supply device 1A includes a load 8 connected in parallel to an output terminal of a rectifying and smoothing circuit, an output voltage V ₀ obtained by stepping up or stepping down a DC voltage by switching operation of the transistor 4 under the control of the control circuit 5A. To supply.

  The snubber circuit 9A includes a resonance capacitor 10, a first diode 11, a second diode 12, a third diode 13, and an auxiliary transformer 14 including a primary side winding 14a and a secondary side winding 14b. is doing.

  The capacitor 10 is charged when the transistor 4 is turned off and is discharged when the transistor 4 is turned on. The other end of the primary winding 3a of the transformer 3 via the second diode 12 (in FIG. 1). One end is connected to the emitter of the transistor 4, and the other end is connected to the emitter of the transistor 4.

  The first diode 11 has an anode connected to the other end of the primary winding 3 a of the transformer 3 and a cathode connected to the collector of the transistor 4. The second diode 12 has an anode connected to the other end of the primary winding 3 a of the transformer 3 (a connection portion between the first diode 11 and the primary winding 3 a of the transformer 3), and a cathode connected to one end of the capacitor 10. It is connected. The third diode 13 has an anode connected to one end of the secondary winding 14 b of the auxiliary transformer 14 and a cathode connected to one end of the primary winding 3 a of the transformer 3. The first diode 11 has a current substantially the same as the collector current of the transistor 4 and a voltage substantially the same as the charging voltage of the capacitor 10 is applied thereto. Fast diodes are used.

  The primary winding 14 a of the auxiliary transformer 14 has one end connected to the connection portion between the cathode of the second diode 12 and the capacitor 10, and the other end connected to the connection portion between the cathode of the first diode 11 and the collector of the transistor 4. It is connected.

  Next, with reference to FIGS. 2A to 2F, the operation of each unit when the transistor 4 performs a switching operation under the control of the control circuit 5A will be described.

At time t ₀ , a high-level control signal is output from the control circuit 5A, and the transistor 4 is turned on with the base-emitter voltage V _BE maintained at a high level [H] (FIG. 2). (See (A)). Further, between the collector and emitter of the transistor 4, a current I ₀ flowing through the primary winding 3 a of the transformer 3 flows via the first diode 11, and the collector-emitter voltage V _CE of the transistor 4 is substantially equal. Therefore, it is zero (see FIGS. 2B and 2C).

At time t ₁ , when the control signal output from the control circuit 5A is switched from the high level to the low level, and the base-emitter voltage V _{BE of} the transistor 4 is switched from the high level [H] to the low level [L], That is, when the transistor 4 is turned off, the collector current I _CE of the transistor 4 is rapidly cut off (see FIG. 2C), and the current I ₀ flowing through the primary winding 3a of the transformer 3 passes through the second diode 12. And flows into the capacitor 10 (see FIGS. 2D and 2F). Therefore, the collector-emitter voltage V _CE of the transistor 4 does not rise rapidly but rises gently as the capacitor 10 is charged (see FIG. 2B).

On the other hand, when the control signal output from the control circuit 5A is switched from the low level to the high level at the time t ₂ and the transistor 4 is turned on, the discharge current I _C of the capacitor 10 causes the primary winding 14a of the auxiliary transformer 14 to flow. After flowing into the connection portion between the cathode of the first diode 11 and the collector of the transistor 4 via, it flows between the collector and the emitter of the transistor 4 (see FIGS. 2C and 2F). Since there is the first diode 11, the discharge current I _C of the capacitor 10 does not flow toward the primary winding 3 a of the transformer 3.

Further, the discharge current I _C in the primary winding 14a of the auxiliary transformer 14 flows, a secondary voltage corresponding to the discharge current I _C is generated in the secondary winding 14b of the auxiliary transformer 14, based on the secondary voltage A secondary current flows into the third diode 13. This secondary current becomes the forward current I _D3 of the third diode 13 (see FIG. _2E ) and is used as a part of the current I ₀ flowing through the primary winding 3a of the transformer 3.

In summary, the switching power supply device 1A according to the present embodiment controls the current I ₀ flowing through the primary side winding 3a of the transformer 3 with one transistor 4 and flows through the primary side winding 14a of the auxiliary transformer 14. Control of the discharge current I _C is performed. For this reason, according to the switching power supply device 1A according to the present embodiment, the auxiliary transistor 15 of the conventional switching power supply device 1B shown in FIG. 3 is deleted to reduce the number of parts and to make the control circuit 5B simpler. Nevertheless, the same loss reduction effect as before can be obtained.

  Furthermore, according to the switching power supply device 1A according to the present embodiment, a current is supplied only in one direction from the primary winding 3a of the transformer 3 to the transistor 4 between the primary winding 3a of the transformer 3 and the transistor 4. Since the first diode 11 that flows is provided, even if the discharge of the capacitor 10 is finished and the voltage generated in the primary winding 14a of the auxiliary transformer 14 is inverted, the primary winding 14a of the auxiliary transformer 14 is reversed. Can prevent the circulating current from flowing from the other end of the primary side winding 14a to the one end of the primary side winding 14a via the second diode 12, and the loss due to this circulating current can be reduced. Can be prevented.

  In the switching power supply 1A according to the present embodiment, the loss due to the forward current of the first diode 11 and the slight increase loss of the transistor 4 due to the deletion of the auxiliary transistor 15 of the conventional switching power supply 1B are the same as those of the conventional switching power supply. By selecting the first diode 11 that is less than or equal to the loss due to the current flowing through the auxiliary transistor 15 of the device 1B, it is possible to achieve a higher efficiency than that of the conventional switching power supply device 1B. That is, in the switching power supply device 1A according to the present embodiment, the loss due to the forward current of the first diode 11 (the power loss due to the product of the forward current of the first diode 11 and the forward voltage (VF) of the first diode 11). ) And a slight increase loss of the transistor 4 (the amount by which the current flowing in the auxiliary transistor 15 of the conventional switching power supply device 1B increases in the transistor 4 of the switching power supply device 1A according to the present embodiment) is the auxiliary transistor 15 is a sum of the power loss due to the product of the collector current of the auxiliary transistor 15 and the collector-emitter saturation voltage and the drive power loss consumed by the base current for driving the auxiliary transistor 15. Select the first diode 11 so that it is less than or equal to Preferred.

  As mentioned above, although preferable embodiment of the switching power supply device which concerns on this invention was described, this invention is not limited to the structure of the said embodiment.

For example, the switching power supply according to the present invention may further include a smoothing capacitor connected in parallel to the DC power supply 2. Thereby, the secondary current generated in the secondary winding 14b of the auxiliary transformer 14 according to the discharge current I _C cannot be consumed as the current I ₀ flowing in the primary winding 3a of the transformer 3. However, since this secondary current can be regenerated in the smoothing capacitor, further improvement in efficiency can be realized.

  Further, the switching element is not limited to the NPN transistor 4, and other switches that can be switched between an on state (conducting state) and an off state (blocking state) can be used.

  Furthermore, the DC power source 2 is not limited to a power source or a battery that outputs a DC voltage, but includes any circuit that outputs a DC voltage, for example, a single-phase or three-phase AC power source and a rectifier circuit such as a converter. It may be a circuit that converts a voltage and outputs a DC voltage.

  Further, the circuit system of the switching power supply device according to the present invention can employ not only the forward system but also the flyback system.

1A Switching power supply device 2 DC power supply 3 Transformer 4 Transistor (switching element)
5A Control circuit 6 Diode 7 Capacitor 8 Load 9A Snubber circuit 10 Capacitor 11 First diode 12 Second diode 13 Third diode 14 Auxiliary transformer

Claims (4)

A main transformer in which a primary side winding is connected in series to a DC power source that supplies a DC voltage; a switching element connected in series to a primary side winding of the main transformer; and a control circuit that controls a switching operation of the switching element; A capacitor that is charged through the primary winding of the main transformer when the switching element is turned off and that is discharged when the switching element is turned on; a primary winding through which a discharge current of the capacitor flows; and A switching power supply device comprising: an auxiliary transformer including a secondary winding that generates a secondary current corresponding to a discharge current, wherein the secondary current is used as a part of a current flowing in the primary winding of the main transformer Because
A first diode provided between the primary winding of the main transformer and the switching element, and further forward-connected in a direction from the primary winding of the main transformer toward the switching element;
The switching power supply device according to claim 1, wherein the discharge current flows into a connection portion between the first diode and the switching element through a primary winding of the auxiliary transformer and then flows to the switching element side. A second diode having an anode connected to a connection portion between the first diode and the primary side winding of the main transformer, and a cathode connected to the capacitor;
The first diode has an anode connected to a primary winding of the main transformer, and a cathode connected to the switching element.
The primary winding of the auxiliary transformer has one end connected to the connection between the second diode and the capacitor, and the other end connected to the connection between the first diode and the switching element. The switching power supply device according to claim 1, wherein   The third diode according to claim 1, further comprising a third diode having an anode connected to the secondary winding of the auxiliary transformer and a cathode conductively connected to the primary winding of the main transformer. Switching power supply.   The switching power supply according to any one of claims 1 to 3, further comprising a smoothing capacitor connected in parallel to the DC power supply.

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