JP2006288094A - Voltage converting circuit and power supply - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a voltage converting circuit in which high withstand voltage is not required for a switching means being arranged on the primary of a transformer. <P>SOLUTION: A transformer T1 has a primary coil P1 and a secondary coil S1 coupled magnetically with the coil P1, whereas a transformer T2 has a primary coil P21 connected in series with the coil P1, and a primary coil P22 coupled magnetically with the coil P21. A transistor Q1 is connected with the coils P21 and P22 and turns DC voltage supply to the coil P1 on/off. When the transistor Q1 is turned on and a voltage is supplied to the coil P1, a diode D1 short-circuits the opposite ends of the coil P22. When the transistor Q1 is turned off and voltage supply is interrupted, a diode D2 short-circuits the series circuit of the coils P1 and P21. A DC voltage is outputted based on an electromotive force being induced in the coil S1 under a state where voltage supply is turned on by the transistor Q1. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a voltage conversion circuit and a power supply device including the voltage conversion circuit.

  A voltage conversion circuit (DC-DC converter) that converts a DC voltage is widely used in a switching power supply circuit and the like (for example, see Non-Patent Document 1).

Cosel, “About Power Supply”, P.36-37, [online], [Search July 15, 2004], Internet <URL: http://www.cosel.co.jp/jp/products/ img / technotes.pdf>

  FIG. 4 is a typical example of a circuit called “single-ended forward system” among the switching power supply circuits described in Non-Patent Document 1. The switching power supply circuit 30 is connected to the primary side of the transformer T from the DC power supply 1. The supply of DC voltage to the coil P is turned on / off by a transistor Q such as an FET (Field Effect Transistor).

When a pulse voltage is applied to the gate G of the transistor Q and the transistor Q is turned on and a DC voltage is supplied to the primary coil P, the coil is generated by the induced electromotive force generated in the secondary coil S of the transformer T. A current flows from S through the diode D31 and the choke coil L31, and a DC voltage is output from the output terminals 3 and 4. Here, a smoothing capacitor C is provided in parallel with the output terminals 3 and 4. When the transistor Q is switched from on to off, the voltage supply to the choke coil L31 is stopped, so that a counter electromotive force is generated in the choke coil L31. Here, due to the back electromotive force of the choke coil L31, a current flows from the diode D32 through the choke coil L31, and a DC voltage is output from the output terminals 3 and 4.
That is, the switching power supply circuit 30 shown in FIG. 4 outputs a DC voltage by the electromotive force generated in the coil S when the transistor Q is on, and when the transistor Q is switched off, the energy accumulated in the choke coil L31 is output. Output DC voltage.

  The conventional voltage conversion circuit shown in FIG. 4 transmits energy from the coil P of the transformer T to the coil S in the on state by switching on / off of the transistor Q, and accumulates in the choke coil L31 in the off state. The direct current voltage is output by releasing the generated energy. However, the back electromotive force generated in the coil P when the transistor Q is switched from on to off shows a very large voltage value in a transient manner, and the sum of this voltage and the supplied DC voltage is temporarily stored in the transistor Q. Therefore, it is necessary to use a transistor having a sufficiently higher withstand voltage than such a voltage. For this reason, the circuit is relatively expensive although it can be configured with a small number of parts.

  Accordingly, an object of the present invention is to provide a voltage conversion circuit in which high withstand voltage characteristics are not required for the switching means disposed on the primary side of the transformer.

  In order to achieve the above object, a voltage conversion circuit according to one aspect of the present invention includes a primary side first coil and a secondary side second coil magnetically coupled to the first coil. A first transformer, a third coil on the primary side connected in series to the first coil, and a second transformer having a fourth coil on the primary side magnetically coupled to the third coil; A sixth coil disposed on an output line connected to one end of the second coil, and a DC voltage supply to the first coil connected to the third coil and the fourth coil. Switching means for switching on / off, first short-circuit means for short-circuiting both ends of the fourth coil when the voltage supply to the first coil is turned on by the switching means, and the switching means First Voltage supply to the first coil by the switching means. The second short-circuit means for short-circuiting the series circuit of the first coil and the third coil when the voltage supply to the coil is off. Is turned on, a DC voltage is output based on an electromotive force generated in the second coil, and the voltage supply to the first coil is turned off by the switching means. A DC voltage is output based on an electromotive force generated in the coil.

  In the voltage conversion circuit of the above invention, one end of the first coil is connected to the second short-circuit means, the other end is connected to one end of the third coil, and the fourth coil One end of which is connected to the other end of the third coil, the other end is connected to the first short-circuit means, and the switching means includes a series circuit of the fourth coil and the first short-circuit means. The second short-circuit means is connected to the connection point between the other end of the third coil and the one end of the fourth coil so as to be connected in parallel. It can be set as the structure connected to the connection point of the said other end of the said 3rd coil, and the said one end of the said 4th coil so that it may be connected in parallel with the series circuit of 3 coils.

  Here, in the voltage conversion circuit of the above-described invention, it is preferable to use a rectifying element, for example, a diode, as the first short-circuit means and the second short-circuit means.

  A voltage conversion circuit according to another aspect of the present invention includes a first transformer having a primary side first coil, a secondary side second coil magnetically coupled to the first coil, and the first transformer. A third coil on the primary side connected in series to the first coil, a fourth coil on the primary side magnetically coupled to the third coil, and a secondary side magnetically coupled to the third coil A second transformer having a fifth coil; a sixth coil disposed on an output line connected to one end of the second coil; and the third coil and the fourth coil. Switching means for switching on / off of DC voltage supply to the first coil, and both ends of the fourth coil are short-circuited when the voltage supply to the first coil is turned on by the switching means. First short-circuit means And second shorting means for short-circuiting a series circuit of the first coil and the third coil when voltage supply to the first coil is turned off by the etching means, and the first transformer The second coil of the second transformer and the fifth coil of the second transformer are connected in series, and when the voltage supply to the first coil is turned on by the switching means, the second coil A DC voltage is output based on the electromotive force generated in the coil of the first coil, and the DC voltage is output based on the electromotive force generated in the sixth coil in a state where the voltage supply to the first coil is turned off by the switching means. It is characterized by outputting.

  In the voltage conversion circuit of the above invention, one end of the first coil is connected to the second short-circuit means, the other end is connected to one end of the third coil, and the fourth coil One end of which is connected to the other end of the third coil, the other end is connected to the first short-circuit means, and the switching means includes a series circuit of the fourth coil and the first short-circuit means. The second short-circuit means is connected to the connection point between the other end of the third coil and the one end of the fourth coil so as to be connected in parallel. It can be set as the structure connected to the connection point of the said other end of the said 3rd coil, and the said one end of the said 4th coil so that it may be connected in parallel with the series circuit of 3 coils.

  Here, in the voltage conversion circuit of the above-described invention, it is preferable to use a rectifying element, for example, a diode, as the first short-circuit means and the second short-circuit means.

  According to still another aspect of the present invention, a voltage conversion circuit includes a first transformer, a second transformer, and switching means for switching on / off of a DC voltage supply to a first coil existing in the first transformer. A voltage conversion circuit comprising: at least the first coil present in the first transformer; the third coil present in the second transformer; and the switching means. A second current path comprising a current path, the first coil present in the first transformer, the third coil present in the second transformer, and a second short-circuit means; And a fourth current path comprising a second coil present in the first transformer magnetically coupled to the first coil present in the first transformer, and the switching means is turned on to turn on the first When a current flows in the current path, a current flows in the fourth current path based on a voltage generated in the second coil, and the switching means is turned off to interrupt the current flowing in the first current path. The second current path is a closed circuit, and the back electromotive force generated in the first coil is applied to the switching means by the second short-circuit means provided in the second current path. It is characterized by preventing this.

  According to still another aspect of the present invention, a voltage conversion circuit includes a first transformer, a second transformer, and switching means for switching on / off of a DC voltage supply to a first coil existing in the first transformer. A voltage conversion circuit comprising: at least the first coil present in the first transformer; the third coil present in the second transformer; and the switching means. A first path comprising: a current path; a fourth coil present in the second transformer magnetically coupled to the third coil present in the second transformer; the switching means; and a first short-circuit means. 3 current paths, and a fourth current path comprising a second coil present in the first transformer magnetically coupled to the first coil present in the first transformer, When the chucking means is turned on and a current flows in the first current path, a current flows in the third current path and the fourth current path, and a magnetic flux generated in the third and fourth coils is generated. It is characterized by substantially canceling out.

  In the voltage conversion circuit of the above invention, the fifth coil existing in the second transformer magnetically coupled to the third coil existing in the second transformer, the second coil, and the second coil A series circuit in which 5 coils are connected in series, and the voltage generated at both ends of the series circuit when the switching means is turned off and the current flowing through the first current path is cut off. The voltage generated in the second coil and the voltage generated in the fifth coil can be substantially offset.

  Furthermore, you may comprise the power supply device carrying the voltage conversion circuit of this invention.

According to the voltage conversion circuit according to one aspect of the present invention, when the voltage supply to the first coil is turned on by the switching means, the first short-circuit means causes both ends of the fourth coil to be short-circuited. Therefore, the voltage between both ends of the fourth coil of the second transformer and the third coil magnetically coupled to the fourth coil is substantially 0 (zero) volts, and magnetic energy is not accumulated in the magnetic core of the second transformer. The energy supplied from the DC power supply is almost all given to the first transformer. On the other hand, since no magnetic flux is accumulated in the magnetic circuit of the second transformer, the third coil of the second transformer has a sufficiently large reactance.
When the voltage supply to the first coil is turned off by the switching means, a large spike voltage due to the counter electromotive force generated in the first coil is instantaneously applied to the switching means. Is provided with a closed circuit of a third coil and a second short-circuit means (for example, a rectifying element such as a diode), and the second short-circuit means short-circuits the series circuit of the first coil and the third coil. This spike voltage prevents the spike voltage from being applied directly to the switching means. For example, when the second short-circuit means is a rectifying element such as a diode, the spike voltage is the forward voltage of the rectifying element, so that the voltage applied to the switching means is clamped to a substantially DC power supply voltage by the rectifying means. Is done. Therefore, it is sufficient for the switching means to have a withstand voltage characteristic of approximately the DC power supply voltage.
In addition, although the first coil → the third coil → the second short circuit means → the first coil and the closed circuit are configured, the large reactance of the third coil existing in the second transformer In this closed circuit, almost no current flows. Therefore, since the magnetic flux existing in the magnetic circuit of the first transformer can be rapidly attenuated, the switching frequency for turning on / off the switching means can be increased. Thereby, the output of a voltage conversion circuit can be made into a high output thing. Also, substantially all of the energy of the magnetic circuit of the first transformer can be released to the second coil.

Further, according to the voltage conversion circuit according to another aspect of the present invention, when the voltage supply to the first coil is turned on by the switching means, the first short-circuit means short-circuits both ends of the fourth coil. Let Therefore, the voltage between both ends of the fourth coil of the second transformer and the third coil magnetically coupled to the fourth coil is substantially 0 (zero) volts, and magnetic energy is not accumulated in the magnetic core of the second transformer. The energy supplied from the DC power supply is almost all given to the first transformer. On the other hand, since no magnetic flux is accumulated in the magnetic circuit of the second transformer, the third coil of the second transformer has a sufficiently large reactance.
When the voltage supply to the first coil is turned off by the switching means, a large spike voltage due to the counter electromotive force generated in the first coil is instantaneously applied to the switching means. Is provided with a closed circuit of a third coil and a second short-circuit means (for example, a rectifying element such as a diode), and the second short-circuit means short-circuits the series circuit of the first coil and the third coil. This spike voltage prevents the spike voltage from being applied directly to the switching means. For example, when the second short-circuit means is a rectifying element such as a diode, the spike voltage is the forward voltage of the rectifying element, so that the voltage applied to the switching means is clamped to a substantially DC power supply voltage by the rectifying means. Is done. Therefore, it is sufficient for the switching means to have a withstand voltage characteristic of approximately the DC power supply voltage.

  In addition, although the first coil → the third coil → the second short circuit means → the first coil and the closed circuit are configured, the large reactance of the third coil existing in the second transformer In this closed circuit, almost no current flows. Therefore, since the magnetic flux existing in the magnetic circuit of the first transformer can be rapidly attenuated, the switching frequency for turning on / off the switching means can be increased. Thereby, the output of a voltage conversion circuit can be made into a high output thing. Also, substantially all of the energy of the magnetic circuit of the first transformer can be released to the second coil.

  According to the voltage conversion circuit of another aspect of the present invention, in addition to the above effect, the second transformer includes the secondary coil and the fifth coil magnetically coupled to the third coil. Since the second coil of the first transformer and the fifth coil of the second transformer are connected in series, when the voltage supply to the first transformer is turned off by the switching means, the second coil Is canceled by the electromotive force generated in the fifth coil. Therefore, a large potential increase based on the electromotive force generated on the secondary side of the first transformer and the secondary side of the second transformer can be suppressed.

  Moreover, the power supply apparatus of the present invention can realize an inexpensive apparatus with a small number of parts by mounting the above voltage conversion circuit.

  The above objects and advantages of the present invention, as well as other objects and advantages, will be more clearly understood through the following description of embodiments. However, the embodiments described below are merely examples, and the present invention is not limited to these.

[First Embodiment]
FIG. 1 is a circuit diagram showing a basic configuration of a conversion circuit 200 in the first embodiment to which the present invention is applied.

  A conversion circuit 200 shown in FIG. 1 is a circuit that performs voltage conversion based on a DC voltage having a predetermined voltage value and outputs DC voltages having different voltage values, and includes a transformer T1 and a transformer T2. The conversion circuit 200 includes a positive output terminal 13 and a negative output terminal 14, and a predetermined load L is connected between the output terminal 13 and the output terminal 14.

  The transformer T1 includes a primary coil P1 and a secondary coil S1 magnetically coupled to the coil P1. The transformer T2 includes a primary side first coil P21 and a primary side second coil P22 magnetically coupled to the first coil P21.

  One end (winding start side) of the coil P1 is connected to the positive electrode of the DC power supply 11, and the other end (winding end side) is connected to one end (winding start side) of the first coil P21 on the primary side of the transformer T2. The One end (winding start side) of the second coil P22 is connected to the other end of the first coil P21, and the other end (winding end side) is connected to the cathode side of the diode D1.

The drain of the transistor (FET in this embodiment) Q1 is connected to a connection point between the other end of the first coil P21 on the primary side of the transformer T2 and one end of the second coil P22, and a pulse voltage is applied to the gate G1. And the source is connected to the anode side of the diode D1 and the negative electrode of the DC power supply 11. The conversion circuit 200 includes a diode D2 connected in parallel with the series circuit of the coil P1 and the coil P21. The anode side of the diode D2 is connected to the drain of the transistor Q1, and the positive electrode of the DC power supply 11 is connected to the cathode side. Connected.
The transistor Q1 performs an on / off switching operation in accordance with the pulse voltage input to the gate G1, and when the transistor Q1 is on, a DC voltage is supplied from the DC power supply 11 to the coil P1, but the transistor Q1 is off. In this state, the supply of DC voltage is cut off.

Also, the anode of the diode D13 is connected to one end (winding start side) of the secondary coil S1 of the transformer T1, and the coil L11 is disposed on the output line extending from the cathode of the diode D13. That is, one end of the coil L11 is connected to one end (winding start side) of the coil S1 via the diode D13, and the other end is connected to the output terminal 13. Further, the other end (winding end side) of the coil S <b> 1 is connected to the other output terminal 14. Further, the cathode of the diode D14 is connected to the connection point between the diode D13 and the coil L11, and the anode of the diode D14 is connected to the other end (winding end side) of the coil S1.
Therefore, on the secondary side of the transformer T1, the current flows only in the direction from the diode D13 to the output terminal 13 via the coil L11 or the direction from the diode D14 to the output terminal 13 via the coil L11. ing.

  A smoothing capacitor C1 is connected between the output terminal 13 and the output terminal 14, and a DC voltage smoothed by the capacitor C1 is output from the output terminals 13 and 14.

  The conversion circuit 200 configured as described above outputs a DC voltage to the load L connected to the output terminals 13 and 14 based on the DC voltage supplied from the DC power supply 11.

Next, the operation of the conversion circuit 200 will be described.
When a pulse voltage is input to the gate G1 of the transistor Q1 and the transistor Q1 is turned on, a DC voltage is supplied to the primary coil P1 of the transformer T1 and the primary coil P21 of the transformer T2, and the coil P1, the coil A current flows through the path reaching P21 and transistor Q1. Since the current flows through the primary coil P1 of the transformer T1, the number of turns of the coil P1 and the coil S1 is positive in the secondary coil S1 of the transformer T1, with the winding start side (black circle) of the coil S1 being positive. An induced electromotive force according to the ratio is generated.

Further, when a current flows through the primary side coil P21 of the transformer T2, an induced electromotive force is also generated in the coil P22 magnetically coupled to the coil P21. This electromotive force is an electromotive force in which the winding start side (black circle) of the coil P22 is positive. Here, since the transistor Q1 is turned on, the electromotive force generated in the coil P22 acts as a forward voltage with the anode side of the diode D1 being positive. As a result, both ends of the coil P22 are short-circuited through the transistor Q1 and the diode D1, and a current flows from the coil P22 through the transistor Q1 and the diode D1 to the coil P22 again. As a result of the current flowing in the closed circuit in this way, the voltage across the coil P22 becomes approximately 0 (zero) volts. Further, since the voltage of the coil P22 of the transformer T2 is approximately 0 (zero) volts, the voltage across the coil P21 magnetically coupled thereto is also approximately 0 (zero) volts. Here, considering the directions of the currents flowing through the coils P21 and P22, current flows from the winding start side (black circle mark) to the winding end side in the coil P21, whereas in the coil P22 from the winding end side. A closed circuit current is flowing on the winding start side (black circle). Since the winding end side of the coil P21 is connected to the winding start side (black circle) of the coil P22, the magnetic flux generated by the current flowing through the coil P21 and the magnetic flux generated by the current flowing through the coil P22 cancel each other.
That is, when the transistor Q1 is on, magnetic energy is not accumulated in the magnetic core of the transformer T2. This is because the addition of the transformer T2 does not cause any energy loss due to the transformer T2 itself because magnetic energy is not accumulated in the transformer T2 although a significant effect as described later is obtained. means.
As described above, the magnetic flux generated by the current flowing through the coil P21 and the magnetic flux generated by the current flowing through the coil P22 cancel each other, and the magnetic flux is not accumulated in the magnetic circuit of the transformer T2. (There is almost no magnetic flux passing through the coil P21 and the coil P22). Therefore, the coil P21 of the transformer T2 (the same applies to the coil P22) has a sufficiently large reactance.

  As described above, since no magnetic energy is accumulated in the magnetic core of the transformer T2 when the transistor Q1 is on, no energy loss is caused by the transformer T2 itself, while the DC voltage supplied from the DC power supply 11 is all of the transformer T1. The energy is applied to the coil P1, and energy is transmitted to the coil S1 only through the transformer T1.

As described above, an induced electromotive force is generated in the coil S1 on the secondary side of the transformer T1, and the electromotive force is positive on the diode D13 side of the coil S1. The terminal 13 side becomes negative. Therefore, since a forward voltage with the anode side being positive is applied to the diode D13, a current flows from the diode D13 to the output terminal 13 through the coil L11.
That is, when the transistor Q1 is on, a DC voltage based on the induced electromotive force generated in the coil S1 is output from the output terminals 13 and 14.
Further, when current flows as described above when the transistor Q1 is on, energy is stored in the coil L11. The energy stored in the coil L11 becomes a source for outputting an output voltage when the transistor Q1 is off, as will be described later.

  Thereafter, when the transistor Q1 is switched off by the pulse voltage, the supply of the DC voltage to the coil P1 is cut off, and a counter electromotive force (flyback voltage) due to the self-inductance of the coil P1 is generated. Since the back electromotive force generated at this time is large as already described, the potential on the drain side of the transistor greatly increases rapidly in the conventional switching power supply circuit. Therefore, conventionally, it has been necessary to use a transistor having a high withstand voltage. On the other hand, in the present invention, the rise in the drain potential of the transistor Q1 is suppressed by connecting the diode D2 in parallel to the series circuit of the coil P1 and the coil P21.

  That is, in FIG. 1, when the transistor Q1 is switched off, a large spike voltage due to the counter electromotive force in the direction in which the winding end side of the coil P1 is positive is instantaneously applied to the drain of the transistor Q1. The coil P1 is provided with a closed circuit of the coil P21 and the diode D2, and since this spike voltage is a forward voltage with the anode side of the diode D2 being positive, the drain potential of the transistor Q1 is substantially DC by the diode D2. Clamped to the positive potential of the power supply. Therefore, it is sufficient that the transistor Q1 has a withstand voltage characteristic of approximately the DC power supply voltage.

  In the above state, when the transistor Q1 is on, energy is transmitted from the coil S1 to the load side by mutual induction of the transformer T1, and almost no magnetic energy is accumulated in the magnetic core of the transformer T1, but a little remains. Therefore, when the transistor Q1 is turned off, back electromotive force is generated in the coils P1 and S1, and the back electromotive force is negative on the diode D13 side of the coil S1 and positive on the output terminal 14 side. Accordingly, since a reverse voltage with the anode side being negative is applied to the diode D13, no current flows from the diode D13 to the output terminal 13. Therefore, the DC voltage based on the counter electromotive force generated in the coil S1 is not output from the output terminals 13 and 14.

  On the other hand, when the transistor Q1 is switched off and the potential on the diode D13 side of the coil L11 decreases, a counter electromotive force is generated in the coil L11 due to self-inductance. The counter electromotive force causes a current to flow from the diode D14 to the output terminal 13 through the coil L11. Accordingly, a DC voltage based on the counter electromotive force generated in the coil L11 is smoothed by the capacitor C1 and output to the output terminals 13 and 14.

  As described above, the diode D2 has a role of suppressing a potential rise on the drain side of the transistor Q1 when the transistor Q1 is switched from on to off. However, the present invention adds a transformer T2 (coil P21) in addition to the diode D2. And the coil P22) and the diode D1 are significant. This is clearly understood when compared to the operation in the case where the transformer T2 (coil P21, coil P22) and the diode D1 are not provided in the conversion circuit 200.

  In FIG. 1, when the coil P21, the coil P22, and the diode D1 are not provided (the case where the coil P21 is not provided here) means that the winding end of the coil P1 is directly connected to the anode of the diode D2 and the drain of the transistor Q1. )think of. When the transistor Q1 is switched from on to off, the direction of the counter electromotive force generated in the coil P1 corresponds to the forward voltage of the diode D2, so that both ends of the coil P1 are short-circuited by the diode D2. Therefore, even without the coil P21, the potential on the drain side of the transistor Q1 is clamped to the positive potential of the substantially DC power source. Here, when both ends of the coil P1 are short-circuited without the coil P21, a current flows through the closed circuit of the coil P1 and the diode D2, so that the magnetic flux accumulated in the magnetic core of the transformer T1 is not attenuated. The magnetic flux is stored as it is, and the magnetic flux existing in the magnetic circuit of the transformer T1 cannot be rapidly attenuated. This means that the switching frequency cannot be increased, and therefore the output of the conversion circuit cannot be made high. Further, when magnetic energy is stored in the primary coil P1 of the transformer T1, electric energy cannot be released by the secondary coil S11.

  On the other hand, in the conversion circuit 200 according to the present embodiment, when the transistor Q1 is switched from on to off, the closed circuit of the coil P1 to the coil P21 and the diode D2 exists, so that the drain of the transistor Q1 is as described above. Is clamped, and almost no current flows through the closed circuit due to the large reactance of the coil P21 as described above. Accordingly, since the magnetic flux existing in the magnetic circuit of the transformer T1 can be rapidly attenuated, the switching frequency for turning on / off the transistor Q1 can be increased. Thereby, the output of the conversion circuit 200 can be made high output. In addition, since magnetic energy is not stored in the primary coil P1 of the transformer T1, electric energy can be emitted by the secondary coil S11.

  As described above, according to the conversion circuit 200, (1) since a high voltage can be prevented from being applied to the drain of the transistor Q1 when the transistor Q1 is switched from on to off, the transistor Q1 has a low withstand voltage. (2) Since the magnetic energy is not stored in the magnetic core of the transformer T2 even if the transformer T2 is added, all of the energy supplied from the DC power source can be transmitted to the transformer T1, There is an advantage that energy conversion efficiency is not impaired, and (3) a high output can be obtained because the switching frequency of the transistor Q1 can be increased.

  Of course, according to the conversion circuit 200, a desired output voltage can be obtained by adjusting the number of turns of the coil S1 on the secondary side of the transformer T1.

  By the way, in the conversion circuit 200, when the transistor Q1 is on and / or off, a current flows through the coil P21 and the coil P22 of the transformer T2, and the direction of the current is the winding start side (black circle) in the coil P21. Mark) from the winding end side to the winding end side, and in the coil P22, from the winding end side to the winding start side (black circle mark). Therefore, magnetic fluxes in opposite directions pass through the magnetic core of the transformer T2, and the magnetic fluxes cancel each other and are not accumulated. In order to solve this problem, in this embodiment, it is preferable to use a magnetic core that has been permanently magnetized in advance as the magnetic core of the transformer T2. As such a magnetic core material, a ferrite magnet or the like is suitable. The selection of the magnetic core material is the same for the transformer T1.

[Second Embodiment]
FIG. 2 is a circuit diagram showing a basic configuration of a conversion circuit 210 according to the second embodiment to which the present invention is applied. The conversion circuit 210 shown in FIG. 2 is obtained by adding a coil S21 to the secondary side of the transformer T2 in the conversion circuit 200 according to the first embodiment. Accordingly, the circuit elements and the like arranged in the same manner as the conversion circuit 200 of FIG. 1 are denoted by the same reference numerals except for the secondary coil of the transformer T1, and the description thereof is omitted.

A conversion circuit 210 shown in FIG. 2 includes a secondary coil S21 of the transformer T2 in the conversion circuit 200 shown in FIG. 1, and one end (starting point) of the coil S21 is the other side of the secondary coil S11 of the transformer T1. One end (winding end point) is connected to the output terminal 14.
Therefore, on the secondary side of the transformer T1 and the secondary side of the transformer T2, a current flows in a direction from the coil S21 to the output terminal 13 through the coil S11 and the diode D13.

  The conversion circuit 210 configured as described above outputs a DC voltage to the load L connected to the output terminals 13 and 14 based on the DC voltage supplied from the DC power supply 11.

Next, the operation of the conversion circuit 210 will be described.
When a pulse voltage is input to the gate G1 of the transistor Q1 and the transistor Q1 is turned on, a DC voltage is supplied to the primary coil P1 of the transformer T1 and the coil P21 of the transformer T2, and the coil P1, the coil P21, and the transistor A current flows through the path leading to Q1. Since current flows through the primary coil P1 of the transformer T1, the number of turns of the coil P1 and the coil S11 is positive in the secondary coil S11 of the transformer T1, with the winding start side (black circle) of the coil S11 being positive. An induced electromotive force according to the ratio is generated. In addition, when a current flows through the coil P21 on the primary side of the transformer T2, an induced electromotive force (an electromotive force whose positive side is the winding start side (black circle)) of the coil P22 is also generated in the coil P22 magnetically coupled to the coil P21. Arise. Here, since the transistor Q1 is turned on, the electromotive force generated in the coil P22 acts as a forward voltage with the anode side of the diode D1 being positive. As a result, both ends of the coil P22 are short-circuited through the transistor Q1 and the diode D1, and a current flows from the coil P22 to the coil P22 again through the transistor Q1 and the diode D1, and the voltage across the coil P22, the coil P21. The voltage between both ends of is approximately 0 (zero) volts. As a result, when the transistor Q1 is on, all the DC voltage supplied from the DC power supply 11 is applied to the coil P1 of the transformer T1, and almost all the energy supplied from the DC power supply 11 is given to the transformer T1. On the other hand, the voltage between both ends of the coil P21 and the coil P22 is approximately 0 (zero) volts, and no magnetic flux is accumulated in the magnetic circuit of the transformer T2. Moreover, since the voltage between both ends of the coil P21 and the coil P22 is approximately 0 (zero) volts, almost no electromotive force is generated in the coil S21 on the secondary side of the transformer T2.

  On the other hand, an induced electromotive force is generated in the coil S11 with the winding start side (black circle) of the coil S11 being positive, and this electromotive force is positive on the diode D13 side of the coil S11 and negative on the output terminal 14 side. And a DC voltage based on the induced electromotive force generated in the coil S11 is output from the output terminals 13 and 14.

  As described above, the operation when the transistor Q1 is on is basically the same as the operation in the conversion circuit 200 according to the first embodiment. In the conversion circuit 210 according to the present embodiment, the transformer T2 includes a secondary coil S21, and the coil S21 is connected in series with the secondary coil S11 of the transformer T1, so that the transistor Q1 is turned from on to off. It is characterized in that the reverse voltage applied to the diode D13 when switched is reduced.

  That is, after that, when the transistor Q1 is switched off by the pulse voltage, the supply of the DC voltage to the coil P1 is cut off, and a counter electromotive force (flyback voltage) due to the self-inductance of the coil P1 occurs. This counter electromotive force is an electromotive force in a direction in which the winding end side of the coil P1 is positive, and corresponds to a forward voltage in which the anode side of the diode D2 is positive in the closed circuit of the coil P1, the coil P21, and the diode D2. To do. Therefore, the series circuit of the coil P1 and the coil P21 is short-circuited through the diode D2. As a result of the presence of the closed circuit in this way, the potential on the drain side of the transistor Q1 is clamped to the positive potential of the substantially DC power supply by the diode D2.

  By configuring a closed circuit of the coil P1, the coil P21, the diode D2, and the coil P1, a voltage having a positive winding start side (black circle) is applied to the primary coil P21 of the transformer T2. For this reason, due to the mutual induction action of the transformer T2, an induced electromotive force is generated in the coil S21 on the secondary side of the transformer T2, with the winding start side (black circle) being positive, according to the turn ratio of the coil P21 and the coil S21. To do. At this time, the induced electromotive force generated in the coil S21 is opposite in polarity to the counter electromotive force generated in the coil S11 due to the counter electromotive force (flyback voltage) generated in the coil P1 of the transformer T1, and thus the counter electromotive force generated in the coil S11. The electric power is canceled by the electromotive force generated in the coil S21. Therefore, since the reverse voltage applied to the anode side of the diode D13 when the transistor Q1 is turned off is reduced and a large potential rise is suppressed, it is sufficient to use a diode having a relatively low withstand voltage for the diode D13.

  That is, when the transistor is switched off, the conversion circuit 210 generates a voltage (referenced to the end of winding) generated in the secondary coil S11 based on the counter electromotive force generated in the primary coil P1 of the transformer T1. -VS11) is canceled by the voltage (VS21) generated in the coil S21 on the secondary side of the transformer T2. That is, the voltage generated at both ends of the series circuit of the coil S11 and the coil S21 is reduced to the sum of both (V ′ = − VS11 + VS21).

  In a conventional voltage conversion circuit that performs a forward operation, a voltage from the output voltage smoothing capacitor (reverse voltage for the diode) is applied to the cathode of the diode connected to the secondary coil of the voltage conversion transformer. In addition, since a flyback reverse voltage is further applied, there is a problem that a particularly large withstand voltage is required for the diode. On the other hand, since the conversion circuit 210 of this embodiment can reduce the voltage across the series circuit of the secondary coil S11 of the transformer T1 and the secondary coil S21 of the transformer T2, as described above, the diode D13 There is a further advantage that a particularly large withstand voltage is not required.

  Note that when the transistor Q1 is switched off, a counter electromotive force is generated in the coil L11 due to self-inductance, and this back electromotive force causes a current to flow in the direction from the diode D14 to the output terminal 13 through the coil L11. Similar to the case of the circuit 200, also in the conversion circuit 210, a DC voltage based on the counter electromotive force generated in the coil L <b> 11 is smoothed by the capacitor C <b> 1 and output to the output terminals 13 and 14.

  Of course, according to the conversion circuit 210, a desired output voltage can be obtained by adjusting the number of turns of the coil S11 of the transformer T1.

  Further, in the conversion circuit 210, similarly to the conversion circuit 210 according to the first embodiment, when a magnetic core that is permanently magnetized in advance is used as the magnetic core of the transformer T2, the magnetic flux passing through the magnetic core of the transformer T2 is canceled out. It is possible to solve problems that may accumulate without being stored. This also applies to the transformer T1.

FIG. 3 is a voltage waveform showing the operation of the conversion circuit 210 according to the second embodiment shown in FIG.
Each voltage waveform in FIG. 3 shows a change in voltage value in each part (CH1 to CH3, CH6) when the conversion circuit 210 is operated. In FIG. 3, the horizontal axis indicates the passage of time, and the vertical axis indicates the voltage value.

  In FIG. 3, the channel CH1 indicates a voltage value on the drain side of the transistor Q1, as indicated by “CH1” in FIG. Similarly, the channel CH2 is a voltage value on the cathode side of the diode D1, the channel CH3 is a voltage value at a connection point between the other end (winding end side) of the coil P1 and one end (winding start side) of the coil P21, and CH6 is The voltage value of one end (winding start side) of coil S11 is shown.

  In FIG. 3, the transistor Q1 (FIG. 2) is switched from OFF to ON at time Z21, and the transistor Q1 is switched from ON to OFF at time Z22. Time Z23 is a time when the flyback voltage in the coil P1 is lowered to a predetermined level, and time Z24 is a time when the back electromotive force in the coil L11 is substantially lost.

When the transistor Q1 of the conversion circuit 210 (FIG. 2) is switched on at time Z1 in FIG. 3, the DC power supply 11 side of the coil P1 becomes positive and the coil P21 side becomes negative, and a predetermined current flows through the coil P1. At this time, the voltage value on the drain side of the transistor Q1 is approximately 0 (zero) volts (channel CH1), and the voltage on the cathode side of the diode D1 cannot be distinguished from 0 (zero) volts on the waveform, but 0.6 Volts (residual voltage of diode) (channel CH2). The potential at the connection point between the other end (winding end side) of the coil P1 and one end (winding start side) of the coil P21 shows a waveform that gradually rises with time, but is considered to be practically zero. The voltage value is low enough to obtain (channel CH3).
Here, due to the electromotive force generated in the coil S11, a positive voltage corresponding to the turn ratio of the coil P1 and the coil S11 is applied to the anode side of the diode D13 (channel CH6). For this reason, the diode D13 is forward-biased and a current flows.

Next, when the transistor Q1 is switched from on to off at time Z22 and the supply of the DC voltage to the coil P1 is cut off, a large back electromotive force (flyback voltage) is generated in the coil P1. This flyback voltage is a large voltage with the coil P1 side of the coil P1 being positive, and in this example, its value exceeds twice the power supply voltage (channel CH3). However, the potential on the drain side of the transistor Q1 is suppressed to the voltage value of the DC power supply (channel CH1). However, in the experimental circuit, a slight transient occurs due to the stray capacitance of the wiring or the like, but settles to the DC power supply potential. This is because the series circuit of the coil P1 and the coil P21 is short-circuited by the presence of the closed circuit composed of the coil P1, the coil P21, and the diode D2, and the potential on the drain side of the transistor Q1 is reduced by the diode D2. This is because it is clamped at the positive potential of the power supply voltage.
This flyback voltage generates a counter electromotive force (-VS11 when the winding end side is used as a reference) with the winding start side (black circle side) being negative (winding end side is positive) in the coil S11. Further, there is a closed circuit composed of the coil P1, the coil P21, and the diode D2, and a positive potential is applied at the start of winding of the coil P21, whereby the winding start side (black circle mark) is positive in the coil S21. An induced voltage (VS21) is generated. Therefore, the sum of these voltages (V ′ = − VS11 + VS21) is applied as the reverse voltage to the anode side of the diode D13 (channel CH6).

  Here, focusing on the voltage (channel CH6) applied to the diode D13, when the voltage supply to the coil P1 is off (time Z22 to time Z23), the amplitude is an alternating potential that attenuates with time. This is due to the reactance and stray capacitance of the coil L11. However, when comparing the flyback voltage (channel CH3) with this alternating potential (channel CH6), the negative amplitude applied to the anode side of the diode D13 is clearly smaller than the large amplitude of the flyback voltage (channel CH3). , Channel CH6). This means that the reverse voltage applied to the diode D13 is reduced when the voltage supply to the coil P1 is off.

  Thereafter, the flyback voltage in the coil P1 decreases with time and almost disappears at time Z23 (channel CH3). Thereafter, the back electromotive force generated in the coil L11 also substantially disappears at time Z24 (channel CH3).

  As described above, in the conversion circuit 210, (1) when the voltage supply to the coil P1 is switched from on to off (from time Z22), regardless of the generation of a large flyback voltage at the coil P1, the transistor Q1 The potential on the drain side can be suppressed to a substantially power supply voltage value, and (2) the reverse voltage applied to the diode D13 when the voltage supply to the coil P1 is off (time Z22 to time Z23) is small. The voltage waveform can be confirmed.

In the first and second embodiments, the specific form of the DC power supply 11 in the conversion circuits 200 and 210 is arbitrary, and a battery or a switching power supply device may be used, or an AC power supply. It is also possible to use as the DC power supply 11 a circuit that rectifies and supplies a DC voltage, and the same effect can be obtained in any case.
In particular, when a circuit (rectifier bridge circuit or the like) that rectifies an AC power supply and supplies a DC voltage is used as the DC power supply 11, the conversion circuits 200 and 210 can be used as a constituent circuit of the DC power supply circuit. . The DC power supply circuit is mounted on many electrical appliances and electronic devices connected to household AC power supplies, and it is extremely useful if the conversion circuit of the present invention is applied to these electrical appliances and electronic devices.

  Furthermore, in the first and second embodiments, it is of course possible to attach the diodes arranged in the conversion circuits 200 and 210 so that the polarities are reversed. In this case, the output DC voltage The same effect as in the first and second embodiments can be obtained only by reversing the polarity.

  Further, the specific configuration of the conversion circuits 200 and 210 is not particularly limited, and it is of course possible to replace part or all of the conversion circuits 200 and 210 with an equivalent circuit. For example, the diodes included in the conversion circuits 200 and 210 are replaced with circuits having a rectifying function, and / or the transistors included in the conversion circuits 200 and 210 have a switching function that can be on / off controlled by an external input signal. Of course, it can be replaced by a circuit, and other details can be changed as appropriate.

  The voltage conversion circuit of the present invention can be applied not only to a device that converts a DC voltage, but also, for example, an alternating current is connected to the input stage (DC power supply 11 in FIGS. 1 and 2) of the voltage conversion circuit of the present invention. If a rectifier circuit that rectifies the voltage is connected, it can be used as a power supply circuit (for example, a switching power supply circuit) that outputs a desired DC voltage from an AC voltage. As described above, the voltage conversion circuit of the present invention can be applied to all circuits that require voltage conversion of a DC voltage and devices equipped with the circuits.

It is a circuit diagram which shows the structure of the conversion circuit 200 in 1st Embodiment to which this invention is applied. It is a circuit diagram which shows the structure of the conversion circuit 210 in 2nd Embodiment to which this invention is applied. 3 is a voltage waveform showing an operation state of the conversion circuit 210 shown in FIG. 2. It is a circuit diagram which shows the example of the conventional voltage conversion circuit.

Explanation of symbols

200, 210 Conversion circuit 11 DC power supply 13, 14 Output terminal Q1 Transistor C1 Capacitor D1, D2, D13, D14 Diode L11 Coil P1, P21, P22 Primary side coil S1, S11, S21 Secondary side coil T1, T2 Transformer

Claims (10)

A first transformer having a first coil on the primary side and a second coil on the secondary side magnetically coupled to the first coil;
A third transformer on the primary side connected in series to the first coil; a second transformer having a fourth coil on the primary side magnetically coupled to the third coil;
A sixth coil disposed on an output line connected to one end of the second coil;
Switching means connected to the third coil and the fourth coil, for switching on / off of a DC voltage supply to the first coil;
First short-circuiting means for causing both ends of the fourth coil to be short-circuited when voltage supply to the first coil is turned on by the switching means;
A second short-circuit means for short-circuiting the series circuit of the first coil and the third coil when the voltage supply to the first coil is off by the switching means;
A DC voltage is output based on an electromotive force generated in the second coil in a state where the voltage supply to the first coil is turned on by the switching means, and the voltage supply to the first coil is supplied by the switching means. Output a DC voltage based on an electromotive force generated in the sixth coil in a state where is turned off,
A voltage conversion circuit characterized by the above. One end of the first coil is connected to the second short-circuit means, the other end is connected to one end of the third coil,
One end of the fourth coil is connected to the other end of the third coil, the other end is connected to the first short-circuit means,
The switching means is connected between the other end of the third coil and the one end of the fourth coil so as to be connected in parallel with a series circuit of the fourth coil and the first short-circuit means. Connected to the point
The second short-circuit means includes the other end of the third coil and the one end of the fourth coil so as to be connected in parallel with a series circuit of the first coil and the third coil. The voltage conversion circuit according to claim 1, wherein the voltage conversion circuit is connected to a connection point.   3. The voltage conversion circuit according to claim 1, wherein the first short-circuit unit and the second short-circuit unit are rectifier elements. A first transformer having a first coil on the primary side and a second coil on the secondary side magnetically coupled to the first coil;
A primary third coil connected in series to the first coil; a primary fourth magnetic coil magnetically coupled to the third coil; and a second magnetically coupled to the third coil. A second transformer having a fifth coil on the secondary side;
A sixth coil disposed on an output line connected to one end of the second coil;
Switching means connected to the third coil and the fourth coil, for switching on / off of a DC voltage supply to the first coil;
First short-circuiting means for causing both ends of the fourth coil to be short-circuited when voltage supply to the first coil is turned on by the switching means;
A second short-circuit means for short-circuiting the series circuit of the first coil and the third coil when the voltage supply to the first coil is off by the switching means;
The second coil of the first transformer and the fifth coil of the second transformer are connected in series, and the voltage supply to the first coil is turned on by the switching means The DC voltage is output based on the electromotive force generated in the second coil, and the electromotive force generated in the sixth coil in a state where the voltage supply to the first coil is turned off by the switching means. Output DC voltage based on
A voltage conversion circuit characterized by the above. One end of the first coil is connected to the second short-circuit means, the other end is connected to one end of the third coil,
One end of the fourth coil is connected to the other end of the third coil, the other end is connected to the first short-circuit means,
The switching means is connected between the other end of the third coil and the one end of the fourth coil so as to be connected in parallel with a series circuit of the fourth coil and the first short-circuit means. Connected to the point
The second short-circuit means includes the other end of the third coil and the one end of the fourth coil so as to be connected in parallel with a series circuit of the first coil and the third coil. The voltage conversion circuit according to claim 4, wherein the voltage conversion circuit is connected to a connection point.   6. The voltage conversion circuit according to claim 4, wherein the first short-circuit means and the second short-circuit means are rectifier elements. A voltage conversion circuit comprising a first transformer, a second transformer, and switching means for switching on / off of a DC voltage supply to a first coil existing in the first transformer, wherein at least
A first current path comprising the first coil present in the first transformer, a third coil present in the second transformer, and the switching means;
A second current path comprising the first coil present in the first transformer, the third coil present in the second transformer, and a second short-circuit means;
A fourth current path comprising a second coil present in the first transformer magnetically coupled to the first coil present in the first transformer;
When the switching means is turned on and a current flows in the first current path, a current flows in the fourth current path based on a voltage generated in the second coil,
When the switching means is turned off and the current flowing in the first current path is interrupted, the second current path is closed, and the second short-circuit means provided in the second current path allows the Blocking back electromotive force generated in the first coil from being applied to the switching means;
A voltage conversion circuit characterized by the above. A voltage conversion circuit comprising a first transformer, a second transformer, and switching means for switching on / off of a DC voltage supply to a first coil existing in the first transformer, wherein at least
A first current path comprising the first coil present in the first transformer, a third coil present in the second transformer, and the switching means;
A third current path comprising: a fourth coil present in the second transformer magnetically coupled to the third coil present in the second transformer; the switching means; and a first short-circuit means. When,
A fourth current path comprising a second coil present in the first transformer magnetically coupled to the first coil present in the first transformer;
When the switching means is turned on and a current flows through the first current path, a current flows through the third current path and the fourth current path, and a magnetic flux is generated in the third and fourth coils. Substantially offset
A voltage conversion circuit characterized by the above. A fifth coil present in the second transformer magnetically coupled to the third coil present in the second transformer;
A series circuit in which the second coil and the fifth coil are connected in series;
When the switching means is turned off and the current flowing through the first current path is cut off, the voltage generated at both ends of the series circuit is generated at the voltage generated at the second coil and the fifth coil. Is substantially offset by the voltage
9. The voltage conversion circuit according to claim 7 or 8, wherein: A power supply apparatus comprising the voltage conversion circuit according to claim 1.

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