JP4176090B2 - Voltage conversion circuit and power supply device - Google Patents

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-end flyback system” among the switching power supply circuits described in Non-Patent Document 1. The switching power supply circuit 10 is a primary side of the transformer T from the DC power supply 1. The DC voltage supply to the coil P is turned on / off by a transistor Q such as a 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 side coil P, a diode is generated by an induced electromotive force generated in the secondary side coil S of the transformer T. Since the anode side of D is negative, no current flows. When the transistor Q is switched from on to off, the anode side of the diode D becomes positive due to the back electromotive force (flyback voltage) generated in the primary side coil P, so that a DC voltage is applied to the output terminals 3 and 4 through the diode D. Is output.

  The conventional voltage conversion circuit shown in FIG. 4 uses a back electromotive force (flyback voltage) generated in the primary coil when the transistor Q is switched from on to off. However, the back electromotive force generated at this time shows a very large voltage value in a transient manner, and the sum of this voltage and the supplied DC voltage is temporarily added to the transistor Q, so that the withstand voltage is higher than this voltage. It was necessary to use a sufficiently large transistor. 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; Switching means connected to the third coil and the fourth coil for switching on / off of the DC voltage supply to the first coil, and when the voltage supply to the first coil is turned on by the switching means A first short-circuit means for short-circuiting both ends of the fourth coil; and when the voltage supply to the first coil by the switching means is off, the first coil and the third coil And a second short-circuit means for short-circuiting the series circuit of the first and second direct currents based on the electromotive force generated in the second coil in a state where the voltage supply to the first coil is turned off by the switching means. A voltage is output.

  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, One end 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 is in parallel with the series circuit of the fourth coil and the first short-circuit means. Connected to a connection point between the other end of the third coil and the one end of the fourth coil so as to be connected, and the second short-circuit means includes the first coil and the third coil 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 a coil.

  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 switching means connected to the third coil and the fourth coil, for switching on / off of a DC voltage supply to the first coil, and the switching means When the voltage supply to the first coil is on, the first short-circuit means for short-circuiting both ends of the fourth coil and the voltage supply to the first coil by the switching means are off The first The second coil of the first transformer and the fifth coil of the second transformer, the second coil of the first transformer and the second coil of the third transformer. DC connected based on the electromotive force generated in the second coil and the electromotive force generated in the fifth coil in the state where the voltage supply to the first coil is turned off by the switching means. A voltage is output.

  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.

  In the voltage conversion circuit of the above invention, the output voltage can be adjusted by the ratio of the number of turns of the third coil and the number of turns of the fifth coil.

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; 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. , A fourth current comprising: a second coil present in the first transformer magnetically coupled to the first coil present in the first transformer; and a rectifying element connected to the second coil. And when the switching means is turned on and the current flowing in the first current path flows from the one end to the other end of the third coil in the second transformer, The generated magnetic flux and the magnetic flux generated in the fourth coil when the current flowing in the third current path flows from the other end to the other end of the fourth coil in the second transformer are mutually When the other end of the third coil and one end of the fourth coil are connected so as to be in the opposite direction, and the switching means is turned off and the current flowing through the first current path is interrupted, The voltage generated in the first coil Therefore, when a current is passed through the fourth current path and the switching means is turned on and a current flows through the first current path, a current is passed through the third current path and the fourth current path is interrupted. The magnetic flux generated in the third and fourth coils is substantially canceled 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. It can be the sum of the voltage generated in the second coil and the voltage generated in the fifth coil.

  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. All of the DC voltage supplied from the DC power source is applied to the first coil of the first transformer, and magnetic energy is accumulated only in the magnetic core of the first transformer. As will be described later, since there is almost no magnetic flux 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 Since almost no current flows through this closed circuit, the increase in counter electromotive force generated in the first coil existing in the first transformer is not hindered, and the first current existing in the first transformer A voltage can be efficiently generated in the second coil magnetically coupled to the coil. That is, it emits the energy stored in the first transformer magnetic core efficiently 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. All of the DC voltage supplied from the DC power source is applied to the first coil of the first transformer, and magnetic energy is accumulated only in the magnetic core of the first transformer.
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 Since almost no current flows through this closed circuit, the increase in counter electromotive force generated in the first coil existing in the first transformer is not hindered, and the first current existing in the first transformer A voltage can be efficiently generated in the second coil magnetically coupled to the coil. That is, the energy stored in the magnetic core of the first transformer can be efficiently 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, the voltage supply to the first transformer is turned off by the switching means. The sum of the electromotive force generated in step 5 and the electromotive force generated in the fifth coil can be output as a DC voltage. That is, since the electromotive force induced in the fifth coil can be effectively used when the voltage supply to the first transformer is off, the number of turns of the second coil can be set to be small, There is no need to increase the number of turns. For this reason, since the induced electromotive force generated in the second coil can be reduced when the voltage supply to the first transformer is turned on by the switching means, the withstand voltage of the rectifying element connected to the second coil is small. Just do it.

  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 100 according to a first embodiment to which the present invention is applied.

  A conversion circuit 100 illustrated 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 100 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 source 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 100 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.

Further, one end (winding end side) of the secondary coil S1 of the transformer T1 is connected to the anode side of the diode D3, and the cathode side of the diode D3 is connected to one output terminal 13. Further, the other end (winding start side) of the coil S <b> 1 is connected to the other output terminal 14.
Therefore, on the secondary side of the transformer T1, the current flows only in the direction from the diode D3 toward the output terminal 13.

  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 100 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 100 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 between both ends of 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, while 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 also means that there is no energy loss due to the addition of the transformer T2.
As described above, since magnetic flux is not accumulated in the magnetic circuit of the transformer T2, the transformer T2 is naturally not in a magnetic saturation state (the state where there is almost no magnetic flux passing through the coils P21 and P22). Therefore, the coil P21 of the transformer T2 (the same applies to the coil P22) has a sufficiently large reactance.

  Since magnetic energy is not accumulated in the magnetic core of the transformer T2 as described above, 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 only to the magnetic core of the transformer T1. Magnetic energy will be stored.

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 D3 side of the coil S1. The terminal 13 side is positive. Therefore, since a reverse voltage with the cathode side being positive is applied to the diode D3, no current flows through the diode D3.
That is, when the transistor Q1 is on, a DC voltage based on the induced electromotive force generated in the coil S1 is not output from the output terminals 13 and 14.

  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 with a high withstand voltage. In contrast, in the present invention, the transistor P1 is connected in series to the coil P1, connected to the drain of the transistor Q1, and the diode D2 is connected in parallel to the series circuit of the coil P1 and the coil P21. The rise in drain potential is suppressed.

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 addition, even though the closed circuit is configured as the coil P1, the coil P21, the D2, and the coil P1, almost no current flows through the closed circuit due to the large reactance of the coil P21 of the transformer T2. Thus, it is possible to efficiently generate a voltage in the coil S1 of the transformer T1 without being hindered from increasing the back electromotive force generated in the coil P1. That is, the energy accumulated in the magnetic core of the transformer T1 can be efficiently released to the coil S1.

  In the above state, in the coil S1, the energy accumulated in the magnetic core of the transformer T1 is transmitted to the coil S1 and becomes the counter electromotive force of the coil S1, and this counter electromotive force is positive on the diode D3 side of the coil S1, and the output terminal. The 14 side is negative. Therefore, since a forward voltage with the anode side being positive is applied to the diode D3, a current from the diode D3 toward the output terminal 13 flows. Therefore, a DC voltage based on the counter electromotive force generated in the coil S1 is smoothed and output from the output terminals 13 and 14 by the capacitor C1.

  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 with the operation in the case where the transformer T2 (coil P21, coil P22) and the diode D1 are not provided in the conversion circuit 100.

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 if the coil P21 is not provided, the potential on the drain side of the transistor Q1 is clamped to the positive potential of the DC power supply. Here, when both ends of the coil P1 are short-circuited without the coil P21, the magnetic energy stored in the magnetic core of the transformer T1 is stored as it is without being consumed. Therefore, even if a counter electromotive force is generated in the coil P1 during flyback, the current flows through the diode D2, so that both ends of the coil P1 are not opened, and the voltage across the coil P1 is sufficiently increased. Can not. Due to this action, the magnetic energy accumulated in the magnetic core of the transformer T1 is not released to the coil S1, but is stored in the magnetic core of the transformer T1 by the closed circuit current of the coil P1 and the diode D2.

  Further, due to the closed circuit current of the coil P1 and the diode D2, the magnetic core of the transformer T1 is in a magnetic saturation state, which means that the reactance of the coil P1 of the transformer T1 is substantially 0 (zero) (only the DC resistance of the coil) Is equivalent to

On the other hand, in the converter circuit 100 according to the present embodiment, during the flyback, since a large reactance of the coil P21 of the transformer T2 causes almost no current to flow through the coil P1, magnetic energy is accumulated in the magnetic core of the transformer T1. The energy is released to the coil S1 without any failure. The reason for this is that when the transistor Q1 was turned on before that, both ends of the coil P22 magnetically coupled to the coil P21 were short-circuited through the diode D1 (and the transistor Q1 in the on state). This is because the magnetic flux generated by the current flowing through and the magnetic flux generated by the closed circuit current flowing through the coil P22 cancel each other, and the magnetic flux is not accumulated in the magnetic circuit of the transformer T2.

  As described above, according to the conversion circuit 100, (1) when the transistor Q1 is switched from on to off (during flyback operation), it is possible to prevent a high voltage from being applied to the drain of the transistor Q1. (2) Even if the transformer T2 is added, no magnetic energy is accumulated in the magnetic core of the transformer T2, so that all the energy supplied from the DC power supply can be transmitted to the transformer T1, and the energy conversion efficiency is impaired. (3) In the transformer T1, there is an advantage that the magnetic energy accumulated in the magnetic core can be efficiently discharged to the coil S1.

  Of course, according to the conversion circuit 100, 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 100, 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 110 according to the second embodiment to which the present invention is applied. The conversion circuit 110 shown in FIG. 2 is obtained by adding a coil S21 to the secondary side of the transformer T2 in the conversion circuit 100 according to the first embodiment. Accordingly, the circuit elements and the like arranged in the same manner as the conversion circuit 100 of FIG. 1 are denoted by the same reference numerals except for the secondary coil of the transformer T1, and description thereof is omitted.

The conversion circuit 110 shown in FIG. 2 includes the secondary coil S21 of the transformer T2 in the conversion circuit 100 shown in FIG. 1, and one end (winding start 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 D3.

  The conversion circuit 110 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 110 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, a current flows from the coil P22 to the coil P22 through the transistor Q1 and the diode D1, and the current across the coil P22. 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 magnetic energy is accumulated in the magnetic core of 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 negative on the diode D3 side of the coil S11 and positive on the output terminal 13 side. Current does not flow. That is, when the transistor Q1 is on, a DC voltage based on the induced electromotive force generated in the coil S1 is not 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 100 according to the first embodiment. In the conversion circuit 110 according to this embodiment, the transformer T2 includes the 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 off. It is characterized in that the electromotive force induced in the coil S21 can be effectively used.

  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 is generated. 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 direction of the counter electromotive force generated in the coil S11 by the counter electromotive force (flyback voltage) generated in the coil P1 of the transformer T1 and the direction of the induced electromotive force generated in the coil S21 of the transformer T2 are both in the coil S11. The direction of the anode of the diode D3 to be connected is positive and the output terminal 14 side is negative. Therefore, since a forward voltage with the anode side being positive is applied to the diode D3, a current from the diode D3 toward the output terminal 13 flows. Accordingly, a DC voltage based on both the back electromotive force generated in the coil S11 and the induced electromotive force generated in the coil S21 is smoothed and output from the output terminals 13 and 14 by the capacitor C1.

  That is, the conversion circuit 110, in the flyback operation, in addition to the voltage (VS11) generated in the secondary coil S11 based on the counter electromotive force generated in the primary coil P1 of the transformer T1, The voltage (VS21) generated in the secondary coil S21 is effectively used as the output voltage. That is, the sum (V = VS11 + VS21) of the voltage generated in the coil S11 and the voltage generated in the coil S21 is obtained as the output voltage.

  Note that, according to conversion circuit 110 according to the present embodiment, the DC voltage output when transistor Q1 is off is the second voltage of transformer T1 based on the back electromotive force generated in coil P1 on the primary side of transformer T1. Since the voltage based on the induced electromotive force generated in the coil S21 is added to the voltage generated in the secondary coil S11, the conversion circuit 100 according to the first embodiment includes the primary coil of the transformer T1. Compared with the case where only the voltage generated in the secondary coil S1 of the transformer T1 is output based on the counter electromotive force generated in P1, the number of turns of the coil S11 can be set smaller, and the number of turns of the coil S21 is also increased. Obviously there is no need to do much. This means that the induced electromotive force generated in the coil S11 when the transistor Q1 is on can be reduced in comparison with the conversion circuit 100 according to the first embodiment, in other words, the diode D3 when the transistor Q1 is on. This means that the reverse voltage applied to can be reduced. Therefore, according to the conversion circuit 110, the further effect that a diode with a lower withstand voltage can be used as the diode D3 is acquired.

  In addition, according to the conversion circuit 110, by adjusting the number of turns of the coil S11 of the transformer T1 and the ratio of the number of turns of the primary side coil P21 of the transformer T2 and the number of turns of the secondary side coil S21, respectively, Of course, an output voltage can be obtained.

  Further, in the conversion circuit 110, similarly to the conversion circuit 100 according to the first embodiment, when a magnetic core that has been permanently magnetized in advance is used as the magnetic core of the transformer T2, the magnetic flux that passes through the magnetic core of the transformer T2 cancels out. It is possible to solve problems that may accumulate without being stored.

FIG. 3 is a voltage waveform showing the operation of the conversion circuit 110 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 CH5) when the conversion circuit 110 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 CH4 is The voltage value at one end (winding start side) of the coil S21 and the channel CH5 indicate the voltage value at one end (winding end side) of the coil S11.

  In FIG. 3, the transistor Q1 (FIG. 2) is switched from OFF to ON at time Z1, and the transistor Q1 is switched from ON to OFF at time Z2. Time Z3 is a time point when the flyback voltage in the coil P1 drops to a predetermined level.

When the transistor Q1 of the conversion circuit 110 (FIG. 2) is switched on at time Z1 in FIG. 3, the DC power supply 11 side of the coil P1 is positive and the coil P21 side is 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 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 is 0.6 volts. (Residual voltage of the 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 induced electromotive force generated in the coil S11, a negative voltage corresponding to the turn ratio of the coil P1 and the coil S11 is applied to the anode side of the diode D3 (channel CH5). For this reason, the diode D3 is reverse-biased and no current flows. On the other hand, the potential on the winding start side of the coil S21 is kept near 0 volts (channel CH4). This is because a current flows through a closed circuit composed of the coil P22, the transistor Q1, and the diode D1, the voltage across the coil P22 is substantially 0 (zero) volts (channel CH1), and the coil P21 magnetically coupled to the coil P22. This is because the voltage between both ends of the coil is substantially 0 (zero) volts, and no induced electromotive force is generated in the coil S21.

Next, when the transistor Q1 is switched from on to off at time Z2 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.
Due to this flyback voltage, an electromotive force (VS11) is generated in the coil S11 with the winding start side (black circle side) being negative (the winding end side being positive). 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 to the anode side of the diode D3 (channel CH5). As a result, the diode D3 is forward-biased, and a current flows in a direction from the diode D3 toward the output terminal 13.

  Here, focusing on the voltage (channel CH5) applied to the diode D3, the reverse voltage applied to the anode side of the diode D3 when the voltage supply to the coil P1 is on (time Z1 to time Z2) Although it was a negative voltage corresponding to the turn ratio between P1 and coil S11, the output voltage is obtained by adding the voltage generated in coil S21 to the voltage generated in coil S11 during the flyback operation (V = VS11 + VS21). Therefore, the number of turns of the coil S11 can be reduced as compared with the coil S1 according to the first embodiment. As a result, the mutual induction voltage generated in the coil S11 when the voltage supply to the coil P1 is on. It is because can be made small. This means that the reverse voltage applied to the diode D3 is lowered when the voltage supply to the coil P1 is on.

  Thereafter, the flyback voltage in the coil P1 decreases with time and almost disappears at time Z3 (channel CH3). The voltage generated in the coil S11 and the mutual induction voltage generated in the coil S21 also decrease with the decrease of the flyback voltage, and disappear with the disappearance of the flyback voltage (channels CH4 and CH5).

  As described above, in the conversion circuit 110, (1) when the voltage supply to the coil P1 is switched from on to off (time Z2), regardless of the generation of a large flyback voltage in the coil P1, the transistor Q1 (2) Compared to the case where only the voltage based on the counter electromotive force generated in the secondary coil S1 of the transformer T1 is output as shown in FIG. Since the number of turns of the coil S11 can be set small, it is confirmed from the voltage waveform of FIG. 3 that the reverse voltage applied to the diode D3 is small when the voltage supply to the coil P1 is on (time Z1 to time Z2). it can.

In the first and second embodiments, a specific form of the DC power supply 11 in the conversion circuits 100 and 110 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 100 and 110 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 mount the diodes arranged in the conversion circuits 100 and 110 with the polarities 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 100 and 110 is not particularly limited, and it is of course possible to replace some or all of the conversion circuits 100 and 110 with equivalent circuits. For example, the diodes included in the conversion circuits 100 and 110 are replaced with circuits having a rectifying function, and / or the transistors included in the conversion circuits 100 and 110 have a switching function that can be turned on / off 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.

1 is a circuit diagram showing a configuration of a conversion circuit 100 according to a first embodiment to which the present invention is applied. It is a circuit diagram which shows the structure of the conversion circuit 110 in 2nd Embodiment to which this invention is applied. 3 is a voltage waveform showing an operation state of the conversion circuit 110 shown in FIG. It is a circuit diagram which shows the example of the conventional voltage conversion circuit.

Explanation of symbols

100, 110 Conversion circuit 11 DC power supply 13, 14 Output terminal Q1 Transistor C1 Capacitor D1, D2, D3, D4 Diode P1, P21, P22 Primary side coil S1, S11, S21 Secondary side coil T1, T2 Transformer

Claims (8)

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;
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;
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. Connected to the connection point of
Outputting a DC voltage based on an electromotive force generated in the second coil in a state where the voltage supply to the first coil is turned off by the switching means;
A voltage conversion circuit characterized by the above. Voltage conversion circuit according to claim 1, wherein said first shorting means and said second short-circuit means is a rectifying element. 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;
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;
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. And the second coil of the first transformer and the fifth coil of the second transformer are connected in series, and are connected to the first coil by the switching means. Outputting a DC voltage based on an electromotive force generated in the second coil and an electromotive force generated in the fifth coil in a state where the voltage supply is turned off;
A voltage conversion circuit characterized by the above. Voltage conversion circuit according to claim 3, wherein said first shorting means and said second short-circuit means is a rectifying element. 5. The voltage conversion circuit according to claim 3 , wherein the output voltage can be adjusted by a ratio between the number of turns of the third coil and the number of turns of the fifth coil. 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 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 comprising: a second coil present in the first transformer magnetically coupled to the first coil present in the first transformer; and a rectifying element connected to the second coil. With roads,
Magnetic flux generated in the third coil when the switching means is turned on and current flowing in the first current path flows from one end to the other end of the third coil existing in the second transformer; Magnetic fluxes generated in the fourth coil when the current flowing in the third current path flows from the other end to the one end of the fourth coil existing in the second transformer are opposite to each other. , The other end of the third coil and one end of the fourth coil are connected,
When the switching means is turned off and the current flowing through the first current path is interrupted, a current is passed through the fourth current path based on the voltage generated in the first coil,
When the switching means is turned on and a current flows through the first current path, a current is passed through the third current path and the fourth current path is shut off, and the third and fourth coils are connected. Substantially canceling the generated magnetic flux,
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. The sum of the voltage and
The voltage conversion circuit according to claim 6 . A power supply apparatus comprising the voltage conversion circuit according to claim 1 .

Images