JP2011217485A - Step-up/down converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a step-up/down converter which can set a large step-down ratio while maintaining high efficiency and supplying a negative voltage to a load.SOLUTION: Only a switching element S1 is turned on for a first period, both of the switching element S1 and a switching element S2 are turned off for a second period, only the switching element S2 is turned on for a third period, and both of the switching elements S1, S2 are turned off in a fourth period. An excitation current is generated in a transformer T1 for the first period, and an excitation current is generated in the transformer T2 for the third period. Then, an excitation current generated in the transformer T1 is rectified by a rectifying element S3 during the second, third, and fourth periods, an excitation current generated in the transformer T2 is rectified by a rectifying element S4 during the first, second, and fourth periods, and an output voltage Vo obtained by inverting the polarity of an input voltage Vi is supplied to a load 20.

Description

  The present invention converts the input voltage into an output voltage whose polarity is inverted without insulation and supplies the output voltage to a load. The present invention relates to a buck-boost converter that realizes voltage characteristics.

  A step-up / step-down type non-insulated converter is often used when the polarity of a voltage is inverted as is well known, and is disclosed in, for example, Patent Document 1. FIG. 11 shows a conventional non-insulated buck-boost converter, which connects a series circuit of a switching element S made of a MOS type FET and an inductor L between both ends of the input power supply 10, and A series circuit of a diode D as a rectifying element and an output capacitor Co is connected between both ends, and the switching element S is switched by a pulse drive signal from a control circuit (not shown).

  Then, during the ON period of the switching element S, energy is stored in the inductor L by the current flowing from the input power supply 10 to the inductor L, and during the OFF period of the switching element S, the energy previously stored in the inductor L is stored. Is discharged to the output side through the diode D, and a positive induced electromotive voltage is generated at the other end of the grounded inductor L with reference to one end of the inductor L connected to the cathode of the diode D at this time. A negative output voltage Vo is supplied to a load 20 connected between both ends of the capacitor Co.

  Here, if the input voltage is Vin, the output voltage is Vo, and the time ratio of the switching element (the ratio of the ON period to the switching period) is D, the ratio of the input voltage Vin to the output voltage Vo is Show.

JP 2003-348834 A JP 2008-72834 A

  According to the above equation 1, the output voltage Vo can be stepped down to almost an infinitesimal multiple of the input voltage Vin as long as the operation can be performed with the duty ratio D of the switching element S close to zero. However, in practice, it is impossible to maintain high efficiency while setting the time ratio D to be almost zero due to the dead time of the control IC that controls the switching element S and the parasitic capacitance of the switching element S itself. The step-down ratio of the output voltage Vo with respect to the input voltage Vin can be changed only to some extent.

  Further, a non-insulated converter that can obtain a larger step-down ratio even when the time ratio D is almost zero is disclosed in Patent Document 2, for example, but this is not a circuit configuration that can reverse the polarity of the input voltage. , Can not generate negative voltage. Therefore, there has been a demand for a step-up / step-down converter that maintains a high efficiency, can take a large step-down ratio of the output voltage Vo to the input voltage Vin, and can supply a negative voltage to the load.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a buck-boost converter capable of taking a large step-down ratio and supplying a negative voltage to a load while maintaining high efficiency.

  The buck-boost converter in the present invention includes a first transformer formed by magnetically coupling a primary winding and a secondary winding, a second transformer formed by magnetically coupling the primary winding and the secondary winding, A voltage dividing capacitor; first and second switching elements; first and second rectifying elements; and an output capacitor; turning on only the first switching element during a first period; Both the first and second switching elements are turned off in a period, only the second switching element is turned on in a third period, and the first and second switching elements are turned on in a fourth period. By repeating the operation of turning off both, a series circuit including the voltage dividing capacitor, the primary winding of the first transformer, and the primary winding of the second transformer is connected to the input power source in the first period. Said Connected in series to the secondary winding of the transformer, and connected in series to the secondary winding of the second transformer and the output capacitor during the third period, to the first and second transformers. Two-phase excitation currents are respectively generated, and the excitation current generated in the first transformer is rectified by the first rectifier element in the second, third and fourth periods, and the first, second, In the fourth period, the excitation current generated in the second transformer is rectified by the second rectifier element, so that a DC voltage obtained by inverting the polarity of the input voltage from the input power source is supplied to the load. I have.

  The buck-boost converter according to the present invention includes first and second inductors, a voltage dividing capacitor, first and second switching elements, first and second rectifying elements, and an output capacitor. Only the first switching element is turned on in the first period, both the first and second switching elements are turned off in the second period, and only the second switching element is turned on in the third period. By turning on and repeating the operation of turning off both the first and second switching elements in the fourth period, the voltage dividing capacitor is connected to the input power source and the first inductor in the first period. In series connection, and in the third period, the second inductor and the output capacitor are connected in series, and the first and second inductors are two-phased. An exciting current is generated, and the exciting current generated in the first inductor is rectified by the first rectifier element in the second, third and fourth periods, and the first, second and fourth In this period, the exciting current generated in the second inductor is rectified by the second rectifying element, and thereby a DC voltage obtained by inverting the input voltage from the input power source is supplied to the load. .

  In the step-up / down converter, the first inductor is used as a primary winding, the first transformer having a secondary winding magnetically coupled to the primary winding, and the second inductor as a primary winding. A second transformer having a secondary winding magnetically coupled to the primary winding, and electrically insulating the input side and the output side by the first and second transformers. It is preferable to adopt a configuration in which the DC voltage of polarity inversion or non-inversion of polarity is supplied to the load.

  Further, in common with each of the above-described configurations, the first and second rectifying elements are configured by FETs that are turned on / off in synchronization with the first and second switching elements. preferable.

  According to the first aspect of the present invention, with respect to the existing non-insulated buck-boost converter, the input voltage can be reduced without taking a large turns ratio between the primary winding and the secondary winding of the first and second transformers. The voltage ratio of the output voltage can be increased, and the voltage conversion rate as a non-insulated buck-boost converter can be greatly improved. Further, the loss and surge of the first and second switching elements and the first and second rectifying elements can be reduced, and the voltage ratio can be increased while maintaining high efficiency. Further, since the current flowing through the first and second transformers is automatically balanced by the voltage generated across the voltage dividing capacitor, it is not necessary to provide a separate current balance circuit, and the circuit configuration can be simplified.

  According to the second aspect of the present invention, the voltage ratio of the output voltage to the input voltage can be increased with respect to the existing non-insulated buck-boost converter, and the voltage conversion rate as the non-insulated converter can be greatly improved. . Further, the loss and surge of the first and second switching elements and the first and second rectifying elements can be reduced, and the boost ratio can be increased while maintaining high efficiency. Further, since the current flowing through the first and second inductors is automatically balanced by the voltage generated across the voltage dividing capacitor, it is not necessary to provide a separate current balance circuit, and the circuit configuration can be simplified.

  According to the invention of claim 3, by replacing the first and second inductors with the first and second transformers respectively, a short circuit on the input side or the output side is not propagated to the output side or the input side. Therefore, it is possible to provide a buck-boost converter with higher reliability.

  According to the fourth aspect of the present invention, since the first and second rectifying elements are FETs, loss when a current flows through these rectifying elements can be reduced, and a more efficient buck-boost converter can be provided. .

It is a circuit diagram of the non-insulated buck-boost converter in one example of the present invention. It is a wave form diagram of each part of the circuit shown in FIG. It is an equivalent circuit diagram of the state 1 of the circuit shown in FIG. FIG. 2 is an equivalent circuit diagram of state 2 and state 4 of the circuit shown in FIG. 1. It is an equivalent circuit diagram of the state 3 of the circuit shown in FIG. It is a graph which shows the relationship between a duty ratio and the voltage ratio of input / output in a present Example and a prior art example. It is a circuit diagram of the non-insulated buck-boost converter which shows another modification. It is a circuit diagram of the non-insulated buck-boost converter which shows another modification. FIG. 9 is a circuit diagram of an insulating buck-boost converter showing an example in which the inductor in FIG. 8 is replaced with an insulating transformer. FIG. 10 is a circuit diagram of an insulated buck-boost converter that is a modification of FIG. 9. It is a circuit diagram of a conventionally known non-insulated buck-boost converter.

  Hereinafter, preferred circuit examples according to the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a circuit diagram of a non-insulated converter showing an embodiment of the present invention. In the figure, 1 is a two-phase tapped inductor buck-boost converter circuit (hereinafter simply referred to as a converter circuit) that reverses the polarity of the input voltage Vin to step down to the output voltage Vo, and 30 controls the operation of the converter circuit 1. It is a control circuit. The non-insulated converter here includes a converter circuit 1 and a control circuit 30.

  The converter circuit 1 steps down the DC input voltage Vin from the input power supply 10 and supplies a negative output voltage Vo to the load 20, and magnetically connects the input capacitor C, the primary winding np1, and the secondary winding ns1. A transformer T1 as a coupled first inductance element, a transformer T2 as a second inductance element in which a primary winding np2 and a secondary winding ns2 are magnetically coupled, a voltage dividing capacitor Cin, and a first The switching element S1, the second switching element S2, a first rectifying element S3 configured by a diode, a second rectifying element S4 also configured by a diode, and an output capacitor Co are included. The converter circuit 1 includes a first transformer T1, a first switching element S1, and a first rectifying element S3 as a first phase circuit, and a second transformer T2 and a second phase circuit as a second phase circuit. Switching element S2 and second rectifying element S4. A voltage dividing capacitor Cin is connected in series with the primary winding np1 of the transformer T1 and the primary winding np2 of the transformer T2, and the smoothing input capacitor C is connected to the input terminals of the first phase circuit and the second phase circuit. Are connected in common, and a smoothing output capacitor Co is commonly connected to the output terminals of the first phase circuit and the second phase circuit.

  The switching elements S1 and S2 are both composed of MOS type FETs, and the gates of these switching elements S1 and S2 are given a pulse drive signal preferably having the same time ratio D and shifted in phase by 180 ° from the control circuit 30. It is done. Further, the control circuit 30 monitors the output voltage Vout and adjusts the conduction width of the pulse drive signal and the time ratio D of the switching elements S1 and S2 according to the output voltage Vout. Accordingly, the switching elements S1 and S2 are switched with a phase difference, but when the duty ratio D of each switching element S1 and S2 is 0.5 (50%) or more, the input and output of the converter circuit 1 are short-circuited. Therefore, the duty ratio D needs to be limited to a range of 0 ≦ D <0.5. Therefore, in the converter circuit 1, only the switching element S1 is turned on (state 1) → both switching elements S1, S2 are turned off (state 2) → only the switching element S2 is turned on (state 3) → both switching elements S1, S2 are turned off ( The operation of state 4) is repeated.

  In addition, Lm1 shown in FIG. 1 is an exciting inductance of the transformer T1, and Lm2 is an exciting inductance of the transformer T2. The exciting inductance Lm1 of the transformer T1 is connected in parallel with the same polarity as the primary winding np1, and the exciting inductance Lm2 of the transformer T2 is connected in parallel with the same polarity as the primary winding np2. R1 and r2 are equivalent resistances corresponding to internal losses of the first-phase circuit and the second-phase circuit, respectively, and rc is an equivalent series resistance of the output capacitor Co. Furthermore, the voltage dividing capacitor Cin, the output capacitor Co, the equivalent series resistance rc, and the load 20 are each marked with a dot on one side, but this is based on the other side where no dot is marked. This means that a positive voltage is generated on the dot side.

  Next, connection between each element in the converter circuit 1 will be described. However, the excitation inductances Lm1 and Lm2 are included in the transformers T1 and T2, and the equivalent resistances r1, r2, and rc do not exist as actual elements.

  The input power supply 10 has a negative terminal grounded, and one end of the input capacitor C and the drain of the switching element S1 are connected to the positive terminal. The source of the switching element S1 is connected to the dot side terminal which is one end of the voltage dividing capacitor Cin and the drain of the switching element S2. A non-dot terminal which is the other end of the primary winding np2 of the transformer T2 is connected to a non-dot side terminal which is the other end of the voltage dividing capacitor Cin. A transformer T1 is connected to a dot terminal which is one end of the primary winding np2. The dot terminal which is one end of the primary winding np1 is connected, and the non-dot terminal which is the other end of the primary winding np1 is connected to the cathode of the rectifying element S3 and the dot which is one end of the secondary winding ns1 of the transformer T1. Each terminal is connected. The non-dot terminal which is the other end of the secondary winding ns1 of the transformer T1 is grounded together with the other end of the input capacitor C.

  On the other hand, the source of the switching element S2 is connected to the cathode of the rectifying element S4 and the dot terminal which is one end of the secondary winding ns2 of the transformer T1. The anode of the rectifying element S4 is connected to one end of the output capacitor Co together with the anode of the rectifying element S3, and the other end of the output capacitor Co is grounded together with the non-dot terminal which is the other end of the secondary winding ns2 of the transformer T2. Is done. The output voltage Vo is supplied from the converter circuit 1 to the load 20 by connecting the load 20 to both ends of the output capacitor Co.

  As a configuration of the converter circuit 1, for example, the voltage dividing capacitor Cin may be inserted and connected between the primary winding np1 of the transformer T1 and the primary winding np2 of the transformer T2, and divided from the primary windings np1 and np2. A series circuit with the pressure capacitor Cin may be formed. Further, as the rectifying elements S3 and S4, switching elements such as MOS type FETs that operate complementarily to the switching element S1 may be used. A specific example will be described in detail later.

  Next, the details of the operation in the above configuration will be described with reference to the waveform diagrams of the respective parts in FIG. 2 and the equivalent circuit diagrams of the respective states in FIGS. In FIG. 2, Vgs1 is the gate-source voltage of the switching element S1, Vgs2 is the gate-source voltage of the switching element S2, Vs1 is the drain voltage with reference to the source of the switching element S1, and Vs2 is the source of the switching element S2. Is the drain voltage of the switching element S1, Is2 is the drain current of the switching element S2, Vc1 is the voltage across the voltage dividing capacitor Cin, Ic1 is the current flowing through the voltage dividing capacitor Cin, and Ilm1 is the excitation inductance The exciting current of transformer T1 flowing through Lm1, Ilm2 is the exciting current of transformer T2 flowing through exciting inductance Lm2, Vs3 is the voltage applied to rectifying element S3, Vs4 is the voltage applied to rectifying element S4, and Is3 is the current flowing through rectifying element S3. , Is4 is the current flowing through the rectifier S4, Vo is the output A pressure, a dotted line indicates a 0V or 0A.

  When a pulse drive signal is supplied from the control circuit 30 to the gates of the switching elements S1 and S2, the switching elements S1 and S2 are repeatedly turned on and off while shifting their phases while having a period during which both are turned on. At this time, the switching elements S1 and S2 and the rectifying elements S3 and S4 transition from the state 1 to the state 4 in this order as shown in the following table.

図３に示すように、スイッチング素子Ｓ１のみオンする状態１の期間では、スイッチング素子Ｓ２はオフしており、分圧用コンデンサＣｉｎとトランスＴ１の一次巻線ｎｐ１とトランスＴ２の一次巻線ｎｐ２との直列回路が、入力電源１０とトランスＴ１の二次巻線ｎｓ１に連結され、これらの各素子による閉回路が形成される。このとき、整流素子Ｓ３は逆バイアスされるので、トランスＴ１は一次巻線ｎｐ１と二次巻線ｎｓ１を直列に接続した単なるインダクタとして機能し、入力電源１０からスイッチング素子Ｓ１，分圧用コンデンサＣｉｎ，トランスＴ２の一次巻線ｎｐ２，トランスＴ１の一次巻線ｎｐ１，トランスＴ１の二次巻線ｎｓ１を順に通して電流ｉ１が流れ、トランスＴ１の励磁電流は直線的に増加する。また、トランスＴ１に流れる電流がトランスＴ２の一次巻線ｎｐ２にも流れることにより、順バイアスされた整流素子Ｓ４を通して、トランスＴ２の二次巻線ｎｓ２から負荷２０の接地された他端側へ電流ｉ２が流れ込む。さらに、トランスＴ２に蓄えられる励磁エネルギーが二次巻線ｎｓ２から負荷２０側へ放出するので、トランスＴ２の励磁電流は直線的に減少する。

As shown in FIG. 3, in the period of the state 1 in which only the switching element S1 is turned on, the switching element S2 is off, and the voltage dividing capacitor Cin, the primary winding np1 of the transformer T1, and the primary winding np2 of the transformer T2 A series circuit is connected to the input power supply 10 and the secondary winding ns1 of the transformer T1, and a closed circuit is formed by these elements. At this time, since the rectifying element S3 is reverse-biased, the transformer T1 functions as a simple inductor in which the primary winding np1 and the secondary winding ns1 are connected in series, and the switching element S1, the voltage dividing capacitor Cin, The current i1 flows through the primary winding np2, the primary winding np1 of the transformer T2, and the secondary winding ns1 of the transformer T1, in order, and the exciting current of the transformer T1 increases linearly. Further, since the current flowing through the transformer T1 also flows through the primary winding np2 of the transformer T2, the current flows from the secondary winding ns2 of the transformer T2 to the grounded other end side of the load 20 through the forward-biased rectifying element S4. i2 flows in. Further, since the excitation energy stored in the transformer T2 is released from the secondary winding ns2 to the load 20 side, the excitation current of the transformer T2 decreases linearly.

  Subsequently, as shown in FIG. 4, in the period 2 in which both switching elements S1 and S2 are turned off, the rectifying elements S3 and S4 are both forward-biased, and the excitation energy of the transformer T1 is secondary through the rectifying element S3. While being released from the winding ns1, the excitation energy of the transformer T2 is released from the secondary winding ns2 through the rectifying element S4. Therefore, the current i1 flows in the order of the secondary winding ns1, output capacitor Co (and load 20) of the transformer T1, and the rectifying element S3, and the secondary winding ns2, output capacitor Co (and load 20) of the transformer T2 continues. The current i2 flows in the order of the rectifying element S4, and the exciting currents of the transformers T1 and T2 decrease linearly.

  Next, as shown in FIG. 5, when the period of the state 3 in which only the switching element S2 is turned on, the switching element S1 is turned off, and the voltage dividing capacitor Cin, the primary winding np1 of the transformer T1, and the primary winding of the transformer T2 A series circuit with np2 is connected to the output capacitor Co through the secondary winding ns2 of the transformer T2 and the rectifying element S3, and a closed circuit is formed by these elements. At this time, since the rectifying element S4 is reverse-biased, the transformer T2 functions as a simple inductor in which the primary winding np2 and the secondary winding ns2 are connected in series, and the voltage dividing capacitor Cin is connected to the switching element S2 and the transformer T2. The current i2 flows through the secondary winding ns2, the output capacitor Co (and the load 20), the rectifier S3, the primary winding np1 of the transformer T1, and the primary winding np2 of the transformer T2 in this order, and the exciting current of the transformer T2 is linear. To increase. Further, since the current flowing through the transformer T2 also flows through the primary winding np1 of the transformer T1, the secondary winding ns1 of the transformer T1 continues from the secondary winding ns1 of the transformer T1 to the grounded other end side through the forward-biased rectifying element S3. Current i1 flows. Furthermore, since the excitation energy stored in the transformer T1 is released from the secondary winding ns1 to the load 20 side, the excitation current of the transformer T1 decreases linearly.

  Then, as shown in FIG. 4 again, in the period 4 in which both the switching elements S1 and S2 are turned off, the rectifying elements S3 and S4 are both forward-biased, and the excitation energy of the transformer T1 is two through the rectifying element S3. While being released from the secondary winding ns1, the excitation energy of the transformer T2 is released from the secondary winding ns2 through the rectifying element S4. Therefore, the current i1 continues to flow in the order of the secondary winding ns1, the output capacitor Co (and the load 20) of the transformer T1, and the rectifier S3, and the secondary winding ns2, the output capacitor Co (and the load 20) of the transformer T2 The current i2 flows in the order of the rectifying element S4, and the exciting currents of the transformers T1 and T2 decrease linearly.

  When the differential equation is calculated in the above states 1 to 4 and the equivalent resistances r1, r2, rc are ignored as an ideal model and the static characteristics of the converter circuit 1 are calculated by the state averaging method, the excitation of the transformer T1 The current im1, the exciting current im2 of the transformer T2, the voltage Vc1 across the voltage dividing capacitor Cin, and the output voltage Vo are respectively expressed as follows.

なお、上記Ｒは負荷２０の抵抗値であり、またｎは、トランスＴ１，Ｔ２において、二次巻線ｎｓ１，ｎｓ２に対する一次巻線ｎｐ１，ｎｐ２の巻数比（ｎ＝ｎｐ１／ｎｓ１＝ｎｐ２／ｎｓ２）である。

Note that R is the resistance value of the load 20, and n is the turn ratio of the primary windings np1 and np2 to the secondary windings ns1 and ns2 (n = np1 / ns1 = np2 / ns2) in the transformers T1 and T2. ).

  In Equation 2, it can be seen that the voltage Vc1 across the voltage dividing capacitor Cin is (n + 1) / D times the output voltage Vo. Further, the ratio of the output voltage Vo to the input voltage Vin is determined by -D / (2 (n + 1) -D). For example, when the turn ratio n = 1, the ratio of the output voltage Vo to the input voltage Vin is -D / (4-D). FIG. 6 shows a graph comparing the relationship between the duty ratio D and the ratio of the output voltage Vo to the input voltage Vin in this case between the present embodiment and the conventional example. It can be seen that a larger step-down ratio can be obtained in this embodiment at the same duty ratio D.

  As described above, in this embodiment, the first transformer T1 formed by magnetically coupling the primary winding np1 and the secondary winding ns1, and the primary winding np2 and the secondary winding ns2 are magnetically coupled. A second transformer T2, a voltage dividing capacitor Cin, a first switching element S1 and a second switching element S2, a first rectifying element S3 and a second rectifying element S4, and an output capacitor Co; Only the switching element S1 is turned on in the first period, both the switching elements S1 and S2 are turned off in the second period, only the switching element S2 is turned on in the third period, and the switching element S1 is turned on in the fourth period. , S2 are repeatedly turned off, so that the voltage dividing capacitor Cin, the primary winding np1 of the transformer T1, and the primary winding np2 of the transformer T2 are connected in series. The path is connected in series to the input power supply 10 and the secondary winding ns1 of the transformer T1 in the first period, and is connected in series to the secondary winding ns2 of the transformer T2 and the output capacitor Co in the third period. Two-phase excitation currents are respectively generated in the transformers T1 and T2, and the excitation current generated in the transformer T1 is rectified by the rectifying element S3 in the second, third and fourth periods, and the first, second and second In the fourth period, the exciting current generated in the transformer T2 is rectified by the rectifying element S4, so that the DC voltage Vo obtained by inverting and stepping down the voltage of the input voltage Vin from the input power supply 10 is supplied to the load 20. It has a configuration.

  In this case, the voltage ratio of the output voltage Vo to the input voltage Vin is increased with respect to the existing non-insulated buck-boost converter without increasing the turns ratio of the primary winding np1 and the secondary winding ns1 of the transformer T1. Thus, the voltage conversion rate as a non-insulated buck-boost converter can be greatly improved. Further, the loss and surge of the switching elements S1 and S2 and the rectifying elements S3 and S4 can be reduced, and the voltage ratio can be increased while maintaining high efficiency. Furthermore, since the currents flowing through the transformers T1 and T2 are automatically balanced by the voltage generated across the voltage dividing capacitor Cin, it is not necessary to provide a separate current balance circuit, and the circuit configuration can be simplified.

  Next, various modifications related to the above embodiment will be described.

  A converter circuit 1 'shown in FIG. 7 is obtained by replacing the rectifying elements S3 and S4 shown in FIG. 1 with MOS type FETs. In this case, the rectifying elements S3 and S4 are connected so that the source of the FET corresponds to the anode of the diode and the drain of the FET corresponds to the cathode of the diode. The control circuit 30 supplies a pulse drive signal to the gate of the rectifying element S3 so that the rectifying element S3 performs a switching operation contrary to the switching element S1, and the rectifying element S4 performs a switching operation contrary to the switching element S2. Thus, the pulse drive signal is supplied to the gate of the rectifying element S4. Thereby, in the states 2, 3, and 4 in which the switching element S1 is turned off, the rectifying element S3 is turned on, and a current flows from the drain to the source of the rectifying element S3, and the switching element S2 is turned off. Since the rectifying element S4 is turned on and a current flows from the drain to the source of the rectifying element S4, the conduction loss of the rectifying elements S3 and S4 can be reduced, and the efficiency as the converter circuit 1 ′ can be further increased.

  That is, since the rectifying elements S3 and S4 here are FETs that are turned on and off in synchronization with the switching elements S1 and S2, loss when a current flows through these rectifying elements S3 and S4 can be reduced. A more efficient non-insulated converter can be provided.

  FIG. 8 shows another modification of the circuit shown in FIG. 1, in which the converter circuit 1 ″ removes both the primary winding np1 of the transformer T1 and the primary winding np2 of the transformer T2, and the remaining two The next windings ns1 and ns2 are an inductor L1 that is a first inductance element that is not magnetically coupled and an inductor L2 that is a second inductance element. Other configurations and operations are the same as those shown in FIG. The rectifying elements S3 and S4 may be MOS type FETs as shown in FIG.

  When only the switching element S1 is turned on in the state 1, the switching element S2 is turned off, so that the voltage dividing capacitor Cin is connected to the input power supply 10 and the inductor L1, and a closed circuit is formed by these elements. At this time, the rectifying element S3 is reverse-biased, a current flows in order from the input power supply 10 through the switching element S1, the voltage dividing capacitor Cin, and the inductor L1, and the exciting current flowing through the inductor L1 increases linearly. Further, when current flows from the inductor L2 to the other end of the load 20 that is grounded through the forward-biased rectifying element S4, the excitation energy stored in the inductor L2 is released to the load 20 side, so that the excitation of the inductor L2 is performed. The current decreases linearly.

  Subsequently, in the period 2 in which both the switching elements S1 and S2 are turned off, the rectifying elements S3 and S4 are both forward-biased, and the exciting energy of the inductor L1 is released through the rectifying element S3 and the rectifying element S4. Through this, the excitation energy of the inductor L2 is released. Therefore, a current flows in the order of the inductor L1, the output capacitor Co (and the load 20), and the rectifying element S3, and subsequently, a current flows in the order of the inductor L2, the output capacitor Co (and the load 20), and the rectifying element S4. , L2 excitation current decreases linearly.

  Next, when the period of the state 3 in which only the switching element S2 is turned on, the switching element S1 is turned off, the voltage dividing capacitor Cin is connected to the inductor L2 and the output capacitor Co, respectively, and a closed circuit by these elements is formed. It is formed. At this time, the rectifying element S4 is reverse-biased, a current flows through the voltage dividing capacitor Cin, the switching element S2, the inductor L2, the output capacitor Co (and the load 20), and the rectifying element S3 in this order, and the exciting current flowing through the inductor L2 is Increases linearly. Further, the current continues to flow from the inductor L1 to the grounded other end side of the load 20 through the forward-biased rectifying element S3, so that the excitation energy stored in the inductor L1 is released to the load 20 side. The excitation current decreases linearly.

  In the state 4 in which both switching elements S1 and S2 are turned on again, both the rectifying elements S3 and S4 are forward-biased, and the exciting energy of the inductor L1 is released through the rectifying element S3 and the rectifying element S4. Through this, the excitation energy of the inductor L2 is released. Therefore, the current continues to flow in the order of the inductor L1, the output capacitor Co (and the load 20), and the rectifying element S3, and the current flows in the order of the inductor L2, the output capacitor Co (and the load 20), and the rectifying element S4. , L2 excitation current decreases linearly.

  In the circuit shown in FIG. 8, in the transformers T1 and T2, the number of turns of the primary windings np1 and np2 is 0, that is, the turn ratio n of the primary windings np1 and np2 with respect to the secondary windings ns1 and ns2 is 0. Can think. Therefore, the ratio of the output voltage Vo to the input voltage Vin here is -D / (2-D), and a larger step-down ratio than the conventional one can be obtained with the same time ratio D. For example, when the duty ratio D is 0.2, the ratio of the input voltage Vin to the output voltage Vo is -4: 1 in the past, whereas in this example, it is -9: 1, and the step-down ratio is twice or more. Is obtained. Further, the voltage Vc1 between both ends of the voltage dividing capacitor Cin is 1 / D times the output voltage Vo.

As described above, in this example, the first inductor L1 and the second inductor L2, the voltage dividing capacitor Cin, the first switching element S1 and the second switching element S2, the first rectifying element S3 and the second 2 rectifying elements S4 and an output capacitor Co, only the switching element S1 is turned on in the first period, both the switching elements S1 and S2 are turned off in the second period, and the switching element in the third period By repeating the operation of turning on only S2 and turning off both of the switching elements S1 and S2 in the fourth period, the voltage dividing capacitor Cin is connected in series to the input power source 10 and the inductor L1 in the first period, and In the third period, the inductor L2 and the output capacitor Co are connected in series, and two-phase excitation current is applied to the inductors L1 and L2. Each generates Re,
The exciting current generated in the inductor L1 is rectified by the rectifying element S3 in the second, third, and fourth periods, and the exciting current generated in the inductor L2 is rectified in the rectifying element S4 in the first, second, and fourth periods. By rectifying, the polarity of the input voltage Vin from the input power supply 10 is inverted and the stepped-down DC voltage Vo is supplied to the load 20.

  Also in this case, it is possible to increase the step-up ratio of the output voltage Vo with respect to the input voltage Vin under the same condition of the time ratio D of the switching elements S1 and S2 as compared with the existing non-insulated buck-boost converter. The voltage conversion rate as an insulated buck-boost converter can be greatly improved. Further, the loss and surge of the switching elements S1 and S2 and the rectifying elements S3 and S4 can be reduced, and the boost ratio can be increased while maintaining high efficiency. Furthermore, since the currents flowing through the inductors L1 and L2 are automatically balanced by the voltage generated across the voltage dividing capacitor Cin, it is not necessary to provide a separate current balance circuit, and the circuit configuration can be simplified.

  FIG. 9 shows a further improvement of the modification of FIG. 8, wherein the inductor L1 is used as a primary winding np1 ′ of a transformer T1 ′, and a secondary winding ns1 ′ magnetically coupled to the primary winding np1 ′ is used. At the same time, the inductor L2 is used as the primary winding np2 ′ of the transformer T2 ′, and the secondary winding ns2 ′ magnetically coupled to the primary winding np2 ′ is provided, and the dot side terminal which is one end of the secondary winding ns1 ′ is provided. The cathode of the rectifying element S3 is connected, the cathode of the rectifying element S4 is connected to the dot side terminal which is one end of the secondary winding ns2 ', and the non-dot which is the other end of these secondary windings ns1' and ns2 ' By grounding all the side terminals, the input side and the output side of the converter circuit 1 ′ ″ are electrically insulated by transformers T1 ′ and T2 ′. Other configurations and operations are the same as those shown in FIG. 8, but the rectifying elements S3 and S4 may be MOS type FETs as shown in FIG.

  In state 1, when only the switching element S1 is turned on, the switching element S2 is turned off, so that the voltage dividing capacitor Cin is connected to the input power supply 10 and the transformer T1 ', and a closed circuit is formed by these elements. At this time, current flows from the input power source 10 through the switching element S1, the voltage dividing capacitor Cin, and the primary winding np1 ′ of the transformer T1 ′ in order, and the exciting current flowing through the transformer T1 ′ increases linearly. Since a positive voltage is generated on the dot side of the “secondary winding ns1”, the rectifying element S3 is reverse-biased, and excitation energy is stored in the transformer T1 ′. On the other hand, the secondary winding ns2 ′ of the transformer T2 ′ generates a positive voltage on the non-dot side, so that the load 20 is grounded from the secondary winding ns2 ′ of the transformer T2 ′ through the forward-biased rectifier S4. The current flows into the other end side and the excitation energy stored in the transformer T2 ′ is released to the load 20 side, so the excitation current of the transformer T2 ′ decreases linearly.

  Subsequently, in the period 2 in which both the switching elements S1 and S2 are turned off, the rectifying elements S3 and S4 are both forward-biased, and the excitation energy of the transformer T1 ′ is released through the rectifying element S3. Excitation energy of the transformer T2 ′ is released through S4. Accordingly, a current flows in the order of the transformer T1 ′, the output capacitor Co (and the load 20), and the rectifying element S3. Subsequently, a current flows in the order of the transformer T2 ′, the output capacitor Co (and the load 20), and the rectifying element S4. The exciting current of the transformer T1′T2 ′ decreases linearly.

  Next, in the period of the state 3 in which only the switching element S2 is turned on, the switching element S1 is turned off, and the voltage dividing capacitor Cin is connected to the output capacitor Co through the transformer T2 ′ and the transformer T1 ′. A closed circuit is formed by each element. At this time, from the voltage dividing capacitor Cin to the switching element S2, the primary winding np2 'of the transformer T2', the output capacitor Co (and the load 20), the rectifying element S3, the secondary winding ns1 'of the transformer T1', and the transformer T1 ' The current flows through the primary winding np1 ′ in order, and the excitation current flowing through the transformer T2 ′ increases linearly, but a positive voltage is generated on the dot side of the secondary winding ns2 ′ of the transformer T2 ′. The rectifying element S4 is reverse-biased, and excitation energy is stored in the transformer T2 ′. Further, since the current i1 continues to flow from the transformer T1 ′ to the grounded other end side of the load 20 through the forward-biased rectifying element S3, the excitation energy stored in the transformer T1 ′ is released to the load 20 side. The exciting current of the transformer T1 ′ decreases linearly.

  In the state 4 in which both the switching elements S1 and S2 are turned on again, both the rectifying elements S3 and S4 are forward-biased, and the excitation energy of the transformer T1 ′ is released through the rectifying element S3. Excitation energy of the transformer T2 ′ is released through S4. Accordingly, a current flows in the order of the transformer T1 ′, the output capacitor Co (and the load 20), and the rectifying element S3. Subsequently, a current flows in the order of the transformer T2 ′, the output capacitor Co (and the load 20), and the rectifying element S4. The exciting current of the transformer T1′T2 ′ decreases linearly.

  As described above, in this example, the inductor L1 is used as the primary winding np1 ′, and the first transformer T1 ′ including the secondary winding ns1 ′ magnetically coupled to the primary winding np1 ′ and the second winding And the second transformer T2 ′ having the secondary winding ns2 ′ magnetically coupled to the primary winding np2 ′, and these insulating transformers T1 ′ and T2 ′. The input side and the output side of the converter circuit 1 ′ ″ are electrically insulated.

  In this way, by replacing the inductors L1 and L2 with the isolation transformers T1 ′ and T2 ′, the converter circuit 1 is further improved in reliability by preventing a short circuit on the input side or the output side from spreading to the output side or the input side. It becomes possible to provide '' '.

  In addition, as a modification of FIG. 9, as shown in FIG. 10, the polarities of the secondary winding ns1 ′ of the transformer T1 ′ and the secondary winding ns2 ′ of the transformer T2 ′ are both reversed, and the rectifying element By connecting the anodes and cathodes of S3 and S4 in opposite directions, the converter circuit 1 ″ ″ can be operated as a so-called isolated flyback converter.

  In this case, during the period of the state 1 in which the switching element S1 is turned on, the excitation energy is stored in the transformer T1 ′ by the current flowing into the primary winding np1 ′ of the transformer T1 ′, and the switching element S1 is turned off in the states 2, 3, Excitation energy stored in the transformer T1 ′ during the period 4 is sent from the rectifying element S3 to the output capacitor Co (and the load 20), and the primary winding of the transformer T2 ′ during the period 3 in which the switching element S2 is turned on. The excitation energy is stored in the transformer T2 ′ by the current flowing into the line np2 ′, and the excitation energy stored in the transformer T2 ′ is output from the rectifying element S4 during the periods 1, 2, and 4 in which the switching element S2 is turned off. By sending it to the capacitor Co (and the load 20), the load 20 has a positive polarity that does not reverse the polarity. It is possible to supply the power voltage Vo. Therefore, it is possible to provide a converter circuit 1 ″ ″ ″ with higher reliability without causing a short circuit on the input side or the output side to propagate to the output side or the input side.

  The present invention is not limited to the present embodiment, and various modifications can be made within the scope of the gist of the present invention. For example, the circuit examples shown in FIG. 1 and FIG. 7 show a series circuit in which the voltage dividing capacitor Cin, the primary winding np2, and the secondary winding np1 are connected in this order, but for example, the primary winding np2, the voltage dividing capacitor Cin. , Secondary winding np1 may be connected in this order. Further, as the switching elements S1 and S2 and the rectifying elements S3 and S4, various semiconductor elements with control terminals (for example, power transistors) other than FETs can be used. Further, a P-channel MOS FET may be used instead of the N-channel MOS FET in each of the above examples.

10 Input power supply 20 Load T1 First transformer T2 Second transformer np1 Primary winding np2 (Second transformer) Primary winding ns1 (First transformer) Secondary winding ns2 Secondary winding (of the second transformer) T1 'first transformer T2' second transformer np1 'primary winding (of the first transformer) np2' primary winding (of the second transformer) ns1 '( Secondary winding ns2 '(of the second transformer) Secondary winding (of the second transformer) S1 First switching element S2 Second switching element S3 First rectifying element S4 Second rectifying element Cin For voltage division Capacitor Co Output capacitor L1 First inductor L2 Second inductor

Claims (4)

A first transformer formed by magnetically coupling the primary winding and the secondary winding; a second transformer formed by magnetically coupling the primary winding and the secondary winding; a voltage dividing capacitor; A second switching element, first and second rectifying elements, and an output capacitor;
Only the first switching element is turned on in the first period, both the first and second switching elements are turned off in the second period, and only the second switching element is turned on in the third period. By repeating the operation of turning on and turning off both the first and second switching elements in the fourth period,
A series circuit composed of the voltage dividing capacitor, the primary winding of the first transformer, and the primary winding of the second transformer is connected to an input power source and a secondary winding of the first transformer in the first period. And in series with the secondary winding of the second transformer and the output capacitor during the third period, two-phase excitation currents are respectively supplied to the first and second transformers. Generate
The exciting current generated in the first transformer is rectified by the first rectifier element in the second, third, and fourth periods, and the second current is rectified in the first, second, and fourth periods. A step-up / step-down converter characterized in that a DC voltage obtained by inverting the polarity of an input voltage from the input power source is supplied to a load by rectifying the exciting current generated in the transformer of the first rectifier by the second rectifying element. A first and second inductor, a voltage dividing capacitor, first and second switching elements, first and second rectifying elements, and an output capacitor;
Only the first switching element is turned on in the first period, both the first and second switching elements are turned off in the second period, and only the second switching element is turned on in the third period. By repeating the operation of turning on and turning off both the first and second switching elements in the fourth period,
The voltage dividing capacitor is connected in series to the input power source and the first inductor in the first period, and is connected in series to the second inductor and the output capacitor in the third period. Two-phase exciting currents are respectively generated in the first and second inductors;
The exciting current generated in the first inductor is rectified by the first rectifier element in the second, third, and fourth periods, and the second current is rectified in the first, second, and fourth periods. A step-up / step-down converter characterized in that a DC voltage obtained by reversing the polarity of the input voltage from the input power source is supplied to a load by rectifying the exciting current generated in the inductor of the second rectifier by the second rectifying element. A first transformer having a secondary winding magnetically coupled to the primary winding, wherein the first inductor is a primary winding;
A second transformer having a secondary winding magnetically coupled to the primary winding, the second inductor serving as a primary winding;
The first and second transformers are configured to electrically insulate between the input side and the output side and supply the DC voltage of polarity inversion or non-inversion to the load. The step-up / step-down converter according to claim 2.   The first and second rectifying elements are FETs that are turned on / off in synchronization with the first and second switching elements, respectively. The buck-boost converter described in 1.

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