JPS6314588B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a switching power supply device in which input and output are isolated by a transformer in terms of direct current, and in particular, the present invention relates to a switching power supply device that uses a transformer to provide direct current isolation between input and output. This provides a DC-DC converter that can be actively used as an element.

This type of conventional switching power supply device includes the ones shown in Figures 1 and 2, respectively, which control the output voltage relative to the input voltage by controlling the switching of a semiconductor switch element while providing direct current isolation between the input and output. It is possible to step up and step down the voltage and supply it to the load.

For the DC-DC converter shown in Figure 1,
During the ON period of the transistor 2 used as a semiconductor switch element, energy is stored in the excitation inductance of the transformer having the primary winding N ₁ and the secondary winding N ₂ by the output from the DC power supply 1, and during the OFF period of the transistor 2. The stored energy is transferred to the secondary winding N ₂ of the transformer 3 and the rectifier 4.
and is supplied to the load 6 via the filter capacitor 5. In such a converter, by controlling the on-off ratio, that is, the duty cycle, of the transistor 2, the output voltage is stepped up or down relative to the input voltage, and the output voltage is adjusted and stabilized.

Furthermore, the one shown in FIG. 2 can operate in either a boost operation mode or a buck operation mode. For example, in the step-up operation mode, energy is stored in the choke coil 8 in the section where both transistors 2A and 2D are on, and the next operation is performed. When the transistor 2D is turned off and the transistors 2A and 2C are turned on, the current flows from the chiyoke coil 8 and the DC power supply ₁ to the primary winding N1, secondary winding _N2 , and rectifier 4 of the transformer 3.
The energy stored in the chiyoke coil 8 and the power of the DC power source 1 are supplied to the load 6 via A.
Next, when both transistors 2B and 2C are turned on, the electric power from the DC power supply 1 causes
Energy is stored in the transformer 3, when the transistor 2C is turned off and both the transistors 2B and 2D are on.
It is supplied to the load 6 via the rectifier 4B. Repeat this operation below.

In the case of the step-down operation mode, in the section where one pair of transistors 2A and 2C are both in the on state, energy is stored in the electric coil 8 using the power from the DC power supply 1, and power is supplied to the load side via the transformer 3. . Next, by turning off both transistors 2A and 2C, the chiyoke coil 8
The energy stored in the DC power source 1 is returned to the DC power supply 1 via the diode 7. Next, the other pair of transistors 2B and 2D are both turned on, and the same operation is repeated.

In any of the above operating modes, the output voltage is controlled and stabilized by controlling the duty cycles of the transistors 2A, 2C, 2B and 2D _. If the coupling between N and secondary winding N ₂ is not made tight, leakage inductance will increase, which will not only significantly reduce power efficiency but also generate unnecessary surge voltage due to leakage inductance. Therefore, the primary winding _N1 and the secondary winding _N2 of the transformer 3 must be arranged as close to each other as possible in terms of spatial arrangement.
For this reason, it has the drawback that it is extremely difficult to achieve this, especially when a large dielectric strength is required between the primary and secondary sides, or when it is desired to minimize the capacitive coupling between the primary and secondary windings. It was hot.

In order to eliminate the drawbacks of the conventional power supply device, the present invention provides a semiconductor switching element that can short-circuit at least a portion of the secondary winding of the transformer, and controls the opening and closing of the element to prevent leakage from the transformer. It is characterized by a structure that actively utilizes inductance as an energy charging/discharging element.

First, one embodiment of the present invention will be described in detail with reference to FIG. The transformer 3 is relatively loosely coupled to the primary winding _N1 connected between the connection points of two sets of transistors 2A and 2D, 2B and 2C connected in series between the DC power supply 1. It has a secondary winding _N2 . Antiparallel diodes 7A to 7D are provided for each of the transistors 2A to 2D, and a transistor 9 as a semiconductor switching element is provided between the center tap of the secondary winding _N2 of the transformer 3 and the cathodes of the rectifiers 4A and 4B. is provided. Note that 10 is a backflow blocking diode.

The power supply device of this embodiment can be roughly divided into two types of operation modes.
The operating current waveform diagrams of the secondary winding N ₂ of the transformer 3 are shown in FIGS. Figures 4b and d show the operating current waveform diagrams of ₂ . In addition, in the following explanation, it is assumed that the primary winding and the secondary winding of the transformer 3 have the same number of turns, but the operating waveform in this case is the fourth one.
It becomes as shown by the solid line in Figures a to d. First, to explain the operation mode, t ₀ in Fig. 4a
In the period _-t1 , the transistors 2A and 2C and the transistor 9 are on, and in this state, energy is stored in the leakage inductance of the transformer 3 from the DC power supply 1, and power is not supplied to the load 6 from the transformer 3 side. At time t ₁ , the transistor 9, which had short-circuited the secondary winding N ₂ of the transformer 3 from the state of the previous interval, turns on, and in the interval t ₁ - _{t 2} , the primary winding of the transformer 3 is disconnected from the power supply 1. , secondary winding N ₁ ,
Power is supplied to the load 6 via N ₂ , the rectifier 4A, the diode 10 and the capacitor 5. Next, at time _t2 , only one of the transistors 2A and 2C is turned off, while the other remains on.
For example, when transistor 2A is held on, the primary winding _N1 of transformer 3 is connected to transistor 2
The series circuit including A and diode 7B becomes almost short-circuited, and the energy stored in the leakage inductance of transformer 3 is released to the load side, and ends at time _t3 . Next, in the interval _t4 - _t5 , transistors 2B, 2D, and 9 are turned on, and energy is stored in the leakage inductance of the transformer 3 in the opposite direction to that in the half cycle. When the transistor 9 turns off at time _t5 , power is supplied from the DC power supply 1 to the load 6 via the transformer 3 and the like. Then, at time _t6 , one of the transistors 2B and 2D that is in the on state is turned off.
For example, when transistor 2B connects the on state, the primary winding _N1 of transformer 3 is connected to transistor 2
Since the series circuit including B and diode 7A is substantially short-circuited, the energy stored in the leakage inductance of transformer 3 is released to load 6. The same operation is repeated below.

_{Next , the} operation _mode will be _explained with reference _{to FIG .} The same process is performed, but in the next period t ₂ - t ₃ , both transistors 2A and 2C are turned off. As a result,
The energy stored in the leakage inductance of the transformer 3 during the interval t ₀ - _{t 1} is simultaneously released to the load side and transferred to the DC power supply 1 via diodes 7B and 7D.
will be returned to. Next, in the interval t ₄ - t ₆ , the same operation as in the operation mode interval t ₄ - t ₆ is performed, and the next t ₆ -
In the interval _t7 , both transistors 2B and 2D are turned off. As a result, the energy stored in the leakage inductance of the transformer 3 in the interval t ₄ - _{t 5} is released to the load side and at the same time is transferred to the diode 7.
It is fed back to the DC power supply 1 via A and 7C. The same operation is repeated below.

In addition, as a variation of the operation mode, there is an operation mode' in which the sections t ₁ - _{t 2} and t ₅ - _{t 6} of the operation mode are removed, as shown in Figure 4b. As shown in d, there is also an operation mode ' in which the operation in the sections t ₁ -t ₂ and t ₅ -t ₆ in the operation mode is removed.

In the above explanation, the case where the input voltage and the output voltage are almost equal has been explained, but even in the same operation, when the input voltage is larger than the output voltage, the operation waveform is as shown by the chain lines in Fig. 4 a to d. The operating waveforms when the input voltage is smaller than the output voltage are shown in Figure 4 a~
It becomes as shown by the dashed line d.

Next, FIG. 5 shows a circuit showing another embodiment of the present invention, which differs from the previous embodiment in that the primary side circuit has a push-pull connection configuration. The DC-DC converter in this example is shown in Figure 4.
The transistors 2A and 2B operate in the operating modes shown in C' and d, respectively, and the operations of the transistors 2A and 2B in the circuit of FIG.
This corresponds to the operations of C, 2B and 2D. In the circuit shown in FIG. 5, a semiconductor switch element is provided that can short-circuit at least a portion of the primary winding _N1 , and when the energy stored in the leakage inductance of the transformer 3 is released, the semiconductor switch element If you operate it so that it turns on, the operation mode,
′ operation is also possible. In these embodiments, it is possible to adjust and control the output voltage by changing the duty cycle ratio of each transistor, but it is also possible to fix the duty cycle of the primary side transistor. The output voltage can also be adjusted and controlled by controlling the off time of the transistor 9 provided on the secondary side.

As is clear from the above memories, in these embodiments, the leakage inductance of the transformer, which was considered unnecessary in the past, is actively used as an energy transfer element, so the value of the leakage inductance of the transformer is not changed from the conventional value. Since the transformer can be made larger in comparison and the primary and secondary windings of the transformer can be sufficiently insulated, a transformer with high withstand voltage and high input/output insulation can be easily realized. Furthermore, as mentioned above, the duty cycle of the transistor provided on the primary side is fixed,
Since the output power can be controlled only by controlling the transistors on the secondary side, not only control becomes easy, but also insulation of the control system between input and output can be easily achieved.

Next, other different embodiments of the present invention will be explained with reference to FIGS. 6 to 10. The circuit connected to the primary side of the transformer 3 is a primary circuit as shown in FIG. 3 or 5. Either one of the side circuits or a circuit obtained by modifying these primary side circuits is connected, but is omitted. Figures 6 to 8 are similar to Figures 3 and 5.
The figure shows a modified form of the secondary circuit of the transformer 3, and is characterized by the fact that rectifiers 4C and 4D that carry the current flowing through the semiconductor switching element 9 are provided separately from the rectifiers 4A and 4B that carry the load current. According to this embodiment, the number of rectifiers through which the load current flows can be halved compared to the above embodiments, so power loss can be reduced. Particularly, in the embodiment shown in FIG. 7, it is possible to use a semiconductor switching element 9 having a smaller current capacity than the output current in the case of low voltage and large current output. In the embodiment shown in FIG. 8, especially when obtaining a high output voltage, by reducing the portion of the secondary winding short-circuited by the semiconductor switching element 9, the required breakdown voltage of the semiconductor switching element can be lowered. Furthermore, the ninth
As shown in the figure, a full-wave rectifier 4' may be used, the secondary winding _N2 of the transformer 3 may be connected to its AC side terminal, and the semiconductor switching element 9 may be connected between its DC side terminals. Furthermore, in any of the above embodiments, the secondary winding is composed of a plurality of windings that are closely coupled to each other, and the windings that are not connected to the load are short-circuited. Semiconductor switching elements may be connected so as to obtain the same.

Further, as shown in FIG. 10, a plurality of windings that are loosely coupled to each other are provided as secondary windings, and a rectifier and a semiconductor switching element are provided in each of these windings.
By extracting the output from each, a multi-output power supply whose output voltage can be controlled independently can be realized. still,
In the above embodiments, the semiconductor switch element and the semiconductor switching element were explained as transistors, but
Ordinary silicon controlled rectifier, triax or
Of course, a thyristor like GTO or FET is also suitable.

As described above, according to the present invention, the leakage inductance of the transformer, which was conventionally considered to be as small as possible, is actively utilized as an energy transfer element. Therefore, a transformer with high withstand voltage and high input/output insulation can be easily realized. Furthermore, the leakage inductance of the transformer can limit the inrush current that tends to flow into the capacitive load, and can prevent a sudden increase in current even in the case of a load short circuit. Furthermore, the output voltage can be adjusted and controlled by fixing the duty cycle of the semiconductor switching element on the primary side and changing the duty cycle of the semiconductor switching element provided on the secondary side. Not only can the control circuit be simplified, but also insulation between the input and output of the control circuit can be easily achieved.

[Brief explanation of the drawing]

1 and 2 show a conventional power supply circuit, FIGS. 3 and 5 each show an embodiment of a different power supply device of the present invention, and FIGS. 4a to 4d illustrate the present invention. Operating waveform diagram of current in transformer for
6 to 10 are diagrams showing partial circuits of different embodiments of the present invention, respectively. 1...DC power supply, 2A to 2D...Semiconductor switch element, 3...Transformer, 4A to 4D, 4'...
Rectifier, 6...Load, 7A to 7D...Diode, 9...Semiconductor switching element.

Claims (1)

[Scope of Claims] 1. A DC power supply, at least one pair of semiconductor switch elements connected to the DC power supply, diodes connected in anti-parallel to each of these semiconductor switch elements, and 1 connected to the semiconductor switch elements. A power supply device comprising a transformer having at least a secondary winding and a secondary winding magnetically coupled to the primary winding, and a rectifier and a load connected to the secondary winding. A semiconductor switching element is connected to the secondary winding, and when the semiconductor switching element is turned on in synchronization with the turn-on of the semiconductor switch element, at least a portion of the secondary winding is short-circuited and connected to the primary winding of the transformer. A power supply device characterized in that energy is stored in a leakage inductance between secondary windings, and at least a portion of the energy is supplied to a load when the semiconductor switching element is turned off. 2. The secondary winding of the transformer is composed of a plurality of windings that are closely coupled to each other, and a semiconductor switching element is connected to one of the windings that is not connected to a load. A power supply device according to claim 1, characterized in that: 3. The power supply device according to claim 1, wherein the semiconductor switching element is connected to a secondary winding of a transformer via the rectifier.