JPS61142973A - Current type converter - Google Patents

Abstract

PURPOSE:To set the withstand voltage of a switching element to the same value as that of a power source voltage by connecting two switching elements and an energy storing reactor in series, and providing an output transformer between the neutral point of the reactor and one terminal of the power source. CONSTITUTION:A power source voltage Vin is divided by 1/2 by capacitors C1, C2 having large capacity, and transistors (Tr) Q1, Q2 and an energy storing reactor L are connected symmetrically with respect to a midpoint O in series with both terminals of a power source. Further, the primary winding N1 of an output transformer T is connected between the neutral point O and the connecting point P of the capacitors C1, C2. A reset winding NR and reset diode DR are connected in series with both terminals of the power source. Thus, the Trs Q1, Q2 are alternately turned ON and OFF by a drive signal from the exterior, the ON time is controlled to control the output voltage Vout.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is directed to a DC-DC power supply used in a switching power supply, etc.
The present invention relates to a converter, particularly a current type converter having an energy storage reactor on the primary side of an output transformer.

[Conventional technology]

Conventionally, as a current type converter, a converter having a push-pull configuration as shown in FIG. 5 is known. In the figure, Ql and Q2 are transistors as switching elements, L is an energy storage reactor, NR is a reset winding, DR is a reset diode, T is an output transformer, N1 is its primary winding, and N2 is its second winding. In the next winding, vIN is the power supply (input) voltage, and Vouy is the output voltage. In such a current type converter, if a large number of circuits similar to those shown in the figure are provided on the secondary side of the output transformer, the same number of choke coils are required. First, it has the feature that it is possible to stabilize multiple outputs with a single glue axle, and its operation is stable.

[Problem that the invention seeks to solve]

In FIG. 5, transistor Q1. Q2 is alternately turned on and off by an external drive signal, but since the voltage superimposed on the power supply voltage VIN is applied to the transistor on the off side by the primary winding N1 of the transformer T, A switching element with a breakdown voltage more than double that is required. In addition, a reset winding NR with good coupling to the energy storage reactor is required. These points are disadvantageous from a cost standpoint.

Therefore, an object of the present invention is to provide a current type converter that allows the switching element to have the same breakdown voltage as the power supply voltage, and that can be configured to eliminate the need for a reset winding coupled to the energy storage reactor.

[Means for solving problems]

In order to achieve the above object, the present invention provides
Two switching elements that alternately turn on and off and an energy storage reactor are connected in series and symmetrically with respect to a midpoint, and an output transformer 1? is connected between this midpoint and one end of the power supply. ! ! ? The winding and the capacitor are connected in series, and the output voltage is taken out from the secondary winding side of the output transformer.

[Effect]

When one of the two switching elements is on, the capacitor is charged with the power supply voltage, and when the other switching element is on, the charge is discharged. Therefore, the voltage applied across the switching element when it is off does not exceed the power supply voltage.

〔Example〕

1 to 3 are circuit diagrams showing three embodiments of the present invention. FIG. 4 is a waveform diagram showing the operation of these embodiments. In these figures, parts corresponding to those in FIG. 5 are given the same reference numerals.

C1 and C2 are capacitors having a sufficiently large capacity for the amount of charge transferred by turning on and off the transistors Ql and Q2, and the power supply voltage VIN is divided into 1/2 by these two capacitors Cz and C2. The transistors Ql and Q2 and the energy storage reactor L are connected to both ends of the power supply VIN,
They are connected in series and symmetrically about the midpoint O. Also,
Between this midpoint 0 and the connection point P of capacitor C, C2,
The primary winding N1 of the output transformer T is connected. The reset winding NR and the reset diode DR are connected in series across the power supply VIN as in the conventional case. ■+iL2 indicates the emitter-collector voltage of transistor Q2.Transistors Q1 and C2 are driven by an external drive signal
As shown in the figure, they are turned on and off alternately, and by controlling these on-times, the output voltage VolJT is controlled. The two switching elements are turned on and off alternately in this way.
When the output transformer T is turned off, a biased magnetism phenomenon due to biased direct current being applied to the output transformer T does not occur.

The embodiment shown in FIG. 1 is a basic one in which the principle of a current type converter is applied to a half bridge type converter circuit. The embodiment shown in FIG. 2 is a modification in which the winding of the energy storage reactor L shown in FIG. 1 is divided into two parts, and the operation is the same as that shown in FIG. 1. In the embodiment of FIG. 3, the reset winding NR is removed and the reset diode DR is replaced with 2.
It is made into individual pieces. In this example, a dedicated reset winding NR
Since this is not necessary, the winding structure of the reactor L is simplified, and it is possible to prevent transient spike voltages from being applied to the switching elements. That is, the output transformer T
A transient spike-like voltage is generated when the primary voltage of the diode D fluctuates due to ringing, etc.
Since R absorbs this voltage into the power supply, this spike voltage can be prevented.

In these example circuits, capacitor Ci +02
is transistor Q2. Since QL is alternately charged by the power supply voltage VIN when QL is on and discharged when transistor QllQ2 is on, the voltage applied across the transistor Q1°C2 never exceeds the power supply voltage VIN when it is off. The waveform of V&2 in Figure 4 is the switching element Q
2. During operation, the voltage V&2 across it is the input voltage Vo.
Indicates that it does not exceed w.

In other words, it is possible to configure a current-type converter with a switching element that has a lower withstand voltage than conventional converters, and the above-mentioned features of current-type converters (the ability to stabilize multiple outputs with a single glue handle, stable operation, etc.) ). In addition, in the above embodiment, the capacitor is 2
Although both are used, it is also possible to omit one of them.

In this case, one capacitor is charged and discharged,
By repeating charging and discharging, a balance point is gradually reached. Furthermore, the switching element is not necessarily limited to a transistor.

〔Effect of the invention〕

As explained above, according to the present invention, a current type converter can be realized using a switching element having a lower breakdown voltage than the conventional one. In addition, it is possible to take advantage of the original feature of a half bridge, which is that there is no unbalanced magnetism in the transformer.

Furthermore, as in the third embodiment, the winding structure of the reactor is simplified by omitting the dedicated glue sensor l-8 wire, and by using two reset diodes, transient spike-like voltage is not generated in the switching element. can be prevented from joining.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing a first (basic) embodiment of the present invention, FIG. 2 is a circuit diagram showing a second (modified) embodiment, and FIG.
FIG. 4 is a circuit diagram showing the third embodiment, FIG. 4 is a waveform diagram showing the operation of these embodiments, and FIG. 2 is a circuit diagram showing a conventional example. VIN...Power supply (input) voltage, Ql, Q2...
Switching element, L... Energy storage reactor, 0... Midpoint, T... Output transformer, N1...
Its primary winding, N2... its secondary winding, C1, C2...
...Capacitor, VOIJT...Output voltage.

Claims (1)

[Claims] Two switching elements that are alternately turned on and off by a drive signal and an energy storage reactor are connected to both ends of the power supply in series and symmetrically with respect to the midpoint,
A current type converter, in which a primary winding of an output transformer and a capacitor are connected in series between this midpoint and one end of the power supply, and an output voltage is taken out from the secondary winding side of the output transformer.