JP2676982B2 - DC-DC converter - Google Patents

Description

TECHNICAL FIELD The present invention relates to a DC-DC converter, and more particularly to a DC-DC converter that generates a DC voltage higher than a DC input voltage.

2. Related Art A conventional DC-DC converter of this type has a configuration shown in FIG. A series connection circuit of the transformer 1 and the switching transistor 2 is provided between the DC input terminals,
The first and second outputs are taken out from the secondary windings N2 and N3 of the transformer 1, respectively.

The first output becomes the first DC output V01 by the rectifying / smoothing circuit composed of the diode 3 and the capacitor 5, and the second output becomes the second DC output V02 by the rectifying / smoothing circuit composed of the diode 4 and the capacitor 6. .

The control circuit 7 detects the first DC output V01 and controls the conduction angle of the switching transistor 2 in accordance with the detected voltage to keep the DC output V01 constant and at the same time to output the second DC output V02. It is supposed to be stabilized.

A series circuit of a diode 14 and a capacitor 16 is connected in parallel with the primary winding N1 of the transformer 1, and a resistor 15 is provided in parallel with the capacitor 16.

The circuit composed of the diode 14, the capacitor 16, and the resistor 15 is a flyback energy that appears until the switching transistor 2 is turned off and the excitation energy of the transformer 1 is discharged from the secondary windings N1 and N2. Is a circuit for absorbing.

Part of the flyback energy is fed back to the DC input side through the capacitor 16 and the diode 14, but part of it is consumed by the resistor 15.

If there is no circuit for absorbing the flyback energy, not only a large spike noise is generated, but also the collector voltage of the transistor 2 reaches the breakdown voltage and the transistor may be destroyed.

Although a Zener diode may be used instead of the resistor 15 and the capacitor 16, the flyback energy is partially consumed by the Zener diode even in this case.

In such a conventional DC-DC converter, the flyback energy generated in the primary winding is fed back to the DC input side until the switching transistor 2 is turned off and the exciting energy of the transformer 1 is discharged from the secondary winding. However, not all of this energy is fed back, but some of it is consumed inside the feedback circuit. Therefore, when the coupling of the transformer is poor, or when the switching frequency is high, the flyback energy becomes particularly large, so that the efficiency of the DC-DC converter decreases.

SUMMARY OF THE INVENTION Therefore, the present invention has been made to solve the drawbacks of the prior art, and an object of the present invention is to suppress flyback voltage generated when a switching transistor is turned off and prevent the transistor from being destroyed. It is also efficient because it eliminates the loss of flyback energy.
It is to provide a DC-DC converter.

According to the present invention, the series connection circuit of the transformer and the switching transistor provided between the DC input terminals, and the DC output higher than the DC input voltage by rectifying and smoothing the output of the secondary winding of the transformer. A DC-DC converter including a rectifying / smoothing circuit for generating and a control circuit for performing on / off control of the switching transistor according to the DC output, wherein the DC output from a series connection portion of the switching transistor and the transformer An energy supply circuit for supplying flyback energy of the transformer to the unit, the energy supply circuit including a capacitor and a unidirectional element connected in series with each other between the series connection section and the DC output section. A transistor element that is connected in parallel to the capacitor and is on-controlled by the generation of the DC output. DC-DC converter, wherein Rukoto is obtained.

Embodiment Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a circuit diagram of an embodiment of the present invention, and the same parts as those in FIG. 2 are designated by the same reference numerals. The circuit for processing the flyback energy of the transformer 1 is different from the example of FIG. 2, and in this example, the connection point between the primary side N1 of the transformer 1 and the collector of the switching transistor 2 and the second DC output V02. A capacitor 9 and a unidirectional diode 8 are inserted and connected in series between and.

A PNP transistor 10 is provided in parallel with the capacitor 9, and the NPN transistor 12 controls ON of the transistor 10. That is, the first DC output V01 is applied to the base of the transistor 12 via the resistor 13, and the collector output of the transistor 12 is applied to the base of the transistor 10 via the resistor 11.

The other structure is the same as that of the circuit shown in FIG. 2, and the description thereof is omitted.

In this circuit, the second DC output V02 is the DC input Vin
As shown in the drawing, the anode is connected to the capacitor 9 and the cathode is connected to the second DC output as the connection polarity of the diode 8. Therefore, the diode 8 is turned off during the normal time when the flyback voltage is not generated, and the backflow of energy from the second DC output to the input side is blocked.

The transistor 10 is off until the DC-DC converter turns on and the first DC output V01 appears,
The direct current input is prevented from being directly led out to the second direct current output side via the diode 8.

In such a configuration, when the switching transistor 2 is turned on, a current flows through the primary winding N1. Secondary winding N2, N
A reverse voltage is applied to 3, no current flows, and excitation energy is stored in the transformer 1.

Next, when the switching transistor 2 is turned off, the excitation energy of the transformer 1 tends to be discharged from the secondary windings N2 and N3 through the diodes 3 and 4, respectively. However, since there is a time delay until the excitation energy is released from the secondary windings N2 and N3, during this delay, the excitation energy tends to be released as flyback energy from the primary winding N1.

The current at this time passes through the capacitor 9 when the transistor 10 is off at the time of starting the DC-DC converter, and when the transistor 10 is already on, the current flows through the capacitor 9.
Through 10 are respectively supplied to the second DC output V02. Therefore, the collector voltage of the switching transistor 2 can be suppressed to be sufficiently low (below the value of V02).

Further, in the steady state, when the excitation energy is supplied from the windings N2 and N3, the reverse voltage appearing in the winding N1 becomes small, and the collector voltage of the switching transistor 2 becomes the second DC output V02. Lower, there is no current supply through diode 8.

As described above, according to the present invention, the flyback energy generated in the transformer when the switching transistor is turned off is supplied to the secondary side output, so the flyback generated in the collector of the switching transistor is achieved. The voltage is suppressed, and the flyback energy can be efficiently supplied to the DC output.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention, and FIG.
It is a circuit diagram of a DC converter. Description of main part symbols 1 ... Transformer 2 ... Switching transistor 3,4 ... Rectifying diode 5,6 ... Smoothing capacitor 7 ... Control circuit 8 ... Unidirectional diode 9 ... Energy supply Capacitor 10 ... Transistor for energy supply

Claims (1)

(57) [Claims] 1. A rectifier for serially connecting a transformer and a switching transistor provided between DC input terminals, and rectifying and smoothing an output of a secondary winding of the transformer to generate a DC output higher than a DC input voltage. A DC-D converter including a smoothing circuit and a control circuit for performing on / off control of the switching transistor according to the DC output,
An energy supply circuit for supplying flyback energy of the transformer from a series connection section of the switching transistor and the transformer to the DC output section, the energy supply circuit including the series connection section and the DC output section A DC-D converter comprising: a capacitor and a unidirectional element connected in series between each other, and a transistor element connected in parallel to the capacitor and on-controlled by generation of the DC output.