JPH05219732A - Dc-dc converter - Google Patents

Abstract

PURPOSE:To obtain a DC-DC converter favorable to downsizing and insulation treatment of a step-up transformer by suppressing the reverse voltage of the step-up transformer equipped in the DC-DC converter. CONSTITUTION:In a DC-DC converter which is equipped with a step-up transformer 11 and raises the DC voltage of a battery power supply connected with an input side to supply power to a load connected with an output side, the step-up transformer 11 is provided with a plurality of output coils 18a, 18b and with a one-way semiconductor device 16 between respective output coils 18a, 18b so that these output coils 18a, 18b are connected with each other.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC-DC converter for boosting and outputting a DC voltage, for example, a DC-DC converter used as a power supply circuit for a flash device for photography. ..

[0002]

2. Description of the Related Art FIG. 3 is a circuit diagram showing an example of a DC-DC converter incorporated in a flash device for photographing. In the figure, each member such as a step-up transformer 11, an oscillation transistor 12, an oscillation control transistor 13, a resistor 14 and a capacitor 15 forming a feedback circuit, and a rectifying diode 16 form a DC-DC converter. There is.

The step-up transformer 11 includes input coils 17a and 17b connected in parallel and an output coil 18 connected in series.
a, 18b, and a feedback coil 19. One end a of the parallel circuit of the input coils 17a and 17b is connected to the positive side of the battery power source 20 via the oscillation transistor 12, and the other end b is connected.
Is connected to the negative side of the battery power source 20.

One end c of the series circuit of the output coils 18a and 18b is connected to the main capacitor 21 via the diode 16.
And the other end portion d is connected to the oscillation control transistor 1
It is connected to 3 collectors. In addition, the feedback coil 19
Is connected to the emitter of the oscillation transistor 12 via the resistor 14 and the capacitor 15.

In addition, the Zener diode 22 is for detecting the battery voltage which becomes non-conductive when the battery power source 20 drops below a predetermined voltage, and the transistor 23 is an oscillation starting transistor which is turned on when the power switch 24 is turned on. Is.
Further, the parallel circuit of the diode 25 and the capacitor 26 forms a discharge path of the main capacitor 21 and prevents an excessive feedback action to the oscillation transistor 12.

In the above DC-DC converter, when the battery voltage is a predetermined value or more, by turning on the power switch 24, the transistor 23 is turned on while the Zener diode 22 is in conduction, and the Therefore, the oscillation control transistor 13 is turned on and the oscillation transistor 12 is turned on to start oscillation.

When the oscillating transistor 12 is turned on, a power supply current flows through the input coils 17a and 17b of the step-up transformer 11, and a voltage in the direction of the arrow in the figure is generated in the input coils 17a and 17b. Further, at this time, the oscillation transistor 12 is subjected to the positive feedback action by the voltage generated in the feedback coil 19 in the direction of the arrow in the figure, and the input coil current is further increased.

By the above operation of the step-up transformer 11, a voltage in the direction of the arrow in the drawing is generated in the output coils 18a and 18b, and the main capacitor 21 is charged by this output voltage.

When the oscillation is started as described above, the oscillation transistor 12 is turned off due to the magnetic saturation of the step-up transformer 11 and the transistor characteristics. Then, the oscillation control transistor 13 is turned on, the oscillation transistor 12 is turned on again, and the main capacitor 21 is charged by the output voltage of the step-up transformer 11. After that, the oscillation transistor 12 is repeatedly turned on and off in the same manner as the DC-DC converter.
To oscillate.

When the main capacitor 21 is charged in this way and reaches a predetermined charge pressure, when a xenon discharge tube (not shown) is triggered, the xenon discharge tube discharges the charge of the main capacitor 21. To emit light.

[0011]

In the DC-DC converter described above, the small step-up transformer 11 is used, so that the electric treatment of the transformer becomes a problem. This is because every time the oscillation transistor 12 changes from ON to OFF,
This is because a large reverse voltage is generated in the output coils 18a and 18b.

That is, the output coils 18a and 18b have
The output voltage (+ E) shown in FIG. 4 (A) is generated each time the oscillation transistor 12 is turned on, and the reverse voltage (-E) shown in FIG. 4 (A) is generated each time the oscillation transistor 12 is turned off. .. The output voltage (+ E) is the voltage in the direction of the arrow in FIG.
For example, the reverse voltage (-E), which is about 300 to 400 volts, is a very large voltage for this type of converter, for example, 1800 to 2000 volts.

The reverse voltage (-
When E) occurs, each circuit portion enters the withstand voltage state as shown in FIG. That is, the output coil 18
Since a reverse voltage of −E / 2 is generated in each of a and 18b,
The circuit part c is -E, the circuit part e is -E / 2, and the circuit part f is Vo.
Becomes

Vo is the charging voltage of the main capacitor 21. Further, the connection part b between the input coils 17a and 17b and the negative side of the main capacitor 21 are connected to the ground, but one end part d of the output coil 18b has a feedback coil 19, an oscillation control transistor 13 and a diode. 25
Since the capacitor 26 and the capacitor 26 are connected to each other, the voltage is not necessarily the ground potential, but the voltage at the one end d is extremely small and is considered to be almost the ground potential when compared with the reverse voltage (−E).

As a result, a reverse voltage of -E is generated in the circuit portion c as compared with the ground potential. Therefore, between the circuit portion c and the transformer core, and also between the circuit portion c
Insulation between the input coils 17a and 17b becomes a problem.

Actually, since the input coils 17a and 17b and the output coils 18a and 18b are wound on the bobbin, the circuit portion c and the transformer core are insulated by this bobbin, but the transformer is made compact. Since the thickness of the bobbin becomes smaller, insulation breakdown may occur between the circuit portion c and the transformer core, which may cause an electric leakage accident. That is,
The input coil 17a from the circuit part c through the transformer core,
Leakage current flows to other parts of 17b and output coils 18a and 18b.

Insulation tape or the like is provided between the input coils 17a and 17b and the output coils 18a and 18b for insulation. An electric leakage accident may occur between the circuit part c and the input coils 17a and 17b due to a cause such as a rupture of the battery.

In view of the above situation, it is an object of the present invention to develop a DC-DC converter equipped with a step-up transformer which is advantageous in withstanding voltage.

[0019]

In order to achieve the above-mentioned object, the present invention comprises a step-up transformer for stepping up the DC voltage of a battery power source connected to the input side to supply the load connected to the output side. In the DC-DC converter, the step-up transformer is provided with a plurality of output coils, and a unidirectional semiconductor element is provided between the output coils to connect the output coils. −
Suggest a data.

[0020]

The forward voltage and the reverse voltage are alternately generated in each output coil of the step-up transformer due to the oscillation of the DC-DC converter, and the forward voltage of each output coil is added to form an output voltage. The load is powered by.

Further, since the reverse voltage generated in each output coil is divided by the unidirectional semiconductor element, this reverse voltage is not added. Therefore, the reverse voltage generated in each output coil is the largest voltage. However, when a load is connected, the load voltage is added to the reverse voltage of the output coil to which the load is connected, so the voltage obtained by adding the reverse voltage and the load voltage is the largest voltage.

As a result, since the reverse voltage generated in each output coil is not added, the reverse voltage = (1 / the number of output coils), which is the sum of the reverse voltage and the load voltage. For this reason, it is only necessary to subject the reverse voltage, which is much lower than the reverse voltage (sum of reverse voltages) generated in the entire output coil, to electric resistance treatment, and to reduce the size of the step-up transformer used in this type of converter. It is extremely advantageous for insulation treatment.

[0023]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 is a DC-DC showing an embodiment of the present invention.
It is a partial circuit diagram of a converter. As shown, in this embodiment, the rectifying diode 16 is connected to the output coil 18a.
And 18b. In addition,
Others are the same as those of the conventional circuit shown in FIG.

In this embodiment, the output coils 18a, 18a
If a voltage in the direction of the arrow in the figure is generated in b, this voltage is in the forward direction of the diode 16, so that the output coils 18a, 1
The voltages generated in the respective 8b are added, and the added voltage is output to charge the main capacitor 21.

When a reverse voltage is generated in the output coils 18a and 18b in the opposite direction to the arrow shown in the figure, this reverse voltage is in the opposite direction to the diode 16, so that the output coil 18a
And the reverse voltage of the output coil 18b is the diode 1
It is divided by 6 and these reverse voltages are not added.

FIG. 2 is a simplified diagram similar to FIG. 4B, but the circuit distribution state of the reverse voltage will be described with reference to this diagram. The circuit part c has a charging voltage of the main capacitor 21, which is Vo, the circuit part g has a voltage increase of E / 2 from the circuit part c by (E / 2) + Vo, and the circuit part h has the circuit part d at the ground potential. Considering it, it becomes (-E / 2). At this time, a forward voltage of (E + Vo) is applied to the diode 16.

For example, if the charging voltage Vo of the main capacitor 21 is 330 volts and the reverse voltage E is 1800 volts, c = 330 volts, g = 1230 volts, h = 90.
It will be 0 volts. As a result, it suffices to perform an insulation treatment that can sufficiently endure 1230 volts.
It is extremely advantageous for downsizing and insulation processing configuration of 1.

In the above embodiment, two output coils 1
Although the case where 8a and 18b are provided has been described, the reverse voltage can be further suppressed by further increasing the number of output coils and connecting the output coils with a diode. The diode connected between the output coils is
The same effect can be obtained even if it is replaced with another unidirectional semiconductor element such as an SCR element or a Zener diode.

As shown in the above embodiment, the step-up transformer capable of implementing the present invention has two input coils 17a and 17a.
It does not need to be b and can be one input coil. In the case of a step-up transformer having one input coil and one output coil, the output coil is divided into a plurality of coil parts, and the output coil parts are connected by a unidirectional semiconductor element in the same manner. Can be implemented.

[0030]

As described above, the DC-DC according to the present invention
Since the converter sufficiently suppresses the reverse voltage generated in the step-up transformer, it is extremely advantageous for downsizing the step-up transformer and insulation treatment. Moreover, the converter can be implemented with a simple structure, which makes it a practical converter. ..

[Brief description of drawings]

FIG. 1 is a DC-DC converter showing an embodiment of the present invention.
It is a partial circuit diagram of the data.

FIG. 2 is a simplified diagram for explaining the operation of the DC-DC converter described above.

FIG. 3 is a circuit diagram of a DC-DC converter shown as a conventional example.

FIG. 4 (A) is an output voltage waveform diagram of the conventional converter. FIG. 4B is a simplified diagram for explaining the operation of the conventional converter.

[Explanation of symbols]

 11 step-up transformer 12 oscillation transistor 16 diode 17a, 17b input coil 18a, 18b output coil 19 feedback coil 21 main capacitor

Claims (1)

[Claims] 1. A DC-DC converter comprising a step-up transformer for stepping up a DC voltage of a battery power source connected to an input side to supply a load connected to an output side, wherein the step-up transformer has a plurality of outputs. A DC-DC converter characterized in that a coil is provided and a unidirectional semiconductor element is provided between the output coils to connect the output coils.