JPH07203686A - Method for lowering inductance of switching circuit - Google Patents

Abstract

PURPOSE:To lower the inductance of circuit which causes abrupt increase of voltage when a switching element functions to feed or interrupt the current. CONSTITUTION:An electrolytic capacitor 8 and three sets of two series connected switching transistors 1, 4, 2, 5, 3 and 6 are connected in parallel with the DC output terminals of a rectifier 13 for AC power supply, wherein the electrolytic capacitor 8 is connected with the switching transistors 1-6 through two sheets of conductors 9, 10 having wide area.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching power supply circuit for supplying a direct current to a motor or the like, or a method of reducing inductance in a switching circuit used where pulse current is required.

[0002]

2. Description of the Related Art A DC power supply terminal of a conventional switching circuit and a switching element are connected by a single conductor. Therefore, there is a circuit inductance, and if the current changes abruptly due to opening and closing of the switching element, the voltage may fluctuate rapidly even with a small inductance, which may damage the element. For example, when looped with a 10 cm conductor wire having a diameter of 3 mm, there is a circuit inductance of about 0.3 μH, and the change in current when the switching element is opened and closed is 3
When it is set to 00 A / 1 μs to 300 A / 100 ns, a voltage close to several hundred to 1,000 volts is applied to the switching element. In particular, in the case of a high-speed switching element with a large current, it has been a serious problem. Conventionally, a power transistor was used as a switching element, but nowadays a higher speed ICBT is used, which has become a particular problem. In order to prevent this, there is a method of connecting a capacitor and a resistor in parallel with the switching element, but this has a problem that power consumption increases, cost also increases, and a mounting space becomes large.

[0003]

SUMMARY OF THE INVENTION The present invention solves the problems of the prior art and provides a method for reducing the circuit inductance of a switching circuit that lowers the circuit inductance that causes a sharp rise in voltage when switching a current. To do.

[0004]

SUMMARY OF THE INVENTION The gist of the present invention, which has solved the above-mentioned problems, is to provide a feeding circuit having a wide area for a feeding path having different current directions in a switching circuit for feeding a DC voltage to a plurality of switching elements in parallel. There is a method of reducing the circuit inductance of a switching circuit, which is characterized in that the circuit inductance is reduced by arranging them close to each other.

[0005]

According to the present invention, the conductive paths having a large area are brought close to each other in the connection paths which connect the DC supply terminal and the switching element and whose current directions are opposite to each other. By doing so, the magnetic fields generated by the reverse currents cancel each other out, and the inductance decreases. As a result, the voltage does not suddenly rise even with a large current change caused by opening / closing of the switching element, and damage to the switching element is reduced.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a switching power supply circuit for driving a motor according to the present invention will be described below with reference to the drawings. 1 is a circuit diagram of the embodiment, FIG. 2 is a plan view showing a mounting circuit of a main part of the embodiment, and FIG. 3 is a front view of the mounting circuit. 1-6 in the figure
Is a switching transistor, 7 is a motor, 8 is an electrolytic capacitor, 9 and 10 are the electrolytic capacitors 8 and the switching transistors 1 to 6 having a thickness of 2 mm.
A copper conductor having a wide area of 20 cm × 30 cm, 11 a 2 mm thick insulator between the conductors 9 and 10, 12 a wiring inductance coil generated by wiring, 13 a rectifier, and 14 a heat sink plate. is there.

In this embodiment, the AC power supply is rectified by the rectifier 13, smoothed by the electrolytic capacitor 8, and DC voltage is applied to the switching transistors 1 to 6 via the conductors 9 and 10. A control voltage is applied to the base of the switching transistor so that the switching transistors 1 to 6 are opened / closed to cause a current to flow to the motor 7. At this time, the conductor connecting the electrolytic capacitor 8 and the switching transistors 1 to 6 is as shown in FIG.
As shown in FIG. 3, the conductors 9 and 10 have a large area. Since the insulators 11 are present between the conductors 9 and 10 and are close to each other, currents in opposite directions flow to the conductors 9 and 10, and the generated magnetic fields cancel each other out. Only a weak magnetic field is generated, and as a result, the circuit inductance can be greatly reduced. As a result, the induced voltage generated when the current suddenly rises could be reduced to about 50V for a voltage of several hundreds.

[0008]

As described above, according to the present invention, the wiring circuit portions in which the current directions are reversed are formed by arranging the conductors having a large area close to each other, thereby canceling the magnetic field caused by the current. It is possible to reduce the inductance and prevent a high voltage from being generated due to a sudden change in the current when the switching transistor is opened and closed.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention.

FIG. 2 is a plan view showing a mounted circuit of a main part of the embodiment.

FIG. 3 is a front view of the same mounted circuit of the essential part of the embodiment.

[Explanation of symbols]

 1 Switching Transistor 2 Switching Transistor 3 Switching Transistor 4 Switching Transistor 5 Switching Transistor 6 Switching Transistor 7 Motor 8 Electrolytic Capacitor 9 Conductor 10 Conductor 11 Insulator 12 Wiring Inductance Coil 13 Rectifier 14 Heat sink plate

Claims (1)

[Claims] 1. In a switching circuit for feeding a DC voltage to a plurality of switching elements in parallel, by forming feeding paths having different current directions in close proximity to each other with conductive plates having a large area, the circuit inductance is reduced. A method for reducing the circuit inductance of a switching circuit, which is characterized by the following.