JPS6019211B2 - Surge absorption circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a surge absorption circuit used to absorb switching surge voltages generated when switching an inductive load connected to a DC power supply. The purpose of the present invention is to provide a surge absorption circuit that greatly reduces the inrush current of the circuit, extends the life of the switch contacts used for switching, and at the same time absorbs large surge forces.

When an inductive load is switched on and off, a surge of power ranging from several times the power supply voltage to as high as 1M is generated across the load, and propagates to other circuits as a surge voltage or as a noise voltage with high frequency components. However, it is very likely that the equipment will stop functioning or malfunction.

In addition, these surge voltages are extremely harmful voltages that shorten the life of contacts of switches, such as relays, used to switch on and off inductive loads.

This surge voltage is caused by the fact that when the circuit is opened, the energy E = Li2 (where L is the inductance of the inductive load and i is the breaking current) left behind in the inductive load is charged to the stray capacitance between the load lines. It occurs when Conventionally, the circuit shown in FIG. 1 has been widely used to absorb this surge voltage.

In the figure, 1 is a DC wire, 2 is a switch, 3 is an inductive load, and 4 is a surge absorber. Arrow 5 indicates the direction of current flowing into surge absorber 4 during surge absorption. The surge absorber 4
Its function is to limit the surge voltage generated in the inductive load 3 to a lower level, prevent the surge voltage and noise voltage from propagating to other circuits, and at the same time extend the life of the contacts of the switch 2.

However, conventional surge absorbers or surge absorption circuits that have been used for these purposes have not been able to fully achieve their purposes.

For example, when a SIC varistor is used as the surge absorber 4, the leakage current at normal circuit voltage is large, and the limiting voltage is also high, which is not sufficient. CR series composite product (
For example, C=0.01〃F. R=100Q) What is generally called a spark killer also has a high limiting voltage and cannot be said to be sufficient. A relatively newly developed circuit among these is shown in FIG.

In the figure, 6 is a ceramic varistor which is mainly made of metal oxide such as zinc oxide and has an excellent voltage non-linearity index. 7 is a capacitor made of ceramic or polyester film, and is connected in parallel with the ceramic varistor 6. The circuit is connected in parallel with the inductive load 3 to form a surge absorption circuit. The operation of the surge absorption circuit is as follows.

First, the capacitor 1 absorbs a shower-like surge voltage having a high frequency that occurs at the initial moment when the switch 2 is opened. At this time, the ceramic varistor 6 does not operate.
This is because the ceramic varistor 6 operates as an insulator at voltages below a certain value. Since the capacitor 7 absorbs this shower-like surge voltage, no spark discharge occurs between the contacts of the switch 2. Next, as time passes, the surge energy stored in the inductive load 3 is stored in the capacitor 7 in the form of charge, and the voltage across the capacitor 7, that is, across the ceramic ballast 6, begins to rise. However, once a certain voltage value is reached,
Ceramic burrs 6 ensures continuity and limits surge voltage. In this way, the capacitor 7 absorbs high-frequency components and the contact spark discharge of the switch 2, and the ceramic varistor 6 suppresses surge voltage. It exhibits excellent characteristics that have never existed before.However, the second
The circuit shown in the figure also has two problems. One is that a relatively large charging current (inrush current) flows to the capacitor 7 in the route shown by arrow 8 when the switch 2 is closed and released, which prevents the contact life of the switch 2 from increasing. One is that no spark discharge occurs at the contacts of the switch 2 when the switch 2 is in the dark.
All of the energy stored in the inductive load 3 must be dissipated by the ceramic varistor 6 and capacitor 7. However, in this case, since the capacitor 7 does not have the characteristic of consuming power, the entire surge force must be consumed by the ceramic varistor 6 after all. According to experiments, the surge energy (power) that must be dissipated by the ceramic varistor 6 in the circuit shown in FIG. 6 is required. In other words, this means that the ceramic varistor 6 must also absorb the energy once absorbed by the capacitor 1. The present invention solves these two problems.

FIG. 3 and FIG. 4 each show a surge absorption circuit according to the present invention. Components in the figure that are the same as those in FIG. 2 are designated by the same numbers and will be explained. First, FIG. 3 will be explained.

In the figure, t9 is a resistor connected in parallel to the capacitor 7, 10' is a diode connected in series to the parallel circuit of the capacitor 7 and the resistor 9, and the series circuit is connected in parallel to the ceramic varistor S. By constructing a circuit like this, it is possible to solve the problems that the secondary surge absorption circuit had.Firstly, the charging current to the capacitor 7 can be reversed by inserting the diode 10. A voltage is applied, and therefore no charging current flows to the capacitor T.

Regarding the surge absorption characteristics due to the insertion of the diode 10, as shown in FIG. 1, the surge current flows as indicated by the arrow 5, in the forward direction of the diode 80, and does not impede the surge absorption characteristics in any way. On the other hand, the surge force consumed by the ceramic varistor 6 can be significantly reduced.

This is because the energy charged in the capacitor 7 via the diode 10 cannot be dissipated via the diode 10, but is discharged within the CR closed circuit via the resistor 9 as shown by the arrow 11. The surge energy will be consumed by resistance 9. This is because the conventional ceramic varistor 6
This means that the surge energy to be consumed by the ceramic varistor 6 is less than half compared to when the surge absorption energy of the capacitor 7 had to be consumed. ``The circuit shown in FIG. 4 is similarly constructed for the purpose of reducing the above two problems.

In the figure, l2 is a diode, and i3 is a capacitor, which replaces the capacitor 7 and diode 10 in the circuit shown in Figure 3. In this circuit, the charging current (rush current) flowing into the capacitor 13 flows through the resistor 9. In addition, the surge energy accumulated in the capacitor 3 is discharged as shown by the arrow 14 through the ceramic varistor 6 and the resistor 9, and more than half of it is consumed by the resistor 9. ceramic barista 6
The power consumption burden is reduced. Note that the surge absorption characteristics of the circuit shown in FIGS. 2 and 3 are exactly the same as those shown in FIGS. As explained above, according to the present invention, by configuring the circuit as described above, the following effects can be achieved without reducing the surge absorption characteristics.

i It becomes possible to greatly reduce or eliminate the rush current to the capacitor when the circuit is closed, and it becomes possible to greatly extend the life of the contacts of the switch used for switching loads.

By setting the value of the U resistance to an appropriate value, it is possible to reduce the surge power that the ceramic varistor should consume, and it is possible to use an inexpensive small ceramic varistor with a small rating.

[Brief explanation of drawings]

Figures 2 and 2 are circuit diagrams of conventional surge absorption circuits to Figure 3.
FIG. 4 is a circuit diagram of a surge absorption circuit according to an embodiment of the present invention. Tortoise: DC power supply, 2: Switch, 3: Inductive negative current, S: Ceramic varistor, 7, 13: Capacitor t g: Resistor, 10, 12... diode. Figure 1 Figure 2 Figure 3 Figure 4

Claims (1)

[Claims] 1. A ceramic varistor made of a metal oxide such as zinc oxide and having an excellent voltage non-linearity index is connected in parallel with a capacitor, and this parallel circuit is connected in parallel with an inductive load, and a capacitor is connected in parallel with an inductive load. A surge absorption circuit comprising an element for blocking the flow of charging current from a DC power source and an element for consuming energy charged in the capacitor, connected to the parallel circuit. 2 A parallel circuit of a ceramic varistor and a capacitor is connected in parallel to an inductive load, a resistor is connected in parallel to the capacitor, and a diode is connected in series to the parallel circuit of the capacitor and the resistor. The surge absorption circuit described in item 1. 3. A parallel circuit of a ceramic varistor and a capacitor is connected in parallel to an inductive load to form a parallel circuit of a resistor and a diode, and this parallel circuit is connected in series to the capacitor. Surge absorption circuit.