JPS6139823A - Rush current preventing circuit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to an inrush current prevention circuit for a capacitor input type rectifier circuit such as a surge voltage absorption circuit, and in particular to an inrush current prevention circuit that simplifies the circuit configuration and reduces costs. Regarding the prevention circuit.

[Prior art] A surge absorption circuit absorbs the surge voltage superimposed on the power supply,
This is provided to prevent load circuits connected to the power supply from being destroyed by surge voltage.

Such a surge absorption circuit is formed, for example, by a rectifier circuit and a surge absorption capacitor connected between a DC output terminal of the rectifier circuit. However, when the power is turned on, a transient phenomenon occurs due to rush current to the surge absorbing capacitor, causing a problem in that a surge occurs on the output side.

Therefore, in order to solve such problems, in the conventional technology, a timer circuit (delay circuit) is provided separately from the main circuit, and the timer circuit connects a resistor, etc. in series with the surge absorption capacitor for two fixed periods after the power is turned on. There are two methods of connecting the current limiting element, a zero-cross switch configuration in which the power switch is closed when the power supply voltage is zero, a method that does not include the current limiting element, and a method that does not include a surge absorbing capacitor. A system is used in which a circuit element such as a power thermistor is connected in series, and the current is limited until the resistance value of the power thermistor decreases due to self-heating of the power thermistor.

However, the first. The second method is not only expensive but also has a complicated circuit configuration, so it is not a good idea.
The problem with this method was that there was always a loss.

FIG. 1 shows a conventional circuit configuration of this type, in which 1 is an AC power source such as a commercial power source, 2 is a rectifier circuit,
3 is a timer circuit, 4 is a resistor for input current limiting, 5 is an input switch, 6 is a contact point of the timer circuit 3 connected in parallel with the resistor 4, and after the input switch 5 is opened, a predetermined hour is measured by the timer circuit 3. This is a contact that will be closed later to short-circuit the resistor 4. Reference numeral 7 indicates a smoothing capacitor connected in parallel to the DC voltage output terminal, and 8 indicates a load. In addition, load 8,
If is an AC load, if this load is connected to the AC terminal side of the rectifier circuit 2 or to the AC power supply 1 via the switch 5,
The rectifier circuit 2 and capacitor 7 function as a surge absorption circuit. In this case, it is necessary to connect a discharge circuit, such as a resistor, in parallel to the surge absorbing capacitor 7.

According to the same configuration, as described above, the cost increases due to the provision of the timer circuit 3.

[Object of the Invention] The present invention has been developed in view of the problems in the prior art described above, and provides an inrush current prevention circuit that is inexpensive and can efficiently prevent rush current when the power is turned on. The purpose is to

[Summary of the Invention] The present invention is characterized by an inrush current prevention circuit that absorbs inrush current when power is turned on to a capacitor input rectifier circuit,
A resistor connected in series with the input capacitor, a relay contact connected in parallel with the resistor, and a relay contact connected in parallel with the capacitor and closing the relay contact when the voltage across the capacitor reaches a predetermined value or more. The point is that it is equipped with a relay solenoid.

[Embodiments of the Invention] Hereinafter, embodiments of the present invention will be described in detail with reference to FIGS. 2 and 3. FIG. 2 shows an embodiment of the present invention, and is an example in which the present invention is applied as a surge absorption port. In FIG. 2, parts common to those in FIG. 1 are given the same reference numerals.

In FIG. 2, a rush current prevention circuit is formed in the charging circuit of the surge absorbing capacitor 7.

A resistor 12 is connected in series with the surge absorbing capacitor 7 to limit the current flowing to the capacitor 7, and functions similarly to the resistor 4 in FIG. 14 beams - Lew coil, contact 1
5. A resistor 16 connected in series with the relay coil 14 is used to limit the excitation current of the relay coil 14, to prevent the relay coil 14 from burning out due to excessive power consumption, and to adjust the voltage for operating the relay contact 15. It is for. Further, the contact 15 corresponds to the contact 6 in FIG. 1, and is connected in parallel with the resistor 12. 11
is an inductor for power factor improvement and noise prevention. In the figure,
The part surrounded by the dashed line is the surge absorption circuit part.

In the same configuration, when the switch 5 is first closed and the power is turned on, the capacitor 7 is gradually charged via the resistor 12 inserted in the charging circuit, so that no large rush current is generated on the input side. When the capacitor voltage increases according to a time constant determined by the resistance value of the resistor 12 and the capacitance of the capacitor 7, and the excitation current flowing to the relay coil 14 via the resistor 16 exceeds a predetermined value, the contact 15 is driven and closed. and resistance 12
short circuit.

Therefore, no rush current flows through the capacitor 7, and no surge voltage is generated due to the rush current 3. In addition, after the resistor 12 is short-circuited, the capacitor 7 is connected via the rectifier circuit 2, so
The surge voltage superimposed on the AC power source 1 flows into the capacitor 7 via the rectifier circuit 2, and is not applied to the load 8. When this surge voltage occurs, the charged power is discharged through the series circuit of the resistor 16 and the relay solenoid 14, so that the capacitor 7 can absorb the next surge voltage. In addition, under normal conditions when no surge voltage occurs, the current to the above-mentioned discharge circuit only flows through the rectifier circuit 2, and the capacitor 7 is substantially cut off by the rectifier circuit 2, so there is no influence on the AC circuit. (for example, leading power factor) is extremely small.

FIG. 3 shows another embodiment, which differs from the embodiment shown in FIG. 2 in that the capacitor 7 is for smoothing and the load 8 is a DC load.

The operation of the inrush current prevention circuit is the same as described above, so the explanation here will be omitted.

In addition, in the embodiments shown in FIGS. 2 and 3, the relay coil 1
By inserting a Zener diode or the like in series with 4, the operating voltage can be brought closer to a steady value.

As described above, in this embodiment, by connecting the resistor 12 in series with the capacitor 7, the current flowing to the capacitor 7 is limited when the power is turned on, and during normal operation, the resistor 12 is connected by the relay contact 15. Because it is shorted,
An excessive surge voltage is no longer generated on the output side due to a transient phenomenon caused by a rush current when the power is turned on. Further, since the relay circuit is operated by the terminal voltage of the capacitor 7 which increases due to the time constant of the rush current limiting resistor 12 and the capacitor 7, a separate timer circuit is not required, and therefore costs can be reduced.

In addition, since the discharge circuit of the capacitor 7 required when the present invention is applied to a surge absorption circuit is constituted by the relay solenoid 14, the power consumption of the relay solenoid 14 does not increase, and the discharging resistor can reduce the power capacity or eliminate the resistance. From this point as well, cost reduction can be achieved.

[Effects of the Invention] As is clear from the above description, according to the present invention, inrush current can be prevented with a simple circuit configuration, and there is no need to provide a separate discharge circuit, reducing costs and reducing power consumption. There is an advantage in that it can be reduced.

[Brief explanation of the drawing]

1 and 2 are diagrams for explaining a conventional inrush current prevention circuit configuration, and FIG. 3 is an implementation circuit diagram for explaining the inrush current prevention circuit configuration of the present invention. 2... Rectifier circuit, 12.16... Resistor, 7... Capacitor, 14... Relay coil, 15... Contact.

Claims (1)

[Claims] An inrush current prevention circuit that absorbs an inrush current when power is turned on to a capacitor input rectifier circuit, which includes a resistor connected in series with the input capacitor, a relay contact connected in parallel with the resistor, and the capacitor. 1. A rush current prevention circuit comprising: a relay solenoid connected in parallel and closing the relay contact when the voltage across the capacitor exceeds a predetermined value.