JP2000092695A - Rush current suppression circuit and element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rush current suppression circuit and an element for surely suppression a rush current without requiring a number of parts even when power is turned on again in a short time after a power supply is broken or when the on/off of the power supply is repeated with a short cycle. SOLUTION: A series circuit of a two-contact relay drive coil L1 and a negative characteristics thermistor Rt2 is connected between power supply lines, a parallel circuit of a power thermistor Rt1 that is thermally coupled to Rt2 and a first contact P1 of the relay is connected in series with one of the power supply lines, and a second contact P2 of the relay is connected in parallel with the thermistor Rt2 with negative characteristic. With this structure, the temperature of the thermistor Rt2 with negative characteristics increases due to the generation of heat of the power thermistor Rt1 after power is turned on, thus driving the relay, turning on the contacts P1 and P2, and rapidly decreasing the temperature of the negative characteristic thermistor Rt2 and the power thermistor Rt1 for preparing for the re-turning on after the next power off.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit and an element for suppressing an inrush current generated when power is turned on.

[0002]

2. Description of the Related Art FIG. 5 shows an example of a capacitor input type rectifier circuit which receives a commercial (AC) power supply and rectifies and smoothes it. In such a circuit, when the power is turned on (when the switch SW1 is turned on), normally, no charge is accumulated in the smoothing capacitor C1, so that the impedance of the smoothing capacitor C1 is almost 0Ω, and A large current (rush current) defined only by the resistance of the switch SW1 and the fuse (generally, several tens mΩ in total) flows.
In the case of an AC 100 V line, the inrush current usually reaches several tens to several hundreds of amps, causing problems such as melting of a fuse and burning of the contact of the switch SW1. Also, flicker noise occurs due to the rush current, and unnecessary noise is superimposed on the power supply line.

In order to solve the problem of the inrush current, as shown in FIG. 6, a power negative characteristic thermistor (hereinafter referred to as a power thermistor) R is connected in series with a smoothing capacitor C1.
A method of inserting t1 to suppress the inrush current is generally used. The resistance temperature characteristic of this power thermistor is
At room temperature, it shows a resistance value of about 10Ω, and during normal operation, it generates heat to about 120 ° C due to self-heating and has a resistance value of 1Ω or less. Therefore, when the power is turned on, the inrush current is suppressed by the resistance value of about 10Ω, and the power loss due to the power thermistor is suppressed during the normal operation.

[0004]

However, in the rush current suppressing circuit using the power thermistor as shown in FIG. 6, when the power is turned on again after a short time after the power is cut off, or when the power is In the case where the switching on / off is repeated at the time, a disadvantage occurs as described below.

FIG. 7 is a waveform diagram showing the state of each part shown in FIG. 6, and the broken lines in the figure show the inrush current when there is no power thermistor. As shown in FIG. 7, if the power is turned on at (a) where the resistance value of the power thermistor Rt1 is high,
The inrush current is sufficiently suppressed. However, the power is shut off in (b), and after a short time, for example, about 5 seconds, the switch S is switched in (c).
When W1 is turned on again, the power is turned on again in a state where the resistance value of the power thermistor Rt1 is not sufficiently increased and the difference between the resistance value during normal operation and ΔR is as large as ΔR. The rush current suppressing effect is almost eliminated, and an excessive rush current flows. Also, (c) ~
As shown in (e), even when the power supply is
Since it is used in a state where the resistance value of t1 is not sufficiently recovered, an inrush current flows each time.

On the other hand, in addition to a power thermistor, there has been a device for suppressing an inrush current which comprises a resistor and a relay contact for bypassing a current flowing through the resistor, as shown in FIG. In FIG. 8, L1 is a drive coil of a relay driven by an external control circuit, and P1 is a contact point thereof. As this type of inrush current suppressing circuit, Japanese Unexamined Patent Publication No.
No. 9497. However, in such a circuit in which the both ends of the resistor for suppressing the inrush current are bypassed by the relay contact in the steady state, even if the power is cut off and the power is turned on shortly after the power is turned off, the relay is turned on. In order to operate properly, a complicated external control circuit using many circuit elements had to be provided.

An object of the present invention is to eliminate the need for a large number of components, and to provide an inrush even when the power is turned on and then turned on shortly after the power is turned off, or when the power is repeatedly turned on and off in a short cycle. It is an object of the present invention to provide an inrush current suppression circuit and an element that reliably suppress current.

[0008]

According to the present invention, there is provided an inrush current suppressing circuit comprising a resistor connected between a power supply line and a series circuit of a driving coil for a relay and a negative characteristic thermistor, and thermally connected to the negative characteristic thermistor. And a parallel circuit of a first contact of the relay is connected in series to one of the power supply lines, and a second contact of the relay is connected in parallel to the negative characteristic thermistor, and a steady current is supplied to the resistor. The characteristics of the negative-characteristic thermistor are determined such that the first and second contacts of the relay are in a conductive state while the relay is in the ON state.

With this configuration, when the power is turned on, a current flows to the load via the resistor, and a current also flows to a series circuit of the drive coil of the relay and the negative characteristic thermistor. The resistance value of the negative temperature coefficient thermistor coupled to the relay decreases, and the first and second contacts of the relay conduct. This allows the first contact to bypass the resistor and prevent power loss and heat generation by the resistor. Thereafter, as the temperature of the resistor decreases, the resistance value of the negative characteristic thermistor increases. At this time, since the second contact is in the conductive state, the energized state to the drive coil of the relay is maintained. Then, when the power is cut off, the first
Even if the second contact is turned off immediately and then turned on again after a short time, the resistance of the negative temperature coefficient thermistor is already high, so that a current flows through the load through the resistor, and the rush current again occurs. Will be suppressed.

In the rush current suppressing circuit according to the present invention, the resistor is a negative characteristic thermistor. According to this structure,
Since the change in the resistance value of the negative characteristic thermistor after the power is turned on changes relatively slowly and the first contact point of the relay can be turned on in a state where the resistance value is sufficiently reduced, the first contact point of the relay is turned on. There is almost no inrush current.

Further, the inrush current suppressing element of the present invention accommodates the circuit having the above configuration in one case and provides a terminal connected to a power supply line. According to this configuration, since the circuit is configured with a small number of components, the entire inrush current suppressing element can be configured very small, and can be mounted on the circuit board as one element.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a configuration of an inrush current suppressing circuit and an inrush current suppressing element according to a first embodiment of the present invention.
This will be described with reference to FIG.

FIG. 1 is a circuit diagram of a power supply circuit portion including an inrush current suppression circuit. In FIG. 1, AC 100 V is a commercial power supply, which is input to an AC input terminal of a diode bridge DB via a power switch SW1 and a fuse, and a smoothing capacitor C1 is connected between its DC output terminals to form a rectifying and smoothing circuit portion. I have. A power thermistor Rt1 is connected in series to a power supply line between the diode bridge DB and the smoothing capacitor C1. A series circuit of a drive coil L1 of a two-contact relay and a negative characteristic thermistor Rt2 is connected between the power supply lines. A backlash current absorbing diode D1 is connected to the drive coil L1 of this relay. The first contact P1 of the relay is connected in parallel to the power thermistor Rt1, and the second contact P2 is connected in parallel to the negative characteristic thermistor Rt2. The negative characteristic thermistor Rt2 is a power thermistor Rt1.
Are thermally coupled to each other by disposing them in close proximity to each other.

FIG. 3 is a diagram showing the resistance-temperature characteristics of the negative characteristic thermistor Rt2. As described above, since the thermistor is a negative characteristic thermistor, the resistance value decreases as the temperature increases. In this example, the resistance (Ra) is 5 kΩ at room temperature 25 ° C.
It is 1.85 kΩ at ° C.

The operation of the circuit shown in FIG. 1 is as follows. First, the input power supply voltage AC100V is rectified by the diode bridge DB to generate a DC voltage of approximately 140V. Assuming that a relay having a drive voltage of 100 V is used as the relay and the resistance of the driving coil L1 of the relay is 5 kΩ, the resistance (R
a) of 5 kΩ is used. At this time, V1 = 140 · (5 kΩ / (5 kΩ)
+5 kΩ)) = 70 [V] is applied.

In this state, the relay contacts P1 and P2 remain open due to insufficient operating current for the drive coil of the relay.

Thereafter, when the power thermistor Rt1 generates heat and the temperature of the negative characteristic thermistor Rt2 rises, its resistance value decreases. When the temperature of the negative characteristic thermistor Rt2 becomes, for example, 70 ° C., the resistance value becomes 1.85 kΩ. At this time, V2 = 140 is applied to the driving coil L1 of the relay.
・ (5kΩ / (5kΩ + 1.85kΩ)) ≒ 100
A voltage of [V] is applied. As a result, the relay is driven, and both the contacts P1 and P2 conduct.

FIG. 2 is a waveform diagram showing a state change of each part of the circuit shown in FIG. The operation described above will be described with reference to FIG. 2. At the time (a), the temperature of the power thermistor Rt1 rises due to the self-heating of the power thermistor Rt1 (the resistance value decreases) and is thermally coupled thereto. When the temperature of the negative characteristic thermistor Rt2 rises (resistance decreases) and reaches a certain resistance value (1.85 kΩ), the relay operates. The time ΔT can be variously set depending on the resistance value Ra of the negative temperature coefficient thermistor Rt2 at room temperature 25 ° C. and the value of the B constant of the resistance temperature characteristic and the thermal coupling condition of the power thermistor Rt1 and the negative temperature coefficient thermistor Rt2. Is desirably about several seconds to several tens of seconds.

In FIG. 2, if the switch SW1 is once turned off in (b) and immediately turned on again in (c), the resistance value of the power thermistor Rt1 is already sufficiently high at this point, and The inrush current suppression effect is the same as that at the time of injection in a). Incidentally, in the conventional rush current suppressing circuit shown in FIG. 7, since the power thermistor is turned on again while the temperature of the power thermistor hardly decreases from the operating state (high temperature), the effect of suppressing the rush current is very small. Also, (c) ~
As shown in FIG. 7 (e), in the case of the intermittent power-on / shut-off operation, the rush current flows each time as shown in FIG. For example, as shown in FIG. 2, the rush current is reliably suppressed.

Further, since the diode D1 is connected to the drive coil L1 of the relay, when the switch SW1 is turned off and the current flowing through the drive coil L1 is cut off, the return current flows into a closed loop by the diode D1 and the drive coil L1. Flows to absorb the backlash current. Therefore, no surge occurs.

In the above example, the rated voltage is DC
Although a relay driven at 100 V was used, conduction actually starts at a voltage lower than the rated voltage, for example, 90 V. Therefore, the relay may be selected such that the threshold voltage at which the relay contact becomes conductive becomes a predetermined value, and the circuit constant may be determined.

In FIG. 1, a power thermistor Rt1,
The negative characteristic thermistor Rt2, the two-contact relay and the diode D1 constitute an inrush current suppressing element. In this example, a four-terminal element is used that is inserted between power supply lines. Since the two terminals on the cold side (ground potential side) of the two power supply lines are common, they can be used as one terminal to constitute a three-terminal type rush current suppressing element.

Next, FIG. 4 shows a configuration of an inrush current suppressing circuit according to a second embodiment. Unlike the circuit shown in FIG.
In this example, a normal power resistor R1 is used as a resistor for suppressing inrush current. As described above, even if a normal resistor having almost no temperature dependency is used, the relay contact P
Since this is a period until 1 becomes conductive, power loss can be suppressed to a small value.

In the embodiment described above, a circuit for suppressing the rush current to the smoothing capacitor in the rectifying / smoothing circuit of the capacitor input type is described as an example. However, the present invention relates to the rush current to the heating resistor such as a halogen lamp. Can be similarly applied to a circuit that suppresses

[0025]

According to the first aspect of the present invention, when the suppression of the inrush current at the time of turning on the power supply ends, the relay contact is turned on and the current to the negative characteristic thermistor is cut off. The value increases rapidly. Therefore, even if the power is once turned off and then turned on again after a short time,
Since the resistance value of the negative characteristic thermistor has already been increased, a current flows through the load via the resistor, and the inrush current is reliably suppressed.

According to the second aspect of the present invention, the change in the resistance value of the negative characteristic thermistor after the power is turned on changes relatively slowly, and the first contact of the relay conducts in a state where the resistance value is sufficiently reduced. As a result, power loss and heat generation by the negative-characteristic thermistor that limits the inrush current can be effectively suppressed, and the inrush current when the first contact of the relay is turned on is almost eliminated.

According to the third aspect of the present invention, since a circuit is configured with a small number of components, a very small inrush current suppressing element can be configured as a whole, and the element can be easily formed on a circuit board as one element. Be able to implement.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of an inrush current suppression circuit according to a first embodiment.

FIG. 2 is a waveform diagram showing an operation state of each unit in FIG.

FIG. 3 is a diagram showing an example of resistance temperature characteristics of a negative temperature coefficient thermistor;

FIG. 4 is a diagram illustrating a configuration of an inrush current suppression circuit according to a second embodiment;

FIG. 5 is a diagram showing a configuration of a general capacitor input type rectifier circuit.

FIG. 6 is a diagram showing a configuration of a conventional rectifier circuit including an inrush current suppression circuit.

FIG. 7 is a waveform chart showing an operation state of the circuit.

FIG. 8 is a diagram showing a configuration of another rectifier circuit including a conventional inrush current suppression circuit.

[Explanation of symbols]

 DB-diode bridge C1-smoothing capacitor Rt1-power thermistor (negative characteristic thermistor) Rt2-negative characteristic thermistor L1-relay driving coil P1-relay first contact P2-relay second contact D1-diode

Claims (3)

[Claims] 1. A series circuit of a drive coil of a relay and a negative temperature coefficient thermistor is connected between power supply lines, and a parallel circuit of a resistor thermally coupled to the negative temperature coefficient thermistor and a first contact of the relay is connected to the power supply. A second contact of the relay connected in series to one of the lines, a second contact of the relay connected in parallel to the negative characteristic thermistor, and a first and second contact of the relay in a state where a steady current is supplied to the resistor. Wherein the characteristic of the negative characteristic thermistor is determined such that the element is in a conductive state. 2. The inrush current suppression circuit according to claim 1, wherein said resistor is a thermistor having a negative characteristic. 3. An inrush current suppressing element, wherein the circuit according to claim 1 or 2 is housed in one case and provided with a terminal connected to the power supply line.