JPH053118A - Protection circuit for latch type electromagnet - Google Patents

Abstract

PURPOSE:To protect an excitation coil against the abnormality of current applied to the excitation coil of a latch type electromagnet. CONSTITUTION:The normally-opened contact point(ra) of a relay Ry is inserted into the power-feeding path to an excitation coil SOL. When the current applied to the excitation coil becomes abnormally large, the output of a comparison circuit 4 is lowered from an H-level to an L-level. A switch drive circuit 5 stops the application of current to the relay Ry when the output of the comparison circuit 4 becomes L-level, and the normally opened contact point (ra) is turned off.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a protection circuit for a latch type electromagnet, in which the armature retains the position after the displacement even when the excitation coil is energized and the armature is displaced and the energization is stopped.

[0002]

2. Description of the Related Art Conventionally, there has been provided a latch type electromagnet constructed by using an exciting coil and an armature provided with a permanent magnet. Such a latch type electromagnet is, for example,
Used in solenoids, relays, etc., when the armature is displaced when the exciting coil is energized, it has the function of retaining the position after displacement even after the energization is stopped. Therefore, in order to displace the armature, a pulsed current of about several tens of msec may be applied to the exciting coil, and the exciting coil having a small capacity with a rated value set for the instantaneous current can be used. Because,
Compared with an electromagnet of a type that holds an armature in a displacement position by continuous energization, it has an advantage that a large output can be obtained despite its small size. Further, since it is not necessary to continuously energize the drive circuit for supplying a current to the exciting coil, there is an advantage that the power supply capacity and the capacity of circuit components can be reduced.

That is, a conventional drive circuit is constructed as shown in FIG. Excitation coil SOL of solenoid
Are connected in series to the emitter-collector of the transistor Q ₁ which is a switching element. This series circuit is a bridge rectifier R that rectifies an AC power source (for example, 24V).
It is connected across a capacitor C ₁ that smoothes the output of e. Further, the voltage across the capacitor C ₁ is stabilized by the stabilizing circuit 3 formed of an integrated circuit and the smoothing capacitor C _2, and the DC voltage (for example, 5
V) is supplied. The output of the control circuit 1 includes resistors R ₁ and R ₂
And the transistor Q ₁ are input to the drive circuit 2 to control the transistor Q ₁ to be turned on and off. That is, the control circuit 1 outputs a pulsed control signal as shown in FIG. 5, the transistor Q ₁ is momentarily turned on, and the exciting current flows through the exciting coil SOL for a short time. The armature is displaced by this exciting current.
The exciting coil SOL has a diode D ₁ for blocking back electromotive force.
Are connected in parallel.

[0004]

By the way, since the rated value of the latch type electromagnet is set for the instantaneous current as described above, an abnormality occurs in the control circuit 1 and the drive circuit 2, and As shown by the broken line in FIG. 5, the exciting coil S
If the OL is continuously energized, the exciting coil SOL is overheated. In addition, even when the energization coil SOL is not always in the continuous energized state, when the ON period of the control signal generated from the control circuit 1 is long or when the control signal is repeatedly generated and the ON duty exceeds a predetermined value, the exciting coil SOL Will overheat.

Further, if the overheated state of the exciting coil SOL continues for a long time, a rare short circuit may occur in the exciting coil or it may be burnt out. Moreover, when such a state is reached, an excessive current also flows to the circuit side, which may even damage the circuit and the entire device.
Further, the abnormality in the current supplied to the exciting coil SOL may occur not only due to the circuit side but also due to a rare short circuit of the exciting coil SOL or a wrong connection.

Therefore, in order to prevent damage due to an abnormality in the current flowing through the exciting coil SOL, the exciting coil SO
L is designed to have a rated value corresponding to a continuous current to allow a margin for the abnormality of the energized current, or a latch type electromagnet including a temperature fuse arranged close to the exciting coil SOL is constructed, or As for the circuit side, it is considered to deal with it by designing the power source capacity and circuit components so that continuous energization is possible.

However, if the exciting coil SOL has a margin or a temperature fuse is provided, the size of the latch type electromagnet is increased and the mounting space is restricted. Further, since the thermal fuse has a slow response, a rare short circuit due to overheating of the exciting coil SOL cannot be sufficiently prevented. On the other hand, if the circuit side is designed with a margin, a circuit component with a large current capacity is required, and the cost is significantly higher than when a new circuit is added using a circuit component with a similar current capacity. Will increase.

The present invention is intended to solve the above-mentioned problems, and the size is increased to limit the mounting space.
Further, an object of the present invention is to provide a protection circuit for a latch-type electromagnet, which can surely protect against an abnormal current supplied to the exciting coil while preventing the cost of circuit components from significantly increasing. Is.

[0009]

According to a first aspect of the present invention, there is provided a protection circuit for a latch-type electromagnet, wherein the armature holds the position after displacement even after the excitation coil is energized and the armature is displaced when the armature is displaced. , A switching element inserted in the power feeding path to the exciting coil, a comparison circuit that obtains a binary output according to the magnitude relationship between the energizing current to the exciting coil and a predetermined reference value, and the energizing current is set to the reference value. And a switch drive circuit that turns off the switch element in response to the output of the comparison circuit.

According to the second aspect of the present invention, the normally closed contact of the relay is used as the switch element.

[0011]

According to the structure of claim 1, the energizing current to the exciting coil is detected, and when the energizing current is excessive, the switch element inserted in the power feeding path to the exciting coil is turned off. It is possible to prevent an excessive current from flowing. As a result, overheating of the exciting coil can be prevented, and rare short circuit and burnout can be prevented. Further, since an excessive current does not flow to the circuit side, it is possible to use a circuit component having a small capacity that matches the rated value of the exciting coil. Compared with the conventional configuration shown in FIG. Although the points will increase, a significant increase in cost can be avoided. In addition, since the circuit side is designed to prevent overheating of the exciting coil, the latch type electromagnet does not become large, and there is no restriction on the mounting space or the like.

According to the structure of claim 2, since the normally closed contact of the relay is used as the switch element, the control element is supplied with the control current only when the energizing current to the exciting coil is abnormal. The power consumption is smaller than that in the case of using the normally open contact, and the low power consumption characteristic in the case of using the latch type electromagnet is utilized.

[0013]

(Embodiment 1) In this embodiment, as shown in FIG. 1, a normally open contact point ra of a relay Ry is inserted as a switch element between a bridge rectifier Re and a smoothing capacitor C ₁ to excite The normally open contact point ra of the relay Ry is opened / closed according to the magnitude of the current supplied to the coil SOL.

The current supplied to the exciting coil SOL is detected as the voltage across the resistor R ₃ for current detection, which is connected in series to the emitter-collector of the transistor Q ₁ , and is compared with the reference voltage by the comparison circuit 4. A corresponding binary output is obtained. That is, the voltage across the resistor R ₃ is
After being averaged by an integrator circuit composed of a resistor R ₄ and a capacitor C ₃ provided in the above, it is input to a comparator CP and compared with a reference voltage. The reference voltage is obtained by dividing the output voltage of the stabilizing circuit 3 by the resistors R ₅ and R ₆ . A capacitor C ₄ is connected in parallel with the resistor R ₆ . A feedback resistor R ₇ is connected between the output terminal and the inverting input terminal of the comparator CP, and the comparison circuit 4 is configured to have hysteresis. In addition, the comparator C
A pull-up resistor R ₈ is connected to the output terminal of P.
In the comparison circuit 4, when the average voltage corresponding to the current flowing through the exciting coil SOL exceeds the reference voltage, the output becomes L level.

The output of the comparator circuit 4 is the transistor Q ₂ ,
A switch drive circuit 5 composed of resistors R ₉ and R ₁₀ turns on / off a current flowing to the relay Ry. That is, the switch drive circuit 5 includes a transistor Q ₂ as a switching element, the emitter-collector of the transistor Q ₂ is connected in series with the relay Ry, and the comparison circuit 4 is provided at the base.
The output of is input. When the energizing current of the exciting coil SOL is normal, the output of the comparison circuit 4 is at H level, so that the transistor Q ₂ is on and the relay Ry is energized, and as a result, the normally open contact point ra of the relay Ry is on. Hold. On the other hand, when the energizing current to the exciting coil SOL becomes excessive, the output of the comparison circuit 4 becomes L level, the transistor Q ₂ is turned off, and the energization to the relay Ry is stopped. As a result, the normally open contact ra is turned off. Becomes, excitation coil SO
The power supply to L is stopped. This surely prevents overheating of the exciting coil SOL. A diode D ₂ for blocking back electromotive force is connected in parallel to the relay Ry.

By the way, a relay Ry is used as a switch element.
Since the normally open contact ra is used, it is necessary to energize the relay Ry when the power is turned on to turn on the normally open contact ra so that power supply to each circuit is started. Therefore,
Since the timer circuit 6 is provided, the timer circuit 6 is
A pair of resistors R _{11 for} dividing the output of the bridge rectifier Re,
R _12, the resistors R _11, R ₁₂ transistors Q ₃ whose base is connected to the connection point of the capacitor C ₅ is connected in parallel with resistor R _12, provided with a collector resistor R ₁₃ of the transistor Q _3,
While the capacitor C ₅ via a resistor R ₁₁ at power-on is charged, by using the fact that the transistor Q ₃ is turned off, the resistor R _9, transistors Q ₂ to give a bias to the base of the transistor Q ₂ through R ₁₃ It is supposed to be turned on. As a result, the normally open contact r of the relay Ry
Since a is turned on, power is supplied to each circuit. Further, the power supply state to each circuit becomes stable until the voltage across the capacitor C ₅ reaches a predetermined voltage and the transistor Q ₃ is turned on. Thereafter, the transistor Q ₂ is controlled only by the output state of the comparison circuit 4. Become so.

According to the above construction, if the current supplied to the exciting coil SOL is normal, as shown by the solid line in FIG.
Since the voltage across the capacitor C ₃ forming the integrating circuit is kept lower than the reference voltage Vr of the comparison circuit 4,
The normally open contact point ra of the relay Ry maintains the ON state. On the other hand, when the energization current to the exciting coil SOL becomes excessive and the voltage across the capacitor C ₃ becomes higher than the reference voltage Vr, as shown by the broken line in FIG. 2, the normally open contact ra is turned off, and the exciting coil SOL is turned off. The power supply to the SOL is stopped. When the normally open contact point ra is turned off, the power supply to each circuit is stopped thereafter, so that the state where the energization to the exciting coil SOL is stopped continues. In order to release this state and turn on the normally open contact ra again, the power supply may be turned off once, the electric charge of the capacitor C ₅ may be discharged through the resistor R _12, and then the power may be turned on again.

[0018] In the above embodiment, by the comparison voltage for the comparator CP and the output of the integrating circuit, but as compared to the baseline average value of current supplied to the exciting coil SOL, resistor R ₄ and a capacitor If C ₃ is omitted, it is possible to perform control such that the normally open contact point ra is turned off only when an abnormally large current flows through the exciting coil SOL.

(Second Embodiment) In the first embodiment, the normally open contact ra of the relay Ry is used as the switch element, but in the present embodiment, the normally closed contact rb is used as the switch element. Therefore, the configuration of the switch drive circuit 5 is different from that of the first embodiment. That is, the switch drive circuit 5 includes a transistor Q ₂ whose emitter and collector are connected in series to the relay Ry, and the emitter and collector of the transistor Q ₄ are connected to the base and emitter of this transistor Q ₂ . A resistor R ₁₄ is connected to the base-emitter of the transistor Q ₄ . Since the output of the comparison circuit 4 is given to the base of the transistor Q ₄ , when the output of the comparison circuit 4 is at H level, the transistor Q 4
₄ turns on and transistor Q ₂ turns off. That is, the relationship between the on / off state of the transistor Q ₂ and the output level of the comparison circuit 4 is opposite to that in the first embodiment. Therefore, when the energizing current of the exciting coil SOL is abnormal and the output of the comparison circuit 4 becomes L level, the transistor Q
₂ is turned on, the relay Ry is energized, and the normally closed contact rb
Is turned off.

The base of the transistor Q ₂ has a pair of resistors R ₁₁ and R connected between the output terminals of the bridge rectifier Re.
_Twelve series circuits are connected to each other, and a capacitor C ₅ is connected in parallel to the resistor R ₁₂ . Since the transistor Q ₂ cannot be turned on after the power is turned on until the voltage across the capacitor C ₅ becomes sufficiently high, until the circuits can operate stably from the power on. It is possible to prevent the normally closed contact rb of the relay Ry from being turned off. A capacitor C ₆ for preventing chattering is connected in parallel to the relay Ry. Other configurations and operations are similar to those of the first embodiment.

[0021]

According to the first aspect of the invention, the energizing current to the exciting coil is detected, and when the energizing current is excessive, the switch element inserted in the power feeding path to the exciting coil is turned off. It is possible to prevent an excessive current from flowing through the coil. As a result, overheating of the exciting coil can be prevented, and rare short circuit and burnout can be prevented. Further, since an excessive current does not flow to the circuit side, it is possible to use a circuit component having a small capacity matching the rated value of the exciting coil,
Although the number of parts is increased as compared with the conventional configuration, there is an effect that a large increase in cost can be avoided. Moreover, since the circuit side is designed to prevent overheating of the exciting coil, the latch type electromagnet does not become large in size, and there is an advantage that there is no restriction on the mounting space or the like.

According to the second aspect of the invention, since the normally-closed contact of the relay is used as the switch element, the control element is supplied with the control current only when the energizing current to the exciting coil is abnormal. The power consumption can be reduced as compared with the case of using the normally open contact, and there is an advantage that the characteristics of low power consumption in the case of using the latch type electromagnet can be utilized.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a first embodiment.

FIG. 2 is an operation explanatory diagram of the embodiment.

FIG. 3 is a circuit diagram showing a second embodiment.

FIG. 4 is a circuit diagram showing a conventional example.

FIG. 5 is an explanatory diagram of the operation of the control circuit.

[Explanation of symbols]

1 control circuit 2 drive circuit 4 Comparison circuit 5 switch drive circuit Ry relay ra Normally open contact rb normally closed contact SOL Excitation coil

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Masami Chikazawa             1048, Kadoma, Kadoma-shi, Osaka Matsushita Electric Works Co., Ltd.             Inside the company

Claims (2)

[Claims] 1. A protection circuit for a latch-type electromagnet, in which the armature retains the position after the displacement even after the energization of the exciting coil to displace the amateur when the armature is displaced, and the armature is inserted in a power supply path to the exciting coil. A switch element, a comparator circuit that obtains a binary output according to the magnitude relationship between the energizing current to the exciting coil and a predetermined reference value, and in response to the output of the comparing circuit when the energizing current exceeds the reference value. A protection circuit for a latch-type electromagnet, comprising a switch drive circuit for turning off a switch element. 2. A protection circuit for a latch type electromagnet, wherein the switch element is a normally closed contact of a relay.