JPH08275373A - Overcurrent protector - Google Patents

Abstract

PURPOSE: To change overcurrent break property easily as required by generating an integration signal from an integrating circuit when the magnitude of a load current becomes larger than the set value in overcurrent range, and giving a break command signal to a switch circuit when this decreases to the value smaller than the load current detection signal. CONSTITUTION: When a load current is over a first set value to give the lower limit of an overcurrent range, an integrating circuit 8 generates an integration signal, the level of which decreases almost rectilinearly together with the passage of time. When this integration signal becomes smaller than the load current detection signal, this breaks the line by giving a break signal to a switch circuit 3. As a result, the overcurrent can be broken by making it have anti-time- limiting property which shortens the break operation time, accompanying the increase of an overcurrent. Needless breaking operation by rush current, etc., of load is prevented from being performed by making it have reverse time characteristic which shortens break operation time, when the magnitude of the load current gets over the second set value larger than the first set value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an overcurrent protection device for protecting a load by shutting off an overcurrent when it flows from a power source to an electric motor or an electromagnetic solenoid.

[0002]

2. Description of the Related Art In general, if an overcurrent exceeding a rated current continues to flow from an electric power source to an electric load such as an electric motor or an electromagnetic solenoid, the temperature of the load increases so much that dielectric breakdown or burning may occur. Therefore, in the case where there is such a possibility, an overcurrent protection device is provided to shut off the overcurrent and protect the load when an overcurrent flows through the load.

As a conventional overcurrent protection device of this type,
Use an electromagnetic circuit breaker that opens contacts to open the load circuit with an electromagnetic force generated according to the magnitude of the overcurrent, or a temperature-sensitive element such as bimetal. It is known to have an anti-time characteristic in which the interruption operation time until the current is interrupted is shortened as the overcurrent increases.

In an overcurrent protection device using a bimetal as a temperature sensitive element, the bimetal is heated by the heat generated by the overcurrent to displace the bimetal, and the displacement directly or in combination with an electromagnetic breaker causes a load circuit. Is open. Further, as seen in Japanese Utility Model Publication No. 48-11604, a temperature-sensitive element which is made of ferrite whose magnetic permeability sharply decreases when reaching a certain temperature and is provided to detect heat generated by an overcurrent, An overcurrent protection device having a contact that maintains a closed state when a predetermined magnetic force is applied through a ferrite is also known. In this overcurrent protection device, the contact opens when the magnetic force applied through the ferrite that constitutes the temperature sensitive element decreases due to the heat generated by the overcurrent, and the opening of this contact disconnects the load circuit from the power supply and shuts off the overcurrent. To be done.

FIG. 9 shows a general overcurrent interruption characteristic of a conventional overcurrent protection device in which a temperature-sensitive element such as a bimetal is used to provide an interruption time characteristic with a reverse time limit characteristic. As is clear from the figure, in this type of overcurrent protection device, when the magnitude of the load current exceeds the set value i1 which gives the lower limit of the overcurrent region, the breaking operation time T increases with the increase of the load current. When the magnitude of the load current exceeds the set value i2 of the overcurrent as the load current becomes shorter, the interruption operation time T becomes almost zero, and the overcurrent is instantaneously interrupted.

[0006]

The conventional overcurrent protection device has a problem that there are large variations in overcurrent cutoff characteristics because there are many parts that are mechanically operated, such as parts that are displaced according to temperature. Further, in the conventional overcurrent protection device, it is possible to easily change the lower limit value of the overcurrent at which the breaking operation is performed and the characteristic value such as the slope of the anti-time limit characteristic indicating the relationship between the magnitude of the overcurrent and the breaking operation time. There was a problem that I could not.

Further, when the load is, for example, an electric motor and a large inrush current flows for a short time at the time of starting the electric motor, if the conventional overcurrent protection device is used, the breaking operation is caused by the inrush current generated at the time of starting the load. In order to prevent this, it is necessary to add a special device that prevents the breaking operation against inrush current, which makes the device expensive, or due to inrush current There is a problem that it is necessary to lengthen the interruption operation time as a whole so that the interruption operation is not performed, and it becomes impossible to obtain the optimum overcurrent interruption characteristics that match the characteristics of the load. .

An object of the present invention is to make it possible to easily change the overcurrent cutoff characteristic without using a temperature sensitive element such as a bimetal and to prevent a large overcurrent such as an inrush current. An object of the present invention is to provide an overcurrent protection device which prevents the load circuit from being opened unnecessarily due to the overcurrent when the current flows only for a short time.

[0009]

SUMMARY OF THE INVENTION The present invention relates to an overcurrent protection device for protecting a load from an overcurrent by shutting off the current flowing from a power source to a load when the current is excessive. The overcurrent protection device according to claim 1, which is provided with a switch circuit provided to cut off an overcurrent flowing from a power source through a load when a cutoff command signal is given, and a magnitude of the overcurrent which gives a lower limit of an overcurrent region. When it is in the range from the set value i1 of 1 to the second set value i2 which is larger than the first set value i1, the cutoff operation time from the flow of the overcurrent to the cutoff of the overcurrent is In order to cut off the overcurrent by providing it with the anti-time characteristic that shortens with increase, and by providing the time characteristic that keeps the breaking operation time constant when the overcurrent exceeds the second set value, According to the cutoff command to the switch circuit And a cutoff control circuit that gives a degree.

The cutoff control circuit detects a load current, and when the load current is less than or equal to the second set value, changes in proportion to the load current, and the load current exceeds the second set value. In the range, the load current detection circuit that outputs the load current detection signal that holds a constant value and the load current detection signal
Compared to a reference signal having a magnitude corresponding to the set value of, the first state is set when the magnitude of the load current detection signal is less than the magnitude of the reference signal, and the magnitude of the load current detection signal is Is greater than the magnitude of the reference signal, a load current determination circuit that outputs a load current determination signal Vin that takes a second state and a load current determination signal Vin are input, and the load current determination signal is the first Holds a constant value when in the state,
When the load current determination signal is in the second state, an integrating circuit that outputs an integrated signal whose level decreases substantially linearly with the passage of time, and the integrated signal is compared with the load current detection signal to determine that the integrated signal is the load current. It can be configured by a cutoff timing detection circuit that outputs a cutoff timing detection signal when it becomes smaller than the detection signal, and a cutoff command signal generation circuit that gives a cutoff command signal to the switch circuit when the cutoff timing detection signal is generated.

In the above configuration, when the magnitude of the overcurrent is in the range from the first set value i1 which gives the lower limit of the overcurrent region to the second set value i2 which is larger than the first set value i1. The cut-off control circuit is configured to cut off the overcurrent by providing the time-delay characteristic with the time-delayed time characteristic and when the overcurrent exceeds the second set value. When it is in the range from the first set value i1 which gives the lower limit of the basin to the second set value i2 which is larger than the first set value i1, a cutoff operation from the flow of the overcurrent until the cutoff of the overcurrent The first anti-time characteristic which shortens the time at the first rate with the increase of the overcurrent is provided, and when the overcurrent exceeds the second set value, the breaking operation time is set to the first with the increase of the overcurrent. With a second anti-time characteristic that shortens at a second rate that is smaller than In order to cut off the current, it is also possible to configure the interruption control circuit to provide a shutoff signal to the switch circuit in accordance with the magnitude of the overcurrent. in this case,
The load current detection circuit outputs a load current detection signal that changes at a first rate of change substantially in proportion to the load current when the load current is less than or equal to the second set value, and the load current changes to the second set value. In a range exceeding the limit, the load current detection signal that changes in proportion to the load current and changes in the second change rate smaller than the first change rate is output.

[0012]

In the overcurrent protection device of the present invention, when the magnitude of the load current becomes larger than the first set value i1 which gives the lower limit of the overcurrent region, the level is almost linearly changed with time from the integrating circuit. A decreasing integration signal is generated, and when the integration signal decreases to a value smaller than the magnitude of the load current detection signal, the interruption timing detection circuit outputs the interruption timing detection signal. With this, the cutoff command signal generator gives a cutoff command signal to the switch circuit to open the switch circuit,
Cut off overcurrent.

When the magnitude of the overcurrent is in the range from the first set value i1 to the second set value i2, the load current detection signal changes substantially in proportion to the magnitude of the load current. The time has an anti-time-delay characteristic that shortens almost linearly as the overcurrent increases.

When the load current detection circuit is configured so that the load current detection signal maintains a constant value in the range where the magnitude of the overcurrent exceeds the second set value i2, the overcurrent is set to the second set value. The cutoff operation time becomes constant in the range exceeding i2. Therefore, in this case, even if the magnitude of the overcurrent due to the inrush current of the load exceeds the second set value i2, the second set value i2
As long as the period of time that is longer than is shorter than the predetermined breaking operation time, the switch circuit is not opened by the inrush current or the like.

Further, the magnitude of the overcurrent is the second set value i2
The load current detection signal in the range exceeding the range changes substantially in proportion to the load current at the second change rate smaller than the change rate (first change rate) of the load current detection signal at the second set value i2 or less. If the load current detection circuit is configured as described above, the breaking operation time in the range where the magnitude of the overcurrent exceeds the second set value i2 is in the range from the first set value i1 to the second set value i2. At the second rate smaller than the rate (first rate) of the change of the breaking operation time in (1), the second anti-time characteristic is shortened as the overcurrent increases. Therefore, in this case, even if the magnitude of the overcurrent due to the inrush current of the load exceeds the second set value i2, the duration of the overcurrent is longer than the interruption operation time determined by the second anti-time limit characteristic. As long as it is short, the switch circuit is not opened by the inrush current or the like.

Since the overcurrent interruption characteristic which gives the relation between the magnitude of the overcurrent and the interruption operation time is determined by the circuit constant of the interruption control circuit, there is no great variation unlike the case using the bimetal. Further, the overcurrent cutoff characteristic can be easily changed by changing only a part of the circuit constant of the control circuit.

[0017]

1 is a block diagram showing the overall configuration of the present invention. In FIG. 1, 1 is a power source, 2 is a load to which a load current i is supplied from a power source 1, 3 is a switch circuit, and 4 is a switch circuit. The operation switches 5 for starting and stopping the load 2 are cutoff control circuits that give a cutoff command signal to the switch circuit 3 in accordance with the magnitude of the overcurrent.

The cutoff control circuit 5 detects the load current i and outputs the load current detection signal Vo, and the load current detection circuit 6
And a load current determination circuit 7 that outputs the load current determination signal Vin by comparing the load current detection signal Vo with a reference voltage, and the load current determination signal Vin is input to the load current determination signal in the first state. An integrator circuit 8 that holds a constant value at and outputs an integral signal whose level decreases substantially linearly with the passage of time when the load current determination signal is in the second state.
And a cutoff timing detection circuit 9 for comparing the integrated signal Vout with the load current detection signal Vo and outputting a cutoff timing detection signal St.
And a cutoff command signal generation circuit 10 which gives a cutoff command signal Sb to the switch circuit 3 when the cutoff timing detection signal St is generated.

FIG. 2 shows an embodiment of the present invention in which the circuit configuration of each part of FIG. 1 is concretely shown.

In this embodiment, the power source 1 is a DC power source composed of a battery whose negative electrode side is grounded, and the load 2 is a DC motor which is rotated by being supplied with load current from the power source 1 through the power switch SW and the switch circuit 3. The direction of rotation of the DC motor is reversed by reversing the polarity of the applied voltage.

In the switch circuit 3, the first exciting coil 31 to which the diode D1 is connected in parallel and the movable contact 32a when the exciting coil 31 is excited are one fixed contact 32.
A first electromagnetic switch having a first changeover switch 32 that is connected to the other fixed contact 32c from b, a second exciting coil 33 to which a diode D2 is connected in parallel, and the exciting coil are excited. Sometimes, the movable contact 34a is provided with a second electromagnetic switch having a second changeover switch 34 that is connected to the other fixed contact 34c from one fixed contact 34b, and the anode is connected to the DC power source 1 via the power switch SW. Of the diode D3, which is connected to the positive side output terminal of and the cathode of which is commonly connected to one end of each of the first and second exciting coils 31 and 33.

First and second changeover switches 32 and 34
The movable contacts 32a and 34a are connected to one input terminal and the other input terminal of the load (DC motor) 2, respectively. One of the fixed contacts 32b and 34b of each of the changeover switches 32 and 34 is grounded through a load current detecting resistor R1 provided in the cutoff control circuit 5, and the other fixed contacts 32c and 34c are connected via a power switch SW. And is commonly connected to the positive output terminal of the DC power supply 1.

The start / stop operation switch 4 is, in this example, the first operation switch 41 and the second operation switch connected between the other ends of the first and second exciting coils 31 and 33 and the ground. It consists of 42. When the first operation switch 41 is closed, the exciting coil 31 is excited and the movable contact 32a of the changeover switch 32 is switched to the fixed contact 32c side, so that the DC motor 2 rotates in one direction. On the contrary, when the second operation switch 42 is closed, the exciting coil 33 is excited to move the movable contact 34 of the changeover switch 34.
Since a is switched to the fixed contact 34c side, the DC motor 2 rotates in the other direction. When both the first and second operation switches 41 and 42 are closed, the exciting coil 31
Since 33 and 33 are both excited, the load current to the DC motor 2 is cut off.

The load current detection circuit 6 used in this embodiment is
It consists of a load current detecting resistor R1 through which the load current i flows, and an amplifier circuit consisting of an operational amplifier 61, a diode D4 and resistors R2 to R5. The voltage across the load current detecting resistor R1 is the positive phase input of the operational amplifier 61. It is input to the terminal. The cathode of a diode D4 is connected to the output terminal of the operational amplifier 61, a resistor R3 is provided between the anode of the diode D4 and the negative phase input terminal of the operational amplifier 61, and between the negative phase input terminal of the operational amplifier 61 and ground. The resistors R2 are connected to each other. Resistors R4 and R5 are connected between the anode of the diode D4 and the positive terminal of a DC power source (not shown) and between the anode of the diode D4 and ground, respectively, and a constant DC voltage E is applied across the series circuit of the resistors R4 and R5. Is being applied.

In the load current detection circuit 6, the load current i is equal to or less than the second set value i2 which is larger than the first set value i1 which gives the lower limit of the overcurrent region, and the forward voltage is applied to the diode D4. Load current detection signal Vo = iR1 (R2 + R3) / R that changes in proportion to the load current i
Outputs 2. When the load current i exceeds the second set value i2, a reverse voltage is applied to the diode D4,
The load current detection signal Vo is held at a constant value V1. FIG.
Shows the relationship between the load current i and the load current detection signal Vo. Here, the magnitude of the constant value V1 is the resistance R2.
Is the voltage across the resistor R5 in the circuit consisting of R5 to R5, and V1 = E.R5 (R2 + R3) / {R4 (R2
+ R3 + R5) + R5 (R2 + R3)}. The second set value i2 of the load current is i2 = V1 R2 / R
It is given by 1 (R2 + R3).

The load current discriminating circuit 7 is composed of an open collector output comparator 71 and a comparing circuit consisting of resistors R7 and R8, and an impedance converting circuit consisting of an operational amplifier 72 and resistors R9 and R10. Comparator 7
The load current detection signal Vo output from the load current detection circuit 6 is input to the non-inverting input terminal of 1, and the constant voltage E is obtained by dividing the constant voltage E into the resistors R7 and R8 at the inverting input terminal of the comparator 71. Reference voltage Vr1 = E.R7 / (R7 + R
8) has been entered. The magnitude of the reference voltage Vr1 is set to a value equal to the magnitude i1 R1 (R2 + R3) / R2 corresponding to the first set value i1 which gives the lower limit of the overcurrent region. Therefore, the first set value i1 that gives the lower limit of the overcurrent region of the load current is i1 = R2 R7 E / R1 (R2 + R3)
It is represented by (R7 + R8). The resistors R9 and R10 are connected in series to each other to form a voltage dividing circuit, and a constant DC voltage E is applied to both ends of this voltage dividing circuit. The voltage dividing point of this voltage dividing circuit is connected to the output terminal of the comparator 71 and the positive phase input terminal of the operational amplifier 72. When the output stage of the comparator 71 is in the open state, the voltage dividing point is composed of resistors R9 and R10. The voltage V2 = ER10 / (R9 + R10) is obtained at the voltage dividing point of the voltage circuit. The negative phase input terminal of the operational amplifier 72 is connected to the output terminal of the operational amplifier 72,
The voltage follower circuit is configured by.

The load current discrimination circuit 7 is composed of a comparator 71.
Thus, the load current detection signal Vo and the reference voltage Vr1 are compared, and the operational amplifier 72 outputs the load current determination signal Vin. When the load current i is less than the first set value i1 and Vo <Vr1, the output stage transistor of the comparator 71 is turned on, so that the load current determination signal Vin is in the first state (V
in = 0), and when the load current i is equal to or greater than the first set value i1 and Vo ≧ Vr1, the transistor of the output stage of the comparator 71 is turned off, so that the load current determination signal Vin is in the second state ( Vin = V2).

The integrating circuit 8 is composed of a series circuit of resistors R12 and R13 and has a divided voltage V3 = ER12 of the constant DC voltage E.
A voltage divider circuit that outputs / (R12 + R13) and a divided voltage V3
Is input to the positive phase input terminal, a resistor R11 connected between the negative phase input terminal of the operational amplifier 81 and the output terminal of the load current determination circuit 7, and the negative phase input terminal of the operational amplifier 81. Capacitor C connected between the output and the output terminal
1 and a diode D5 and a Zener diode ZD1 connected in series with their anodes connected to each other,
Cathode of diode D5 and Zener diode ZD
The cathode of 1 is connected to the negative phase input terminal and the output terminal of the operational amplifier 81, respectively. The magnitude of the divided voltage V3 input to the positive phase input terminal of the operational amplifier 81 is V3 <
V2 (for example, V2 = 2 [V], V3 = 1)
[V]).

The integrating circuit 8 receives the load current determination signal Vin and outputs an integrated signal Vout. When the magnitude of the load current i is less than the first set value i1 (i <i1) and the load current determination signal Vin is in the first state (Vin = 0 state), the integrated signal Vout is the Zener diode ZD1.
Clamped by Vout = Vx = V3 + Vz (V
z is the Zener voltage of the Zener diode ZD1) and is held at a constant value Vx as shown by the straight line a in FIG. The magnitude of the load current i is the first set value i1 or more (i ≧
i1) Therefore, the load current discrimination signal Vin is in the second state (V
In the state of in = V2), the integrated signal Vout is V
out = Vx-{(V2-V3) / C1 R11} t (t is time), and as shown by the straight line b in FIG. 4, the signal decreases almost linearly with the passage of time t.

The cutoff timing detection circuit 9 comprises a comparator 91 having an open collector output, and the load current detection signal Vo output from the load current detection circuit 6 is applied to the inverting input terminal of the comparator 91, and the non-inverting input terminal is applied. The integrated signal Vout is input to each.

The comparator 91 compares the integrated signal Vout with the load current detection signal Vo, turns off the transistor of the output stage when Vout> Vo, and outputs Vout.
When ≤Vo, the output stage transistor is turned on. In the present embodiment, the cutoff timing detection signal St is generated when the output stage transistor of the comparator 91 is turned on and the potential of the output terminal of the comparator is zero. That is, in the present embodiment, when the integrated signal Vout decreases and Vout = Vo, the cutoff timing detection signal St is generated, and when this cutoff timing detection signal is generated, a cutoff command generation circuit described later. A disconnection command signal is generated from 10 to interrupt the load current.

The cutoff command signal generation circuit 10 includes a transistor Tr1, a resistor R14 connected between the base of the transistor Tr1 and the output terminal of the comparator 91 of the cutoff timing detection circuit 9, and a collector of the transistor Tr1. A resistor R15 connected to the resistor R15, a resistor R16 connected between the other end of the resistor R15 and the ground, and a capacitor C2 connected in parallel to the resistor R16.
A thyristor Th whose cathode is grounded and whose gate is connected to the non-grounded side terminal of the capacitor C2, and diode D6 whose cathode is commonly connected to the anode of the thyristor.
And D7. A constant DC voltage E is applied to the emitter of the transistor Tr1 and the diode D6
The respective anodes of D7 and D7 are the first of the switch circuit 3.
And the other ends of the second exciting coils 31 and 33, respectively.

The cutoff command signal generation circuit 10 applies a cutoff command signal Sb to the switch circuit 3 when the cutoff timing detection signal St is input from the cutoff timing detection circuit 9 and holds the cutoff command signal. Doubles as

When the cutoff timing detection circuit St generates the cutoff timing detection signal St (the potential of the output terminal of the comparator 91 becomes zero), a base current flows through the transistor Tr1 and the transistor Tr1 becomes conductive. As a result, a gate current is applied to the thyristor Th to render the thyristor conductive, and the other ends of the first and second exciting coils 31 and 33 of the switch circuit 3 are grounded through the diodes D6 and D7 and the thyristor Th, respectively. , The first and second exciting coils are both excited. In this example, the state where the thyristor Th is conductive and the other ends of the exciting coils 31 and 33 are grounded through the thyristor is the state in which the cutoff command signal Sb is generated.

Excitation coil 31 is supplied with a cutoff command signal.
And 33 are both in the excitation state (however, since the operation switch 41 or 42 is closed when the load 2 is operating, one of the excitation coils is already in the excitation state), the changeover switches 32 and 34 Movable contact 32a
And 34 are switched to the fixed contacts 32c side and 34c side, respectively, so that the overcurrent flowing in the load 2 is cut off.

When the load current i is cut off and the load current detection signal Vo becomes zero, the output transistor in the comparator 91 of the cutoff timing detection circuit 9 is turned off and the transistor T is turned off.
Although r1 is non-conducting, the thyristor Th holds the conducting state, so that the cut-off state of the load current is maintained. Load 2
In the case of re-driving, the power switch SW is turned off once, and the power supply flowing through the thyristor Th is made below the holding current to bring the thyristor into the non-conducting state.
Close again.

In the present embodiment, when the magnitude of the load current i is less than the first set value i1, the integrated signal Vout holds the constant value Vx as shown by the straight line a in FIG.
Since the comparison circuit 9 does not generate the shutoff timing detection signal St,
The cutoff command signal is not generated, and the load 2 is continuously driven. The magnitude of the load current i is the first set value i1 or more (i ≧
i1 and the load current determination signal Vin is in the second state (V
In the state of in = V2), the level of the integrated signal Vout decreases with the passage of time t, as indicated by the straight line b in FIG. In this case, when i = i1 and Vo = Vr1 (straight line c), the cutoff timing (the time when Vout = Vo) is T1 = (Vx-Vr1) C1 R11 / (V2-V3
) Is given. In the range of i> i2, Vo = V1
= Constant (straight line d), so the cutoff time is T2 =
(Vx-V1) .C1 R11 / (V2-V3) [= constant]
Given in. In the range of i1≤i≤i2, Vo = iR
Since 1 (R2 + R3) / R2, the cutoff time is T =
{Vx-iR1 (R2 + R3) / R2} C1 R11 / (V
2-V3), the cut-off time T shortens substantially linearly as the load current i increases. (Note that i1 ≤
The load current detection signal Vo when i≤i2 is represented by a straight line e. ) FIG. 5 shows the relationship between the magnitude of the load current i and the interruption operation time T from the flow of the overcurrent to the interruption of the overcurrent. In the figure, the shaded area is the overcurrent. Represents the area where the power is cut off. The cutoff operation time T is the time when the cutoff timing detection signal is output from the cutoff timing detection circuit 9, and the cutoff is performed when the magnitude of the overcurrent is in the range from the first set value i1 to the second set value i2. The characteristic is an anti-time characteristic in which the breaking operation time T is shortened substantially linearly from T1 to T2 as the overcurrent increases. Further, the breaking characteristic in the range in which the magnitude of the overcurrent exceeds the second set value i2 is the fixed time characteristic (breaking operation time T = T2).

As described above, if the breaking operation time is set to the constant value T2 in the range where the magnitude of the overcurrent exceeds the second set value i2, the magnitude of the overcurrent causes the inrush current at the time of starting the load. Even if the second set value i2 may be exceeded due to factors such as the above, if the time during which the inrush current exceeds the second set value i2 is shorter than the constant value T2, the load current is cut off by the breaking operation. It will not be done.

In the above-mentioned embodiment, the magnitude of the first set value i1 which gives the lower limit of the overcurrent region is determined by the resistance values of the voltage dividing resistors R7 and R8 of the load current discriminating circuit 7 in the circuit shown in FIG. It can be appropriately adjusted by changing the magnitude of the reference signal Vr1. When the magnitude of the overcurrent is in the range from the first set value i1 to the second set value i2, the slope of the characteristic line of the inversion time of the breaking operation time is calculated by the integration circuit 8
It can be adjusted by changing the value of the integration time constant R11.C1 of. Further, the magnitude of the overcurrent is the second set value i
The length of the breaking operation time T2 (constant) in the range exceeding 2 is changed by changing the resistance value of the resistor R4 or R5 of the load current detection circuit 6 and changing the value V1 of the load current detection signal. be able to.

In the above embodiment, the load current detection signal is changed substantially in proportion to the load current when the load current is less than or equal to the second set value i2, and when the load current exceeds the second set value i2, The load current detection signal is held at a constant value so that the magnitude of the overcurrent changes from the first set value i1 to the second set value i2.
The disconnection control circuit is configured so that the disconnection operation time has the anti-time characteristic when the range is up to the above range, and the interruption operation time has the timed characteristic when the magnitude of the overcurrent exceeds the second set value i2. , A first anti-time limit for shortening the breaking operation time at a first rate as the overcurrent increases when the magnitude of the overcurrent is in the range from the first set value i1 to the second set value i2 When the magnitude of the overcurrent exceeds the second set value i2, the cutoff operation time is shortened at a second rate smaller than the first rate as the overcurrent increases. It is also possible to configure the cutoff control circuit so as to cut off the overcurrent by providing the timed characteristic. In such a configuration, when the load current is equal to or less than the second set value i2, the load current detection signal is changed at a first rate of change substantially in proportion to the load current, and the load current is set to the second set value. In the range exceeding i2, the load current detection circuit may be configured to change the load current detection signal in proportion to the load current at the second change rate smaller than the first change rate.

FIG. 6 shows an example of the configuration of the portion of the load current detection circuit 6 of the embodiment which has the first anti-time limit characteristic and the second anti-time limit characteristic in the overcurrent region as described above. In this embodiment, the configuration of the portion other than the load current detection circuit 6 is the same as that of the embodiment of FIG.

The load current detecting circuit 6 shown in FIG. 6 has a load current detecting resistor R1 whose one end is grounded and a load current i is conducted, an operational amplifier 61 and a zener diode ZD2.
And an amplifier circuit composed of resistors R2, R3 and R6. The non-grounded terminal of the resistor R1 is the operational amplifier 6
A resistor R2 is connected between the positive phase input terminal 1 and the negative phase input terminal of the operational amplifier and the ground. The resistor R3 is connected between the output terminal of the operational amplifier 61 and the negative phase input terminal, and the cathode is provided at both ends of the resistor R3.
A series circuit of a Zener diode ZD2 and a resistor R6 directed toward the output terminal side of is connected in parallel.

In this load current detection circuit, when the Zener diode ZD2 is in the non-conducting state, the operational amplifier 6
The load current detection signal Vo obtained at the output terminal of 1 is Vo =
iR1 (R2 + R3) / R2, and the load current detection signal Vo changes at a first rate of change [= R1 (R2 + R3) / R2] almost in proportion to the load current i.

As the load current i increases, the magnitude iR1 R3 / R2 of the voltage across the resistor R3 becomes zener diode ZD.
When the Zener voltage Vz of 2 is exceeded, the Zener diode becomes conductive. In this embodiment, when the magnitude of the load current i is the second set value i2, the resistance values of the resistors R2 and R3 and the zener voltage Vz are set so that the relationship of i2 = Vz R2 / R1 R3 is established. The selected load current exceeds the second set value i2 and the load current detection signal Vo is i.
2 Zener diode ZD2 becomes conductive when R1 (R2 + R3) / R2 = V1 is exceeded.

In the range where the magnitude of the load current i exceeds the second set value i2 and the Zener diode ZD2 is in the conductive state, the load current detection signal Vo is Vo = V1 + (i
-I2) R1 {R2 + R3 / (1 + R3 / R6)} / R
2 and the load current detection signal Vo has a second rate of change [= R1 {R2 + R3 (1
+ R3 / R6)} / R2] and changes in proportion to the load current i.

FIG. 7 shows the load current i and the load current detection signal Vo.
The load current detection signal Vo is
When the load current i is less than or equal to the second set value i2, the load current i changes at the first rate of change shown by the solid line portion of the straight line a, and the load current i changes to the second
When the set value i2 of the above is exceeded, it changes at the second change rate shown by the solid line portion of the straight line b. This second rate of change is the resistance R
It can be changed appropriately by changing the resistance value of 6.

In this embodiment, the circuits other than the load current detection circuit 6 are the same as those in the embodiment of FIG. 2, and the cutoff timing detection circuit 9 receives the integration signal Vout and load current detection signal Vo input from the integration circuit 8. When compared with Vout <Vo, the shutoff timing detection signal St is output. When the shutoff timing detection signal St is generated, the shutoff command signal generating circuit 10 sends a shutoff command signal to the switch circuit 3 to shut off the overcurrent.

When the magnitude of the load current is equal to or larger than the first set value i1 which gives the lower limit of the overcurrent region, the integrated signal Vout is expressed by the same formula Vout = Vx-as in the embodiment of FIG.
Since it is given by {(V2-V3) / C1 R11} t, the magnitude of the overcurrent is from the first set value i1 to the second set value i2.
In the range up to, the breaking operation time T is T = {V
x-iR1 (R2 + R3) / R2} C1 R11 / (V2-
V3), and the breaking operation time is the first ratio R1 (R2 + R3) C1 R11 / R2 (V2
It has the first anti-time characteristic which becomes shorter at -V3). When the magnitude of the overcurrent exceeds the second set value i2, the breaking operation time T is T = [(Vx-V1)-(i-i2) R1 {R2
+ R3 / (1 + R3 / R6)} / R2] ・ C1 R11 /
(V2-V3), and the breaking operation time is smaller than the first ratio as the overcurrent increases.
{R2 + R3 / (1 + R3 / R6)} C1 R11 / R2
It has a second anti-time limit characteristic that becomes shorter at (V2 + V3).

FIG. 8 shows the relationship between the load current i and the breaking operation time T in the present embodiment. In the figure, the shaded region represents the region for blocking overcurrent. The breaking operation time T has a first anti-time limit characteristic indicated by a straight line a when the magnitude of the overcurrent is in the range from the first set value i1 to the second set value i2, and the magnitude of the overcurrent is Has a second anti-time limit characteristic indicated by a straight line b in a range exceeding the second set value i2.

As described above, the load current is set to the second set value i.
If the cutoff operation time is shortened at a second ratio that is smaller than the first ratio in a range exceeding 2, the duration of load inrush current, etc. is shorter than the cutoff operation time shown by the second anti-time limit characteristic. As long as it is short, the switch circuit will not be interrupted.

The change rate (second rate) of the breaking operation time in the range where the magnitude of the overcurrent exceeds the second set value i2, that is, the magnitude of the slope of the second anti-time limit characteristic, is the load current detection value. It can be appropriately changed by changing the resistance value of the resistor R6 of the circuit 6.

In the above embodiment, the load 2 is a DC motor whose rotation direction can be reversed. However, as in the case where a load is a DC motor or an electromagnetic solenoid that can rotate only in one direction. If it is not necessary to reverse the polarity of the voltage applied to the load, the first operation switch 41 or the second operation switch 41 is used as the start / stop switch.
One having only one of the operation switches 42 may be used.

[0053]

As described above, according to the present invention, the load current is detected and the load current provides the lower limit of the overcurrent region.
When the set value is exceeded, the integrator circuit generates an integrated signal whose level decreases almost linearly with the passage of time, and when this integrated signal becomes smaller than the load current detection signal, a disconnection command is sent to the switch circuit. Since a signal is applied to shut off the overcurrent, it is possible to shut off the overcurrent by providing a counter-time characteristic that shortens the shutoff operation time as the overcurrent increases without using a temperature sensitive element such as a bimetal. You can

Further, in the present invention, when the magnitude of the load current exceeds the second set value which is larger than the first set value, the breaking operation time is given a time-definite characteristic, or the overcurrent is set to the first value. Since it has the anti-time characteristic that shortens the breaking operation time with the increase of the overcurrent at a rate smaller than that of the setting value of 2 or less, the overcurrent exceeding the 2nd setting value is caused by the inrush current of the load. It is possible to prevent an unnecessary shut-off operation from being performed when the current flows for a short time.

Further, according to the present invention, the overcurrent cutoff characteristic can be easily changed as necessary by only changing a part of the circuit constant of the cutoff control circuit. It is possible to obtain an overcurrent protection device capable of easily setting the overcurrent cutoff characteristic in accordance with the characteristics of the above.

[Brief description of drawings]

FIG. 1 is a block diagram showing an overall configuration of an exemplary embodiment of the present invention.

FIG. 2 is a circuit diagram showing an embodiment of the present invention in which each part of FIG. 1 is specifically shown.

FIG. 3 is a diagram showing a relationship between a load current and a load current detection signal in the embodiment of FIG.

FIG. 4 is a diagram showing a comparison between integrated signals and load current detection signals over time in the embodiment of FIG.

5 is a diagram showing a relationship between a load current and a breaking operation time in the embodiment of FIG.

FIG. 6 is a circuit diagram showing a configuration of a load current detection circuit used in another embodiment of the present invention.

7 is a diagram showing a relationship between a load current and a load current detection signal in the load current detection circuit used in the embodiment of FIG.

FIG. 8 is a diagram showing a relationship between load current and breaking operation time in the embodiment of FIG.

FIG. 9 is a diagram showing a general relationship between load current and breaking operation time in a conventional device.

[Explanation of symbols]

 1 Power Supply 2 Load (DC Motor) 3 Switch Circuit 31 First Excitation Coil 32 First Changeover Switch 33 Second Excitation Coil 34 Second Changeover Switch 4 Start / Stop Operation Switch 5 Break Control Circuit 6 Load Current Detection Circuit 61 operational amplifier 7 load current discrimination circuit 71 comparator 72 operational amplifier 8 integrating circuit 81 operational amplifier 9 shutoff timing detection circuit 91 comparator 10 shutoff command signal generating circuit Tr1 transistor Th thyristor D1 to D7 diode ZD1, ZD2 zener diode C1, C2 Capacitor R1 Load current detection resistor R2 to R16 resistor

Claims (2)

[Claims] 1. A switch circuit provided to cut off an overcurrent flowing from a power source to a load when a cutoff command signal is given, and a first setting in which the magnitude of the overcurrent gives a lower limit of an overcurrent region. From the value (i1) to the second value larger than the first set value (i1)
When it is in the range up to the set value (i2) of, the anti-time characteristic is shortened as the overcurrent increases after the overcurrent flows until the overcurrent is interrupted. A shutoff control circuit for giving a shutoff command signal to the switch circuit in accordance with the magnitude of the overcurrent so as to shut off the overcurrent by providing a timed characteristic for making the shutoff operation time constant when the second set value is exceeded. The cutoff control circuit detects a load current, and when the load current is less than or equal to the second set value, changes substantially in proportion to the load current, and the load current changes the second set value. A load current detection circuit that outputs a load current detection signal that holds a constant value in a range that exceeds the limit, and the load current detection circuit compares the load current detection signal with a reference signal having a magnitude corresponding to the first set value. The magnitude of the detection signal A load current determination signal (Vin) that takes the first state when the magnitude of the quasi-signal is less than the magnitude of the reference signal and takes the second state when the magnitude of the load current detection signal becomes greater than or equal to the magnitude of the reference signal. A load current determination circuit for outputting and the load current determination signal (Vin) are input, and when the load current determination signal is in the first state, a constant value is held, and the load current determination signal is in the second state. In some cases, an integrating circuit that outputs an integrated signal whose level decreases substantially linearly with the passage of time, and when the integrated signal is compared with the load current detection signal and the integrated signal becomes smaller than the load current detection signal A cutoff timing detection circuit for outputting a cutoff timing detection signal, and a cutoff command signal generation circuit for giving a cutoff command signal to the switch circuit when the cutoff timing detection signal is generated. Current protection device. 2. A switch circuit provided to cut off an overcurrent flowing from a power source through a load when a cutoff command signal is given, and a first setting in which the magnitude of the overcurrent gives a lower limit of an overcurrent region. From the value (i1) to the second value larger than the first set value (i1)
Within the range up to the set value (i2) of, the first anti-time limit time for shortening the interruption operation time from the flow of the overcurrent until the interruption of the overcurrent at the first rate with the increase of the overcurrent. When the overcurrent exceeds the second set value, the breaking operation time is set to the first value as the overcurrent increases.
And a cutoff control circuit that gives a cutoff command signal to the switch circuit according to the magnitude of the overcurrent in order to cut off the overcurrent by providing a second anti-time limit characteristic that is shortened at a second rate that is smaller than The cutoff control circuit detects a load current, and when the load current is less than or equal to the second set value, the cutoff control circuit changes at a first rate of change substantially in proportion to the load current. A load current detection circuit that outputs a load current detection signal that changes in a second rate of change that is smaller than the first rate of change in a range that exceeds the set value of The load current detection signal is set to the first state when the magnitude of the load current detection signal is less than the magnitude of the reference signal as compared with the reference signal having the magnitude corresponding to the first set value. Is larger than the reference signal A load current discriminating circuit that outputs a load current discriminating signal (Vin) that sometimes takes the second state, and a constant when the load current discriminating signal is in the first state by inputting the load current discriminating signal (Vin). An integrating circuit that holds the value and outputs an integrated signal whose level decreases substantially linearly with the passage of time when the load current determination signal is in the second state; and the integrated signal as the load current detection signal. By comparison, a cutoff timing detection circuit that outputs a cutoff timing detection signal when the integrated signal becomes smaller than the load current detection signal, and a cutoff command signal to the switch circuit when the cutoff timing detection signal occurs An overcurrent protection device comprising a shutoff command signal generating circuit.