JPH08228427A - Overcurrent protective device - Google Patents

Abstract

PURPOSE: To easily change the current cutoff characteristic of a switch circuit as required by giving a cutoff commanding signal to the switch circuit when detecting that the magnitude of a load current is larger than the lower limit value of an overcurrent region. CONSTITUTION: A cutoff control circuit 5 is composed of a load current detecting circuit 6, load current discriminating circuit 7, integration circuit 8, cutoff timing detecting circuit 9, and cutoff commanding signal generating circuit 10 and, when a load current falls within an overcurrent region and a zero-level cutoff timing detecting signal St is inputted to the circuit 10 from the circuit 9, a transistor is conducted and gives a trigger signal to a thyristor in the circuit 10. Then the circuit 10 gives a cutoff commanding signal Sb to a switching circuit 4 so as to cutoff the load current flowing through a load 3 from a power source 2. When a power switch is against turned on after the switch is once turned off and the thyristor is turned off, the load 3 can be redriven. Therefore, an overcurrent protective circuit, the current cutting-off characteristic of which can be easily set, can be obtained.

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 (electromagnet).

[0002]

2. Description of the Related Art Generally, when an overcurrent 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 insulation breakdown may occur or the load may burn. . Therefore, when there is such a possibility, an overcurrent protection device that shuts off the overcurrent to protect the load is provided.

In order to properly protect the load, when the magnitude of the load current enters the overcurrent region, the interruption operation time from the detection of the overcurrent to the interruption of the load current is It is desirable to have a so-called anti-time limit characteristic that shortens as the current value increases.

In a conventional overcurrent protection device having an anti-time limit characteristic, a temperature sensitive element such as a bimetal which senses heat generated by a load current and causes mechanical displacement is provided.
When the switch is opened directly by the displacement of the temperature sensitive element, or a switch operated by the displacement of the temperature sensitive element is provided in the exciting circuit of the electromagnetic circuit breaker, when the predetermined displacement occurs in the temperature sensitive element. The load current is cut off by performing the breaking operation of the electromagnetic breaker.

[0005]

As described above, in the conventional overcurrent protection device in which the current cut-off characteristic has the anti-time-delay characteristic, there are many mechanically operating parts and the characteristic variation is relatively large. Since the overcurrent is detected using the temperature sensitive element such as bimetal, there is a problem that the variation of the current cutoff characteristic becomes large.

Further, in the conventional overcurrent protection device of this type,
It is not possible to easily change various conditions such as the current value that gives the lower limit of the overcurrent region where the current cutoff operation starts and the slope of the anti-time characteristic line that gives the relationship between the magnitude of the overcurrent and the cutoff operation time. There was a problem.

Further, in the overcurrent protection device using the temperature sensitive element, after the overcurrent is detected and the breaking operation is performed, the energization of the load is restarted until the temperature of the temperature sensitive element decreases. Therefore, there is a problem in that, when it is requested to urgently restart the load after removing the cause of the overload, the request cannot be met.

The object of the present invention is not only to detect an overcurrent without using a temperature sensitive element such as a bimetal to have anti-time limit characteristics, but also to easily change the current interruption characteristics as necessary. An object of the present invention is to provide an overcurrent protection device that can be used.

Another object of the present invention is to provide an overcurrent protection device capable of restarting a load without a long waiting time after the load current is cut off.

[0010]

According to the present invention, as shown in FIG. 1 which shows the entire structure, the present invention is provided between a power source 2 and a load 3 and shuts off when a shutoff command signal Sb is given. The switch circuit 4 that operates to cut off the load current flowing from the power source through the load, and the switch circuit 4 when it is detected that the magnitude of the load current is equal to or greater than the set value i1 that gives the lower limit of the overcurrent region. The present invention relates to an overcurrent protection device having a shutoff control circuit 5 for giving a shutoff command signal to the.

In FIG. 1, reference numeral 1 denotes a start / stop switch operated when starting and stopping the load.

In the present invention, the cutoff control circuit 5 detects the load current i and outputs the load current detection signal Vo which changes substantially in proportion to the load current.
And comparing the load current detection signal Vo with a reference signal having a magnitude corresponding to the set value i1 and setting the first state when the magnitude of the load current detection signal Vo is smaller than the magnitude of the reference signal. Thus, when the magnitude of the load current detection signal Vo is equal to or greater than the reference signal, the load current determination circuit 7 that outputs the load current determination signal Vin that assumes the second state and the load current determination signal Vin are input to the load. When the current discriminating signal Vin is in the first state, it keeps a constant magnitude larger than the load current detecting signal Vo, and when the load current discriminating signal Vin is in the second state, the level is substantially linear with time. Is reduced to output an integrated signal Vout that is smaller than the load current detection signal Vo, and the integrated signal Vout is compared with the load current detection signal Vo. o A cutoff timing detection circuit 9 that outputs a cutoff timing detection signal St when
Switch circuit 4 when the shutoff timing detection signal St is generated
Cutoff command signal generation circuit 10 for giving a cutoff command signal Sb to
It has and.

[0013]

With the above configuration, the load current detection signal V
When o is smaller than the reference signal corresponding to the set value i1 that gives the lower limit of the overcurrent region (when no overcurrent is flowing), the load current determination signal Vin is in the first state. At this time, the integrated signal Vout output from the integration circuit 8 holds a constant value larger than the load current detection signal Vo, and the cutoff timing detection signal is not output from the cutoff timing detection circuit 9. Therefore, since the cutoff command signal is not given from the cutoff command signal generation circuit 10 to the switch circuit 4, the load current is not cut off.

When the load current i becomes equal to or more than the set value i1 which gives the lower limit of the overcurrent region and the load current detection signal Vo becomes equal to or more than the reference signal, the load current discrimination signal Vin takes the second state and the integration circuit 8 The output integrated signal Vout becomes a signal whose level decreases linearly with the passage of time. When the integrated signal Vout becomes equal to or less than the load current detection signal Vo, the cutoff timing detection circuit 9 outputs a cutoff timing detection signal St which determines the cutoff timing, and the cutoff command signal generation circuit 10 outputs a cutoff command according to the signal St. The signal Sb is output. Since the switch circuit 4 performs the shutoff operation in response to the shutoff command signal, the overcurrent is shut off. The interruption operation time from the detection of the overcurrent to the interruption operation of the switch circuit is shortened substantially linearly as the magnitude of the load current detection signal Vo, that is, the magnitude of the load current i increases.
Anti-time characteristic can be obtained.

According to the present invention, it is possible to easily change the set value i1 which gives the lower limit of the overcurrent region by changing the magnitude of the reference signal. Further, the relationship between the magnitude of the overcurrent and the breaking operation time can be easily changed by changing the integration time constant of the integrating circuit to change the slope of the integration signal with respect to time. Therefore, it is possible to easily change the current cutoff characteristic of the overcurrent protection device as needed.

Further, in the present invention, since it is not necessary to use a temperature sensitive element having a large thermal time constant for detecting an overcurrent, it is possible to restart the load immediately after the cause of the overload is removed. is there.

[0017]

2 is a circuit diagram of an embodiment of the present invention embodying the respective parts of FIG. 1, in which 1 is a start / stop operation switch, 2 is a power supply, and 3 is a load. Reference numeral 4 is a switch circuit, 5 is an interruption control circuit, and SW is a power switch.

In this embodiment, the power source 2 is a DC power source including a battery whose negative electrode side is grounded, and the load 3
Is a direct current motor to which a drive current is supplied from the power source 2, and the direction of rotation of the direct current motor is reversed by reversing the polarity of the applied voltage.

The switch circuit 4 in this embodiment is the first
A first electromagnetic switch having an exciting coil 41 and a changeover switch means 42 driven by the first exciting coil 41, and an exciting coil 43 and a changeover switch means 44 driven by the exciting coil 43. It is composed of two electromagnetic switches and diodes D1 to D3.

One ends of the first and second exciting coils 41 and 43 are commonly connected to the cathode of the diode D3, and the anode of the diode D3 is the power switch S.
It is connected to the positive electrode terminal of the power supply 2 through W. The diodes D1 and D2 are connected in parallel to both ends of the exciting coils 41 and 43 with their cathodes facing the positive electrode side of the power supply 2.

The first changeover switch means 42 has a movable contact 42a and fixed contacts 42b and 42c. When the first exciting coil 41 is in a non-excited state, the movable contact 42a contacts the fixed contact 42b. Then, when the first exciting coil 41 is excited, the movable contact 42a becomes the fixed contact 42a.
Contact c.

The second changeover switch means 44 has a movable contact 44a and fixed contacts 44b and 44c. When the second exciting coil 43 is in a non-excited state, the movable contact 44a contacts the fixed contact 44b. However, when the second exciting coil 43 is excited, the movable contact 44a becomes the fixed contact 44a.
Contact c.

The fixed contacts 42c and 44c of the first and second changeover switch means 42 and 44 are commonly connected to the connection point between the power switch SW and the diode D3. First
And the fixed contact 4 of the second changeover switch means 42 and 44.
2b and 44b are commonly connected to each other, and both fixed contacts 4
A common connection point of 2b and 44b is grounded through a current detecting resistor R1 of a load current detecting circuit 6 described later.

The start / stop operation switch 1 used in the present embodiment is composed of first and second exciting coils 41 and 43.
And a second operation switch 12 connected between the other end of each and the ground.

When the first operation switch 11 is closed,
Since the exciting coil 41 is excited and the movable contact 42a of the changeover switch means 42 is switched to the fixed contact 42c side,
The DC motor as the load 3 is rotated in one direction.
When the second operation switch 12 is closed, the exciting coil 43 is excited and the changeover switch means 44 causes the fixed contact 4 to move.
Since it is switched to the 4c side, the DC motor as the load 3 is rotated in the other direction.

First and second operation switches 11 and 12
When both are open and the exciting coils 41 and 43 are both in the non-excited state, the changeover switch means 42 and 4
4 movable contacts 42a and 44a are fixed contacts 42, respectively.
The load 3 is not driven because it contacts b and 44b to short circuit both ends of the load 3. Even when both the first and second operation switches 11 and 12 are closed, the movable contacts 42a and 44a contact the movable contacts 42c and 44c to short-circuit both ends of the load 3, so that the load 3 is not driven. .

The cutoff control circuit 5 includes a load current detection circuit 6, a load current determination circuit 7, an integration circuit 8, and a cutoff timing detection circuit 9.
And a shutoff command signal generating circuit 10.

The load current detection circuit 6 is connected between the common connection point of the fixed contacts 42b and 44b and the ground to connect the load current i.
Is composed of a load current detecting resistor R1 having a sufficiently small resistance value to be energized, and a known amplifier circuit for amplifying the voltage generated across the resistor R1 and comprising an operational amplifier 61 and resistors R2 and R3. At the output terminal of 61, a load current detection signal Vo that changes substantially in proportion to the load current i
{= IR1 (R2 + R3) / R2} is obtained.

The load current discriminating circuit 7 comprises an open collector output comparator 71 and a comparator circuit comprising resistors R7 and R8, and an impedance conversion circuit comprising an operational amplifier 72 and resistors R9 and R10. The resistors R7 and R8 are connected in series to form a voltage dividing circuit, which divides the constant voltage E output from a DC constant voltage circuit (not shown) to generate a reference signal Vr1 = ER7 / (R7 + R8).
The magnitude of the reference signal Vr1 is set to a magnitude corresponding to the set value i1 which gives the lower limit of the overcurrent region of the load current. The reference signal Vr1 is input to the inverting input terminal of the comparator 71, and the operational amplifier 61 is input to the non-inverting input terminal of the comparator 71.
The load current detection signal Vo obtained from the above is input.

The operational amplifier 72 has its output terminal and negative-phase input terminal connected so as to form a voltage follower circuit, and the positive-phase input terminal of the operational amplifier 72 is a comparator 7.
1 is connected to the output terminal.

The resistors R9 and R10 are connected in series to form a voltage dividing circuit for dividing the constant voltage E. The divided voltage obtained by this voltage dividing circuit V1 = ER9 / (R9 + R10)
Is input to the positive phase input terminal of the operational amplifier 72.

In the load current discrimination circuit 7, the comparator 71 compares the load current detection signal Vo with the reference voltage Vr1 and outputs the load current discrimination signal Vin from the operational amplifier 72 according to the magnitude relation between the two signals. . When the load current is smaller than the set value i1 that gives the lower limit of the overcurrent region and the load current detection signal Vo is smaller than the reference signal Vr1 (when Vo <Vr1), the transistor at the output stage of the comparator 71 is turned on. Since it is in the state, the load current determination signal Vin is in a state of almost zero level (ground level). In this embodiment, this state is the first state of the load current discrimination signal Vin.

On the other hand, when the load current exceeds the set value i1 which gives the lower limit of the overcurrent region, the load current detection signal Vo
Is above the reference signal Vr1 (when Vo ≧ Vr1), the output stage transistor of the comparator 71 is turned off, and the load current determination signal Vin = V1.
In this embodiment, this state is set as the second value of the load current determination signal Vin.
State.

The integrating circuit 8 is composed of an operational amplifier 81, a resistor R11 connected between the negative-phase input terminal of the operational amplifier and the output terminal of the operational amplifier 72, and a voltage divider composed of a series circuit of resistors R12 and R13. The circuit, the capacitor C1 connected between the negative-phase input terminal and the output terminal of the operational amplifier 81, and the cathode were connected to the negative-phase input terminal and the output terminal of the operational amplifier 81, respectively, with the anodes connected to each other. It is composed of a diode D5 and a zener diode ZD1. The voltage dividing circuit consisting of the resistors R12 and R13 divides the constant voltage E to divide the divided voltage V2 = ER12 / (R12 + R1
3) is generated and this divided voltage is applied to the positive phase input terminal of the operational amplifier 81. In the present embodiment, the magnitude of the divided voltage V2 is selected so that V2 <V1 (for example, V2).
1 = 2 [V] and V2 = 1 [V]).

In the integrator circuit 8 described above, when the load current determination signal Vin input from the load current determination circuit 7 is in the first state (Vin = 0) (the load current i is set to give the lower limit of the overcurrent region). (When it is smaller than the value i1), the integrated signal Vout output from the output terminal is clamped by the Zener diode ZD1, and a constant value Vx = V2 + Vz (Vz is the Zener diode ZD1) as shown by the straight line (a) in FIG. Zener voltage of) is held. On the other hand, the load current enters the overcurrent region, and the load current determination signal Vin is
(Vin = V1), the integrated signal Vout becomes Vou.
t = Vx-{(V1 -V2) / C1 R11} t (t is time), and the integrated signal Vout is linearly leveled with the passage of time t as shown by a straight line (b) in FIG. Becomes a signal that decreases.

The cutoff timing detection circuit 9 comprises a comparator 91 having an open collector output, and a non-inverting input terminal of the comparator 91 has an integrated signal Vou output from the integration circuit 8.
t is input, and the load current detection signal Vo output from the load current detection circuit 6 is input to the inverting input terminal.
The comparator 91 compares the integrated signal Vout with the load current detection signal Vo, and when the integrated signal Vout is larger than the load current detection signal Vo (when Vout> Vo), the output stage transistor is turned off. The integrated signal Vou
When t falls below the load current detection signal Vo (Vout ≤
When the state becomes Vo), the transistor of the output stage is turned on.

FIG. 3 shows the load current detection signal Vo [straight line (c)] together with the integrated signal Vout. When the load current is in the overcurrent region, the load current determination signal Vin is in the second state (Vin = V1 state), and the level of the integrated signal Vout is decreasing with the elapse of the time t, " In the case of the straight line (b)], the integrated signal V
out becomes the load current detection signal Vo or less. In this embodiment, when Vout≤Vo, the transistor at the output stage of the comparator 91 is turned on, the potential of the output terminal of the comparator becomes zero, and this zero potential state is cut off. It is output as the timing detection signal St.

The cutoff command signal generation circuit 10 has a comparator 9 whose base constitutes a cutoff timing detection circuit 9 via a resistor R14.
1 is connected to the output terminal and the collectors are resistors R15 and R16
PNP transistor Tr1 grounded via a series circuit
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 diodes D6 and D whose cathodes are commonly connected to the anode of the thyristor.
It consists of 7. A constant voltage E is applied to the emitter of the transistor Tr1. The anodes of the diodes D6 and D7 are connected to the other ends of the first and second exciting coils 41 and 43 of the switch circuit 4, respectively.

In the cutoff command signal generation circuit 10, the load current is in the overcurrent region, and the cutoff timing detection circuit 9
When the shut-off timing detection signal St of zero level is input from the transistor Tr1, the transistor Tr1 becomes conductive and gives a trigger signal to the thyristor Th. As a result, the thyristor Th is turned on and the cutoff command signal Sb is given to the switch circuit 4.

When the thyristor Th is turned on, the exciting coils 41 and 43 are both in the excited state (the cutoff command signal is given to the switch circuit 4), and the movable contacts 42a and 44a of the changeover switches 42 and 44 are fixed contacts 4 respectively.
The state is switched to the 2c side and the 44c side, and the power source 2
The load current flowing through the load 3 from is blocked.

When the load current i is cut off and the load current detection signal Vo becomes 0, the transistor at the output stage of the comparator 91 is turned off and the base current is not given to the transistor Tr1. Therefore, the transistor Tr1 is turned off. However, since the thyristor Th maintains the conductive state,
The load current is maintained in a cutoff state.

To re-drive the load 3, the power switch S
The current passing through the thyristor Th is reduced to a holding current or less by turning off W once, the thyristor is turned off, the cause of the overload is removed, and then the power switch SW may be turned on again.

In the above embodiment, the cutoff operation time from when the overcurrent flows through the load (DC motor) 3 to when the overcurrent is cut off is shown in FIG.
Is given by the time t = T, and the breaking operation time is represented by T = (Vx-Vo) C1R11 / (V1-V2). As is clear from this equation, the load current i is equal to or greater than the set value i1 that gives the lower limit of the overcurrent region,
When the magnitude of the load current detection signal Vo is equal to or larger than the reference signal Vr1 (Vo ≧ Vr1),
As the magnitude of the load current detection signal Vo (that is, the magnitude of the load current i) increases, the breaking operation time T decreases linearly.

FIG. 4 shows the relationship between the load current i and the breaking operation time T. The load current is not cut off in a region where the load current i is smaller than the set value i1 which gives the lower limit of the overcurrent region. When the magnitude of the load current i becomes equal to or larger than the set value i1 and enters the overcurrent region, the cutoff operation time T is the initial value T1 =
x-Vr1) C1 R11 / (V1-V2) gradually decreases, and when the load current i becomes i2 or more, the breaking operation time T becomes 0, and an overcurrent flows and the circuit is cut off at the same time.

The magnitude of the set value i1 which gives the lower limit of the overcurrent region is changed by changing the values of the voltage dividing resistors R7 and R8 of the load current discrimination circuit 7 in the circuit shown in FIG. By doing so, it can be easily changed.
Further, the slope of the current cutoff characteristic line representing the relationship between the load current i and the cutoff operation time T is the integration time constant R11 of the integration circuit 8.
-It can be changed appropriately by changing the value of C1. The magnitude of the overcurrent i2 when the breaking operation time T becomes zero is determined by the magnitude of Vx = V2 + Vz.
It can be appropriately changed by changing the resistance values of the voltage dividing resistors R12 and R13 of the integrating circuit 8 and changing the magnitude of the divided voltage V2 input to the positive phase input terminal of the operational amplifier 81.

In the above embodiment, the load 3 is a DC motor, but it goes without saying that the present invention can be applied to the case of driving another load such as an electromagnetic solenoid.

In the above embodiment, since the load 3 is a DC motor and it is necessary to rotate the motor in the forward and reverse directions, two electromagnetic switches having changeover switch means are provided in the switch circuit 4. When it is not necessary to switch the direction of the load current, the switch circuit 4 can be composed of an electromagnetic switch that simply performs an on / off operation. In this case, the start / stop operation switch 1 must be composed of a single switch. You can

The switch circuit 4 does not necessarily have to be an electromagnetic switch, but may be a semiconductor switch capable of on / off control.

In the above embodiment, the first state of the load current discrimination signal is set to the zero level state and the second state is set to the high level state, but the first and second states of the load current discrimination signal are set. May have different levels, and depending on the configuration of the integrating circuit 8, the first state may be a high level state and the second state may be a zero level (or low level) state.

In the above embodiment, the shutoff timing detection signal St
Is a zero level signal, but the cutoff command signal generation circuit 10
Depending on the configuration, the cutoff timing detection signal may be a high level signal.

[0051]

As described above, according to the present invention, when the load current is detected and the load current becomes equal to or more than the set value which gives the lower limit of the overcurrent region, the integration circuit almost eliminates the passage of time. The integrated signal whose level decreases linearly is output,
When this integrated signal becomes less than the load current detection signal, a cutoff command signal is given to the switch circuit to cut off the overcurrent.Therefore, the cutoff operation time is set to the load current without using a temperature sensitive element such as bimetal. It is possible to provide an overcurrent protection device that has an anti-time-delay characteristic that is shortened with an increase in the current, to cut off an overcurrent, and to obtain an overcurrent protection device with less variation in characteristics.

Further, the current cutoff characteristics such as the set value of the load current which gives the lower limit of the overcurrent region and the slope of the anti-time characteristic line of the cutoff operation time can be easily changed as necessary by changing a part of the circuit constant. Therefore, there is an advantage that it is possible to obtain an overcurrent protection device with higher accuracy and easier setting of the current cutoff characteristic than the conventional one.

Furthermore, according to the present invention, since it is not necessary to use a temperature sensitive element having a large thermal time constant for detecting an overcurrent, it is possible to restart the load immediately after the cause of the overload is removed. There are advantages.

[Brief description of drawings]

FIG. 1 is a block diagram showing an overall configuration 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 an example of an integrated signal and a load current detection signal used in the embodiment of FIG.

FIG. 4 is a diagram showing an example of a relationship between a load current and a breaking operation time in the example of the present invention.

[Explanation of symbols]

 1 Start / Stop Operation Switch 2 Power Supply 3 Load (DC Motor) 4 Switch Circuit 41 First Excitation Coil 42 First Changeover Switch Means 43 Second Excitation Coil 44 Second Changeover Switch Means 5 Breaking 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 Interruption timing detection circuit 91 Comparator 10 Interruption command signal generation circuit Tr1 Transistor Th Thyristor D1 to D3, D5 to D7 Diode ZD1 Zener Diode C1, C2 Capacitor R1 Load current detection resistance R2, R3, R7 to R16 resistance

Claims (1)

[Claims] 1. A switch circuit, which is provided between a power source and a load, performs a shutoff operation when a shutoff command signal is given to shut off a load current flowing from the power source through the load, and a magnitude of the load current. An overcurrent protection device comprising: a cutoff control circuit that gives a cutoff command signal to the switch circuit when it is detected that the value is equal to or more than a set value that gives a lower limit of an overcurrent region, wherein the cutoff control circuit is A load current detection circuit that detects a load current and outputs a load current detection signal that changes substantially in proportion to the load current; and compares the load current detection signal with a reference signal having a magnitude corresponding to the set value. Then, the first state is set when the magnitude of the load current detection signal is smaller than the magnitude of the reference signal, and the second state is set when the magnitude of the load current detection signal is equal to or larger than the reference signal. Negative charge A load current determination circuit that outputs a flow determination signal, and the load current determination signal as an input, and when the load current determination signal is in the first state, holds a constant magnitude larger than the load current detection signal, 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 time and becomes smaller than the load current detection signal; Compared with the detection signal, a cutoff timing detection circuit that outputs a cutoff timing detection signal when the integrated signal becomes less than or equal to the load current detection signal and a cutoff command signal to the switch circuit when the cutoff timing detection signal is generated. An overcurrent protection device comprising: a cutoff command signal generating circuit for giving.