JPH10106416A - Drive circuit for electromagnetic relay - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make power loss generated by a drive circuit not to be excess even if the voltage fluctuation coefficient of the DC power source of an electromagnetic relay is large. SOLUTION: A drive circuit is provided with first comparator 451 in which the detection voltage VK of a detection resistor 43 connected to an exciting coil 3 in series is compared with a threshold value VH produced by first threshold voltage source 441 and which outputs a Low comparison signal S1 when the detection signal VK is smaller than the threshold value VH and outputs a High comparison signal S1 when the detection signal CK is higher than the threshold value VH, and second comparator 452 is which the detection voltage VK is compared with a threshold value VL producted by second threshold voltage source 442 and which outputs a High comparison signal S2 when the detection signal VK is smaller than the threshold value VL and outputs a Low comparison signal S2 when the detection signal VK is larger than the threshold valve VL, and a latch circuit 46 which outputs a control signal SR when the signal S1 is input to a reset terminal R and a signal S2 is input to a signal terminal S respectively. The on and off of a transistor 41, as a switching element, is controlled by the control signal SR so as confine an exciting coil current between two threshold currents.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving circuit for an electromagnetic relay used in a control circuit or an output device of a control device, and more particularly to a driving circuit for an electromagnetic relay used in a DC power supply having a large voltage fluctuation.

[0002]

2. Description of the Related Art FIG. 4 is a circuit diagram showing a conventional driving circuit for an electromagnetic relay (hereinafter simply referred to as a relay). In this figure, 1 is a DC power supply that is not stabilized and has a voltage fluctuation,
Reference numeral 3 denotes an exciting coil of the relay, and the constant voltage circuit 2 is provided between them. If the voltage applied to the exciting coil 3 becomes excessively large, the current increases and the temperature rise becomes excessively large, possibly causing a burnout accident. Therefore, the DC power supply 1 whose voltage value fluctuates is used as a power supply for the relay. In such a case, such a constant voltage circuit 2 is used. The constant voltage circuit 2 is one of the so-called negative feedback constant voltage circuits (see “Basic Electronic Circuit” on page 174 of the Institute of Electrical Engineers of Japan).

The constant voltage circuit 2 has a transistor 21 inserted in series between the DC power supply 1 and the exciting coil 3. A constant voltage circuit having an anode connected to the base terminal of the transistor 21 and a cathode connected to the negative electrode of the DC power supply 1. It comprises a voltage diode 22 and a resistor 23 connected between the collector terminal and the base terminal of the transistor 21. The outline of the operation of the constant voltage circuit 2 for stabilizing the voltage applied to the exciting coil 3 is as follows. Assuming that the voltage of the DC power supply 1 is E and the voltage applied to the exciting coil 3 is V, the voltage V is a value obtained by subtracting the voltage V _EB between the emitter and the base of the transistor 21 from the zener voltage V _z of the constant voltage diode 22. Become. That is,

[0004]

V = V _z −V _{EB The} zener voltage V _z is substantially constant, and the voltage V _EB is a small value of 1 volt or less and almost constant if the base current is a relatively large value. As a result, the voltage V is kept substantially constant even if the voltage E fluctuates.

[0005] In short, the excitation coil 3 has a voltage V _z
There is applied, E-V _z is the voltage difference between the voltage E will be the transistor 21 is borne.

[0006]

As described above, in the constant voltage circuit 2, the voltage applied to the exciting coil 3 is kept constant because the transistor 21 bears the difference voltage. A power loss corresponding to the product of the flowing current, in other words, the current I flowing through the exciting coil 3 and the difference voltage E- _Vz occurs. The constant voltage diode 22 is selected such that the Zener voltage has a value slightly smaller than the minimum value of the voltage E. Therefore, when the ratio of the voltage fluctuation of the DC power supply 1 is small, the maximum value of the difference voltage E- _Vz can be made small, but when the voltage fluctuation is large, the difference between the maximum value and the minimum value of the voltage E naturally becomes large. Difference voltage E
The maximum value of -V _z becomes necessarily large. If this difference voltage is large, the power loss of the transistor 21 becomes excessive and the temperature rise becomes a problem. In addition, the temperature rise inside a device such as a control device in which this relay is incorporated causes a rise in the temperature of electronic components. There is a problem that deterioration is accelerated and the life of the device is shortened. In order to use a DC power supply having a large voltage fluctuation and prevent such a problem from occurring, there is a need to increase the cooling efficiency of the transistor 21 and the cooling efficiency of the device. This leads to a problem that the price of the entire apparatus increases.

An object of the present invention is to solve such a problem and to provide a drive circuit for an electromagnetic relay which does not need to improve the cooling efficiency even when the voltage fluctuation rate of the DC power supply of the relay is large.

[0008]

According to the present invention, to solve the above-mentioned problems, the present invention turns on when a voltage is applied from a DC power supply for supplying a current to an exciting coil of an electromagnetic relay. Is turned off when becomes larger than a first threshold value, and turned on when becomes smaller than a second threshold value which is smaller than the first threshold value. Is inserted into the
By providing a diode whose cathode is connected to the negative side of the DC power supply in parallel with the exciting coil,
The current flowing through the exciting coil after exceeding the threshold value does not reciprocate between the first threshold value and the second threshold value and does not become larger than the second threshold value. It will not be less than the first threshold. In addition, there is no power loss equivalent to that of the exciting coil in the circuit elements other than the exciting coil. When the switching element is off, the current flowing through the exciting coil flows through the diode.

A detection resistor connected in series with the exciting coil,
A detection voltage at both ends of the detection resistor is compared with a first threshold value, and when the detection voltage is smaller than the first threshold value, a first comparison signal is output which is low and high when the detection voltage is high. The comparator compares the detection voltage with the second threshold value, and when the detection voltage is lower than the second threshold value, it is High, and when the detection voltage is higher,
A second comparator for outputting a low second comparison signal;
A latch circuit that outputs a control signal when the comparison signal is input to the reset terminal and the second comparison signal is input to the signal terminal, and the switching element turns off when the control signal is high and turns on when the control signal is low. With such a configuration, the above-described means can be specifically realized.

If the switching element is kept on for a predetermined time after the application of the voltage by the DC power supply, a sufficient current value for the operation of the relay to be turned on from off to off is obtained within this time. On the other hand, the current required to maintain the ON state is less than half the current required for the operation of turning the relay from OFF to ON, so the values of the first and second threshold currents are set as described above. Even if it is set to a value smaller than one-half of those values, a current value sufficient to maintain the ON state can be secured, so that the power loss of the exciting coil is reduced to a quarter of that of the above-described drive circuit. Of 1 or less. In the case of a specific circuit configuration using the above-described latch circuit and comparator,
A series circuit of a resistor and a capacitor connected in parallel to a DC power supply, and an AND circuit for inputting the voltage between the terminals of the capacitor and the output signal of the latch circuit are provided. When the output signal of the AND circuit is high, the switching element is provided. Is off, Lo
It can be realized by turning on when w.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION

[0012]

Embodiment 1 The present invention will be described below based on an embodiment. FIG. 1 is a circuit diagram of a drive circuit for an electromagnetic relay according to a first embodiment of the present invention. The same circuit elements as those in FIG. However, the arrangement of the other components of the drive circuit in this figure and the excitation coil is different from that in FIG. That is, FIG. 4 shows a circuit configuration in which the constant voltage circuit 2 is inserted between the DC power supply 1 and the exciting coil 3, but in FIG. 1, a large surrounding drive circuit 2A indicated by a dashed line is shown.
The excitation coil 3 shown by an equivalent circuit is surrounded by a dashed line. The exciting coil 3 is shown as a series circuit of an inductance 31 and a resistor 32. However, such a difference in the circuit diagram is not essential, but is for the purpose of illustrating the circuit configuration of the drive circuit 4 as an embodiment in an easily understandable manner.

In FIG. 1, a drive circuit 4 includes a transistor 41 as a switching element connected in series to the exciting coil 3 and a detecting resistor 43, and an exciting coil 3 and a detecting resistor 43.
A first and a second signal in which the voltage between the terminals of the diode 42 and the detection resistor 43 connected in parallel to the series circuit of
, Two comparators 451 and 452,
The first and second two threshold voltage sources 441 and 442 for setting the threshold voltages of 1,452, and the first comparator 451
The first comparison signal S ₁ which is the output signal of the reset terminal R
The latch circuit 46 compares the signal S ₂ second is the output signal of the second comparator 272 outputs the control signal S _R is input from the output terminal Q to the signal input terminal S, the control signal S
_R is input to the base terminal of the transistor 41 via the resistor 47.

The first threshold voltage generated by the first threshold voltage source 441 is V _H , and the second threshold voltage source 442
Let V _L be the second threshold voltage generated by V _H > V _H >
_VL is set. When the transistor 41 is on and a current flows through the exciting coil 3, the detection resistor 43
Of the detected voltage V _K of the product of the resistance value and the current value of the first + input terminal of the comparator 451 of the second comparator 452 - are input to the input terminal, a first threshold voltage V
_H is applied to the-input terminal of the first comparator 451, and the second threshold voltage _VL is applied to the + input terminal of the second comparator 452.

When the second comparison signal S ₂ is high, the latch circuit 46 is in a reset state and the first comparison signal S ₁
Control signal S _R Any High Any Low becomes Low. If the second comparison signal S ₂ is low, the first comparison signal S ₁ changes from low to high when the latch circuit 46 is not reset.
The control signal S _R changes to become High, thereafter maintains the state of the High unless reset. That is, the latch circuit 46 sets the output signal of the second comparator 451 to High.
It has a holding function to hold the state when it becomes.

When the control signal S _R, which is the output signal of the latch circuit 46, is low, the base-emitter voltage of the transistor 41 increases, so that a base current flows and the transistor 41 is turned on. . FIG. 2 is a glass showing the time change of the current for explaining the operation of the constant current circuit 2A of FIG. 1. The horizontal axis represents time t, and the vertical axis represents the current I flowing through the exciting coil 3.

Now, it is assumed that the voltage of the DC power supply 1 is applied at time t ₀ . The operation of the drive circuit 4 after this is as follows. In this figure, the subscripts 1 to 3 and a and b at the time t relate to the operation described here.
Relates to the operation of a second embodiment of the present invention described later. After the voltage t ₀ <t <t ₁ is applied, even if a current flows through the exciting coil 3 via the transistor 41, the current rise is limited by the inductance 31 and rises linearly as shown in the figure. Therefore, immediately after the application, the voltage V _K of the detection resistor 43 is small, and the output signal of the first comparator 451 is low.
Therefore, the second comparison signal S _1, which is the output signal of the second comparator 452, is High, and thus the latch circuit 4
6 is in a reset state and the control signal S _R is low, so that the transistor 41 is turned on. That is, most of the voltage of the DC power supply 1 is applied to the exciting coil 3, and the current increases at a rate of increase determined by the voltage value and the value of the inductance 31. When the inter-terminal voltage V _K of the detection resistor 43 becomes higher than the threshold voltage V _L , the second comparator 45
The comparison signal S ₂ of the second, which is the output signal 2 is reset in the latch circuit 46 becomes Low is released (this time current I
Is the second threshold current I _L , but the time code is not given), but the current I further increases.

The voltage V detected by the detection resistor 43_KFThreshold
Value voltage V_HIs larger than the output of the first comparator 271.
When the force signal changes from Low to High, the control signal S_RIs Low
High from the start, and as a result, the transistor 41
It turns off and the current is interrupted (at this time, the time t
₁And the current I is the first threshold current I_HIs). t₁<T <t_Two The current I flowing through the exciting coil 3 and the detection resistor 43 is
Through the resistor 42, and the inductance 31 and the resistance 32
Drop at a current drop rate corresponding to the time constant determined by this
The detection voltage V_KAlso drop in proportion to the current I. t_Two<T <t_Three Voltage V_KIs the threshold voltage V_LIf it is smaller than
At time t_TwoAnd the value of the current I at this time is
Threshold current I_L), The second comparison signal S _TwoIs Low
To high, resetting the latch circuit 46
Control signal S_RChanges from High to Low. So Tran
The register 41 is turned on again, and the voltage of the DC power supply 1 is excited.
The current I applied to the coil 3 increases again, and the time t_Threeso
The transistor 41 is turned off again, and the current I does not turn down.
You.

The above operation is repeated, and the current I reciprocates between the two threshold currents I _H and I _L determined by the two threshold voltages V _H and V _L. It does not exceed the first threshold current I _H. Further, the transistor 41 functions as a switching element, and the current is substantially 0 when the voltage is off when the voltage is off, and the voltage is substantially 0 when the current is on when the current is flowing. Only the generated loss occurs, and the loss value is much smaller than the resistance loss generated by the resistance of the coil 3. Of course,
It is much smaller than the loss generated by the transistor 21 of the conventional constant voltage circuit 2 described above. Therefore, in consideration of the cooling efficiency of the control device or the like in which the relay is incorporated, the loss generated by the drive circuit 2A can be neglected.

The time points t _a and t _b are used to explain the change when the voltage E of the DC power supply 1 increases.
When the voltage E and increased at time t _a, the rate of increase in current I becomes large, the second threshold current I at time t _a
L value time reaching the first threshold current I _H at the time t _a from of, smaller than the spacing between the time t ₃ from the time t ₂ if Katoe. However, the current I does not protrude above or below the two threshold currents.

[0021]

Embodiment 2 FIG. 3 is a circuit diagram of a drive circuit of an electromagnetic relay according to a second embodiment of the present invention. In FIG. 3, the same circuit elements as those in FIG. Subscript A
To eliminate duplicate descriptions. 1 is different from FIG. 1 in that a series circuit of a resistor 491 and a capacitor 492 is connected between the terminals of the DC power supply 1, and two signals of a signal S _C and a signal S _R which are voltages between terminals of the capacitor 492 are provided. Is provided as an input signal.
8 is input to the base terminal of the transistor 41, and the two threshold voltages of the first and second threshold voltage sources 441A and 442A are changed to the first and second threshold voltages of FIG. This is the point that V _LA and V _HA are set to values smaller than the threshold voltages V _L and V _{H of the} second threshold voltage sources 441 and 442.

The operation of the drive circuit 4A of FIG. 3 will be described below mainly on the points different from the drive circuit 4 of FIG. The above-described graph showing the time change of the current shown by the broken line in FIG. 2 is for explaining the operation of the drive circuit 4A. A, the solid line and the dashed line show that the phase of the change after time t ₆ coincides, but this is only for the sake of simplicity of explanation, and the phase of the vertical change in both current waveforms is shown. There is no necessity to match. Immediately after the DC power supply 1 is applied at time t ₀ <t <t ₄ at time t ₀ , similarly to the drive circuit 4, the current I increases at a rising rate determined by the voltage value of the DC power supply 1 and the inductance value of the exciting coil 3. .
The same holds for the point that the signal S _R maintains the low state. On the other hand, a signal S which is a voltage between terminals of the capacitor 492
_C is low at the beginning of application of the DC power supply 1, and rises exponentially with a time constant determined by the resistance value of the resistor 491 and the capacitance of the capacitor 492. And the AND circuit 48 is Hig
Until the processing of h, it is treated as a signal that takes a Low value. Therefore, initially, since the two input signals of the AND circuit 48 are both low, the output signal of the AND circuit 48 is also low.
Thus, as in the case of FIG. 1, the transistor 41 can be turned on to supply a current to the exciting coil 3.

The voltage V _K is the first threshold value V signal the second comparison signal S ₂ reaches the _HA becomes the High S _R is signal S _C is also turned to High, as will remain Low Since it is set, the output signal of the AND circuit 48 is Low, and therefore, the transistor 41 remains ON. Current I reaches a saturation value I _A further rises above the first threshold current I _HA. The t ₄ <t <t ₅ signal S _C eventually saturates at the voltage E of the DC power supply 1, but before reaching the voltage value that the AND circuit 48 processes as High, the AND at the time t ₄ , which is the current time. Circuit 48
Since both input signals become high, the output signal changes from low to high, the transistor 41 is turned off from on, and the current I drops. After this, the signal S _C
Since still maintaining the state of the High, the current I, the first corresponding to the second threshold current I _LA and first threshold voltage V _HA corresponding to the second threshold voltage V _LA Threshold current I
_The point of reciprocation with the _HA is the same as the operation of the drive circuit 4 in FIG.

As described above, the two threshold voltages V shown in FIG.
_Since the values of V _LA and V _HA are set to be lower than _L and V _H by half or less, the current thresholds have the same relationship. In addition, the subsequent current I repeats up and down at a position lower than the current change in FIG. The reason why the current flowing through the exciting coil 3 is increased immediately after the DC power supply 1 is applied and maintained at a small value thereafter is as follows.

In general, comparing the current of the exciting coil 3 required for the relay to operate, that is, turning on from the off state, and the current required for maintaining the on state, the latter is half or half of the former. It is actually less than that. Therefore, the relay is normally turned on and off even if the current immediately after voltage application for operating the relay is increased and the current for maintaining the state after the operation is set to a value smaller than one half of the current instead. Works. Instead, the power loss of the exciting coil 3 can be greatly reduced. The value of the second threshold current I _L in the case of the first embodiment is set to a value slightly larger than the value required for the operation of the relay, while I _{LA in} the case of the second embodiment is The power loss of the exciting coil 3 of the drive circuit is reduced to about 1/4 since about 1/4 is sufficient.

Although the specific circuit configuration of the drive circuit of the electromagnetic relay is shown in FIGS. 1 and 3 as an embodiment, in order to attain the object of the present invention, in addition to the above-described embodiment, a conventional technology will be described. Various circuit configurations are adopted within the range.

[0027]

According to the present invention, as described above, the current of the exciting coil is controlled between ON and OFF of the switching element to take only a value between two large and small threshold currents. Since the current of the exciting coil does not become excessive, and there is no circuit element equivalent to the power loss generated by the exciting coil, even if the voltage fluctuation rate of the DC power supply is large, the electromagnetic relay according to the present invention is used. There is no need to improve the cooling efficiency of the used control device and the like, and the effect of contributing to cost reduction of the target device can be obtained.

If the switching element is maintained in the ON state for a predetermined time after the application of the voltage by the DC power supply, it is necessary to maintain the ON state with respect to the current required for the operation of turning the relay from OFF to ON. Since the required current is actually less than half, the value of the two threshold currents can be set to a value less than one half of those described above, so that the power loss generated by the exciting coil is reduced. Can be reduced to 以下 or less.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a drive circuit of an electromagnetic relay according to a first embodiment of the present invention.

FIG. 2 is a graph showing a temporal change of a current for explaining the operation of the drive circuit of the present invention;

FIG. 3 is a circuit diagram of a drive circuit of an electromagnetic relay according to a second embodiment of the present invention.

FIG. 4 is a circuit diagram of a drive circuit of a conventional electromagnetic relay.

[Explanation of symbols]

1 DC power supply 2 Constant voltage circuit 3 Excitation coil 4
4A: drive circuit, 41: transistor (switching element), 42: diode, 43: detection resistor, 441, 4
41A: first threshold voltage source, 442, 442A: second threshold voltage source, 451: first comparator, 452 ...
2nd comparator, 46 ... latch circuit, 48 ... AND circuit,
491: resistance, 492: capacitor

Claims (4)

[Claims] 1. A switch is turned on when a voltage is applied from a DC power supply that supplies current to an exciting coil of an electromagnetic relay, and is turned off when a current flowing through the exciting coil becomes larger than a first threshold value. A switching element that is turned on when the value becomes smaller than a second threshold value smaller than the threshold value of 1 is inserted in series with the DC power supply, and the cathode is connected to the negative side of the DC power supply. A driving circuit for an electromagnetic relay, wherein a diode is provided in parallel with an exciting coil. A detection resistor connected in series with the exciting coil;
A detection voltage at both ends of the detection resistor is compared with a first threshold value, and when the detection voltage is smaller than the first threshold value, a first comparison signal is output which is low and high when the detection voltage is high. The comparator compares the detection voltage with the second threshold value, and when the detection voltage is lower than the second threshold value, it is High, and when the detection voltage is higher,
A second comparator for outputting a low second comparison signal;
A latch circuit that outputs a control signal when the comparison signal is input to the reset terminal and the second comparison signal is input to the signal terminal, and the switching element turns off when the control signal is high and turns on when the control signal is low. The driving circuit for an electromagnetic relay according to claim 1, wherein: 3. The driving circuit for an electromagnetic relay according to claim 1, wherein the switching element is kept on for a predetermined time after a voltage is applied by the DC power supply. 4. A series circuit of a resistor and a capacitor connected in parallel to a DC power supply, and an AND circuit for inputting a voltage between terminals of the capacitor and an output signal of a latch circuit is provided.
3. The driving circuit for an electromagnetic relay according to claim 2, wherein the switching element is turned off when the output signal of the AND circuit is high and turned on when the output signal is low.