JP2774226B2 - Relay drive circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a relay driving circuit, and more particularly to a relay driving circuit for driving a relay for supplying power to a load such as a motor using a switching element such as a transistor.

[0002]

2. Description of the Related Art FIG. 3 shows an example of a conventional relay drive circuit. The operation of the circuit of FIG. 3 will be described briefly.

When no signal is input from the control circuit 80, when the switch 82 is turned on, a base current flows to the transistor Tr01 through the resistors R00 and R01, the transistor Tr01 is turned on, the relay coil 84B is excited, and the relay coil 84B is excited. 84 turns on. As a result, power is supplied to the load (motor or the like) 86 via the relay contact 84A, and the load 86 is driven.

When the load 86 is driven, the switch 82
Is turned off, the base current of the transistor Tr01 stops flowing, so that the transistor Tr01 is turned off, the relay coil 84B is de-energized, and the
4 turns off. Thus, the driving of the load 84 is stopped.

[0005] However, even if the switch 82 is in the off state, the transistor Tr01 is turned on and off by the control circuit 80.
If an off signal is input, on / off control is performed accordingly.

[0006]

In the above-described conventional relay drive circuit, there is a case where it is desired to delay or hold the operation of the transistor Tr01 for relay drive. In such a case, the control circuit 80 includes a capacitor, a resistor, and a transistor. A circuit that gradually changes the base current of the transistor Tr01 by combining the above is used.

In such a case, if the current flowing through the load is large (the resistance value of the load is small), the following problem occurs.

That is, when the transistor 84 is off and the relay 84 is off, part of the current flowing through the resistor R01 flows as the base current of the transistor Tr01, and the rest flows to the control circuit 80. In this case, when the current flowing into the control circuit 80 gradually decreases, the base current of the transistor Tr01 increases. When the base current reaches a certain value, the transistor Tr01 turns on, the relay 84 turns on, and a current flows to the load 86. Then, a large current for driving the load 86 flows through the resistance R00 (resistance of the power supply line) of the wiring, so that the circuit power supply voltage (voltage at point A in FIG. 3) decreases, and the current value passing through the resistance R01 decreases. Therefore, the base current of the transistor Tr01 decreases. For this reason, the transistor Tr01 cannot be maintained in the on state, and is turned off.
4 turns off. Then, the voltage drop due to the resistance R00 of the wiring is eliminated, so that the base current of the transistor Tr01 increases again, the transistor Tr01 is turned on again, and the relay 84 is turned on. In this manner, the relay 84 repeatedly turns on and off, so-called chattering of the relay 84 occurs.

Conversely, when the current flowing into the control circuit 80 increases when the relay 84 is on, the base current of the transistor Tr01 decreases, and chattering of the relay occurs according to the same principle.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a relay capable of effectively preventing the occurrence of relay chattering due to fluctuations in power supply voltage caused by driving and stopping a load. It is to provide a drive circuit.

[0011]

A relay drive circuit according to the present invention includes an operation terminal, and a switching element for turning on / off a relay for supplying power to a load in accordance with an amount of current input to the operation terminal. A switch that is connected between an operation terminal of the switching element and a power supply, and that connects the power supply to the operation terminal of the switching element in an on state and releases the connection in an off state, and an operation terminal of the switching element. Connected, a control circuit for controlling the amount of current flowing to the operation terminal side to control the on / off of the switching element, and connected between the operation terminal of the switching element and the load, and from the operation terminal only in the relay off state And a bypass circuit for passing only a current toward the load.

[0012]

According to the above arrangement, when the switch is turned on when the switching element is off and the relay is off, the power supply is connected to the operation terminal of the switching element, and the power supply current flows to the operation terminal. At this time, the power supply current also flows from the operation terminal side to the load side via the bypass circuit because the relay is still off. When the switching element is turned on by the power supply current flowing to the operation terminal side, the relay is turned on. As a result, power is supplied to the load, and the load is driven. At this time, since the relay is in the ON state, no current flows to the bypass circuit, and the power supply current flows only to the operation terminal side of the switching element. For this reason, the current flowing to the operation terminal side of the switching element when the relay is on is greater than when the relay is off. This keeps the relay on. In this case, even if the control circuit gradually increases the amount of current flowing to the operation terminal of the switching element and the relay is turned on, the current flowing to the operation terminal side of the switching element is larger when the relay is on than when the relay is off. Relay chattering does not occur.

On the other hand, when the switching element is on and the relay is on, no current flows in the bypass circuit, and the power supply current flows only to the operation terminal side of the switching element via the switch. Here, even if the control circuit gradually reduces the current flowing to the operation terminal of the switching element, the power supply current flows only to the operation terminal side. The ON state is maintained. Further, when the current flowing to the operation terminal side of the switching element further decreases and the switching element turns off, the relay turns off. When the relay is turned off, the current that has been flowing only to the operation terminal side of the switching element is branched off to the load side via the bypass circuit, so that the current that flows to the operation terminal side of the switching element is further reduced. For this reason, the relay maintains the off state, and chattering of the relay does not occur.

[0014]

An embodiment of the present invention will be described below with reference to FIG.

FIG. 1 shows a relay drive circuit 10 according to one embodiment of the present invention. The relay drive circuit 10 is a circuit that drives the relay 12 that supplies power to the load 14, and includes a transistor Tr11 as a switching element for controlling on / off of the relay 12, and a transistor Tr11 as an operation terminal of the transistor Tr11. A switch 20 having one end connected to a power terminal (hereinafter referred to as a "base") via resistors R11 and R12 and the other end connected to a power supply via a resistor R10.

A load (for example, a motor) 1 is connected between the power supply and the ground via a resistor R01 and a relay contact 12A.
4 are connected. Here, the resistance R01 is the wiring resistance of the power supply line.

A power supply is connected to a relay via a resistor R01.
One end of the coil 12B is connected to the relay coil 12B.
The other end of B is the emitter-grounded NPN transistor Tr11.
Connected to the collector.

Further, one end of a bypass circuit 22 is connected to a point B between the relay contact 12A and the load 16, and the other end of the bypass circuit 22 is connected to a circuit 18 extending from the switch 20 to the base of the transistor Tr11. Resistors R11 and R12
Are connected to a point C between them. The bypass circuit 22
A diode D11 whose cathode is connected to the point B;
And one end is connected to the anode of this diode D11,
The other end is constituted by a resistor R13 connected to the point C.

The control circuit 30 includes a common emitter NPN transistor Tr21, resistors R21, R22, R23, a capacitor C21, and a resistor R in accordance with the output of a sensor (not shown).
And a control circuit 32 that outputs a control signal to the 21 side. The collector of the transistor Tr21 is connected to the base of the transistor Tr11. Therefore, the control circuit 30 controls the transistor Tr.
Eleven base currents are increased or decreased.

Next, in the present embodiment constructed as described above,
The operation will be described. When the relay 12 is off and the load 14
When the switch 20 is turned on during driving, the resistors R10, R11
And a base current flows through the transistor Tr11 through the transistor R12.
It is. At this time, the capacitor constituting the control circuit 30
C21 is charged, and the transistor Tr21 is turned on.
If so, a power supply current also flows to the control circuit 30. This
, The transistor Tr11 is turned off (the transistor Tr11
11 base voltage = 0 [V]), and the resistance of the load 14 is R
Because it is very small compared to 13 mag, the potential V at point B ₁₂≒
0 [V]. The potential V at the point C₁₁Ha
The power supply voltage is determined by the parallel resistance of the resistors R12 and R13 and the resistor R11.
Is a divided voltage. Therefore, the resistor R13,
Power supply current is also flowing to the load 14 via the diode D11.
You. At this time, the base of the transistor Tr11 and the control circuit
30 is equal to V₁₁/ R12.

Here, when the capacitor C21 is started to be discharged by the control circuit 32 constituting the control circuit 30, the base current of the transistor Tr21 decreases and the current flowing from the resistor R12 to the control circuit 30 decreases accordingly. Eventually, the transistor Tr21 turns off. As a result, the base current of the transistor Tr11 gradually increases,
Eventually, the transistor Tr11 turns on (the transistor Tr11
Is positive). Therefore, the relay coil 1
2B is excited, and the relay 12 is turned on. At this time, the potential V ₁₂ at point B is V _12> V ₁₁ at the supply voltage (them if ignored R10). As a result, the diode D11 is turned off, and no current flows through the resistor R13. At this time, the potential V ₁₁ of point C, the power supply voltage by resistors R11 R12 and becomes a divided value, a current value flowing through the resistor R12 at that time increases from the off relay 12.

Specifically, when the relay 12 is turned on rather than when the relay 12 is turned off, [R11R12 / ｛(R11 + R12) (R12R13 + R11R12 +
R11R13)}] · V _CC only to increase. This calculation is performed ignoring circuit elements having small resistance values other than R11, R12, and R13.

For this reason, the base current of the transistor Tr11 increases more when the relay is turned on than when the relay is turned off. As a result, the relay 12 maintains the ON state.

On the other hand, when the transistor Tr11 is on and the relay 12 is on, no current flows through the bypass circuit 22, and the power supply current flows only through the switch 20 and the circuit 18 to the base terminal side of the transistor Tr11. . In this case, the control circuit 30 controls the transistor T
Even if the current flowing through the base of r11 is gradually reduced,
Since the power supply current flows only to the base side of the transistor Tr11, the transistor Tr11 maintains the ON state to some extent, and the ON state of the relay 12 is maintained. Further, the current flowing to the base of the transistor Tr11 further decreases,
When the transistor Tr11 turns off, the relay 12 turns off. When the relay 12 is turned off, the current that has been flowing only to the base of the transistor Tr11 is branched off to the load 14 via the bypass circuit 22, so that the base current of the transistor Tr11 is further reduced. For this reason, the relay 12 maintains the off state.

As described above, according to this embodiment, the current flowing to the base of the transistor Tr11 is
When the relay 12 is turned on and becomes less when the relay is turned off, the relay 12 is turned on from the off state, or conversely, when the relay 12 is turned off from the on state, the power supply current flows through the wiring resistance R10 of the power supply line, and the circuit Even if there is some fluctuation in the power supply voltage, it is possible to prevent the relay 12 from chattering.

FIG. 2 shows another configuration example of the control circuit.

[0027]

As described above, according to the present invention,
Due to the function of the bypass circuit, the amount of current flowing to the operating terminal of the switching element when the relay is on is greater than that when the relay is off. Is gradually increased, and when the relay is turned on, the on state of the relay is maintained. On the other hand, when the switching element is on and the relay is on, the control circuit gradually reduces the current flowing to the operation terminal of the switching element, and when the switching element is finally turned off and the relay is turned off, the switching element is turned off. Since the current flowing to the operation terminal side of the relay becomes smaller than when the relay is turned on, the off state of the relay is maintained. Therefore, even if the power supply voltage slightly varies due to the wiring resistance of the power supply line immediately after the start of power supply to the load or immediately after the power supply is stopped, chattering of the relay can be effectively prevented. effective.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a configuration of one embodiment of the present invention.

FIG. 2 is a circuit diagram showing another configuration example of the control circuit.

FIG. 3 is a circuit diagram showing a conventional example.

[Explanation of symbols]

 Reference Signs List 10 relay drive circuit 12 relay 14 load 22 bypass circuit Tr11 transistor (switching element)

Claims (1)

(57) [Claims] An operation terminal is provided, and a relay for supplying power to a load according to an amount of current input to the operation terminal is turned on.
A switching element to be turned off, a switch connected between an operation terminal of the switching element and a power supply, the switch connecting the power supply to an operation terminal of the switching element in an on state, and releasing the connection in an off state; A control circuit that is connected to an operation terminal of the element and controls an on / off of the switching element by controlling an amount of current flowing to the operation terminal side; and a relay off state that is connected between the operation terminal of the switching element and a load. And a bypass circuit for passing only a current flowing from the operation terminal side to the load.