JPH01279533A - Relay driver circuit - Google Patents

Abstract

PURPOSE:To heighten the upper limit value of a circuit DC resistance capable of adaptation by furnishing a voltage dividing circuit to give a gate voltage to a thyristor, sensitively moving by the current obtained through charging/ discharging of a capacitor, and by changing over the switch. CONSTITUTION:When DC is coming from a circuit, both a diode D and a thyristor SCR are in OFF condition, and charging current is given to a capacitor C through a resistance R1. Attainment of a specified value by the voltage of this capacitor C raises the gate voltage of the thyristor SCR fed with the two- end voltage upon driving by resistances R1, R2. Now the thyristor SCR is turned on to allow current to flow through a coil RL1. Thus discharge current is given to the coil RL1 from the capacitor C, and giving an appropriate value to the capacitance of capacitor C allows the discharge current to exceed the sensitive moving current of a solenoid relay. This enables changeover of a contact 2 due to discharge current, which accomplishes a relay driver circuit, in which the upper limit value of adaptable circuit DC resistance is heightened.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a relay drive circuit, and particularly to a relay drive circuit that drives connection switching of relay contacts in response to a DC voltage sent through a communication line.

[Conventional technology]

As shown in the circuit diagram of FIG. 2, a conventional relay drive circuit of this type includes a coil (RL) 1 for excitation of an electromagnetic relay;
It has a configuration in which a Zener diode ZD for suppressing back electromotive force and overcurrent bypass is connected in parallel, and a coil L for increasing impedance in a communication band is connected in series to this and connected to a communication line. The figure shows a communication method in which a center station and a remote station are connected by a line. In addition to the communication equipment, each station is equipped with test equipment for testing the line. During the line test, DC voltage is sent from the center station. In this example, a remote station is provided with an electromagnetic relay that switches the connection of the line to the test equipment in response to the received data. That is, during communication, since the impedance of the coil L is high, no current passes through the RLI, and the switching contact 2 of the electromagnetic relay is connected to the communication device. When a DC voltage arrives through the line during a line test, it passes through the coil L to the RL
A current flows through I, switching the connection of switching contact 2 towards the test device. At the end of the test, the direct current transmission from the center station is stopped and the connection of the switching contact 2 is returned to the partner device.

[Problem to be solved by the invention]

In the conventional relay drive circuit described above, if the DC resistance of the line exceeds a certain upper limit due to reasons such as the line length being too long or the wire diameter being small, the magnitude of the current flowing through RL'l when DC arrives from the line does not reach the current of the electromagnetic relay, making it impossible to switch the connection of the switching contact 2 to the test equipment.

SUMMARY OF THE INVENTION An object of the present invention is to provide a relay drive circuit that allows the upper limit value of the DC resistance of an applicable line to be higher than before.

[Means for solving problems]

The circuit of the present invention includes a coil for exciting an electromagnetic relay, a thyristor connected in series in the middle of a current path passing through the coil and turning on the current path when the gate voltage rises, and a thyristor that turns on the current path when the gate voltage rises; It includes a capacitor that is charged with a DC signal when the DC signal arrives at the input end, and a voltage divider circuit that divides the voltage across the capacitor to provide the gate voltage of the cycler.

〔Example〕 Next, the present invention will be explained with reference to the drawings.

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

This embodiment differs from the conventional circuit (Fig. 2) in that a thyristor SCR is connected in series in the forward direction in the middle of the current path passing through RLl, and a diode D is further connected to the connection point of fill L and RLI.
and a resistor R1 are connected in parallel, and a capacitor C is connected in series, and the voltage across the capacitor C is connected to the resistor R2 and R1.
It has a configuration in which the voltage is divided by and connected to the gate of the thyristor SCH.

When DC arrives from the line, both diode D and thyristor SC'R are initially off, and resistor R1
A charging current is applied to the capacitor C via the capacitor C. Correspondingly, the voltage across capacitor C increases and when it reaches a certain value, thyristor SCR turns on and RLI
current begins to flow. When the direct current resistance of the line is large, the voltage at the connection point of coil L and RLI becomes lower than the voltage across capacitor C, and diode D turns on.
A discharge current is applied from capacitor C to RLI. By setting the capacitance of capacitor C to an appropriate value, this discharge current can be made to exceed the electromagnetic relay's current, and by exciting the RLI with the discharge current, the connection of switching contact 2 of the electromagnetic relay is switched to the test equipment. be able to. When this discharge progresses and the voltage of the capacitor C decreases, only a current corresponding to the voltage drop and the arriving DC through the line flows through the RLI. If the direct current resistance of the line is large, this current value will be less than the electromagnetic relay's moving current, but since the relay has moved, if this current value is greater than the holding current of the electromagnetic relay, the connection of switching contact 2 will be maintained on the test equipment side. can.

In a normal electromagnetic relay, the holding current is less than half of the moving current, and as mentioned above, when DC voltage arrives from the line, a current exceeding the moving current is first applied to the RLI by charging and discharging capacitor C. After switching the connection of the switching contact 2, if the current flowing through the RLI in response to the DC voltage drop in the line is greater than the holding current, the connection of the switching contact 2 can be switched to the line test side and held. Therefore, in this embodiment, the upper limit value of the applicable line DC resistance can be made higher than before, and a wider range of application than before can be obtained.

〔Effect of the invention〕

As explained above, the present invention provides a relay drive circuit that increases the upper limit of applicable line DC resistance higher than conventional ones by impressing an electromagnetic relay with the current obtained by charging and discharging a capacitor when DC arrives from the line. It has the effect of realizing

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of an embodiment of the present invention, and FIG. 2 is a circuit diagram of a conventional relay drive circuit. 1... Fill (RL), 2... Switching contact, L... Fill, ZD... Zener diode, C... Capacitor, R0~R8・
... Resistor, SCR ... Thyristor, D.
·····diode. Agent Patent Attorney Oto Uchihara

Claims (1)

[Claims] A coil for exciting an electromagnetic relay, a thyristor connected in series in the middle of a current path passing through the coil and turning on the current path when the gate voltage rises, and a DC signal to the current input end of the current path. A relay drive circuit comprising: a capacitor that is charged with the DC signal when the DC signal arrives; and a voltage divider circuit that divides the voltage across the capacitor to provide the gate voltage of the thyristor.