JPS60254532A - Relay drive circuit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] Technical field The present invention relates to a relay drive circuit.

In order to drive a prior art relay, it is necessary to flow a driving current greater than the minimum current determined for each relay coil across both ends of the relay coil. The value of this drive current is generally determined by a resistor inserted in series between the relay coil and the applied voltage source. In this method, the initial drive current continues to flow during the relay operation period, so the power consumption by the relay coil is large, and the power loss in the relay coil becomes unavoidable, especially in devices that require low loss. .

Oigai! An object of the present invention is to provide a relay drive circuit in which the internal power loss of the relay coil is reduced by limiting the current during operation of the relay coil.

11 Sad 11 The relay drive circuit according to the present invention includes a current limiting resistor connected in series to a relay coil, a switch element that controls short-circuiting between both ends of the current limiting resistor, and a switch element that controls a short circuit between both ends of the current limiting resistor, and It has a time constant circuit in which the output voltage changes with a predetermined time constant, and the constant of the time constant circuit is set so that the output voltage of this time constant circuit is used as the control voltage of the switch element and the switch element is turned off after driving the relay coil. It is characterized by:

Example The present invention will be described in detail below using the drawings.

In the figure, a current limiting resistor 2 is provided in series with a relay coil 1, and a power supply +■ is applied to the relay coil 1 via this resistor 2. Switching elements 1 to 3 are provided to short-circuit both ends of the current limiting resistor 2, and the output voltage of the time constant circuit is applied to the gate of the transistor 3. This time constant circuit consists of a series circuit of a resistor 4 and a capacitor 5, and a resistor 6 parallel to the capacitor 5.

In this configuration, the voltage across the capacitor 5 is O■ before a power supply of 10 V is applied. In this state, when the power supply +■ is applied, the voltage across the capacitor 5 is O■, so the gate of the transistor 3 becomes the ground potential. Therefore, this transistor 3 is turned on, and conduction occurs between the source and drain, and the current limiting resistor 2 is short-circuited. Therefore, a voltage of 10 V sufficient for starting is applied to the relay coil 1, and the relay is turned on.

As time elapses in this state, the capacitor 5 is charged via the resistor 4, and its terminal voltage gradually increases. Jζ
As a result, the gate voltage of the transistor 3 gradually increases toward the power supply +V, and is finally clamped by the resistors 4 and 6 to a voltage obtained by dividing the power supply 1V. If the gate voltage at this time is a value sufficient to turn off transistor 3, transistor 3 will be turned off and the short-circuited state of current limiting resistor 2 will be released, thereby limiting the current flowing to relay coil 1. Become.

By appropriately selecting the values of the resistor 4 and capacitor 5, which are the time constants of the time constant circuit, the time during which the transistor 3 is turned on can be set. It is sufficient to set the time to be slightly longer than the time from when the electric current t++V is applied to the relay coil 1 until the relay coil operates. Further, the resistor 4.6 is set so that the transistor 3 is turned off at a value obtained by dividing the voltage of the power supply 1 and 2 by these two resistors. Note that the resistor 6 also has the role of discharging the capacitor 5 when the power supply +V is turned off.

The resistor 2 is selected to have a value that allows the lowest current that can maintain the operation of the relay coil 1 in a steady state to flow therethrough.

In the example shown in the figure, ancillary circuits such as so-called spark killers that limit the voltage generated by intermittent current in the relay coil are omitted, but of course they should be added in actual implementation. .

Effects of the Invention As described above, according to the present invention, there is an effect that not only can the relay coil be reliably activated, but also that the power loss of the relay coil during steady state can be suppressed to a minimum.

[Brief explanation of drawings]

The figure is a circuit diagram of an embodiment of the present invention. Explanation of symbols of main parts 1...Relay coil 2... Current limiting resistance 3...1-Ran resistor 4...Resistance 5... Capacitor Applicant: NEC Corporation Agent: Patent Attorney Makoto Yanagawa

Claims (1)

[Claims] A current-limiting resistor connected in series to the relay coil, a switch element that controls short-circuiting between both ends of the current-limiting resistor,
and a time constant circuit in which the output voltage changes with a predetermined time constant in response to turning on the relay coil drive power, and the output voltage of the time constant circuit is used as the control voltage of the switch element after the relay coil is driven. A relay drive circuit characterized in that a constant of the time constant circuit is set so as to turn off the switch element.