JPH063705B2 - Relay drive circuit - Google Patents

Description

TECHNICAL FIELD The present invention relates to a relay drive circuit, and more particularly to a relay drive circuit configured to supply a drive current to a relay coil via a switching transistor.

BACKGROUND ART FIG. 4 shows a conventional example of this type of relay drive circuit. In the figure, a relay driving transistor Q ₁ and a relay coil 2 are connected in series between the input terminal 1 to which the power supply voltage is supplied and the ground, and the base of the transistor Q ₁ is externally connected to a high voltage via a control terminal 3. When the relay-on control voltage of the level is applied, the current I _c flows from the input terminal 1 to the collector of the transistor Q ₁ , and the drive voltage is applied to the relay coil 2. Then, the relay coil 2 is excited and the relay contact 4 is closed, so that the power supply voltage is supplied to the external device via the output terminal 5. On the contrary, when the transistor Q ₁ is turned off, the current I _c does not flow, so that the drive voltage is not applied to the relay coil 2, the relay contact 4 is opened, and the supply of the power supply voltage to the outside is stopped.

In the relay drive circuit having such a configuration, particularly when it is mounted in an in-vehicle device, the in-vehicle device is apt to change the power supply voltage, and when a momentary interruption of the power supply voltage occurs, the drive voltage applied to the relay coil 2 is increased. Will disappear immediately, so relay contact 4
Will be opened. Therefore, the supply destination of the power supply voltage is forced to stop the operation each time, and the operation is hindered. In addition, the frequent opening / closing operation of the relay contact 4 accelerates the deterioration of the relay contact 4.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and an object of the present invention is to provide a relay drive circuit that prevents the relay contacts from being opened each time due to a temporary drop or momentary interruption of the power supply voltage. .

A relay drive circuit according to the present invention is a relay drive circuit having a relay that intermittently outputs a DC voltage and a switching transistor that supplies a drive current to a relay coil of the relay according to a base input voltage. A stabilizing circuit that uses the signal as the base input voltage via a time constant circuit, a capacitor connected in parallel with the relay coil, and a collector of the switching transistor.
The unidirectional element is connected in series in the forward direction with respect to the current path between the emitters.

Example Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a circuit diagram showing an embodiment of the present invention, for example, a case where it is mounted on an in-vehicle device. In the figure, the same parts as those in FIG. 4 are denoted by the same reference numerals, and the input terminal 1 has a DC power supply voltage I from a battery (not shown).
However, the power supply voltage II generated by turning on a so-called accessory switch (not shown) is supplied to each of the input terminals 6. A diode D, which is a unidirectional element, is connected in series in the forward direction on the collector side of the transistor Q ₁ , and a capacitor C ₁ is connected in parallel to the relay coil 2.

The relay-on control voltage supplied from the outside through the control terminal 3 passes through the inverter 7 including the resistors R ₁ and R ₂ and the transistor Q ₂ and the resistors R ₃ and R ₄ and the transistor Q 2.
₃ is supplied to the buffer 8. The power supply voltage II from the input terminal 6 is applied to the emitter of the transistor Q ₃ in the buffer 8. The collector output of the transistor Q ₃ is connected to the relay driving transistor Q via the resistor R _5.
1 base. Relay drive transistor Q
_A capacitor C ₂ and a Zener diode ZD are connected in parallel between the base of ₁ and the ground, whereby the base voltage of the transistor Q ₁ is stabilized at the Zener voltage of the Zener diode ZD. That is, the relay control voltage signal supplied from the control terminal 3 is used as the base input of the transistor Q1 via the time constant circuit composed of the resistor R5, the capacitor C2 and the zener diode ZD.
Therefore, even if the relay-on control voltage (or the output voltage of the transistor Q3 in this case) is momentarily turned off, an appropriate voltage is input and held in the base of the transistor Q1 for a period determined by the time constant.

Next, the operation of the relay drive circuit having such a configuration will be described. The power supply voltages I and II are always applied to the input terminal 1 while the circuit is operating.
When the relay-on control voltage of high level is input to the control terminal 3, the output of the inverter 7 becomes low level (ground level), which turns on the transistor Q ₃ of the buffer 8. Turned power supply voltage II
Is output. Resistor R ₅ to the _voltage, the capacitor C _2, is supplied to the base of the relay drive transistor Q ₁ together are stabilized through the Zener diode ZD, so that the flow collector current I _c to the transistor Q _1. As a result, a drive voltage is applied to the relay coil 2 and the relay contact 4 changes from the open state to the closed state.

Now, in the closed state of the relay contact 4, if, for example, a momentary interruption occurs in the power supply voltage I, the collector potential of the transistor Q ₁ momentarily becomes 0 [V] state. As a result, the drive voltage is not applied to the relay coil 2, but the voltage due to the accumulated charge of the capacitor C ₁ is applied and the voltage across the relay coil 2 is gradually attenuated. Even after the momentary interruption, the relay contact 4 can maintain the closed state until the voltage across the relay coil 2 drops to the holding voltage of the relay coil 2. Further, in the case where the momentary interruption time is long, it can be dealt with by increasing the capacity of the capacitor C ₁ accordingly.

When the power supply voltage I is interrupted as described above, the transistor Q
_Since the base voltage of ₁ is stabilized, transistor Q
_A forward bias is applied to the PN junction between the base and the collector of the transistor _1. Therefore, the current flows backward between the emitter and the collector in combination with the voltage across the capacitor C ₁ , and the emitter voltage of the transistor Q ₁ is correspondingly increased. It has been clarified by the applicant's experiment that the decrease of Q
A diode D connected in series with the collector of ₁ serves to prevent this. FIG. 2 shows the emitter voltage (B) of the transistor Q ₁ with respect to the drive voltage (A) in which the instantaneous interruption occurred.
The waveform of the solid line a shows the case where the diode D is present, and the waveform of the alternate long and short dash line b shows the case where the diode D is absent. As is clear from this waveform diagram, the emitter voltage of the transistor Q ₁ gradually decreases with and without the diode D, so that the relay holding time can be sufficiently secured, and the capacitor C ₁ is correspondingly increased.
The capacity can be reduced.

In the above embodiment, the diode D is replaced by the transistor Q.
_Although the case of connecting in series to the collector side of No. ₁ has been described, it is also possible to connect in series to the emitter side of the transistor Q ₁ as shown in FIG.

As described above, according to the relay drive circuit of the present invention, the relay control voltage signal is used as the base input voltage of the switching transistor that supplies the drive current to the relay coil via the time constant circuit, and The capacitor is connected in parallel and the unidirectional element such as a diode is connected in series in the forward direction to the current path between the collector and emitter of the switching transistor, so that the relay control voltage signal and the DC power supply voltage drop temporarily. It is possible to prevent the relay contact from opening each time due to a momentary interruption or interruption, which prevents the relay contact from opening and closing more than necessary.
The life of the relay contact can be extended.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIG. 2 is a waveform diagram of an emitter voltage (B) of a transistor Q ₁ with respect to a drive voltage (A) in which an instantaneous interruption occurs. FIG. 3 is a circuit diagram showing another embodiment of the present invention, and FIG. 4 is a circuit diagram showing a conventional example. Main part of the code of Description 2 ...... relay coil 4 ...... relay contacts 7 ...... inverter 8 ...... buffer Q 1 _...... relay driver transistor D ...... backflow preventing diode C 1 _...... emitter voltage decay delay capacitor

Claims (1)

[Claims] 1. A relay drive circuit comprising: a relay for intermittently outputting a DC voltage output; and a switching transistor for supplying a drive current to a relay coil of the relay according to a base input voltage. A stabilizing circuit that uses the base input voltage via a constant circuit, a capacitor that is connected in parallel to the relay coil, and a unidirectional circuit that is connected in series in the forward direction with respect to the collector-emitter current path of the switching transistor. A relay circuit having an element.