JPS5856448B2 - Relay drive circuit - Google Patents

Description

Detailed Description of the Invention The present invention relates to power saving of a drive circuit for a polarized latching relay in which the armature is reversed depending on the direction of the drive current and latched in by a permanent magnet, thereby preventing malfunctions due to voltage fluctuations and pulse noise. It is an object of the present invention to provide the above-mentioned power saving circuit.

Figure 1 shows the basic circuit of a power-saving polarized latching relay drive circuit, in which a DC power supply E, a switch S, a resistor R2, a capacitor C1, and a polarized latching relay L form a series circuit. An SCR equivalent transistor circuit SCR is connected between both ends of the capacitor C1 and the resistor R2.
is connected between the base terminals of one transistor T1, a diode D is connected in parallel to a resistor R2 in the forward direction, and a resistor R1 is connected between the power source E and the switch S.

To explain the operating state of the basic circuit in Figure 1, the DC power supply E
The voltage is set slightly higher than the operating voltage of relay L, and when switch S is closed, charging current flows to capacitor C through diode D, and excitation current flows to relay L in the direction of the solid arrow, closing the contact. Invert r.

At this time, the SCR equivalent circuit is in a forward blocking state and does not conduct.

When capacitor CI is charged to the supply voltage, relay L
The excitation current no longer flows through the relay, but as mentioned above, the relay's armature is attracted to the permanent magnet, so the contacts remain in the same state.

Therefore, the power consumption of the power supply is only that which flows through the resistor R1.

Next, when switch S is opened, the charge in capacitor C is first discharged through resistors R2 and R1, and the voltage drop across resistor R2 causes a base current to flow between the emitter and base of transistor T1, making transistor T1 conductive. As a result, the transistor T2 also becomes conductive, and the SCR circuit becomes conductive, so most of the charge in the capacitor C is discharged through the SCR circuit, and an exciting current flows through the relay L in the direction of the dotted arrow, closing the contact r. Invert.

As the capacitor C continues to discharge and the terminal voltage of the capacitor C decreases, the SCR circuit becomes non-conducting and the excitation current of the relay L stops flowing, but the contacts remain as they are as described above.

As mentioned above, in this basic circuit, when the switch S is in the on state, after the charging current of the capacitor C momentarily flows, the power is only consumed by the resistor R1, and the resistor R1 is connected to the transistor TI. Since only a small base current flows through the resistor, a sufficiently high resistance value can be used, and therefore almost no power is consumed.

However, in the basic circuit shown in Figure 1, when the switch is turned on,
As shown in FIG. 2, if voltage fluctuations or surges are mixed in the power supply voltage E, the terminal voltage of the capacitor C may become higher than the power supply side by JE, so the transistor T,
There is a risk that current will flow from the emitter to the base and the SCR circuit will become conductive, causing the relay to malfunction.

By the way, in order to be less susceptible to such voltage fluctuations or surges, a conventional technique in which the trigger power source for the SCR circuit is taken from both ends of a capacitor is disclosed in, for example, Japanese Utility Model Application Publication No. 52-161433. However, in this prior art, SCR.

The circuit configuration is more complex than the conventional circuit shown in Figure 1, in which the trigger circuit is placed in the capacitor's charging/discharging path. There was a problem in that there was a risk of noise occurring.

The present invention makes it possible to prevent malfunctions of relays due to surge voltage, etc. by making slight improvements to the conventional circuit shown in FIG.

FIG. 3 shows an embodiment of the present invention, in which a Zener diode 2 blocks reverse current when the voltage fluctuation (E) is less than the Zener voltage, giving the circuit a noise margin.

However, even in the circuit shown in Figure 3, due to the junction capacitance C2 of the Zener diode, the impedance of the Zener diode becomes low against steep pulse noise, and the SCR circuit becomes conductive as in the case without the Zener diode 2. It has the disadvantage of being

The present invention aims to prevent malfunctions even due to such pulse noise.

That is, in FIG. 3, the diode D has a junction capacitance Cd.
By using a sufficiently large one, as mentioned above, the pulse noise outside the high frequency flowing through the junction capacitance C2 of the Zener diode can be made to flow to the junction capacitance Cd of the diode instead of flowing to the base emitter of the transistor T1. The ratio of Cd/C2 may be selected to be sufficiently large.

FIG. 4 shows another embodiment of the present invention, in which a capacitor C2 is added instead of using a large diode D in FIG.

3 is suitable for monolithic circuits, and FIG. 4 is suitable for discrete circuits.

In fact, if the capacitor C2 is selected to be at least 10 times the junction capacitance C2 of the Zener diode, the terminal voltage of C2 can be made sufficiently lower than the V voltage of the transistor (approximately 0.4 to 0.7 V).

As described above, according to the present invention, in a power-saving polarized latching relay drive circuit, surge voltage malfunction due to junction capacitance of a Zener diode for absorbing voltage fluctuations can be suppressed by S
There are advantages that can be prevented by inserting an absorption capacitor or equivalent diode junction capacitance between the gate and cathode of the CR or its equivalent circuit.

[Brief explanation of drawings]

Fig. 1 is a basic circuit for implementing the present invention, Fig. 2 is an explanatory diagram of the same operation as above, Fig. 3 is a relay drive circuit diagram showing an embodiment of the present invention, and Fig. 4 is a circuit diagram showing another embodiment. It is. L...Polarized latching relay, C1) C2...Capacitor, SCR...SCR or its equivalent transistor circuit, T1. T2...Transistor, D...Diode, R1) R2...Resistor, 2...Zener diode, S...Switch, E...DC power supply, C2...
... Junction capacitance of Zener diode, Cd... Junction capacitance of diode.

Claims (1)

[Claims] 1 Connect a capacitor in series to a polarized latching relay,
An SCR or an SCR equivalent transistor circuit is connected in parallel to this, a diode and a resistor are connected in parallel between the emitter base of one transistor of the transistor circuit, and a Zener diode and a switch are connected between the base and the emitter of the other transistor. A resistor is connected between the power source and the switch, and the diode has a sufficiently larger junction capacitance than the Zener diode, or a capacitor is connected in parallel with the diode. A relay drive circuit characterized by: