JPH04312729A - Relay drive circuit - Google Patents

Abstract

PURPOSE:To prevent a momentary interruption and an erroneous operation due to voltage drop of an AC power source by providing such a circuit constitution as increasing the applied DC voltage to a relay to an operation voltage or higher to make the relay ON, and reducing the voltage down close to the holding voltage once it is made ON to continue the ON. CONSTITUTION:The DC voltage of a DC power source device 15 is supplied to the coil 16 of a relay through a transistor(Tr) 17. A shown circuit consisting of resistors 18, 26, 21, 23, 24, Zener diodes 19, 25, a NPNTr 20 and PNPTr 22 is connected to the base of the Tr 17. Each Zener voltage of the diodes 19, 25 is set slightly higher than the holding voltage and an operating voltage or higher. When a switch 27 is made ON in this state, the Tr 17 is ON, and the voltage of the coil 16 becomes the operating voltage or higher to make the relay ON. Then, the voltage is dropped down close to the holding voltage to hold the ON. Thus, the momentary interruption an erroneous operation and due to voltage drop of an AC power source 10 is prevented, and the consumed power is reduced.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a relay drive circuit.

0002

2. Description of the Related Art A conventional relay drive circuit will be described below. In FIG. 3, 1 is an AC power supply, 2 is a load such as a heater, 3 is a contact point of a relay that controls the heater 2, and 4 is a contact point of a relay that controls the heater 2.
5 is a coil of a relay that controls the contact 3; 6 is a transistor that controls the current of the coil 5; and 7 is a switch that controls the base current of the transistor 6.

[0003] In some relay drive circuits having such a configuration, when the switch 7 is turned on, the transistor 6 is turned on, the relay contact 3 is closed, and the heater 2 is energized.

0004

[Problems to be Solved by the Invention] However, in the above configuration, the DC power supply 4 needs to maintain sufficient voltage to drive the relay 5 even when the transistor 6 is turned on, so the current in the coil is reduced. It was necessary to prepare a DC power supply device 4 having a sufficiently large current capacity to supply the voltage without causing a voltage drop.

Suppose that the current capacity of the DC power supply device 4 is small and when the transistor 6 is turned on, the output voltage drops below the operating voltage of the relay.

For purposes of explanation, let Vt be the minimum operating voltage required to switch a normally open contact of a relay from off to on, and Vh be the minimum holding voltage that can keep the contact in the on state.

[0007] If the reduced voltage is higher than the lowest holding voltage Vh for keeping the contact 3 of the relay on, the contact 3 remains on and therefore operates normally.

However, if the switch 7 is already turned on when the AC power supply 1 is connected to the circuit, or if a momentary power outage or voltage drop occurs in the AC power supply 1, the transistor 6 remains on and the DC power supply 4 is turned on. When the voltage becomes lower than the holding voltage Vh, the relay contact 3 turns off even though the transistor 6 is on, and even after the voltage recovers, the DC power supply 4 remains on because the transistor 6 is on. Since the output cannot rise above the operating voltage Vt, the relay contact 3 remains in the off state.

The present invention solves the above-mentioned conventional problems, and even if a DC power supply device 4 having a relatively small current capacity and low performance is used, malfunctions due to momentary power outages or voltage drops of the AC power supply can be avoided. The purpose of this invention is to reduce the power consumption of the entire circuit and improve its reliability by providing a relay drive circuit that does not generate electricity.

0010

Means for Solving the Problems In order to achieve the above object, the means of the present invention provides a DC power supply device that obtains DC power from an AC power supply, a coil of a relay connected to this DC power supply, and a coil of a relay connected to the DC power supply. a transistor connected in series to control the coil current, and a first resistor, a first Zener diode, and an NP transistor connected in series to the base of the transistor.
A second resistor and a second Zener diode are connected in series to the bases of the NPN transistor and the PNP transistor, whose bases and collectors are connected to each other. the Zener voltage of the first Zener diode is set to be higher than the minimum voltage that can keep the normally open contacts of the relay in the on state, and
The Zener voltage of the Zener diode is determined by a relay drive circuit that is set to a minimum voltage that can switch the normally open contact of the relay from an off state to an on state.

[0011]

[Operation] The above configuration provides a relay drive circuit that operates reliably without malfunctioning due to instantaneous power outages or voltage drops in the AC power supply, even if a relatively small and low power consumption DC power supply is used. It is something to do.

0012

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples of the present invention will be described below with reference to the drawings.

In FIG. 1, 10 is an AC power supply, 11 is a power switch, 12 is a heater for keeping the food warm, 13 is a thermostat for controlling the temperature of the heater 12 to a constant temperature, and 14 is for controlling power supply to the heater 11. Relay contacts, 15 is a DC power supply, 16 is a relay coil that operates contact 14, 17 is a transistor that controls the current flowing through coil 16, 18 is a first resistor that limits the base current of transistor 17, and 19 is a first resistor. 20 is an NPN transistor connected in series with the first resistor 18 and the first Zener diode 19 by its emitter; 21 is an NPN transistor;
A resistor 22 for stabilizing the operation of the transistor 20
23 is a resistor for stabilizing the operation of the PNP transistor 22; 24 is a second resistor for limiting the base current of the PNP transistor 22; 25 is a PNP transistor whose base and collector are connected to each other;
is a second Zener diode connected in series to the second resistor 24; 26 is a resistor for stabilizing the operation of the transistor 17; and 27 is a switch that turns the relay contact 14 on and off.

Next, the operation of the circuit shown in FIG. 1 will be explained. When the AC power supply 10 is connected to the circuit and the power switch 11 is turned on, a DC output voltage Vo is generated at the output of the DC power supply 15.

When the switch 27 is off, the transistor 17 is also turned off, so the output voltage Vo becomes higher than the lowest operating voltage Vt of the relay.

Furthermore, the Zener voltage V2 of the second Zener diode 25 is set so that a base current that turns on the transistor 22 flows when the output voltage Vo becomes higher than the operating voltage Vt.

When the switch 27 is turned on in this state, the second
Since current flows through the Zener diode 25, the base current of the PNP transistor 22 flows through the second resistor 24 and turns on the transistor 22. This becomes the base current of the transistor 20 and turns on the transistor 20, so the transistor 22 The base current flows to the transistor 17 through the first resistor 18 and the first Zener diode 19, and the base current flows to the transistor 1.
7 is turned on, and current flows through the relay coil 16. Since the voltage Vo applied to the relay coil 16 is higher than the operating voltage Vt, the contact 14 is turned on.

After the contact 14 is turned on, it is only necessary to apply sufficient voltage to the relay coil 16 to hold the contact 14, so the output voltage Vo of the DC power supply 15 is slightly higher than the holding voltage Vh. be lowered to.

In this state, the second Zener diode 2
Although no current flows through transistor 5, the base current of transistor 22 is supplied from the collector current of transistor 20, so transistors 20 and 22 continue to be turned on even if the DC voltage Vo decreases.

Normally, the holding voltage Vh of the relay is equal to the operating voltage V
Since it is about 25% of t, the output voltage Vo at this time is set to about 30% of the output voltage when the relay is off.

If the switch 27 is on when the AC power supply 10 is connected to the circuit, the output voltage Vo of the DC power supply 15 increases from 0V, and the Zener voltage V2 of the second Zener diode 25 and the transistor 22 V
Since the base current of the transistor 22 does not flow while the voltage is lower than the sum of be (base-emitter voltage), the transistor 22 and the transistor 20 are in an off state, and the output voltage Vo is equal to the Zener voltage V2 of the second Zener diode 25. Transistors 22 and 20 are turned on only when the voltage becomes higher than the sum of Vbe (base-emitter voltage) of transistor 22, which turns on transistor 17 and turns on relay contact 14.

After the contact 14 is turned on, the output voltage Vo
The voltage drops to about 30% of the voltage when the relay is turned on.

Next, when a momentary power outage occurs in the AC power supply 10, the output voltage Vo of the DC power supply 15 decreases to below the holding voltage Vh of the relay, and if the first Zener diode 19 is not present, the transistor 20 and 22
continues to be on, so the relay contact 14 is turned off while the transistor 17 remains on.

After that, if the power outage is restored before the transistors 20 and 22 are turned off, the output voltage Vo of the DC power supply 15 will remain slightly higher than the holding voltage Vh even if it rises because the output current is flowing through the coil 16. It only increases up to the voltage. Therefore, although current is flowing through the relay coil 16, the applied voltage does not reach the operating voltage, so the relay contact 14 remains off.

However, because of the presence of the first Zener diode 19, the transistors 20 and 2 are connected to each other before the output voltage Vo decreases to below the holding voltage Vh of the relay.
Since the current that was flowing through transistor 2 no longer flows, transistor 2
0 and transistor 22 are turned off, and transistor 17 is also turned off.

Therefore, when the power outage is restored, since no current flows to the relay coil 16, the output voltage Vo rises to the operating voltage Vt, and then the transistors 20 and 22 are turned on again, and the relay contact 14 is turned on. You can turn it on.

In this embodiment, a relay contact connected in series to the heat retaining heater 12 is controlled by a switch 27 having a small current capacity and withstand voltage for the purpose of child lock.

Furthermore, in this embodiment, the relay coil 16
An NPN transistor is used as the transistor 17 that controls the , but if a PNP transistor is used as this transistor, a circuit like that shown in FIG. 2 is formed and functions in the same way.

[0029]

Effects of the Invention As is clear from the above description, the present invention has a simple circuit configuration using relatively inexpensive components such as a transistor, a Zener diode, and a resistor, and the output voltage of a DC power supply device once drops below the holding voltage Vh. If the voltage drops, the relay will not turn on unless the voltage rises above the operating voltage Vt, and once it is turned on, it will remain on even if the voltage drops to near the holding voltage, thereby preventing momentary power outages and voltage drops in the AC power supply. This prevents malfunctions and allows the use of DC power supplies with relatively small capacity and low power consumption.

Comparing the power consumption between the above embodiment and the conventional case where the voltage is not lowered even when the relay is on, assuming that the voltage when the relay is on is only 30% as in the above embodiment, Since the current is also 30%, the power consumption is 9%, which means that the power consumption of the DC power supply is actually less than 10% compared to the conventional system, and it is also more reliable due to its smaller size and reduced heat generation. It has a huge effect of improving.

[Brief explanation of drawings]

FIG. 1: Circuit diagram of an embodiment of the present invention

FIG. 2 is a circuit diagram of a second embodiment of the present invention.

[Figure 3] Circuit diagram of conventional example

[Explanation of symbols]

15 DC power supply device 16 Relay coil 17 Transistor 18 First resistance 19 First Zener diode 20 NPN transistor 22 PNP transistor 24 Second resistance 25 Second Zener diode

Claims (1)

[Claims] Claim 1: A DC power supply device that obtains a DC voltage from an AC power supply; a relay coil connected to the DC power supply device;
a transistor connected in series to the coil to control the coil current; a first resistor and a first Zener diode connected in series to the base of the transistor; and a first resistor and a first Zener diode connected in series to the base of the transistor; Connect to the emitter of the connected NPN
A second resistor and a second Zener diode are connected in series to the base of the transistor and the PNP transistor whose bases and collectors are connected to each other, and the Zener voltage of the first Zener diode turns on the normally open contact of the relay. The Zener voltage of the second Zener diode is set to be higher than the minimum voltage that can switch the normally open contact of the relay from the OFF state to the ON state.