JPH09288949A - Relay drive circuit - Google Patents

Abstract

(57) [Abstract] [Purpose] An object of the present invention is to reduce the number of parts and suppress heat generation in a relay drive circuit that drives an output relay of a small control device such as a small timer. [Structure] Applying rectified AC voltage to both ends of the relay coil and relay driving transistor connected in series, and turn on the relay driving transistor so that the effective value of the relay current flowing in the relay coil becomes the relay rated current. A transistor control circuit for on / off control is provided.

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 for driving an output relay of a compact control device such as a compact timer.

[0002]

2. Description of the Related Art FIG. 10 is a block diagram of a conventional relay drive circuit of this type. In the figure, the AC voltage output from the AC power supply 50 is rectified into a DC voltage by the constant voltage circuit 51 and applied to both ends of a series circuit including a relay coil 52 and a relay driving transistor 53. The diode 54 connected in parallel with the relay coil 52 is for absorbing the back electromotive force.

The DC voltage output from the constant voltage circuit 51 is applied to the parallel circuit of the timer circuit 56 and the Zener diode 57 via the resistor 55. As a result, the Zener voltage of the Zener diode 57 (5V in this case) is supplied to the timer circuit 56 as the power supply voltage. The output of the timer circuit 56 drives the relay driving transistor 53.

In this structure, when the AC power supply 50 is turned on, the timer circuit 56 starts the timed operation. When the timer circuit 56 times up after a predetermined time, the output turns on the relay driving transistor 53,
A DC voltage (48V in this case) from the constant voltage circuit 51 is applied to the relay coil 52 to operate the relay.

[0005]

In the above-mentioned prior art,
Assuming that the AC power supply 50 outputs an AC voltage of AC100 to 240V, the constant voltage circuit 51 must always output a constant DC voltage (for example, 48V) regardless of changes in the AC voltage. Therefore, the configuration of the constant voltage circuit 51 becomes complicated, the number of parts is large, and the electrical efficiency is low, so that the heat generation becomes large.

The present invention has been made in order to solve such a conventional problem, and an object thereof is to provide a relay drive circuit which is capable of reducing the number of parts and suppressing heat generation.

[0007]

According to a first aspect of the present invention, there is provided a relay drive circuit, wherein a rectified AC voltage is applied to both ends of a relay coil and a relay drive transistor which are connected in series, and the AC voltage flows to the relay coil. A transistor control circuit is provided for on / off controlling the relay driving transistor so that the effective value of the relay current becomes the relay rated current.

According to the present invention, the transistor for controlling the relay is turned on / off by the transistor control circuit so that the effective value of the relay current becomes the relay rated current, so that it can be used in a wide range of applied voltages.

A second invention of the relay driving circuit according to the present invention is the first invention, wherein the transistor control circuit turns off the relay driving transistor when the relay current reaches a predetermined upper limit value and reaches a predetermined lower limit value. The relay drive transistor is configured to be turned on.

According to the present invention, by appropriately setting the upper limit value and the lower limit value, the effective value of the relay current that repeatedly rises and falls during this period can be set to be the relay rated current, and a wide range of applied voltages can be set. It can be used.

A third invention of the relay drive circuit according to the present invention is the first invention, wherein the transistor control circuit turns off the relay drive transistor for a certain period of time when the relay current reaches a predetermined upper limit value, and this certain period of time. When the time has passed, the relay driving transistor is turned on.

According to the present invention, by appropriately setting the upper limit value and the fixed time, it is possible to set the effective value of the relay current that repeatedly rises and falls so as to be the relay rated current, and to use it in a wide range of applied voltages. It will be possible.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION

(Embodiment 1) FIG. 1 is a configuration diagram of a relay drive circuit according to Embodiment 1 of the present invention. In FIG. 1, both ends of the AC power supply 1 are connected to both ends of a series circuit including a relay driving transistor 4, a relay coil 5, and a relay current detecting resistor 6 via a half-wave rectifying circuit including a rectifying diode 2 and a smoothing capacitor 3. It is connected to the. Further, a series circuit including a resistor 7, a transistor 8 and a resistor 9 is connected in parallel with the series circuit, and the AC power supply 1 is also connected to both ends of the series circuit.

The midpoint of connection between the resistor 7 and the transistor 8 is connected to the base terminal of the transistor 4, and the base terminal of the transistor 8 is connected to the Zener diode 10 for stabilizing the base voltage. The relay coil 5
A diode 11 for absorbing back electromotive force is connected in parallel with the series circuit of the resistor 6.

Further, the midpoint of connection between the relay coil 5 and the resistor 6 is connected to the transistor control circuit 12.
The transistor control circuit 12 includes a comparison circuit 13, an RS flip-flop (hereinafter referred to as RSF) circuit 14, an AND circuit 15, and a timer circuit 16.
The magnitude of the relay current i is detected from the voltage across the resistor 6 to control ON / OFF of the relay driving transistor 4.

The comparison circuit 13 includes two comparators 13a and 13a.
b is a window comparator having a voltage (hereinafter, referred to as a detection voltage) Vdt across the resistor 6 and an upper limit voltage Va.
When it is larger, only the comparator 13a outputs a signal of H level by binary logic, and the detection voltage Vdt is lower limit voltage Vb (0 <
When smaller than Vb <Va), only the comparator 13b is configured to output an H level signal.

The output of the comparator 13a is connected to the set terminal of the RSF circuit 14, and the output of the comparator 13b is connected to the reset terminal of the RSF circuit 14. RSF circuit 14
The inverted output Q bar of is connected to the base terminal of the transistor 8 via the AND circuit 15. The AND circuit 15 has a gate function that opens when the timer circuit 16 times out and outputs an H-level signal in binary logic.

In this configuration, if an AC voltage is applied from the AC power supply 1 and the output of the timer circuit 16 is at L level in the binary logic, the AND circuit 15 is closed and its output becomes L level. Therefore, the transistor 8 is turned off, which turns off the transistor 4 as well, and the relay coil 5 is not energized. At this time, since the detection voltage Vdt is lower than or equal to the lower limit voltage Vb, the output of the comparator 13b becomes H level, and the RSF circuit 14 is in the reset state.

In this state, when the timer circuit 16 times out and the output becomes H level, the inverted output Q bar of the RSF circuit 14 becomes H level, the output of the AND circuit 15 also becomes H level, and the transistor 8 is turned on. To do. As a result, the transistor 4 is turned on and the relay coil 5 is energized.

As a result, since the relay coil 5 is equivalently constituted by the series circuit of the coil L and the resistor R, the relay current i is expressed as follows: i = V.multidot. (1-e) ^{-(R / L) t} ) / R, which rises in an exponential curve.

The detection voltage Vdt of the resistor 6 also increases in proportion to the increase of the relay current i, and when it exceeds the upper limit voltage Va, the output of the comparator 13a becomes H level. This gives RSF
Since the circuit 14 is set and the inverted output Q-bar becomes L level, the output of the AND circuit 15 also becomes L level and the transistors 8 and 4 are turned off.

When the transistor 4 is turned off, the energy stored in the relay coil 5 flows through the diode 11. Therefore, when the peak value of the relay current i is i ₀ , i = i ₀ · e ^{− (R / L) t} , And this time it will fall on an exponential curve.

The detection voltage Vdt of the resistor 6 also decreases in proportion to the decrease of the relay current i, and when it falls below the lower limit voltage Vb, the output of the comparator 13b becomes H level. This gives RSF
Since the circuit 14 is reset and the inverted output Q bar becomes H level, the output of the AND circuit 15 becomes H level and the transistors 8 and 4 are turned on. As a result, the relay current i rises again.

As described above, the detection voltage Vdt is equal to the upper limit voltage Va.
By controlling ON / OFF of the transistor 4 so as to repeatedly rise and fall between the lower limit voltage Vb and the lower limit voltage Vb, the relay current i that repeatedly rises and falls between the upper limit value i _a and the lower limit value i _b as shown in FIG. Is obtained. Each value of the circuit is set so that the effective value i _rms of the relay current i becomes the relay rated current. The upper limit value i _a is the relay current when the voltage (detection voltage) Vdt across the resistor 6 is the upper limit voltage Va, and the lower limit value i _b is the relay current when the voltage Vdt across the resistor 6 is the lower limit voltage Vb. It is an electric current.

When the applied voltage from the AC power supply 1 is low, the relay current i rises gently as shown in FIG. 2A, and when it is high, it rises sharply as shown in FIG. 2B. . However, it is possible to use a wide range of AC voltage, and not only AC voltage but also DC voltage may be used.

The structure of the transistor control circuit 12 is not limited to the structure shown in FIG. 1 described above, but may be composed of a comparison circuit 13, a computer 17 and a buffer 18, as shown in FIG. In this case, the computer 17 monitors the two outputs of the comparison circuit 13,
When the output of the comparator 13a is H level during the relay driving period, the output is set to L level to turn off the transistors 8 and 4, and when the output of the comparator 13b is H level, the output is set to H level and the transistor 8 is set. And the transistor 4 is turned on. By doing so, the above-mentioned FIG.
The same operation as can be obtained.

Further, as another configuration of the transistor control circuit 12, as shown in FIG. 4, an AD converter 19, a computer 17 and a buffer 18 can be used. In this case, the computer 17 monitors the level of the detection voltage Vdt converted into a digital signal by the AD converter 19, and when the voltage exceeds the upper limit voltage Va during the relay driving period, the output is set to the L level to turn on the transistors 8 and 4. When it is turned off and falls below the lower limit voltage Vb, the output is set to the H level and the transistors 8 and 4 are turned on. By doing so, the same operation as that in FIG. 1 described above can be obtained.

(Second Embodiment) FIG. 5 is a configuration diagram of a relay drive circuit according to a second embodiment of the present invention. In the figure, the AC power supply 21 is connected to both ends of a series circuit including a relay coil 24, a relay driving transistor 25, and a relay driving current detecting resistor 26 via a half-wave rectifying circuit including a rectifying diode 22 and a smoothing capacitor 23. It is connected to the. A diode 27 for absorbing back electromotive force is connected in parallel with the relay coil 24.

Further, the transistor 25 and the resistor 26
The midpoint of connection is connected to the transistor control circuit 28. The transistor control circuit 28 includes a comparison circuit 29,
The one-shot circuit 30, the AND circuit 31, and the timer circuit 32 are configured to detect the magnitude of the relay current i from the voltage across the resistor 26 to control ON / OFF of the relay driving transistor 25.

When the detection voltage Vdt as the voltage across the resistor 26 exceeds the comparison voltage Vp, the comparison circuit 29 outputs an H-level signal by binary logic and triggers the one-shot circuit 30. The inverted output Q bar of the one-shot circuit 30 is connected to the base terminal of the transistor 25 via the AND circuit 31. The AND circuit 30 has a gate function that opens when the timer circuit 32 times out and outputs an H-level signal in binary logic.

In this configuration, an AC voltage is applied from the AC power supply 21, and the output of the timer circuit 32 is L in binary logic.
If it is at the level, the AND circuit 31 is closed and its output is at the L level. Therefore, the transistor 25 is turned off, and the relay coil 24 is not energized.
At this time, since the current flowing through the resistor 26 is minute, the detection voltage Vdt is equal to or lower than the comparison voltage Vp. Therefore, the comparator 2
The output of 9 is L level, and the inverted output Q bar of the one-shot circuit 30 is H level.

In this state, when the timer circuit 32 times out and the output becomes H level, the output of the AND circuit 31 becomes H level and the transistor 25 is turned on. When the transistor 25 is turned on, the relay coil 24 is energized.

As a result, the relay current i flowing through the relay coil 24 is equal to the applied voltage V because the relay coil 24 is equivalently composed of the series circuit of the coil L and the resistor R.
Then, i = V · (1−e− ^{(R / L) t} ) / R, which rises in an exponential curve.

The detection current i _dt flowing through the resistor 26 also increases in proportion to the increase of the relay current i, and the detection voltage Vdt of the resistor 26 also increases accordingly. When the detection voltage Vdt exceeds the comparison voltage Vp, the output of the comparison circuit 29 becomes H level. As a result, the one-shot circuit 30 is triggered, and the inverted output Q bar is at the L level for the preset time T. As a result, the AND circuit 31 is closed and the transistor 25 is turned off.

When the transistor 25 is turned off, the energy stored in the relay coil 24 flows through the diode 27, and the relay current i becomes i = i ₀ · e ^{− (R / L) t} , and this time it drops in an exponential curve. To do.

On the other hand, the detection current i _dt flowing through the resistor 26 becomes a minute level because the transistor 25 is turned off, and the detection voltage Vdt also becomes a minute level. Therefore, the comparison circuit 29
Is at L level. When the set time T elapses, the inverted output Q bar of the one-shot circuit 30 returns to the H level, the AND circuit 31 opens, and the transistor 25 is turned on. As a result, the relay current i rises again and the detection current i _dt also rises.

As described above, the detection voltage Vdt is equal to the upper limit voltage Vp.
When it exceeds, by turning off the transistor 25 for a certain period of time, as shown in FIG. 6, a relay current i which repeats rising and falling within a predetermined range is obtained. Each value of the circuit T and the circuit is set for a certain time so that the effective value i _rms of the relay current i becomes the relay rated current. In addition, the upper limit value ip is the resistor 26
Is a relay current when the voltage (detection voltage) Vdt at the upper limit is the upper limit voltage Vp. FIG. 7 shows the waveform of the detection current i _dt .

When the applied voltage from the AC power supply 21 is low, the relay current i and the detection current i _dt gradually rise as shown in FIG. 7A, and when the applied voltage is high, the relay current i and steep current i _dt are steep as shown in FIG. Rise to. However, it is possible to use a wide range of AC voltage, and not only AC voltage but also DC voltage may be used.

The structure of the transistor control circuit 28 is not limited to the structure shown in FIG. 5 described above, but may be composed of a comparison circuit 29, a computer 33 and a buffer 34 as shown in FIG. In this case, the computer 33 monitors the output of the comparison circuit 29, and when the output of the comparison circuit 29 is at the H level during the relay driving period, sets the output to the L level for the set time T and the transistor 25.
Is turned off, and when the output of the comparison circuit 29 is at L level in a period other than the set time T, the output is set at H level and the transistor 25 is turned on. By doing so, the same operation as that of FIG. 5 described above can be obtained.

As another configuration of the transistor control circuit 28, an AD converter 35, a computer 33 and a buffer 34 can be used as shown in FIG. In this case, the computer 33 monitors the level of the detection voltage Vdt converted into a digital signal by the AD converter 35, and when the voltage exceeds the comparison voltage Vp during the relay driving period, the output is set to the L level for the set time T and the transistor is set. 25 is turned off, and the comparison circuit 2
When the output of 9 is L level, the output is set to H level and the transistor 25 is turned on. By doing so, the same operation as that of FIG. 5 described above can be obtained.

[0041]

According to the present invention, the relay coil can be directly driven by an AC voltage in a wide voltage range without the need for providing a complicated constant voltage circuit. It can be constructed with a very small number of parts. Further, since the relay of high power is directly driven by the rectified AC voltage, wasteful power consumption is small and heat generation can be suppressed.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a relay drive circuit according to a first embodiment of the present invention.

FIG. 2 is a waveform diagram of a relay current, in which (a) shows a case where an applied voltage is low and (b) shows a case where an applied voltage is high.

FIG. 3 is a configuration diagram showing another configuration example of a transistor control circuit in the relay drive circuit shown in FIG.

4 is a configuration diagram showing still another configuration example of the transistor control circuit in the relay drive circuit shown in FIG. 1. FIG.

FIG. 5 is a configuration diagram of a relay drive circuit according to a second embodiment of the present invention.

FIG. 6 is a waveform diagram of a relay current, in which (a) shows a case where the applied voltage is low, and (b) shows a case where the applied voltage is high.

FIG. 7 is a waveform diagram of a detected current, where (a) shows a case where the applied voltage is low, and (b) shows a case where the applied voltage is high.

8 is a configuration diagram showing another configuration example of the transistor control circuit in the relay drive circuit shown in FIG.

9 is a configuration diagram showing still another configuration example of the transistor control circuit in the relay drive circuit shown in FIG.

FIG. 10 is a configuration diagram of a conventional relay drive circuit.

[Explanation of symbols]

 1,21 AC power supply 2,22 Rectification diode 3,23 Smoothing capacitor 4,25 Relay drive transistor 5,24 Relay coil 6,26 Relay current detection resistor 12,28 Transistor control circuit 13,29 Comparison circuit 14 RS flip-flop circuit 15, 31 AND circuit 16, 32 Timer circuit 17, 33 Computer (CPU) 19, 35 AD converter 30 One-shot circuit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshitaka Murakami 2075 Kaiyoshi, Okayama City, Okayama Prefecture Omron Okayama Co., Ltd.

Claims (3)

[Claims] 1. A relay drive in which a rectified AC voltage is applied to both ends of a relay coil and a relay drive transistor connected in series so that an effective value of a relay current flowing through the relay coil becomes a relay rated current. A relay drive circuit, comprising a transistor control circuit for controlling on / off of an operating transistor. 2. The transistor control circuit is configured to turn off the relay driving transistor when the relay current reaches a predetermined upper limit value and turn on the relay driving transistor when the relay current reaches a predetermined lower limit value. The relay drive circuit according to claim 1, wherein: 3. The transistor control circuit is configured to turn off the relay driving transistor for a predetermined time when the relay current reaches a predetermined upper limit value, and turn on the relay driving transistor when the predetermined time elapses. The relay drive circuit according to claim 1, wherein: