JPH066625Y2 - Load drive circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a load drive circuit for conducting / disconnecting a relay device based on a control signal from a microcomputer or the like.

Prior Art A typical prior art is shown in FIG. FIG. 3 is a block diagram showing the relay drive circuit 1 and circuits related thereto. The relay drive circuit 1 is an NPN type transistor Q.
1 and resistors r1 and r2. The emitter of the transistor Q1 is grounded, and its base and resistor r1
Connected via. A high-level or low-level signal is applied to the base from the control circuit 2 via the resistor r2. The collector is connected to one end of the exciting coil 4 of the relay device 3.

A drive voltage Vr is applied from the power supply circuit 5 to the other end of the exciting coil 4. Further, both ends of the exciting coil 4 are diode 6
Connected by. A contact 7 is provided in association with the exciting coil 4, and the contact 7 is driven to be conductive when the exciting coil 4 is excited, and is cut off when it is demagnetized.

The drive voltage Vc is applied from the power supply circuit 5 to the control circuit 2 through the constant voltage circuit 8, a predetermined operation is performed, and a high level or low level signal is applied to the relay drive circuit 1. The drive voltage Vc is kept constant by the function of the constant voltage circuit 8 against fluctuations in the output voltage of the power supply circuit 5 within a certain range.

When the control circuit 2 outputs a high level signal, the transistor Q1 becomes conductive, the exciting coil 4 is excited, and the contact 7
Are continually driven. When the control circuit 2 outputs a low level signal, the transistor Q1 is cut off, the exciting coil 4 is not excited, and the contact 7 is cut off.

FIG. 4 is a timing chart for explaining changes in the drive voltages Vc and Vr due to turning on / off of the power supply, and the operation of each part accompanying the changes. The drive voltage Vc, V is shown in FIG.
The change of r is shown, (2) in the figure shows the output signal of the control circuit 2, and (3) in the figure shows the state of the contact 7. Time T0
At, when the power is turned on, both drive voltages Vr and Vc start to rise. At time T1, drive voltage Vc
Is a threshold voltage Vc at which the control circuit 2 becomes operable.
The driving voltage Vr exceeds the touching voltage Vth of the relay device 3 at time T2.

At time T3, when the power supply is cut off, the drive voltage Vr
Starts decreasing, and becomes lower than the moving voltage Vth at time T4. At this time, the drive voltage Vc does not immediately drop due to the action of the constant voltage circuit 8, but starts to drop at time T5 and becomes lower than the threshold voltage Vct at time T6.

The control circuit 2 is initialized at time T1,
Start a predetermined operation. After that, the operation is continued for a period up to time T6, the operation is reset at time T6, and a low level signal is given to the relay drive circuit 1. In the relay device 3, when a high-level signal is applied to the base of the transistor Q1 of the relay drive circuit 1 and the exciting coil 4 is excited during the period from time T2 to time T4, the contact 7 is driven to conduct.

Now, assume that the output signal of the control circuit 2 changes from low level to high level at time T7. At this time, the transistor Q1 of the relay drive circuit 1 becomes conductive, the exciting coil 4 of the relay device 3 is excited, and the contact 7 is driven to conduct. When the control circuit 2 is reset at time T6, and therefore its output signal becomes low level, the transistor Q1 is cut off, the exciting coil 4 is demagnetized, and the contact 7 is cut off.

When the contact 7 is driven to the exciting coil 4, the sensing voltage V
Although a drive voltage exceeding th is applied, the holding voltage required to hold the contact 7 in the conductive state may be lower than the touch voltage Vth, which is usually about 15% of the rated voltage of the relay device 3. . Therefore, the relay device 3
In order to reduce the power consumption of the contact 7, after the contact 7 is driven to be conductive, a holding voltage for holding the contact 7 in the conductive state is applied to the exciting coil 4 by a configuration not shown.

Therefore, the contact 7 is not immediately shut off even if the drive voltage Vr falls below the touch voltage Vth, and the holding voltage is usually lower than the threshold voltage Vct of the drive voltage Vc, so that the time when the control circuit 2 is reset. It will be shut off at T6.

Problems to be solved by the invention The output voltage of the power supply circuit 5 drops for some reason,
Suppose that situation continues. FIG. 5 is a timing chart for explaining the operation of each circuit in such a case. FIG. 1A is a graph showing changes in the drive voltages Vr and Vc, FIG. 2B shows a signal output from the control circuit 2, and FIG. 3C shows a state of the contact 7.

At time T8, the output voltage of the power supply circuit 5 drops for some reason, the drive voltage Vr changes as shown in FIG. 1 (1), and at time T9, the drive voltage Vr drops to near the impression voltage Vth of the relay device 3, Suppose the situation is persistent. At this time, the drive voltage Vc is kept constant by the action of the constant voltage circuit 8.

Therefore, the control circuit 2 can perform a normal operation, and outputs a high level / low level signal according to a predetermined operation. At this time, for example, it is assumed that the signal shown in FIG. 2B is output and the output signal changes from the low level to the high level at time T10.

As a result, the transistor Q1 of the relay drive circuit 1 becomes conductive, and the exciting coil 4 of the relay device 3 is excited. However, the drive voltage Vr is the touching voltage Vth of the relay device 3.
Since it has fallen to the vicinity, the exciting coil 4 is not sufficiently excited, and the contact 7 is not completely driven to conduct.
For this reason, the contact 7 causes so-called chattering in which conduction and interruption are repeated in small steps as shown in FIG. At this time, the contact 7 may be physically damaged by welding or burning due to arc discharge or excessive current, and the relay device 3 may lose its function.

For example, in the normal case, the drive voltage Vr is 12
(V) and the driving voltage Vc is 5 (V), the touching voltage Vth of the relay device 3 is usually about 80% of the rated voltage, and thus the touching voltage Vth is about 9.6 (V). At this time, even if the drive voltage Vr changes from 12 (V) to a value near 9.6 (V), the drive voltage Vc is held at 5 (V),
Therefore, the control circuit 2 performs a predetermined operation and outputs a high level / low level signal. In such a case, the contact 7 is in a state where chattering easily occurs.

An object of the present invention is to provide a load driving circuit capable of preventing an undesired operation of a load due to an undesired drop of a driving voltage for driving the load in advance.

The present invention is directed to an AC power supply 12, a diode bridge 14 for full-wave rectifying the output of the AC power supply 12, and a first voltage V for smoothing the output of the diode bridge 14.
A smoothing circuit C1 for deriving R, a constant voltage circuit 15 for stabilizing the output of the smoothing circuit C1 and deriving a second voltage VC that is less than the first voltage VR, and an output of the smoothing circuit C1 supplied to the switching transistor Tr4. A first series circuit including a load L1 and a load, a first resistor R7 connected between the base and the emitter of the transistor Tr4, and a second resistor interposed between the base of the transistor Tr4 and the ground.
The second series circuit, which is a series circuit and includes the second resistor R6, the zener diode ZD3, and the switching means Tr3, and the power of the constant voltage circuit 15 is supplied to the switching means T3.
The control circuit 16 for connecting / disconnecting r3 and the operable minimum voltage VW of the load L1 are
It is selected to be a value smaller than the sum of the base-emitter voltage VBES of r4, the voltage VCES at both ends when the switching means Tr3 is conducting, and the breakdown drop voltage VZ of the Zener diode ZD3, and the minimum voltage VW is It is a load drive circuit characterized by being less than one voltage VR and being more than a second voltage VC.

Operation According to the present invention, when the output voltage of the AC power supply 12 decreases, the control circuit 16 operates to operate the switching means Tr.
3 in the conducting state, and therefore the transistor T
When r4 is conducting, the voltage applied to the load L1 from the smoothing circuit C1 via the transistor Tr4 decreases, and the base-emitter voltage VB of the transistor Tr4 decreases.
When the sum of ES, the voltage VCES at both ends of the switching transistor Tr3 at the time of conduction, and the breakdown drop voltage VZ of the Zener diode ZD3 is less than the sum, the transistor Tr4 is cut off, whereby the load L1 is not supplied with power. Thus, the voltage applied to the load L1 is
Since the transistor Tr4 is cut off before reaching the operable minimum voltage VW, the load L1 is prevented from causing chattering, for example.

Embodiment FIG. 1 is an electric circuit diagram of a relay drive circuit 11 which is an embodiment of the load drive circuit of the present invention and a circuit related thereto. The output voltage of the power supply 12 is stepped down by the transformer 13, full-wave rectified by the diode bridge 14, and smoothed by the capacitor C1. The smoothed voltage is applied to the relay drive circuit 11 and also applied to the constant voltage circuit 15 including the resistor R1, the transistor Tr1, the Zener diode ZD1 and the capacitor C2. Power supply 12, transformer 13, diode bridge 14,
The power supply circuit 20 is configured to include the capacitor C1 and the like.

The constant voltage circuit 15 supplies the drive voltage VC to the power supply terminal TC of the control circuit 16. The drive voltage VC includes resistors R2 and R3, a Zener diode ZD2, and an NPN type transistor Tr2.
It is also given to the reset circuit 17 composed of
The base of the transistor Tr2 is supplied with the drive voltage VC via the resistor R2 and the Zener diode ZD2, and the collector is supplied with the drive voltage VC via the resistor R3. Further, the potential appearing at the collector is controlled by the control circuit 16
Is applied to the reset terminal TR of as a reset signal.
The emitter of the transistor Tr2 and the control circuit 16
The terminal TG of is grounded.

The control circuit 16 operates according to a predetermined procedure and outputs a high level or low level signal as a drive signal. When a high level signal is applied to the reset terminal TR, the control circuit 16 is reset and the output signal becomes low level.

The output signal of the control circuit 16 is given to the relay drive circuit 11, which controls the operation of the relay device 18, which is a load.

The relay drive circuit 11 includes resistors R4, R5, R6, R7,
It is configured to include a Zener diode ZD3, an NPN-type transistor Tr3 that is the first switching means, and a PNP-type transistor Tr4. The transistor Tr
4, the Zener diode ZD3, the resistors R6 and R7, and the like constitute the second switching means. Control circuit 1
The output signal of 6 is given to the base of the transistor Tr3 via the resistor R4. The base of the transistor Tr3 is connected to its emitter through a resistor R5, and the emitter is grounded.

The base of the transistor Tr4 is connected to the collector of the transistor Tr3 via the resistor R6 and the Zener diode ZD3, and is also connected to the emitter of the transistor Tr3 via the resistor R7. The collector current of the transistor Tr4 is given to the exciting coil L1 of the relay device 18. Further, the drive voltage VR is applied to the emitter from the power supply circuit 20.

Both ends of the exciting coil L1 are connected via a diode D1. A contact point 19 is provided in association with the exciting coil L1, and the contact point 19 conducts when the exciting coil L1 is excited and cuts off when it is demagnetized.

When the control circuit 16 outputs a high level signal, the transistor Tr3 becomes conductive and a low level potential appears at the collector of the transistor Tr3. At this time, a low-level signal is given to the base of the transistor Tr4, and the transistor Tr4 becomes conductive. At this time, the exciting coil L1 of the relay device 18 is excited, and the contact 19 is electrically driven.

When the control circuit 16 outputs a low level signal, the transistor Tr3 is cut off, and the potential appearing at the collector of the transistor Tr3 becomes high level. At this time, the transistor Tr4 is cut off, the exciting coil L1 is demagnetized, and the contact 19 is cut off.

In the relay drive circuit 11 of the present embodiment, the sensing voltage Vw of the relay device 18, the base-emitter saturation voltage V _BES with which the transistor Tr4 conducts, the collector-emitter saturation voltage V _CES with which the transistor Tr3 conducts, and the resistor R6.
And the zener diode ZD3 causes the voltage drop V _{Z to} be V _BES Vw− (V _Z + V _CES ) ... (1), that is, V _BES + V _CES + V _Z Vw ... (2), the resistor R6 and the zener diode ZD3. To be elected.

By doing so, when the drive voltage VR drops and becomes a voltage higher than the touch voltage VW near the touch voltage VW, when the transistor Tr3 is conducting, there is a sufficient gap between the base and emitter of the transistor Tr4. A different bias voltage cannot be obtained, and the transistor Tr4 is cut off. Here, the voltage VR is 12.0 V, for example,
The voltage VC is 5.0 V, and the touching voltage VW is 10.
It is 2V.

In this way, when the drive voltage VR drops, the transistor Tr4 is cut off before the voltage of the load L1 becomes less than the touch voltage VW.

FIG. 2 shows the drive voltage VC when the power supply 12 is turned on / off.
It is a figure for demonstrating change of VR and operation | movement of each part accompanying it. FIG. 1A shows changes in the drive voltages VC and VR. FIG. 2B shows an output signal of the reset circuit 17, FIG. 3C shows an output signal of the control circuit 16, and FIG. The state of the contact 19 is shown. Power supply 12 at time t0
When is turned on, the drive voltages VC and VR both start to rise. At time t1, the drive voltage VC exceeds the threshold voltage VT, and at time t2, the drive voltage VR changes to the impression voltage V.
exceeds w. Here, the threshold voltage VT is a voltage necessary for the control circuit 16 not to malfunction, and below the threshold voltage VT, the control circuit 16 is reset as will be described later.

When the power supply 12 is cut off at time t3, the drive voltage V
R starts to fall and becomes lower than the moving voltage Vw at time t4. At this time, the drive voltage VC does not immediately drop due to the action of the constant voltage circuit 15, but starts to drop at time t5 and becomes lower than the threshold voltage VT at time t6.

In the reset circuit 17, the Zener diode ZD2 is cut off during the period from time t0 to t1, therefore the transistor Tr2 is cut off, and the voltage applied to the reset terminal TR of the control circuit 16 increases the drive voltage VC. Along with this, it changes as shown in FIG. At time t1, the Zener diode ZD2 becomes conductive, so that the transistor Tr2 becomes conductive and a low-level signal is applied to the reset terminal TR.

That is, the control circuit 16 is reset during the period from time t0 to t1, is initialized at time t1, and starts a predetermined operation.

Time t when the drive voltage VC becomes lower than the threshold voltage VT
In 6, the Zener diode ZD2 is cut off, the transistor Tr2 is cut off, a high level signal is given to the reset terminal TR, the control circuit 16 is reset, and its output signal becomes low level.

If the control circuit 16 performs a predetermined operation at time t7 and its output signal changes from the low level to the high level and is at the high level during the period until the time t6 when the control circuit 16 is reset. Assume

At this time, in the relay drive circuit 11, at time t7, the transistor Tr3 becomes conductive, the transistor Tr4 becomes conductive, the exciting coil L1 of the relay device 18 is excited, and the contact 19 is conductively driven. At time t4, the drive voltage VR falls below the impression voltage Vw. At this time, the resistance R
6. Since the Zener diode ZD3 is selected so that the above-mentioned second equation is satisfied, the transistor Tr4 is cut off, the exciting coil L1 is demagnetized, and the contact 19 is cut off. That is, even though the output signal of the control circuit 16 is at a high level, the contact 19 is cut off.

As described above, in the present embodiment, when the drive voltage VR output from the power supply circuit 20 drops near the touching voltage Vw of the relay device 18, the transistor Tr4 is cut off and the contact 19 is prevented from being conductively driven. . This makes it possible to prevent chattering due to the drop in the drive voltage VR.

Effects As described above, according to the present invention, it becomes possible to prevent an undesired operation of the load due to an undesired drop in the driving voltage for driving the load, and prevent damage to the load. Be done. That is, according to the present invention, the voltage of the alternating current 12 decreases, and the voltage applied to the load L1 is the touch voltage VW.
The switching means Tr is provided before it is reduced to less than
It is possible to prevent the transistor Tr4 from being cut off when the transistor 3 is conductive, and thus the load L1 from chattering and the like. According to the present invention, not only when the voltage of the AC power supply 12 drops, but also when, for example, one of the four diodes constituting the diode bridge 14 for full-wave rectifying the output of the AC current 12 is short-circuited, the smoothing circuit C1 The output voltage VR of the transistor T drops, and even in such a case, malfunction such as chattering of the load L1 may occur.
It can be prevented by blocking r4. In general, a short circuit accident of the diode forming the diode bridge 14 is relatively easy to occur, and even when the diode bridge 14 fails, the load L can be prevented by the present invention.
The excellent effect that the malfunction of 1 can be reliably prevented is achieved.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an electric circuit diagram of a relay drive circuit 11 which is an embodiment of a load drive circuit of the present invention and a circuit related thereto, and FIG.
FIG. 3 is a timing chart for explaining the changes in the drive voltages VC and VR due to turning on / off of the power supply 12 and the operation of each part accompanying this, and FIG. FIG. 4 is a block diagram showing a related circuit, and FIG. 4 shows a driving voltage Vc associated with turning on / off the power source.
FIG. 5 is a timing chart for explaining the change of Vr and the operation of each part accompanying it, and FIG. 5 is a timing chart for explaining the operation of each part when the drive voltage Vr drops near the impression voltage Vth. 11 ... Relay drive circuit, 15 ... Constant voltage circuit, 16 ... Control circuit, 17 ... Reset circuit, 18 ... Relay device, 19 ...
Contacts, 20 ... power supply circuit, VC, VR ... drive voltage, Vw ...
Touching voltage

Claims (1)

[Scope of utility model registration request] 1. An AC power supply 12, a diode bridge 14 for full-wave rectifying the output of the AC power supply 12, and a first voltage V smoothing the output of the diode bridge 14.
A smoothing circuit C1 for deriving R, a constant voltage circuit 15 for stabilizing the output of the smoothing circuit C1 and deriving a second voltage VC that is less than the first voltage VR, and an output of the smoothing circuit C1 supplied to the switching transistor Tr4. A first series circuit including a load L1 and a load, a first resistor R7 connected between the base and the emitter of the transistor Tr4, and a second resistor interposed between the base of the transistor Tr4 and the ground.
A series circuit, which is composed of a second resistor R6, a zener diode ZD3, and a switching means Tr3, and is supplied with electric power from a constant voltage circuit 15 and a switching means T3.
The control circuit 16 for connecting / disconnecting r3 and the operable minimum voltage VW of the load L1 are
It is selected to be a value smaller than the sum of the base-emitter voltage VBES of r4, the voltage VCES at both ends when the switching means Tr3 is conducting, and the breakdown drop voltage VZ of the Zener diode ZD3, and the minimum voltage VW is A load drive circuit, which is less than one voltage VR and more than a second voltage VC.