JPH0312073Y2 - - Google Patents

Description

[Detailed Description of the Invention] This invention relates to a protection circuit for a load drive circuit such as a motor.

When direct current is supplied to a load, a controlled object may be operated in one control state and another control state depending on the direction in which the current is supplied. For example, when a DC motor is used as a load, the motor may be rotated clockwise or in the opposite direction.

Regarding Fig. 1, a conventional example is 1a.
A first switching transistor 2a and a switching transistor 3a having different conductivity types are connected in series with respect to their collectors and emitters.
This is a series circuit. In this case, the first transistor 2a is of PNP type, and the second transistor is of NPN type. Similarly, the second series circuit 1
b is also configured. 2b and 3b are switching transistors used for this purpose. These series circuits 1a and 1b are each connected in parallel to the DC power supply 4. Also, the first
The connection point between transistors 2a and 3a in the series circuit (referred to as the first connection point Pa) and the connection point between the transistors 2b and 3b in the second series circuit (referred to as the second connection point Pa)
A load 5 such as a motor is connected between the The following explanation will be given assuming that the load is a motor.

Furthermore, first and second transistors 6a for control
and 6b are provided, the bases of which are respectively connected to the first
and second control signal input terminals 7a, 7b, respectively, and their emitters are connected to transistors 3, respectively.
a, 3b, and their collectors are substantially connected to the bases of transistors 2b, 2a, respectively. Also, the first control signal input terminal 7a
is connected to the second connection point through the first diode 8a.
Pb, and the second connection point Pb is further substantially connected to the base of the first protection transistor 9a. Similarly, the second control signal input terminal 7b
is connected to the first connection point Pa through the diode 8b, and the second connection point Pb is further substantially connected to the base of the second protection transistor 9b.

To explain the operation of this configuration, first, when a control signal is supplied to the terminal 7a, the transistor 6a is turned on, and as a result, the transistor 3 is turned on.
a and 3b are turned on, and DC current is supplied from the power supply 4 through the transistor 2b, the motor 5, and the transistor 3a, thereby causing the motor 5 to rotate, for example, in a clockwise direction. Furthermore, when a signal is supplied to the terminal 7b, the transistors 2a and 3b are turned on, so that a current is supplied to the motor 5 in the opposite direction to that described above. The same applies to rotation in the direction.

In such a configuration, the control signal input terminal 7a
When no control signal is supplied to any of transistors 7b and 7b, all transistors are off, so even if the collector-emitter of any transistor is short-circuited, it will not generate heat. It is safe because no circuit is configured.

Next, consider a state in which a signal is supplied to the first control signal input terminal 7a, turning on the transistor 6a, thereby turning on the transistors 2b and 3a, and causing the motor 5 to rotate clockwise. In this state, the transistor 2b becomes conductive, so that a voltage appears at the second connection point Pb, and this voltage is also supplied to the base of the protection transistor 9a through the resistor, so the transistor 9a is in the on state. . Therefore, even if a control signal is applied to the second control signal input terminal 7b in such a state, the transistor 6b will not be turned on.
Therefore, this case is also safe. Of course, the opposite situation is also exactly the same.

Next, when a signal is similarly supplied to the input terminal 7a and the transistors 6a, 2b, and 3a are in the ON state, suppose that the collector-emitter of the second control transistor 6b is shot. At this time, the transistor 3b and 2a are respectively turned on,
Therefore, the protection transistor 9b turns on, and when the transistor 3b turns on, the diode 8a also becomes conductive, so that the input terminal 7a
The signal being supplied to is cut off. That is, in this case, only the direction of rotation of the motor 5 is reversed, and there is no problem in terms of safety.

Furthermore, consider the case where the collector-emitter of the transistor 3b is shot while a terminal is supplied to the input terminal 7a, that is, the transistors 6a, 2b, and 3a are each turned on and the motor 5 is rotating. Since the input terminal 7a is grounded through the collector-emitter or short portion of the diode 8a and the transistor 3b, the transistors 3a and 2b are turned off, and there is no risk of excessive current flowing through the transistor 2b.

Furthermore, consider the case where the emitter-collector of the transistor 2a is shorted while a signal is supplied to the input terminal 7a and the transistors 6a, 2b, and 3a are turned on, as described above. In this case, as mentioned above, the transistor 3
Since transistor a is on, a short circuit between the emitter and collector of transistor 2a causes transistor 3 to
Although it is thought that an excessive current flows through transistor 3a, since the short resistance (approximately OΩ) between the collector and emitter of transistor 2a is sufficiently lower than the internal resistance of transistor 3a in the on state, the collector of transistor 3a The voltage between the emitters turns on transistor 9b, and thus transistors 3a and 2b are turned on to ground input terminal 7a.
are respectively turned off, thereby making it possible to avoid excessive current from flowing through the transistor 3a.

In the above description, the respective explanations were made in a state where a signal was supplied to the control signal input terminal 7a, but conversely, when a control signal was supplied to the control signal input terminal 7b and the transistors 6b, 2a, and 3b were in an on state. It is clear that the same protection applies.

As described above, when a signal is supplied to the input terminal 7a and the transistors 2b and 3a are turned on, a voltage due to the turning on of the transistor 2b is generated at the second connection point Pb, so in this case, the diode 8a is Even if shot, transistor 6
There is no change since this is the direction in which a is driven in the conduction direction. Furthermore, in this case, even if the diode 8b is shot, there is no effect on anything else.

In this way, in the conventional circuit shown in Fig. 1, even if the collector-emitter of any transistor is shorted, the operation immediately operates on the safe side, and there is no risk of excessive current flowing through each transistor. Disadvantages such as the transistor generating heat or causing a fire are eliminated.

By the way, in the case of the conventional circuit configured as described above, when no control signal is applied to the input terminals 7a and 7b, the transistors 3a and 3b are turned off, and if the motor 5 has inertia, the motor 5 is turned off momentarily. has the disadvantage of not being able to stop.

Further, although it is sufficient if the motor 5 continues to rotate as long as there is an input signal, a structure in which the motor 5 rotates and a mechanical mechanism (not shown) is locked in conjunction with this rotation may be used. When the transistors 6a and 6b are shot between their collectors and emitters, when the motor 5 rotates and is mechanically locked, there is no motor back electromotive force, and the motor 5 becomes energized, and the transistors 2b and 6b become energized. There is a drawback that 3a or 2a, 3b generates heat.

In consideration of these points, this invention is capable of instantaneously stopping the drive of a load such as a motor even if the load has inertia, and also eliminates the heat generation that may occur when the load of a mechanical interlocking mechanism is locked and energized. The purpose of the present invention is to provide a protection circuit for a load drive circuit that takes into consideration the possibility of avoiding fires, fires, and the like.

An embodiment of this invention will be described in detail below with reference to FIG. Note that in FIG. 2, parts corresponding to those in FIG. 1 are designated by the same reference numerals and their explanations will be omitted.

In this embodiment, the collector of the first protection transistor 9a is connected to the base of the transistor 3a and also substantially connected to the emitter of the first braking transistor 10a, and the base of the transistor 9a is connected to the first protection transistor 9a having a predetermined delay time. 1 delay circuit 11a
is connected to the common connection point of the collector of the transistor 2b and the anode of the diode 12a via Pb, and the cathode side of the diode 12a is connected to the second connection point Pb.
Connect to. This diode 12a is the delay circuit 1
This is for preventing reverse voltage inflow for 1a. Similarly, the collector of the second protection transistor 9b is connected to the base of the transistor 3b and also substantially connected to the emitter of the second braking transistor 10b, and the base of the transistor 9b is connected to the base of the transistor 9b with a delay equivalent to that of the delay circuit 11a described above. It is connected to a common connection point between the collector of the transistor 2a and the anode of the diode 12b through a second delay circuit 11b having a delay time, and the cathode side of the diode 12b is connected to the first connection point Pa. This diode 12b, like the diode 12a described above, is used to prevent reverse voltage inflow for the delay circuit 11b.

Further, the bases of the transistors 10a and 10b are substantially connected to the bases of the transistors 2a and 2b, respectively, and the collectors of the transistors 10a and 1b are commonly connected to the common connection point of the emitters of the transistors 2a and 2b, that is, the positive side of the power supply 4. Connecting.

Furthermore, a resistor 13a is connected in parallel with the resistors inserted on the base side of the control transistors 6a and 6b.
and a bypass circuit consisting of a capacitor 14a and a bypass circuit consisting of a resistor 13b and a capacitor 14b are connected, respectively. This is because when the motor 5 is stopped, the transistors 3a and 3b are normally turned on and brakes are applied to the motor 5, and even if a control signal is applied from the input terminals 7a and 7b, the transistors 6a and 3b are switched on by the diodes 8a and 8b. 6b cannot be turned on, so when the control signal is applied, the resistor 13a and capacitor 14a and the resistor 13b and capacitor 1
The transistors 6a and 6b are temporarily turned on via the respective bypass circuits 4b.
In other words, these bypass circuits are transistor 6
It acts as a differentiating circuit that applies a kind of trigger pulse to a and 6b. Therefore, the configuration of this bypass circuit is not limited to this, and other configurations may be used as long as the transistors 6a and 6b can be turned on when the control signal is applied.
For example, a capacitor 14 is connected in parallel to two resistors inserted into the bases of transistors 6a and 6b.
A and 14b may be connected, respectively, and resistors 13a and 13b may be connected between these parallel circuits and input terminals 7a and 7b, respectively.

In a circuit with such a configuration, input terminals 7a and 7b
When the control signal applied to transistors 2a and 2b is no longer applied to
0a and 10b, both of these transistors are turned on, and as transistors 10a and 10b are turned on, transistors 3a and 3b are also turned on, respectively. Therefore, when the motor 5 is now operating with the current passing through the transistors 2b and 3a, the input terminal 7a
The voltage generated by the inertia of the motor 5 due to the turning off of transistors 2b and 3a when the control signal applied to the transistor 3b is turned on by the transistor 10b turned on by the loss of the control signal as described above. The collector-emitter of is short-circuited through the earth and the diode connected between this earth and the first connection point Pa, and the motor 5 stops instantaneously. Similarly, when the motor 5 is operated by the current passing through the transistors 2a and 3b, the transistor 1
The collector-emitter of transistor 3a turned on by 0a, the ground and this ground and the second
The inertia voltage at that time is short-circuited through the diode connected between the connection point Pb, and the motor 5 stops instantaneously.

In this way, even if the motor 5 has inertia, the voltage generated by the inertia is released at the same time as the motor 5 stops operating, so the motor 5 is stopped instantaneously.

In addition, as mentioned above, due to the mechanical lock, the control transistors 6a and 6b can be operated for longer than the required driving time of the motor 5.
When the transistors 3a and 3b are turned on, the transistors 3a and 3b are forcibly turned off to stop the power supply to the motor 5. That is, the transistors 6a, 2b, 3a are controlled by the control signal now applied to the input terminal 7a.
is on and the motor 5 is being driven by the current flowing through the transistors 2b and 3a.If the collector-emitter of the transistor 6a is shot regardless of the control signal applied to the input terminal 7a, the collector voltage of the transistor 2b will be After a predetermined period of time has elapsed from the shot point of the delay circuit 11a, the signal is supplied to the base of the transistor 9a to turn on this transistor.
When the transistor 3a is turned on, the transistor 3a is forcibly turned off, and the power supply to the motor 5 is cut off. Similarly, when the collector-emitter of transistor 6b is shorted, the collector voltage of transistor 2a is supplied to the base of transistor 9b after a predetermined time has passed through delay circuit 11b, turning on transistor 9b, and forcing transistor 3b to turn off. state, in which case transistors 2a and 3
Power to the motor 5, which is driven by the current flowing through b, is cut off.

In this way, even if the motor 5 is mechanically locked by shooting the control transistors 6a and 6b between their collectors and emitters so that they are in the same state as the on state by inputting a control signal, the control transistors 6a and 6b are shot and a predetermined period of time elapses after the motor 5 is mechanically locked. Afterwards, the transistors 3a and 3b are forcibly turned off and power to the motor 5 is cut off, thereby preventing heat generation and the risk of fire. Therefore, the delay times of the delay circuits 11a and 11b are set at least within a time period such that each transistor does not generate heat or ignite after the transistors 6a and 6b are fired.

As mentioned above, according to this invention, even if the drive load has inertia, it is possible to stop the drive instantly, making it possible to control the drive of the load with high precision. When applied to threading motors, etc., main ring overrun or unloaded end (UNTHRED
END), gear jamming or tape pull-out arm bounce are improved.

In addition, even if the control transistor is shot and the load of the mechanical interlocking mechanism is locked and becomes energized, the power to the load is immediately cut off.
All drawbacks such as the transistors and the like used generating heat or causing fires are eliminated.

Note that in the above embodiment, the delay circuits 11a and 11
Although the delay time b has been explained with reference to the case where it is set within a time that takes safety measures into consideration, it is not limited to this, and may be set within a time period that takes into account various operating times in the drive circuit, for example.
The setting may also be made taking into account the tape loading time in the VTR.

Further, in the above embodiment, the control transistor 6
This is a safety measure when the motor 5 is mechanically locked and continues to be energized by shorting between the collectors and emitters of transistors 6a and 6b, but upon receiving a control signal, transistors 6a and 6b turn on and operate normally. It goes without saying that the present invention can be similarly applied even when the motor 5 is mechanically locked and energized due to some kind of failure during the process.

[Brief explanation of drawings]

FIG. 1 is a connection diagram showing an example of a conventional circuit, and FIG. 2 is a connection diagram showing an embodiment of this invention. 1a and 1b are first and second series circuits, respectively;
a, 3a and 2b, 3b are respectively switching transistors; 5 is a load such as a motor; 6a, 6b are first and second control transistors, respectively; 8a,
8b are first and second diodes, 9a, 9
b are the first and second protection transistors, respectively;
0a and 10b are first and second braking transistors, respectively, and 11a and 11b are first and second delay circuits, respectively.

Claims (1)

[Claims for Utility Model Registration] A first series circuit in which first and second switching transistors having different conductivity types are connected in series with respect to their collectors and emitters; A second series circuit configured in the same manner as the circuit is connected in parallel, and a common connection point on the first switching transistor side of the first and second series circuits is a terminal of one polarity of the DC power supply. a common connection point on the second switching transistor side of the first and second series circuits is substantially connected to the other polarity terminal of the DC power supply; A load is placed between a first connection point to which each switching transistor of the series circuit is connected in series and a second connection point to which each switching transistor of the second series circuit is connected in series. the base of the first control transistor is connected to the first control signal input terminal, the base of the second control transistor is connected to the second control signal input terminal, and the first control transistor An emitter of the transistor is connected to a base of the second switching transistor of the first series circuit, and an emitter of the second control transistor is connected to a base of the second switching transistor of the second series circuit. The collector of the first control transistor is connected to the base of the first switching transistor of the second series circuit, and the collector of the first control transistor is connected to the base of the first switching transistor of the second series circuit. The base of the first protection transistor is connected to the base of the first switching transistor, and the base of the first protection transistor is substantially connected to the collector of the first switching transistor of the second series circuit through a first delay circuit. , a base of a second protection transistor is substantially connected to the collector of the first switching transistor of the first series circuit through a second delay circuit; connected to the base of the second switching transistor of the first series circuit; the base of the second switching transistor of the second series circuit connected to the collector of the second protection transistor; The emitters of the first and second protection transistors are both connected to the other polarity terminal of the DC power supply, and the base of the first switching transistor of the first series circuit is connected to the base of the first braking transistor. the bases of the second braking transistor are substantially connected to the base of the first switching transistor of the second series circuit, and the emitter of the first braking transistor is substantially connected to the base of the first switching transistor of the second series circuit; substantially connected to the base of the second switching transistor of the first series circuit, the emitter of the second braking transistor being connected to the base of the second switching transistor of the second series circuit; substantially connected to the common connection point of the first and second series circuits, wherein the collectors of the first and second braking transistors are both connected to a terminal of one polarity of the DC power supply; a first diode is substantially connected between the first control signal input terminal and the second connection point, and a first diode is substantially connected between the second control signal input terminal and the first connection point. A protection circuit for a load driving circuit, characterized in that a second diode is substantially connected between the protection circuit and the second diode.