JPS627792B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a current limiting circuit in a bridge detection type DC motor speed control device.

BACKGROUND ART Conventionally, as a bridge detection type DC motor speed control device, a device that utilizes the back electromotive force of a controlled DC motor as shown in FIG. 1 has been considered. Here, FIG. 1 will be explained.

1 is a DC motor whose speed should be controlled, 2, 3, 4
is the resistance, and the equivalent internal resistance of the DC motor 1 is
Resistor 2, resistor 3, and resistor 4 constitute a bridge circuit with each side as each side.

Now, the equivalent internal resistance of this DC motor 1 is R _a
If the resistance values of resistor 2, resistor 3, and resistor 4 are respectively R ₁ , R ₂ , and R ₃ , then when the bridge equilibrium condition R _a /R ₁ = R ₂ /R ₃ is satisfied, as shown in the figure The voltage between detection terminals a and b of the bridge circuit depends only on the rotational speed and is not related to the torque, that is, the armature current.

Therefore, the difference voltage between this voltage and the reference voltage V _ref is compared and amplified by a comparator amplifier 5, the output thereof is amplified by a transistor 6, and the output of the transistor 6 is further connected to a bridge circuit and a DC power supply 7.
In addition to the base of the power supply control transistor 8 inserted between them, when the rotational speed of the controlled DC motor 1 increases, the current I supplied to the bridge circuit is decreased, and on the other hand, when the rotational speed decreases, the current I is increased. By controlling the base current of the power supply control transistor 8 in this way, the rotational speed of the DC motor 1 can be kept constant.

Here, 9 is a constant current source, 10 is a constant voltage circuit, and the output voltage of the constant voltage circuit 10 is divided by a resistive voltage dividing circuit 13 consisting of a resistor 11 and a resistor 12 connected in series. A reference voltage V _ref is obtained as the terminal voltage.

By the way, in the bridge detection type DC motor speed control device as described above, when the DC motor 1 is in an overload state such as a lock state for a long time or an unexpected short circuit state, an excessive current is generated in the speed control device. There was a risk of smoke, fire, etc. due to flow failure or excessive heat generation.

That is, when the DC motor 1 is in an overload state such as a locked state or in a short circuit state, the potential at the detection end point a of the bridge increases compared to before.
Along with this, the potential of the non-inverting input terminal of the comparison amplifier 5 increases, so that the output terminal of the comparison amplifier 5,
In other words, the base potential of the transistor 6 also rises, increasing the collector current, and the power supply control transistor 8 increases.
Fully on. As a result, the DC power supply 7
An excessive current flows through the emitter and collector of the power supply control transistor 8, the DC motor 1, and the resistor 2. If such a state continues for a long time, the power supply control transistor 8, DC motor 1, and resistor 2 may overheat and generate heat due to the excessive current, which may cause smoke or fire.

The present invention solves this problem by reducing the amount of the first voltage generated across the first resistor (diagram number 2) connected in series with the DC motor 1 when viewed from the power supply end of the bridge circuit, and the reference voltage V. A voltage detection circuit is provided whose detection voltage is the output voltage of the constant voltage circuit 10 provided to obtain _ref , or the addition voltage with the second voltage amount obtained by dividing the output voltage. The purpose is to solve this problem by limiting the amount of power supplied to the power supply control transistor 8.

Embodiments of the present invention will be described below with reference to FIG. 2. Elements similar to those shown in FIG. 1 will be denoted by the same reference numbers, and their explanation will be omitted here.

Voltage detection circuit 14 in the embodiment of FIG.
The circuit configuration of will be explained. First, apart from the resistive voltage dividing circuit 13 for dividing the output voltage of the constant voltage circuit 10 to obtain the reference voltage V _ref , a resistive voltage dividing circuit consisting of a resistor 15 and a resistor 16 connected in series is newly provided.
The output voltage of the constant voltage circuit 10 is divided into voltages. Here, one end of the resistor 15 is connected to the positive output terminal of the constant voltage circuit 10, and one end of the resistor 16 is connected to the negative output terminal and to the connection point between the DC motor 1 and the first resistor. Further, the connection point between the resistor 15 and the resistor 16 is the base of the limiting transistor 17, and the emitter of the limiting transistor 17 is the first point.
The collector of the limiting transistor 17 is connected to the base of the transistor 6 preceding the power supply control transistor 8.

Now, in this circuit configuration, if the DC motor 1 is in an overload state such as a locked state or in an unexpected short circuit state, and the current I supplied to the bridge circuit increases, the first resistor 2 will increase accordingly. The terminal voltage, ie, the first voltage amount, also increases. on the other hand,
The second voltage amount is given as the terminal voltage of the resistor 16 obtained by dividing the output voltage of the constant voltage circuit 10 by a resistive voltage divider circuit consisting of a resistor 15 and a resistor 16 connected in series. Then, the constant voltage circuit 1
If the output voltage of 0 and the voltage division ratio of the resistor 15 and the resistor 16 are constant, the second voltage amount will also be a constant value.

Incidentally, an additional voltage of the first voltage amount and the second voltage amount is applied between the base and emitter of the limiting transistor 17, and as the current I increases, the first voltage amount increases. As the voltage increases, the base-emitter voltage of the limiting transistor 17 also increases. and the first voltage amount and the second voltage amount.
The added voltage of the voltage amount is the limiting transistor 17.
When the voltage is sufficient to turn on, the base current of the transistor 6 is shunted as the collector current of the limiting transistor 17, so that the base current of the supply limiting transistor 8 is limited, and as a result, the base current supplied to the bridge circuit is Therefore, the current I that flows is limited.

Now, let's consider what will happen if the voltage division ratio of resistor 15 and resistor 16 is changed.

Now, if the terminal voltage of the resistor 16, that is, the second voltage amount is set to be large by changing the voltage division ratio, the first voltage amount required to turn on the limiting transistor 17 may be small. 1st
Since the voltage amount is given by the voltage drop across the first resistor 2, the fact that the first voltage amount is small means that the value of the current I supplied to the bridge circuit is small. That is, when the second voltage amount is set to be large by changing the voltage division ratio, the current I is limited to a small value. Conversely, by changing the partial pressure ratio,
It goes without saying that if the voltage amount is set small, the current I will be limited to a large value.

As is clear from the above, by changing the voltage division ratio of the resistors 15 and 16, the limit value of the current I can be arbitrarily selected.

Next, another embodiment of the present invention will be described with reference to FIG. 3. Elements similar to those shown in FIGS. 1 and 2 will be denoted by the same figure numbers, and their explanation will be omitted here. .

Voltage detection circuit 14 in the embodiment of FIG.
The circuit configuration of will be explained. First, the output voltage of the constant voltage circuit 10 is divided by a resistive voltage divider circuit including a resistor 11 and a resistor 12 connected in series. Here, resistance 1
One end of 1 is connected to the positive output terminal of the constant voltage circuit 10,
One end of the resistor 12 is connected to the negative output terminal and also to the connection point between the DC motor 1 and the first resistor (number 2 in the figure). Further, the connection point between the resistor 11 and the resistor 12 is connected to the non-inverting input terminal of the comparator amplifier 5, and the base of the limiting transistor 17, and the emitter of the limiting transistor 17 is connected to the first
The collector of the limiting transistor 17 is connected to the base of the transistor 6 preceding the power supply control transistor 8.

As can be seen from the above circuit configuration, in this embodiment, the terminal voltage of the resistor 12 is the reference voltage V
It is designed to serve both as _ref and the second voltage amount.

Since the reference voltage V _ref sets the control rotational speed of the DC motor 1 and is therefore a fixed value, the second voltage amount cannot be arbitrarily selected as in the embodiment shown in FIG. A sum voltage of the terminal voltage of , that is, the first voltage amount, and the second voltage amount, which is the reference voltage V _ref in this case, is applied between the base and emitter of the limiting transistor 17, which is normally off. As a result, the amount of power supplied to the power supply control transistor 8, that is, the current I can be limited.

Next, another embodiment of the present invention will be described with reference to FIG. 4, in which elements similar to those shown in FIGS. is omitted here.

Voltage detection circuit 14 in the embodiment of FIG.
The circuit configuration of will be explained. First, the output voltage of the constant voltage circuit 10 is divided by a resistive voltage divider circuit including a resistor 18, a resistor 19, and a resistor 20 connected in series. Here, one end of the resistor 18 is connected to the positive output terminal of the constant voltage circuit 10, the connection point between the resistor 18 and the resistor 19 is connected to the non-inverting input terminal of the comparison amplifier 5, and the connection point between the resistor 19 and the resistor 20 is connected to the limiting transistor. Each is connected to 17 bases. The other end of the resistor 20 is connected to the negative output terminal of the constant voltage circuit 10 and also to the connection point between the DC motor 1 and the first resistor 2. Further, the emitter of the limiting transistor 17 is connected to the opposite end of the first resistor 2 to which the DC motor 1 is connected, and the collector of the limiting transistor 17 is connected to the front stage transistor 6 of the power supply control transistor 8. connected to the base of.

As can be seen from the above circuit configuration, in this embodiment, the output voltage of the constant voltage circuit 10 is controlled by the resistor 18,
The voltage is divided by a resistor voltage divider circuit consisting of a resistor 19 and a resistor 20 connected in series.
The reference voltage V _ref is the terminal voltage of the series combined resistance of
The terminal voltage of the resistor 20 provides the second voltage amount.

Then, the terminal voltage of the first resistor 2, that is, the first
voltage amount and the terminal voltage of the resistor 20, that is, the second
applying a voltage added to the voltage amount between the base and emitter of the limiting transistor 17 to turn on the limiting transistor 17, which is normally off;
As a result, the amount of power supplied to the power supply control transistor 8, that is, the current I can be limited.

Furthermore, in this embodiment, the second voltage amount can be selected independently from the reference voltage V _ref by selecting the values of the resistors 18, 19, and 20, so that the current I
The limit value can be arbitrarily selected.

As described above, the current limiting circuit for a DC motor of the present invention is a bridge detection type DC motor speed control device, in which the first resistor is connected in series with the controlled DC motor when viewed from the power supply end of the bridge circuit. The output voltage of a constant voltage circuit provided to obtain the first voltage amount generated at both ends and the reference voltage, or the summed voltage of the second voltage amount obtained by dividing the output voltage, is used as a detection voltage in the voltage detection circuit. Turning on the normally OFF limiting transistor provided in the control transistor to limit the amount of power supplied to the power supply control transistor is an extremely simple, inexpensive, and reliable method to prevent overloads such as when the controlled DC motor is locked for a long time. It is possible to limit the flow of excessive current to the speed control device even in the event of a short circuit or an unexpected short circuit, thereby avoiding the risk of smoke or fire caused by destruction or excessive heat generation. This can be very effective as a safety measure for seed speed control devices.

[Brief explanation of the drawing]

FIG. 1 is an electric circuit diagram of a conventional bridge detection type DC motor speed control device, FIG. 2 is a current limiting circuit for a DC motor according to an embodiment of the present invention, and FIG.
4 and 4 show a current limiting circuit for a DC motor according to another embodiment of the present invention. 1... Controlled DC motor, 2... First resistor,
3, 4... Resistor, 5... Comparison amplifier, 6... Pre-stage transistor of power supply control transistor, 7... DC power supply, 8... Power supply control transistor, 9... Constant current source, 10... Constant voltage circuit, 11, 12... Resistor, 13... Resistor voltage divider circuit, 14... Voltage detection circuit, 15, 16... Resistor, 17... Limiting transistor, 18, 19, 20... Resistor.

Claims (1)

[Scope of Claims] 1. A voltage proportional to the rotational speed of the controlled DC motor is obtained from a detection end of a bridge circuit configured to include a controlled DC motor on one side, and the back electromotive force is proportional to the rotational speed. A speed control device for a DC motor that controls the rotational speed of the controlled DC motor by comparing the difference voltage with a reference voltage and controlling a power supply control transistor inserted between the bridge circuit and the power source using the difference voltage. A first voltage amount generated across a first resistor connected in series with the controlled DC motor when viewed from the end, and an output voltage or the output voltage of a constant voltage circuit provided to obtain the reference voltage. A current of a DC motor, characterized in that a voltage detection circuit is provided whose detection voltage is a voltage added to a second voltage amount obtained by voltage division, and the amount of power supplied to the power supply control transistor is limited by the output voltage of the voltage detection circuit. limit circuit. 2 The added voltage of the first voltage amount and the second voltage amount is used as the detection voltage, turns on the normally off limiting transistor, and diverts the base current of the power supply control transistor or the transistor in the preceding stage of the power supply control transistor. 2. A current limiting circuit for a DC motor according to claim 1, wherein the amount of power supplied to said power supply control transistor is limited by: 3. Current limitation of a DC motor according to claim 1, characterized in that a resistive voltage dividing circuit is provided to divide the output voltage of the constant voltage circuit, and the divided voltage is set as the second voltage amount. circuit. 4. According to claim 1, the output voltage of the constant voltage circuit is divided by a resistive voltage divider circuit, and the divided voltage is used as the reference voltage and the second voltage amount. DC motor current limiting circuit. 5. A resistor voltage divider circuit for dividing the output voltage of the constant voltage circuit to obtain the reference voltage, and converting any divided voltage divided by the resistor voltage divider circuit to the second voltage. 2. A current limiting circuit for a DC motor according to claim 1, wherein the current limiting circuit is a current limiting circuit for a DC motor.