JPH0311996A - Speed control circuit of motor - Google Patents

Abstract

PURPOSE:To prevent a noise and a temperature rise of respective elements by providing two output transistors connected serially between first and second power supplies and by connecting the input of one transistor of the two output transistors to the second power supply with a switching transistor. CONSTITUTION:Connection points between output transistors(Tr)4, 5 are connected to driving coils 17-19. The base of a switching transistor(STr)23 is connected to an input terminal 12 via a base resistor 24, and the collector-emitter path of STr23 is connected between the base of Tr4 and earth. When Tr5 is in ON state while Tr4 is in OFF state, if STr23 is turned to ON state, the parasitic capacitor between the base and collector of Tr4 is discharged via the collector-emitter path of STr23. Thereby, no current flows through Tr4 and Tr5, so that the noise from power supplies and the temperature rise of elements are prevented, and a motor can be controlled surely.

Description

DETAILED DESCRIPTION OF THE INVENTION B) Industrial Application Field The present invention is directed to motor speed control circuits, particularly PWM (Pu1
(Width Modulation) This relates to a speed control circuit for a motor that performs speed control.

(b) Prior Art A conventional circuit for rotating a motor at a constant speed using PWM speed control will be explained with reference to FIG.

In FIG. 2, (1), (2), and (3) are speed control circuits, and since the internal circuits of these speed control circuits (1), (2), and (3) are the same, the speed control circuit (1) is The internal circuit of 〉 will be explained below. (4) and (5) are the first and second output transistors, respectively, and the collector-emitter paths of these output transistors (4) and (5) are connected to the source voltage. The emitter and collector of the transistor (7) are connected in series between the power supply terminal (6) to which V.C (the first source is the source) and the ground (the second power source) are connected to the output transistor (7), respectively. 4), and the base of the transistor 7) is connected to the input terminal (8), so that when the input signal S1 is applied to the input terminal (8), the output The transistor (4) and the transistor (7) operate.The shunt resistor (9) connected between the base and emitter of the output transistor (4) shunts the collector output of the transistor (7). This prevents the output transistor (4) from malfunctioning due to leakage current between the emitter and collector of the transistor (7). on the other hand,
The emitter of the transistor (10) connected to the output transistor (5) in Darlington is connected to a shunt resistor (1), which will be described later.
1) and the transistor (10)
Since the base of is connected to the input terminal (12), the output transistor (5) and the transistor (10) operate by applying the input signal S2 to the input terminal (12). Further, the output transistor (5)
Similar to the shunt resistor (9), the shunt resistor (11) connected between the base and emitter of the transistor
This prevents the output transistor (5) from malfunctioning due to leakage current between the collector and emitter of the transistor (5). (14) is a control transistor, and the collector-emitter path of the control transistor (14) is connected to the input terminal (
12) and ground, and the base of the control transistor <14) is connected to the control terminal (16) via the base resistor (15), and a control signal PWM whose duty ratio can be varied is connected to the control transistor (14). The control transistor (14) is operated by applying the voltage to the control terminal (16).

(17) (18) (19) are three-phase drive coils inside the motor, and these drive filters (1, 7) (18) (
19) are respectively connected to the connection points of the output transistors (4) and (5) inside the speed control circuits (1), (2), and (3).

Note that the speed control circuits (1), (2), and (3) are integrated circuits, and the same elements inside the speed control circuits (1) (2>(3)) are given the same reference numerals. .

In FIG. 2, in order to rotate the motor in one direction, a drive current is applied to the drive coils (17) (1g) (19).

It must be flowed repeatedly in the order of arrows b and c. Here, in each case where the drive current flows in the directions of the arrows a, b, and c, the operations among the speed control circuits (1), (2), and (3) have a certain relationship.For example, The operation when a unidirectional drive current is passed through the drive coils (18) and (17) will be described below.

In this case, in order to cause the drive current to flow in only one direction through the drive coils (18) (17>), the input signals S, , S, applied to the speed control circuit (1) are set to a high level (hereinafter referred to as "rH"). input signal St applied to the speed control circuit (2)
, St are set to low level (hereinafter referred to as "L"), and input signals S, , S, which are further applied to the speed control circuit (3).
are set to rH,,'L, respectively. By doing this, the output transistor (5) inside the speed control circuit (1)
and speed control circuit (2) internal output transistor (4)
Only the drive coils (18) and (17) are turned on.
), a unidirectional drive current will flow through it. Here, inside the speed control circuit (1), suppose that the control transistor (
14) is always off, the output transistor (5
> is in a saturated state, so a unidirectional drive current always flows through the drive coil (1g Therefore, the control transistor (I4) cannot be rotated at a constant speed using the control signal PWM.
By turning on and off the output transistor (4)
The on-off period A (the time required to flow a drive current in one direction) of the output transistor (5) when the output transistor (5) is off is intermittently controlled on and off, and the drive current in one direction is applied to the drive coils (18) and (17). The intermittent flow allows the motor to rotate at a constant speed lower than the maximum speed. Incidentally, if the duty ratio of the control signal PWM is varied so that the "L4 period" becomes longer, the on-period of the output transistor (5) becomes longer in the on-possible period A.
The driving current in this direction flows for a long time, and the rotation speed of the motor becomes higher. On the other hand, if the duty ratio is varied so that the "rH" period of the control signal PWM becomes longer, the on-possible period A
In this case, the on period of the output transistor (5) is shortened, so that the drive current in the a direction flows only for a short period of time, and the rotational speed of the motor becomes lower than this. That is, the control signal PWM
PWM speed control is to control the rotation speed of the motor by changing the duty ratio of the motor.

The circuit shown in FIG. 2 is used to control motors of OA equipment and the like.

(c) Problems to be Solved by the Invention However, in the above-mentioned conventional technology, when the output transistor (4) is off, the control signal PWM changes from rH to "
When LJ falls and the output transistor (5) turns on, the emitter potential of the output transistor (4) falls to ground potential at the same time as the output transistor (5) turns on, but the base of the output transistor (4) The first position cannot immediately fall due to the parasitic capacitance between the base and collector of the output transistor (4) and the time constant caused by the shunt resistor (9).

Therefore, at the moment when the output transistor (5) is turned on, there is a one-order difference between the base and emitter of the output transistor (4) that is sufficient to turn on the output transistor (4) (5). ), a through current (large current) will flow through the collector-emitter path.

Due to fluctuations in power supply voltage, the power supply line (26)
There are problems in that noise is superimposed on the device, and the temperature of each element increases, making it impossible to make full use of the characteristics of each element.

(d) Means for Solving the Problems The present invention has been made to solve the above problems, and includes first and second outputs connected in series between a first power source and a second power source. A speed control circuit having a transistor and a control transistor that intermittently controls on/off the on period of the second output transistor when the first output transistor is off is provided for each multiphase drive filter inside the motor. and connecting the connection points of the first and second output transistors in each of the speed control circuits to each of the drive coils, thereby controlling the output of the control transistor in a motor speed control circuit that controls the speed of the motor. Based on this, when the second output transistor is turned on while the first output transistor is turned off, a switching transistor that connects the input of the first output transistor to the second power supply is connected to each speed control circuit. It is characterized by being prepared for.

(E) Effect According to the present invention, when the first output transistor is turned off and the second output transistor is turned on based on the output of the control transistor, the input of the first output transistor is connected to the second power supply. Since a switching transistor is provided for each speed control circuit, no through current flows through the first and second output transistors.

(f) Example The details of the present invention will be specifically explained with reference to illustrated embodiments.

In FIG. 1, (20), (21), and (22) are speed control circuits with the same configuration that are integrated into ICs, and the output transistors (4) ( The connection points of 5) are connected to the respective drive coils (17).
(18) and (19) are connected. Incidentally, the speed control circuits (20), (21), and (22) can also be formed into a one-chip IC.

Here, since the internal circuits of speed control circuits (20), (21), and (22) are the same, only the internal circuit of speed control circuit <20) will be explained. (23> is a switching transistor, and the switching transistor ( The base of 23) is connected to the input terminal (12) via the base resistor (24).
The collector-emitter path of the switching transistor (23) is connected between the base of the output transistor (4) and ground. and input signal S,
The switching transistor (23) operates in response to the control signal PWM in a state in which the switching transistor (23) is set to rHJ. Specifically, the input signal S, is rH.

When the control signal PWM is rL, the switching transistor (23) is turned on, and the input signal S is turned on.

is "H" and the control signal PWM is "rH", the switching transistor (23) is turned off. (25) is a diode connected between the base and emitter of the output transistor (4), its cathode is connected to the base of the output transistor (4), and its anode is connected to the emitter of the output transistor (4). has been done. Note that the same elements as in FIG. 2 are given the same reference numerals.

Hereinafter, similar to the explanation of FIG. 2, the drive coil (18) (1
7), only the case where the drive current in the a direction is caused to flow will be explained. In other words, inside the speed control circuit (20), since the input signals S, , S, are rH, the output transistor (4) is turned off, and the output transistor (5) is controlled on and off according to the control signal PWM. be.

Here, when the control signal PWM falls from rHJ to rL and the output transistor (5) turns on as the control transistor (14) turns off, the output transistor (
At the same time as transistor 5) turns on, the emitter potential of output transistor (4) drops to ground potential. However, the control signal PWM is rH.

When the voltage falls from "L" to "L", the control transistor (14) turns off and the switching transistor (23) turns on, so the parasitic capacitance between the base and the flipter of the output transistor (4) becomes Therefore, even if the control signal PWM falls and the output transistor (5) is turned on, the output transistor (4) is discharged via the collector-emitter path.
) between the base and emitter of the output transistor (4).
A potential difference sufficient to turn on no longer occurs, and no through current flows through the collector-emitter paths of the output transistors (4) and (5). This prevents noise from being superimposed on the power supply line (26) and prevents the internal temperature of the IC from rising.
Accurate speed control of the motor becomes possible.

Also, the control signal PWM rises from "L" to VH,
When the output transistor (5) turns off as the control transistor <14) turns on, the output transistor (5)
) is turned off, there is no path for passing the drive current in the a direction to the drive coils (18) and (17), and the base potential and emitter 1 of the output transistor (4) rise. However, the output transistor (4
) and the resistance value of the shunt resistor (9), the output transistor (
Since the base potential of 4) rises at a slower rate than the emitter potential, a reverse bias is applied to the output transistor (4), which may destroy the output transistor (4).

Therefore, as shown in this embodiment, a diode (25) is provided between the base and emitter of the output transistor (4), and the forward voltage of this diode (25) changes the base potential of the output transistor (4). is made to rise faster than the time constant caused by the parasitic capacitance and the resistance value of the shunt resistor (9), thereby preventing the output transistor (4) from being destroyed.It should be noted that the output transistor (4) is not destroyed. The number of diodes (25) connected in series is selected such that a degree of reverse bias is applied to the output transistor (4).

Furthermore, in the above case where the control signal PWM falls from rHl to "L" and the output transistor (5> is turned on as the control transistor (14) turns off), due to the characteristics of the element, the switching Transistor (
Since the output transistor (23) turns on slightly earlier, a reverse bias is applied to the output transistor (4) in this case as well, but the output transistor (4) is prevented from being destroyed by the diode (25).

From the above, no through current flows even when the control signal PWM falls, and destruction of the output transistor (4) is prevented even when the control signal PWM rises and falls, making it possible to reliably control the speed of the motor. .

(G) Effects of the Invention According to the present invention, when the first output transistor is turned off and the second output transistor is turned on based on the output of the control transistor, the input of the first output transistor is connected to the second power supply. Because the current is connected to Benefits can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing the speed control circuit of the motor of the present invention;
FIG. 2 is a circuit diagram showing a conventional circuit. (4)(5)...Output transistor, (14)...
・Control transistor, (17)(18)(19)...
- Drive coil, (20> (21) (22)... speed control circuit, (23)... switching transistor, (25)... diode.

Claims (2)

[Claims] (1) The first power supply connected in series between the first power supply and the second power supply
and a speed control circuit having a second output transistor and a control transistor that intermittently controls on/off the on period of the second output transistor when the first output transistor is off. provided for each drive coil, and the first
and a motor speed control circuit that controls the speed of the motor by connecting a connection point of a second output transistor to each of the drive coils, wherein the first output transistor is turned off based on the output of the control transistor. The speed of the motor is characterized in that each of the speed control circuits is provided with a switching transistor that connects the input of the first output transistor to the second power supply when the second output transistor is turned on in the state. control circuit. (2) In each of the speed control circuits, the first and second
2. The motor speed control circuit according to claim 1, further comprising a diode connected between a connection point of said output transistor and an input of said first output transistor.