JPH0241276B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a speed control circuit for a small DC motor that uses a current mirror method to drive a DC motor, in which a resistor is connected between a first current mirror circuit and a second current mirror circuit. By doing so, when the collector and emitter voltages of each transistor in the first current mirror circuit reach near the saturation region, the fluctuation in the current ratio due to the variation in characteristics caused by the size of the emitter area between each transistor is reduced. The purpose is to suppress hunting of the DC motor.

An example of a conventional motor speed control circuit is shown in FIG. The part surrounded by the broken line in the figure is monolithic.
It is an IC part, and 1 to 5 are its external lead terminals. Between terminals 1 and 2, between terminals 2 and 3, and between terminals 3 and 4
Resistors R ₁ and R ₂ and a volume VR are connected between them. This volume VR is for speed adjustment. In addition, terminal 5 is a ground terminal and is connected to the power supply Vcc.
is connected between terminals 1 and 5. Motor M is connected between terminals 1 and 4.

On the other hand, in the monolithic IC, the emitters of transistors Q ₁ and Q ₂ that constitute a first current mirror and whose bases are connected in common are grounded via resistors R ₃ and R ₄ , respectively. these transistors
The collectors of Q ₁ and Q ₂ are connected to the respective emitters of transistors Q ₃ and Q ₄ constituting the second current mirror, and these current mirror circuits are connected in cascade. The collectors of transistors Q ₃ and Q ₄ are connected to terminal 1 via terminal 2 and constant current source 6, respectively. The bases of transistors Q ₃ and Q ₄ are connected to each other, and the base and collector of transistor Q ₄ are connected. transistor
The collector of Q ₂ is connected to terminal 4.

A comparator (operational amplifier) 7 is provided with terminals 7a and 7b connected to terminals 1 and 5, the non-inverting input terminal is connected to terminal 3, and the inverting input terminal is connected between terminals 2 and 5. It is connected to a connection point between a Zener diode 8 and a constant current source 9, which are connected in series.

The base-to-emitter voltages V _BE3 and V _BE4 of transistors Q ₃ and Q ₄ are approximately equal, and therefore the collector voltages of transistors Q ₁ and Q ₂ are maintained at approximately equal voltages.

In the above circuit configuration, transistors Q ₁ ,
The emitter area ratio of Q ₂ is 1:K (K is a positive integer)
It is said that Here, the back electromotive force Eg of the motor M,
The internal resistance is Rg, the current flowing through the motor is I _M , the collector currents of transistors Q ₃ and Q ₄ are almost equal, the current flowing through the collector of transistor Q ₁ is I _K , the current flowing through resistor R ₂ is I _S , Let the voltage generated across both ends be V _S , the current flowing through the Zener diode be I _Z , and the resistance value of the volume VR be R〓.
Further, the input impedance of each of the comparator circuits 7 is very high, and if the current flowing into them is ignored, the following relationship holds true.

Eg + I _M Rg = I _S (R ₁ + R ₂ + R〓) + (I _K + I _Z ) R ₁ ... (1) where I _S = V _S /R ₂ ... (2) I _K = 1 / K・I _M, that is, K=I _M /I _K (3) Substituting equations (2) and (3) into equation (1), the following equation is obtained.

Eg＋I _M Rg＝V _S /R ₂ (R ₁ +R ₂ +R〓)＋I _Z R ₁ +I _M /KR ₁ ...
…(4) From the bridge balance condition, the first left side of equation 4
The following equation holds true from the first and second terms on the right side, the second term on the left side, and the second term on the right side.

Eg＝V _S /R ₂ (R ₁ +R ₂ +R〓)＋I _Z R ₁ ...(5) I _M Rg＝I _M /KR ₁ ...(6) From equation 6, R ₁ =KRg ...(7 ) is derived.

Usually, the value of the resistor R ₁ in equation (7) is set slightly larger than the value of KRg on the right side by selecting K a little larger to prevent overcontrol (to prevent hunting).

In this circuit, the comparator 7 differentially amplifies the voltage _VZ of the Zener diode 8, which serves as the reference voltage, the back electromotive force of the DC motor M, and the voltage drop due to the internal resistance Rg of the motor, and converts it into the differential voltage that becomes the output. Therefore, by driving the transistor Q ₂ for driving the DC motor including the transistor Q ₁ and controlling the current flowing to the motor M, the rotation of the DC motor M is controlled to be constant.

In such a conventional circuit, when the power supply voltage decreases, when there is an overload, when starting up, etc., the transistors Q ₁ and Q ₂ forming the first current mirror circuit are
When the collector-to-emitter voltage (hereinafter simply referred to as V _CE ) of Q2 reaches near saturation or reaches the saturation region, as shown in the V _CE −I _C (I _C is collector current) characteristic diagram in Figure 2, the voltage of transistor Q ₂ Collector current I _C2 (This I _C2 is
I _M ) is the transistor Q ₁
As a result, _K shown in equation (3) becomes smaller, and the right side of equation (6) becomes larger than the left side, so the correction becomes excessive and the motor M will start hunting.

The present invention eliminates the problems of the conventional art, and embodiments thereof will be described below with reference to the drawings. Third
The figure shows a speed control circuit according to an embodiment of the present invention. The same components as in Fig. 1 are given the same reference numerals.
The explanation will be omitted.

Collector of transistor Q ₁ and transistor Q ₃
A resistor R is connected between the emitter and the emitter. In this embodiment, the collector currents I _K and I _C2 of transistors Q ₁ and Q ₂ are selected to have a ratio of 1:50, that is, K is 50. Note that the value of K is selected so as to satisfy the following two conditions. The first is to set K to 1, for example.
In this case, the same collector current (for example, 200 mA) as that of Q ₂ flows to the collector of Q ₁ , resulting in a large current loss, so K needs to be sufficiently larger than 1.
Second, in order to avoid the influence of temperature drift of the current I _Z (e.g. 0.1 mA) of the Zener diode 8 flowing through the resistor R ₁ , I _K (e.g. 4 mA) must be selected to a value sufficiently larger than I _Z. be. Therefore I _K
is selected as 50 to satisfy these conditions. Here, for some reason, the transistor Q ₁ ,
When each V _CE of Q ₂ reaches near the saturation region, the respective collector currents I _K and I _C2 start to decrease as in the conventional example, and since the decreasing rate of I _C2 is large, K changes in the direction of decreasing. However, in this case, since a resistor R is connected between the collector of transistor _Q1 , which has a small collector current, and the emitter of transistor _Q3 , a current drop due to this resistor occurs near the saturation region, and the I _K The slope of the current becomes like the _IK curve shown in the V _CE -I _C characteristic shown in Figure 4. In other words, near the saturation region, the resistance R causes the transistor Q ₁
Since the collector current I _K also decreases, I _K and I _C2 (I _C2 ≒ I _M )
The ratio hardly changes, and therefore, no excessive control occurs, no hunting phenomenon occurs, and stable motor speed control is possible.

FIG. 5 is a diagram showing the change in K with respect to the change in V _CE of transistors Q ₁ and Q ₂ , where the dotted line K' is due to the conventional speed control circuit, and the solid line K is the change in K in the embodiment of the present invention. The dotted line K′ is
This shows that V _CE starts to decrease from a relatively large point.

The value of the resistor R is determined by the circuit constant, the magnitude of K, the current capacity of the transistor, etc., and is selected to be 30Ω in this embodiment.

Next, FIG. 6 shows a speed control circuit that is a modification of FIG. 3. Components that are the same as those in FIGS. 1 and 3 are designated by the same reference numerals, and their explanations will be omitted.

The second current mirror circuit is a transistor
The emitter of a PNP transistor _Q5 is connected to _the base of _Q3 , and _the connection point thereof is connected to terminal 1 via a constant current source 6. The base of Q ₅ is connected to the collector of Q ₂ and terminal 4, and the collector is connected to terminal 5. In this circuit, the collector of transistor Q ₅ is connected to terminal 5,
The current flowing into the collector of transistor _Q2 is only its base current, and this base current is very small. Therefore, as shown in Figures 1 and 2, its collector current (this collector current is proportional to load fluctuation Since K (I _C2 /I _{K ) does not flow, K (I C2 /I K} ) can be kept constant without being affected by other fluctuation factors, and the rotational speed of the motor can be controlled stably.

As described above, in the present invention, in a drive circuit for a DC motor M in which a first current mirror circuit constituted by a plurality of transistors having different emitter areas and a second current mirror circuit are connected in cascade, the first
Since the emitter of the current mirror circuit is configured to connect a resistor to the collector of a transistor with a small area, the value of K (I _C2 /I _K ) at or near the saturation of V _CE based on the difference in the characteristics of the transistor can be made almost constant or large, for example, it is possible to prevent hunting from occurring during speed control (operation) at low power supply voltage, overload, startup, etc., and to ensure stable DC motor rotation. The speed can be controlled.

[Brief explanation of drawings]

Figure 1 is a conventional motor speed control circuit diagram, Figure 2
The figure is a V _CE -I _C characteristic diagram of the transistor of the first current mirror circuit in a conventional circuit, Figure 3 is a motor speed control circuit diagram according to an embodiment of the present invention, and Figure 4 is a diagram of a motor speed control circuit according to an embodiment of the present invention.
The figure shows the V _CE -I _C characteristic diagram of the transistor of the first current mirror circuit in the circuit of the embodiment of the present invention, Fig. 5 shows the V _CE -K characteristic diagram, and Fig. 6 shows the characteristic diagram of the transistor of the first current mirror circuit in the circuit of the embodiment of the present invention. 3A and 3B show speed control circuit diagrams of motors showing modified examples, respectively. 1 to 5... terminal, 7... comparison circuit, 8... Zener diode, M... DC motor, Q ₁ to Q ₅ ...
...transistor, _R1 to _R4 , R...resistance, VR...
Volume.

Claims (1)

[Claims] 1. A motor and a first transistor connected in series to one end and the other end of a DC power supply; first, second, and third resistors connected in series in parallel with the motor; a second transistor having an emitter area that is 1/K (K is a positive number) of the emitter area of the first transistor, and whose base is commonly connected to the base of the first transistor; a current mirror circuit consisting of third and fourth transistors whose bases are connected; the collector of the third transistor is connected to the connection point of the first and second resistors; and the emitter is connected to the collector of the second transistor. - Connected to the collectors of the second transistors through resistors to reduce the collector current when the emitter voltage approaches saturation or reaches the saturation region, and the collector of the fourth transistor is connected to one end of the power supply. Also, the emitters are respectively connected to the collectors of the first transistor, and one input terminal is connected to the first and second transistors through a reference voltage source.
The other input terminal is connected to the connection point of the second and third resistors.
A speed control circuit for a small direct current motor, comprising: a comparator connected to a connection point of each of the resistors, and having an output terminal connected to the bases of the first and second transistors.