JPH02146983A - Driver circuit for motor - Google Patents

Abstract

PURPOSE:To protect load such as a motor from damage due to excess output currents by controlling the maximum value of output currents by a control input apart from a servo signal. CONSTITUTION:An output from a servo IC is applied to a differential amplifier 30, bias voltage VB is subtracted, and an output corresponding to a differential output is made to flow through a current mirror circuit 34, converted into voltage and applied to a transistor 40. Bias voltage is applied to a transistor 4 from the transistor 40 while the transistor 4 is supplied with an output corresponding to a servo signal by the current mirror circuit 34. A transistor 42 forms the bypass of the transistor 40, and is transferred to a conductive state or a cut-off state by a control input VTL applied to the base of the transistor 42 and controls the base input of the transistor 4. Accordingly, output currents Iout are limited.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a motor drive circuit that drives a motor according to a servo output of a servo IC.

[Conventional technology]

Conventionally, a motor servo circuit has a servo I as a control section.
A drive IC for supplying a drive output to the motor is installed together with C, and a motor drive circuit for supplying a drive output to an output circuit that flows a drive current to the motor is installed in the drive IC.

FIG. 3 shows a conventional motor drive circuit, in which a servo signal VIN is applied to the input terminal 2 from the servo tC. Servo signal VIN is FC representing motor rotation.
Servo I from the PG multiplied signal that represents the rotational phase of the motor.
C represents the torque command signal for the motor to be driven. When this servo signal VIN is applied, a current 11 corresponding to the servo signal (2) flows through the resistor 6 to the base of the transistor 4. This current ■.

Current in transistor 4 and resistor depending on the date! , flows. This current I is applied to the transistor 101 on the input side of the transistors 101 and 102 of the current mirror circuit 10.
flows to A current 2 flows through the transistor 102 in accordance with the emitter area ratio of the transistors 101 and 102. Current flows into the output circuit 12 through the transistor 102! 2 is supplied, and the power supply voltage ■ is supplied from the power supply terminal 13. has been added.

Further, the output circuit 12 is provided with a current detection terminal 14 for detecting the output current I0°, and this current detection terminal 1
A resistor 16 is connected between 4 and ground. Therefore, the current I is supplied to the current detection terminal 14 from the transistor 4.
, flows through the resistor 8, and current 1. from the output circuit 12 flows. . flows into the resistor 16, and both types of currents L and It flow through the resistor 16. is the combined output current! . U flows, and the current detection terminal 14 receives an output current ■. Voltage according to u7 ■, a. occurs.

A feedback circuit including a resistor 16 is configured at the emitter of the transistor 4, and the voltage generated in the resistor 16 is fed back to the emitter of the transistor 4.

Furthermore, field coils 18a, 18b, 18c of a Y-connected motor 18 are connected to the output circuit 12, and drive angle control signals Va, Vb, Vc are applied to rotation control terminals 20a, 20b, 20c. A control signal is applied from the rotation control section 22 based on. Therefore, motor 1
A drive current based on the control signal is supplied to each field coil 18a=18c of 8, and a rotational output corresponding to the drive angle control signals Va to Vc is obtained to the motor 18.
The rotation signal is fbll according to the servo signal V? Wholesale.

[Problem to be solved by the invention]

Incidentally, this motor drive circuit has characteristics as shown in FIG. 4, and the servo signal VIN has a threshold voltage vl determined by the base-emitter voltage (2) of the transistor 4. Therefore, in the region d where the level of the servo signal VIH does not exceed the threshold voltage v1, the transistor 4 becomes non-conductive.

In addition, in the transition region d2 where the level of the servo signal VIN exceeds the threshold voltage ■, and reaches the voltage ■2, the output current 1011T fluctuates, the resistance value of the resistor 6.8 is set to R1.
, Rz, and the resistance value of resistor 16 is RNF, the output current! . u7 becomes... (1).

In addition, the impedance of the motor drive circuit is high;
・Rz (If Vate is used, formula (1) becomes,
Output current■. ut will be controlled by the servo signal VIN.

And transition area d! In the region d:l where the level of the servo signal VIN becomes higher than d:1, the output current is determined by the limit of the drive ability of the output circuit 12, and even if the level of the servo signal VIN is increased, the output current . L12 maintains a constant value.

Therefore, this motor drive circuit is a voltage input circuit, and the voltage range of the bias operating point of the servo signal VIN is determined, and the output current! . 0. The operating point of is uniquely determined.

In this motor drive circuit, the output current is set to ■ according to the servo signal VIN. ut is determined and the output current I. It is not possible to limit U-cho. Therefore, the output current I is excessive. There is a risk that loads such as the motor 18 may be damaged by u7.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a motor drive circuit in which the output current can be limited by a control input other than a servo signal.

[Means to solve the problem]

The motor drive circuit of the present invention includes: a first current mirror circuit that flows a current corresponding to a servo signal; a current/voltage conversion means that converts the current flowing through the first current mirror circuit into N voltage; a first transistor to which the voltage obtained by the voltage conversion means is applied to the base and through which the current flows through the first current mirror circuit; a second transistor that controls the current flowing through the first transistor in response to the current flow; a third transistor to which the voltage generated in the first transistor is applied to its base; and a second current mirror circuit that supplies the drive output obtained by the transistor.

[For production]

With this configuration, a current corresponding to the servo signal flows through the first current mirror circuit, and is converted into a voltage by the current/voltage conversion means. This converted voltage is applied to the base of the first transistor, and a current corresponding to the servo signal flows through the first transistor through the first current mirror circuit.

A bias voltage is applied to the base of the third transistor through the first transistor, and an output is supplied from the first current mirror circuit in response to the servo signal.

A second (7)j transistor is connected in parallel to the first transistor, and the second transistor forms a bypass with respect to the first transistor, and is turned on or off by a control force applied to its base. Since the current is controlled by entering the cut-off state, the base input of the third transistor is controlled. As a result, the output current is limited and
The motor can be protected from excessive output current.

〔Example〕

FIG. 1 shows an embodiment of a motor drive circuit of the present invention.

A current output type differential amplifier 30 is installed at the input section to which the servo output is applied from the output section of the servo IC, and its positive input terminal (+) receives a servo signal VIN representing a torque signal as the servo output from the servo IC. is applied through the input terminal 32A, and a constant bias voltage (2) is applied to the negative input terminal (-) through the input terminal 32B. Since the differential amplifier 30 is of a current output type, a current I4 corresponding to the servo signal VIN is generated in its differential output, and flows to the first current mirror circuit 34.

The current mirror circuit 34 is provided with a transistor 341 and a resistor 342 on the current input side, and the base and collector of the transistor 341 are short-circuited by the emitter and base of a transistor 343 to form a diode connection.

Since the base of the transistor 341 and the bases of the transistors 344 and 345 are connected in common, a current I corresponding to the emitter area ratio of the transistor 341 and the transistor 344 is transferred to the resistor 346 and the transistor 344 by the current mirror effect. flows to

Current! , flows to the ground side through a resistor 36 installed as a current/voltage conversion means, and if the resistance value of the resistor 36 is R1, then the voltage ■, (=R・Is). Voltage V
3b is a PNP type transistor 4 which forms a buffer circuit and is installed as a first transistor through a resistor 38.
It is added between the base and emitter of 0.

Therefore, the input impedance of the transistor 40 is large, and its collector current l is sufficiently large compared to the base current II of the transistor 40 (IC>II).
In this case, the base-emitter voltage of the transistor 40 is V
Assuming IE4°, the base of the transistor 4 installed as the third transistor is biased with a voltage Vl14 consisting of (114=v3 & 11lE4° (3)). Here, if the resistance value of the resistor 8 is R2 and the current flowing through the transistor 4 is
-RNF...(4) The transistor 4 has a base-emitter voltage of ■
A current I, corresponding to □, flows. Therefore, when the servo signal VIN is determined, the base-emitter voltage IIE4 of the transistor 4 is determined.

The current 3 flowing through the transistor 4 flows through the transistor 101 of the current mirror circuit 10 installed as a second current mirror circuit. The current mirror circuit IO is composed of a transistor 101102,
A current I2 flows through the transistor 102 according to the emitter area ratio of the transistors 101S and 102.

This current! 2 is supplied as a drive output to the output circuit 12 that drives the motor 18, and the current 1 is supplied from the output circuit 12 as a drive output.
1° flows. Therefore, an output current 10LIT, which is a composite current of the current 110 from the output circuit 12 and the current (2) on the transistor 4 side, flows through the resistor 16 connected between the current detection terminal 14 and the ground, and the current is detected. A voltage vatc corresponding to the output current 1011 is generated at the terminal 14.

Therefore, the output current to transistor 4! . . , through a resistor 16, and the voltage V ATC is fed back to the base of the transistor 4.

Therefore, if the resistance value RNF of the resistor 16 is constant and is set to 13 ・Rz(lout ・R□), the output current
The base-emitter voltage V1lE4 of the output current I decreases. Also, as LIT decreases, the output current ■. When R7 attempts to decrease, the base-emitter voltage V8E4 of transistor 4 increases, resulting in an output current ■. A feedback operation is performed to increase U.

The emitters of a transistor 42 installed as a second transistor are commonly connected to the transistor 40, and the transistors 40 and 42 form a differential circuit and perform a comparator operation. In this embodiment, the gain is high because the emitters of the transistors 40 and 42 are directly connected, and the magnitude relationship between the control input voltage Vo applied to the control input terminal 44 from the voltage source 47 and the voltages V, l& is as follows. When VTL>■36, the transistor 42 is in the cutoff state, and when vtt<vth, the transistor 42 is in the cutoff state.
0 is a cutoff state. In this case, transistor 4
When transistor 2 is in the cut-off state, a current 1i=Iq flows through the transistor 40, and when the transistor 40 is in the cut-off state, a current 16=Ill flows through the transistor 42.

Further, in the case of VTL<V3&, if the voltage between the base and emitter of the transistor 42 is vmeat, the base voltage V14 of the transistor 4 is as follows: V14=Vvt+Vmtat...
(5), and equation (5) is equal to equation (4), and by aligning the characteristics of transistors 40 and 42, VIE
411=V 04□. therefore,
In the case of VTL>L&, a current corresponding to the voltage 14 flows as well as when VTL<V'+6, and feedback is added.

The output circuit 12 is connected to Y-connected field coils l8a, 18b, 18c of the motor 18, and rotation control terminals 20a, 20b, 2
A control signal based on the drive angle control signals Va, Vb, and Vc applied to 0c is applied from the rotation control section 22, and the field coils 18a to 18 of the motor 18 are
A drive current is supplied to c. Therefore, a rotational output corresponding to the drive angle control signals Va to Vc can be obtained, and
Its rotational speed is controlled according to the servo signal VIM applied to the input terminal 32A of the motor drive circuit.

By the way, the current 14 flowing through the transistor 341 and the current I flowing through the transistor 344 can be set to the same value by making the emitter area ratio of the transistors 341 and 344 equal. Voltage V.

(=Is-R,), but transistor 4
The input impedance is high! ,・R2(VAtc, output current!.R7 becomes, output current ■.u
T is proportional to the resistance value R, 3 of the resistor 36, and is controlled by the resistance value R1.

Then, the base-emitter voltages of the transistors 40 and 42 V IE4°, V II! If each characteristic of 0 is set equal, each emitter is common, so it is possible to control the base potential of the transistor 4 by the transistors 40 and 42. That is, when the magnitude relationship between the voltage V3& generated in the resistor 36 and the control input voltage ■TL becomes v7L<v, h, the transistor 40
Instead, transistor 42 becomes conductive and transistor 4
The output current is affected by the control input voltage Vtt!
. is controlled. In this case, the output current r out is
becomes. Therefore, as shown in FIG. 2, the control input voltage VTL is set to an arbitrary voltage TL1, VTLI...
VTLI > VTLI > VTL3 > ...)
By setting the output current ■. The maximum value of uT is controlled, and the output current ■ is controlled by the servo signal ■ within the range determined by the control input voltage Vtt. 0. will be controlled.

In FIG. 2, dl represents a region where the transistor 4 is non-conductive, d represents a transition region of the output current r our, and d represents a maximum current region.

〔Effect of the invention〕

According to this invention, the maximum value of the output current can be controlled by a control input separate from the servo signal, and a load such as a motor can be protected from damage caused by excessive output current.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the motor drive circuit of the present invention, FIG. 2 is a diagram showing the operating characteristics of the motor drive circuit shown in FIG. 1, and FIG. 3 is a circuit diagram showing a conventional motor drive circuit. 4 are diagrams showing operating characteristics of the motor drive circuit shown in FIG. 3. 34... First current mirror circuit 36... Resistor (current/voltage conversion means) 40... First
Transistor 42...Second transistor 4...Third transistor 10...Second current mirror circuit 12...Output circuit

Claims (1)

[Scope of Claims] A first current mirror circuit that flows a current corresponding to a servo signal, a current/voltage conversion means that converts the current flowing through the first current mirror circuit into a voltage, and this current/voltage conversion means. a first transistor connected in parallel to the first transistor, to which the voltage obtained by the current mirror circuit is applied to its base, and through which the current flows through the first current mirror circuit; a second transistor that controls the current flowing through the first transistor; a third transistor to which the voltage generated in the first transistor is applied to the base; and an output circuit that drives the motor by the third transistor. and a second current mirror circuit that supplies the obtained drive output.