JP4468517B2 - Current interrupt circuit for motor drive - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a current interruption function of a motor drive circuit and an operation confirmation method thereof.
[0002]
[Prior art]
In the current cutoff function of the motor drive circuit according to the prior art, as shown in FIG. 2, the part connecting the drive circuit and the power supply positive electrode is opened and closed by the cutoff transistor 18, and the part after passing the cutoff transistor 18 is used to confirm the operation of the cutoff function. The voltage is detected by the detector 21.
[0003]
[Problems to be solved by the invention]
The conventional configuration as described above has the following problems.
[0004]
When confirming the operation of each part of the device as an abnormality detection function of the device, the operation of the shut-off function will also be confirmed, but in applications where the operation time is long in the motor drive circuit, it is not sufficient to confirm the operation only when the power is turned on. In this case, it is necessary to check the operation of the blocking function even while the motor is rotating.
When the cutoff transistor 18 is cut off in FIG. 2, the potential of the cutoff transistor operation detection point 23 input to the cutoff transistor operation detection amplifier 21 to which the emitters of the upper transistors 2a, 2b and 2c subsequent to the cutoff transistor 18 are connected is steady. Specifically, the transition time varies depending on the state of the upper transistors 2a, 2b, and 2c and the winding current at that time until the potential settles to a low potential but transitions to a stable potential. When the transition time takes the longest, it takes 100 μs or more until the cutoff transistor operation detection amplifier 21 detects the cutoff after the cutoff process is performed on the cutoff transistor 18, and in particular, the excitation phase has a frequency of several kHz. In a control system or the like that requires control of a stepping motor that switches between and a low vibration, the motor control is hindered, so it is not possible to confirm whether the cutoff function functions normally during rotation.
[0005]
[Means for Solving the Problems]
In order to achieve the above-mentioned object, the current cutoff transistor 11 is inserted between the lower transistors 3a, 3b, 3c and the current detection resistor 8, and the lower transistors 3a, 3b, 3c and the cutoff transistor are used for confirming the operation of the cutoff function. 11 is used to detect the opening / closing of the cutoff transistor 11 by providing an operation detection point 17 between the two.
[0006]
[Action]
In the configuration as described above, the normal operation of the shut-off function can be quickly confirmed in a short period that does not affect the motor rotation control.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows an embodiment according to the present invention.
[0008]
The motor 1 generates torque on the output shaft when the coil winding is energized. In order to obtain continuous output torque, the upper transistor 2a, 2b, 2c and the lower opening / closing transistors 3a, 3b, 3c are opened and closed. It is necessary to switch the current winding as appropriate. The winding current of the motor 1 amplifies the voltage induced in the current detection resistor 8 with the amplification factor set by the amplification factor setting resistors 10a and 10b by the current feedback amplifier 9, and outputs it as a feedback voltage to the control circuit. The control circuit controls the rotation and torque of the motor 1 by opening and closing the transistors 2a, 2b, 2c, 3a, 3b, and 3c using the respective drive buffers 6a, 6b, 6c, 7a, 7b, and 7c.
If the control circuit opens any of the upper transistors 2a, 2b, 2c, which has been closed for the purpose of controlling the amount of current while the winding of the motor 1 is energized, the current continues due to the winding inductance of the motor 1. Assuming that the upper transistor 2a and the lower transistor 3b have been closed and the coil is energized until now, when the upper transistor 2a is opened, the upper transistor from the power supply positive electrode as shown by the arrow in FIG. 4a, the current passing through the winding of the motor 1 and passing from the lower transistor 3b through the current detection resistor 8 to the power supply negative electrode is blocked by the path through the upper transistor 2a from the power supply positive electrode, and is shown by the arrow in FIG. Thus, it passes through the lower freewheeling diode 3a from the power source negative electrode and flows to the motor 1.
[0009]
Here, as shown in FIG. 1, the current cut-off transistor 11 is arranged between a line obtained by binding the collectors of the lower transistors 3a, 3b, and 3c and the current detection resistor 8, and a pull-up resistor 13, a pull-down resistor 14, a diode 15a, The input of the interruption detection circuit which detects by 15b and shapes the waveform by the buffer 16 is connected between the current interruption transistor 11 and the collectors of the lower transistors 3a, 3b and 3c.
[0010]
If the voltage drop of the current detection resistor 8 is set to be sufficiently small within a range where there is no problem in current control, and the saturation voltage of the current cutoff transistor 11 is also sufficiently small, when the current cutoff transistor 11 is closed, the voltage drop to the buffer 16 is reduced. Since the input voltage is substantially the sum of the saturation voltage of the cutoff transistor 11 and the voltage drop of the current detection resistor 8, the input voltage is lower than the threshold voltage of the buffer 16.
[0011]
Next, when the cutoff transistor 11 is opened from the above state, the winding current of the motor 1 is circulated by the upper transistor 2a, the motor winding, and the upper free-wheeling diode 4b as shown in FIG. 5 when the upper transistor 2a is closed. When the upper transistor 2a is opened, as shown in FIG. 6, it flows from the negative power supply through the lower freewheeling diode 5a to the positive power supply via the motor winding and the upper freewheeling diode 4b.
At this time, since the current flowing from the diode 15a to the cutoff transistor 11 is cut off as the input voltage to the buffer 16 when the cutoff transistor 11 is opened, the forward voltage drop of the diode 15b is subtracted from the power supply voltage of the detection circuit. The voltage is obtained by multiplying the resistance value of the pull-down resistor 14 by the sum of the resistance value of the pull-up resistor 13 and the resistance value of the pull-down resistor 14. By setting this voltage to be higher than the threshold voltage of the buffer 16, it can be detected that the cutoff transistor 11 is opened.
[0012]
If the upper transistor 2a and the lower transistor 3b are closed and the winding is energized and the cutoff transistor 11 is opened to cut off the current, the winding current of the motor 1 is transferred from the upper transistor 2a to the motor. 1 passes through the winding 1, and the lower transistor 3b is opened by opening the cutoff transistor 11, so that it flows to the upper transistor 2a through the upper freewheeling diode 4b instead of the lower transistor 3b. Since there is no portion involving the detection circuit in this current path, the operation detection of the cutoff circuit is not affected by the circulating current, and the opening / closing of the cutoff transistor 11 can be detected with a delay of about 1 to 5 μs.
[0013]
Here, when the cutoff transistor 11 is opened, the terminal voltage of the current detection resistor 8 becomes 0 V, and a value different from the actual current value is detected.
However, when the cutoff transistor 11 is opened, the winding current is reduced, and the current control process when returning from the operation check of the cutoff function functions to increase the current anyway. Therefore, if it is immediately closed after detecting the opening, it is sufficiently possible to close the cutoff transistor 11 in about 10 .mu.s. Therefore, in a control system that opens and closes at a frequency of 40 kHz or less, there is almost no trouble in the control. .
[0014]
Here, when the state in which the cutoff transistor 11 is kept open without being closed is continued, the winding current of the motor 1 continues to flow in the above-mentioned path for a while, but the cutoff transistor 11 is opened. Since the connection with the negative electrode of the power source is cut off, when the electrical energy stored in the winding inductance and the kinetic energy stored in the output shaft load of the motor 1 are released, the winding current becomes zero and the output shaft of the motor 1 No torque is generated. This state is a result of exercising the current cutoff function by the cutoff transistor 11 which is the original purpose.
[0015]
【The invention's effect】
In the circuit according to the present invention, since the operation check of the shut-off function can be performed instantaneously, it can be confirmed that the shut-off function operates without affecting the rotation of the motor even when the motor is rotating.
[Brief description of the drawings]
1 is an example of an embodiment according to the present invention. FIG. 2 is a circuit example of the prior art. FIG. 3 is a current path during energization. FIG. 4 is a current path when the upper transistor is opened. Current path [Explanation of symbols]
1 Motor 2a Upper transistor a
2b Upper transistor b
2c Upper transistor c
3a Lower transistor a
3b Lower transistor b
3c Lower transistor c
4a Upper freewheeling diode a
4b Upper freewheeling diode b
4c Upper freewheeling diode c
5a Lower freewheeling diode a
5b Lower freewheeling diode b
5c Lower freewheeling diode c
6a Upper transistor drive buffer a
6b Upper transistor drive buffer b
6c Upper transistor drive buffer c
7a Lower transistor drive buffer a
7b Lower transistor drive buffer b
7c Lower transistor drive buffer c
8 Current detection resistor 9 Current feedback amplifier 10a Amplification factor setting resistor a
10b Gain setting resistor b
11 Cut-off transistor 12 Cut-off transistor drive buffer 13 Pull-up resistor 14 Pull-down resistor 15a Diode a
15b Diode b
16 Buffer 17 Detection transistor operation detection point 18 Conventional example cutoff transistor 19 Gate pull-up resistor 20 Conventional example cutoff transistor drive transistor 21 Conventional example cutoff transistor operation detection amplifier 22a Conventional example cutoff transistor operation detection threshold setting resistor a
22b Conventional example cutoff transistor operation detection threshold setting resistor b

Claims (1)

For each energization terminal of the motor, an upper transistor that performs on / off control for current control and a lower transistor that controls the energization direction of the winding are arranged, and the connection points of the upper and lower transistors are respectively connected to the energization terminals. Connected, and configured to flow the current from the power supply positive electrode to the power supply negative electrode side through the upper transistor, winding and lower transistor, and to detect each current value of the current flowing through the winding, The current detection resistor is connected between the lower transistor and the power supply negative electrode so that the flowing current flows to a common current detection resistor, and the upper transistor on each lower transistor is turned on and off to pass to the current detection resistor a circulating electric current circulating in the winding and the circuit of the motor even when the switching to the reflux diodes each lower transistor, And connection underneath transistors, respectively connected between the connection point between the current detecting resistor supply negative electrode, further, the blocking transistor of the current blocking function only as a function of cutting off the power supply to the winding, A current interrupt circuit for a motor drive device, wherein the current interrupt circuit is connected between each of the lower transistors and the current detection resistor.

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