JPH06101947B2 - Motor speed control circuit - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a speed control circuit for a motor, which is configured to perform feedback control by a signal from a detection sensor that detects the rotation speed of the motor.

[Background Art] Generally, in a motor application device, if the motor locks due to an increase in load, an excessive current flows and the motor burns out, or if a semiconductor element for speed control is in series with the motor, the semiconductor element is There was a problem of burning out. The detection for locking the motor includes a method of detecting a current value with a minute resistance and a method of detecting a decrease in rotation speed. For devices with low voltage and speed control, detecting the number of revolutions is more advantageous. This is because the speed signal is used for speed control, and this signal can also be used for lock detection. In this method, when the speed drops to the number of revolutions before the complete lock, the control element in series with the motor is turned off. The drawback of this method is that the lock protection circuit may operate and fail to start when the number of rotations at start-up is low.

[Object of the Invention] The present invention has been provided in view of the above points, and an object of the present invention is to provide a speed control circuit for a motor that can be smoothly started without the lock protection circuit being activated at the time of startup. is there.

DISCLOSURE OF THE INVENTION An embodiment of the present invention will be described below with reference to the drawings. First,
The overall circuit operation will be described. FIG. 1 is a block diagram of the speed control circuit, and FIG. 2 is a time chart of the steady state. The speed detection circuit 1 that outputs a signal proportional to the number of rotations of the motor includes a frequency generator FG, an operational amplifier OP ₁ , resistors R _F , R _{S, and the} like. The sample / reset pulse generation circuit 2 that generates timing pulses such as a sample pulse and a reset pulse is a trapezoidal wave circuit 11 that generates a trapezoidal wave and a hysteresis comparator.
A trapezoidal wave circuit 11 that is composed of OP ₂ and a sample / reset pulse generator 2a composed of an IC, and inputs a trapezoidal wave to the sample / reset pulse generator 2a is composed of a constant current source I ₁ , a capacitor C _R, etc. There is. The sawtooth wave generation circuit 3 that forms a sawtooth wave by the reset pulse of the sample / reset pulse generator 2a is composed of a constant current source I ₂ , a capacitor C _T, etc. A sample and hold circuit 4 for sampling and holding the square wave voltage is composed of buffers 4a and 4b, a capacitor C _{H and the} like. The speed variable circuit 7 for setting an appropriate speed is composed of a resistor R _X , a volume VR, a buffer 7a, etc.
The output is input to the error amplifier 12 and compared with the output from the sample hold circuit 4, and the difference is inverted and amplified. Further, the output of the error amplifier 12 is compared with the reference triangular wave from the reference triangular wave generating circuit 5 by the comparator 13, and when the output of the comparator 13 is at H level, the output circuit 8
To drive. Then, the output of the output circuit 8 drives the power MOSFET 14 constituting the switching circuit to turn on to drive the motor M. Further, the battery B is used as the power source, and the voltage is boosted by the booster circuit 10 and supplied to the motor M. The FV conversion circuit for FV converting the speed signal of the motor M is composed of the sawtooth wave generation circuit 3 and the sample hold circuit 4.

Next, the operation will be described with reference to FIG. 1 and FIG. The second
(A) to (j) in the figure show the waveforms at points a to j in FIG. A speed signal proportional to the rotation speed of the motor M is output by the frequency generator G, and the output speed signal is amplified by R _F / R _S times by the operational amplifier OP ₁ .
The output of the operational amplifier OP ₁ as shown in FIG. 2 (a) is input to the hysteresis comparator OP ₂ to obtain a square wave pulse having a frequency proportional to the rotation speed as shown in FIG. 2 (b). This square wave causes the trapezoidal wave circuit 11 of the sample / reset pulse generating circuit 2 to generate a trapezoidal wave as shown in FIG. The rising edge of this trapezoidal wave is used as the reference voltage generation circuit 6
From the reference voltages V ₁ , V ₂ and V ₃ from (Fig. 2 (c)),
The timing at which the sample pulse (Fig. 2 (e)) and the reset pulse (Fig. 2 (d)) are generated is determined. on the other hand,
In the sawtooth wave generation circuit 3, the capacitor C _T is charged by the constant current source I ₂ , and the charge charged in the capacitor C _T is discharged when a reset pulse is generated as shown in FIG. Generate a sawtooth wave as shown. In the sample-hold circuit 4, when the sample pulse is generated, the hold capacitor C _H is charged or discharged to sample-hold the sawtooth wave voltage at that time. Therefore,
A DC signal proportional to the rotation speed as shown in FIG. 2 (g) is output to the sample hold circuit 4.

In the error amplifier 12, the voltage V _X set by the speed variable circuit 7
And the output voltage V _O of the sample and hold circuit 4 is inverted and amplified to R _A / R _N times, and its output is compared with the reference triangular wave of the reference triangular wave generating circuit 5 and the comparator 13 as shown in FIG. 2 (h). Then, a square wave is obtained as shown in FIG. This square wave is output through the output circuit 8 to obtain a gate voltage as shown in FIG.
The power supply of the motor M is PWM controlled. The lock protection circuit 9 has the following functions. That is, when the motor M is overloaded, the rotation speed of the motor M decreases. Therefore, the output frequency of the frequency generator FG decreases, and the output voltage of the sample hold circuit 4 increases. The voltage is divided by the resistors R _L1 and R _L2 and detected by the comparator 15, and when the rotation speed falls below a set value, the output pulse is cut off and the motor M is stopped.

Next, the operation at startup will be described. As described above, the capacitor C _H of the sample and hold circuit 4 has a longer sampling time because the frequency of the frequency generator FG decreases when the speed of the motor M is slow.
The voltage of C _H becomes higher. However, the capacitor C _H
Is not charged, the signal is that the speed is high, and no current flows to the motor M. Therefore, the motor M does not start without the starting circuit.

The starting circuit 16 has a structure as shown in FIG. That is, the starting circuit 16 includes resistors R _{1 to} R ₆ and capacitors.
C ₁ , comparator 16a, RS type flip-flop 16b, T
Type flip-flop 16c, etc., and is composed of transistors Q ₁ and Q ₂ . The output terminal of the flip-flop 16b is connected to the capacitor C _H side of the sample hold circuit 4, and the flip-flop 16c is connected to the lock protection circuit 9. The voltage divided by the resistors R ₁ and R ₂ is connected to the inverting input terminal of the comparator 16a, and the connection point between the resistor R ₃ and the capacitor C ₁ is connected to the non-inverting input terminal of the comparator 16a. The outputs are input to the flip-flops 16b and 16c, respectively. The above capacitor C
_1, the resistor R ₁ to R _3, comparators 16a, transistors Q _1, Q ₂
Etc. constitute a time delay generating means.

Next, the operation of the starting circuit 16 will be described with reference to FIGS. First, the first operation by the resistor R ₃ and the capacitor C ₁ will be described. When the power is turned on for start-up, the reference voltage is input to the comparator 16a of the start-up circuit 16 by the resistors R ₁ and R ₂ , and the capacitor C ₁ is charged by the resistor R _{3 as} shown in FIG. 3 (b). To be done. At this time, the comparator 16a
Output is at L level as shown in FIG. 3 (c), and the transistors Q ₁ and Q ₂ are off. On the other hand, the reset signal is given by the resistance R _4, R ₅ to the flip-flop 16b as soon as power is supplied, in this signal output condition, for example, an H level, outputs a start pulse as shown in FIG. 3 (d) The sample and hold circuit 4 is operated to operate so that the voltage V _CT of the capacitor C _T of the sawtooth wave generation circuit 3 and the voltage V _CH of the capacitor C _H of the sample hold circuit 4 become V _CT = V _CH. To charge. When the capacitor C _H of the sample and hold circuit 4 is charged, the output circuit 8 operates and a current flows through the motor M. As shown in FIG. 3 (a), when the motor M starts moving even a little, a signal is input from the frequency generator FG, the sample / reset pulse generating circuit 2 operates, and the sample / hold circuit 4 also starts operating normally. When the charging voltage of the capacitor C ₁ exceeds the reference voltage of the resistors R ₁ and R ₂ , the output of the comparator 16a becomes H level as shown in FIG. 3 (c), and this is added to the flip-flop 16b as a set signal, As shown in FIG. 3 (d), at the same time as stopping the starting pulse, the transistors Q ₁ and Q ₂ are turned on to discharge the electric charge of the capacitor C ₁ (FIG. 3 (b)).

Next, the second operation will be described. When the voltage of the capacitor C ₁ drops to the voltage determined by the resistance R ₁ and the resistances R ₂ and R ₆ as shown in FIG. 3 (b), the output of the comparator 16a is restored as shown in FIG. 3 (c). At the L level, the transistors Q ₁ and Q ₂ are turned off and the capacitor C ₁ is charged to the voltage of the resistors R ₁ and R ₂ . When the capacitor C ₁ is charged to the voltage determined by the resistors R ₁ and R ₂ , the output of the comparator 16a becomes H level and the second pulse is output.

Therefore, these two pulses are T-flip-flop 16c.
The input of this T-flip-flop 16c is inverted. That is, this T-flip-flop 16C
Is automatically reset when the power is turned on by a device such as a two-stage connection of T-type flip-flops, and the operation of the lock protection circuit 9 is stopped by this output signal.
The function of stopping the lock protection operation is released by the sixth pulse, and the lock protection circuit 9 starts the operation (FIG. 3 (e)). At the same time, the electric charge of the capacitor C ₁ is forcibly discharged, and the operation of the starting circuit 16 is stopped.

[Advantages of the Invention] As described above, the present invention detects the number of rotations of the motor, compares the detected number of rotations with the signal of the set number of rotations, and feedback-controls the number of rotations of the motor. In a motor speed control circuit equipped with a lock protection circuit that shuts off the power supply to the motor when the number of motors falls below a predetermined number,
Since the starting circuit is provided with one time delay generating means for generating the second operation signal with the second signal as the motor start signal and the second signal as the operation start signal of the lock protection circuit. A signal for the first activation and a signal for stopping the operation of the lock protection circuit until the second activation is applied can be generated by one time delay generating means, and the lock protection circuit can be activated for the second time. By starting the operation with the signal, the motor can be smoothly rotated from a low rotation speed, and the speed of the motor can be controlled.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is a time chart in the above-mentioned steady state, and FIG. 3 is a time chart in the above-mentioned start-up. Reference numeral 8 is an output circuit, 9 is a lock protection circuit, and 16 is a starting circuit.

Claims (1)

[Claims] 1. A feedback control for detecting the number of revolutions of a motor, comparing the detected number of revolutions with a signal of a set number of revolutions, and controlling the power supply to the motor based on the result of the comparison to perform feedback control of the number of revolutions of the motor. In the motor speed control circuit including the circuit and the lock protection circuit that shuts off the power supply to the motor in response to the detection signal when the number of rotations of the motor is less than or equal to the predetermined number, 2 It has one time delay generating means for generating an operation signal for one time, supplies a starting auxiliary signal to the feedback control circuit immediately after power-on, and terminates the starting auxiliary signal by the first operation signal, A motor speed control circuit comprising a starting circuit for starting the operation of the lock protection circuit in response to a second operation signal.