1 Brief introduction of the appliance
1.1pmm8713 chip
PMM87 13 is a pulse distributor (also known as logic converter) for stepping motor control, which is produced by Sanyo Electric Company of Japan. It is a dual in-line 16-pin monolithic CMOS integrated chip. PMM87 13 can be used for three-phase control and four-phase control. There are three excitation modes: 1 phase, 2-phase and 1-2-phase, and one of them can be selected through circuit design. In addition, PMM87 13 also has single clock or double clock working mode, forward and backward control function and initialization and reset function, and has internal circuits such as clock gating, excitation mode control, reversible loop counting and excitation mode judgment.
Because all inputs of PMM87 13 adopt Schmidt shaping circuit, it has strong anti-interference ability. The output current is more than 20 mA, which can directly drive the micro stepping motor. The logical block diagram is shown in figure 1.
1.2 LM33 1 chip
LM33 1 is an integrated chip with high cost performance produced by NS Company in the United States. LM33 1 can be used as precision frequency-to-voltage (F/V) converter, A/D converter, LFM demodulation, long-time integrator and other related devices. LM33 1 is a dual in-line 8-pin chip, and its logic block diagram is shown in Figure 2.
LM33 1 has input comparison circuit, timing comparison circuit, R-S trigger circuit, reset transistor, output driver, energy gap reference circuit, precision current source circuit, current switch, output protection circuit, etc. The output tube is in the form of open collector, and the logic level of the output pulse can be flexibly changed by selecting logic current and external resistance, thus adapting to different logic circuits such as TTL, DTL and CMOS. Besides. The LM33 1 can be powered by single/dual power supply, with a voltage range of 4 ~ 40 V and a maximum output of 40 V. ..
1.3 voltage-frequency conversion
The external circuit of LM33 1 is simple, and a voltage/frequency (V/F) or frequency/voltage (F/V) conversion circuit can be easily formed by connecting several external components. In this paper, the voltage/frequency (V/F) conversion function of LM33 1 is selected. The structure is shown in Figure 3.
External resistance-capacitance Rt, Ct and internal circuit constitute a monostable circuit. When a positive voltage is input at the input terminal Vi+, Vi+ is greater than Vi-, the input comparator outputs a high level, the R-S trigger is set, and the output high level turns on the output drive tube, and the third pin f0 outputs a logic low level. At the same time, the current source IR charges the capacitor C 1 Because the base of the reset transistor is connected to the inverting output of the R-S flip-flop, the reset transistor is turned off, and the power supply Vcc charges the capacitor Ct through the resistor RT. When Uct is greater than 2/3 Vcc, the input end (pin 5) of the sequential comparator is positive, so the logic high level is output to the reset end of the R-S flip-flop to reset the R-S flip-flop. The noninverting output terminal of the R-S flip-flop outputs a low level to turn off the output driver tube, and Vdd outputs a logic high level at the third pin f0 of LM33 1 through the pull-up resistor R0. At this time, the R-S flip-flop outputs a high level to turn on the reset transistor, and the capacitor Ct discharges to the ground through the reset transistor. When the current switch is turned to the left, the capacitor C 1 discharges to the ground through the resistor R 1. When the discharge voltage of the capacitor CL is equal to the positive input terminal voltage Vi of the input comparator, the input comparator outputs a high level again, the R-S trigger is set, the output driving tube is turned on, and f0 outputs a logic low level. In this way, a pulse signal with a certain frequency is output at f0 terminal. According to the principle of charge balance on capacitor and related electrical knowledge, the charging time of capacitor is t 1 and the discharging time is t2. From C=Q/U, I=Q/t and Q-Amp =Q, we can get I-amp T2 = I-amp t/kloc-0 /→ t2ul/rl = (IR-ul/rl) t/kloc-0 /→ (t1+T2).
F0 = 1/(t 1+T2)= UL/(IRT 1RL)
UL is the voltage across the capacitor c, because UL fluctuates in the range of about 10 mV, so UL=Vi, so:
f0=Vi/(IRt 1RL) ( 1)
As can be seen from the formula (1), the output frequency. F0 of LM33 1 is proportional to the input voltage Vi, thus realizing the conversion between the input voltage and the output frequency. T 1 is determined by external timing elements Rt and Ct, and the relationship is T1=1.1RtCt, so the values of RT and CT can be selected according to the requirements of circuit design. It is provided by an internal precision current source. IR= 1.9 V/Rs。 Equation (1) can become
f0= ViRs/(2.09RLRtCt) (2)
The input resistor Ri makes the 7-pin bias current cancel the 6-pin bias current, thus reducing the frequency deviation. Rs is an adjustable resistor to adjust the gain deviation of LM33 1. Ci is the filter capacitor, generally 0.0 1 ~ 0. 1uF. In the case of good filtering effect, the capacitor of 1 UF can be used. When the RC time constants of pin 6 and pin 7 match, the step change of input voltage will lead to the step change of output frequency. In order to improve the accuracy and stability, resistance-capacitance components with low temperature coefficient are selected.
2 drive circuit design
The driving circuit is shown in Figure 4. External resistor Rt, capacitor Ct, internal timing comparator, reset transistor, R-S trigger, etc. Forming a monostable circuit. F0 outputs a logic low level when the voltage input at the input terminal Vi+ is greater than the voltage input at the input terminal Vi-. At the same time, the current source IR charges the capacitor C 1 The power supply Vcc also charges the capacitor Ct through the resistor RT. When the charging voltage across the capacitor Ct is more than 2/3 of Vcc, the output terminal f0 outputs a logic high level. F0 signal is output to the clock terminal of PMM87 13 chip. After the frequency is processed by PMM87 13, the driving signals with a certain frequency are output at pins A, B and C to control the on-time of the power transistor, thus controlling the rotating speed of the stepping motor.
The direction control circuit consists of LM348 four-channel general operational amplifier. The external direction control signal forms a voltage comparison circuit through LM348 and the reference voltage. When Vdi is greater than the reference voltage VH, the output of U3A is positive, connected to the fourth pin of PMM87 13, and the output terminal is controlled to output the positive phase pulse sequence. When Vdi is less than the reference voltage VH, the output terminal is negative, and the fourth pin connected to PMM87 13 controls the output terminal to output the negative phase pulse sequence, and the corresponding phase drive output terminal outputs the positive and negative rotation pulse sequence, thus controlling the positive and negative rotation of the stepping motor.
The input instructions given by LM33 1 are input clock f0 and direction instruction DIR, which are logically combined in PMM87 13 to convert the sequential logic signals. The driving current of PMM87 13' s phase drive output (PIN 10 ~ PIN 13) is more than 20 mA, which can directly drive the micro stepping motor. R 1 and C 1 are automatic initialization circuits at startup. The r terminal is at a low level within tens of milliseconds of initial power-on, which automatically resets the A ~ D terminals to the initial state. If the power of the external stepping motor is high and the driving ability of the output driving end of PMM87 13 is insufficient, it is necessary to design a power amplification driving circuit and then drive the stepping motor. The on-time logic signal of each phase output of PMM87 13 is sent to the power driving part and converted into the base (or gate) driving signal of the internal power switch. The driving mode of stepping motor can be divided into unipolar driving and bipolar driving according to whether the current flowing through the phase winding is unidirectional or bidirectional. Usually, the three-phase stepping motor is driven by single pole. From the analysis of power driver circuit, there are voltage drive and current drive. This design adopts series resistance voltage drive mode. A resistor with a certain resistance and power is connected in series in the phase winding, which reduces the time constant of the winding loop and limits the current at low frequency and at rest.
Based on the above principle, an automatic gate valve controller is designed. The up and down position of the gate valve is controlled by the limit switch, and the action of the limit switch changes the terminal voltage of the LM348 comparison voltage shown in Figure 5 by using the corresponding circuit, thereby controlling the operation or stop of the stepping motor. Its working principle; The noninverting input terminal of LM348 is the reference voltage terminal, and its inverting input terminal is the comparison voltage input terminal. When the voltage at the input end of the comparison voltage is less than the reference voltage, the 1 pin of LM348 outputs a high level, which turns on BD237 to make the stepping motor rotate forward or backward. When the voltage at the input of the comparison voltage is higher than the reference voltage, the 1 pin of LM348 outputs a low level, BD237 is turned off, and the stepping motor stops running.
3 Conclusion
This design is the main design part of stepping motor driver, with simple structure, low cost and stable performance. The three-phase reactive stepping motor driver designed in this system drives the 55BF004 three-phase reactive stepping motor. The system has been successfully applied to the automatic gate valve control system, and the operation effect is good.