Designing Micromotor Control Circuits with CMOS Drivers Li Jun Designing Micromotor Control Circuits with CMOS Drivers Li Jun (Dalian Railway Institute, Dalian, Liaoning, China Low-power DC servo motor, stepper motor, brushless DC motor drive circuit method.
1 Overview Designing a drive circuit for a miniature motor, on the basis of satisfying the economic efficiency of performance, it is also necessary to make the designed circuit simple and practical, small size, light weight, low power consumption, and low cost. This article describes the use of inexpensive, low-cost, logic-input CMOS integrated circuit designs for motor drive and control circuits to meet these requirements. 2 Logic Inputs for CMOS Quad Driver Integration The TC4469 is a logic-input CMOS four-driver integration The circuit is specifically designed to directly drive small motors and is a full-bridge circuit consisting of MOSFETs. The integrated circuit has the following characteristics: the peak value of the output current is high, and the maximum is 1. The range of the working voltage is wide, and it can work normally in the range of 4.5-18V; the rising and falling time of the output waveform of the driver is symmetrical, both Is 25rs, delay time is equal, are 75rs; there are two ANDfInv logic input selection methods TC4469 internal circuit structure and output stage of the principle of the circuit as shown in the driver components, in order to increase the flexibility of use, each group is configured with two Logic inputs. The driver can output a working current of 250mA for the load and can directly drive various small DC servo motors. The only limitation on the load is that the total power loss of the integrated circuit must not exceed the power dissipation limit allowed by the package. The specified power loss and operating voltage Within the range, the TC4469 will not be latched under any circumstances. All the pins are protected. At least 2000V EDS ICs are available in two form factors: 16-pin SOIC and 14-pin DIP. The circuit input and output logical relationship truth table is shown in Table 1.
Table 1 TC4469 truth table input A input B output terminal Y 3TC4469 in the use of several issues to be noted 3.1 power supply bypass capacitor TC4469 output is composed of CMOS integrated circuits, the equivalent of the ground A large load-equivalent capacitance, which rapidly charges and discharges a large equivalent load capacitor, requires a large amount of current. For example, a 1 000pF load is charged to 18V in 25 ns and requires a working power supply.
72A operating current In order to ensure a very low power supply impedance over a wide frequency range, it is usually necessary to connect a 0.1F film capacitor or two low-resistance ceramics in parallel with the TC4469's Vdd(14) pin. Chip capacitors, and the length of the connection should be particularly short.
3.2 A voltage drop is generated across the impedance from the ground line to the output ground common ground. This voltage drop causes negative feedback and reduces the speed characteristics of the switch. To prevent this, the ground line between the input and output circuits should be short and wide, and on the same side of the printed board 3 power loss The supply current vs. frequency and supply current vs. capacitive load characteristic curves can be used to estimate The integrated circuit power loss, semiconductor CMOS driver has greatly reduced the static power loss of the integrated circuit, and can affect the power loss of the integrated component is the duty cycle of the input signal, the voltage of the operating power supply and the type of load giving power consumption and The thermal impedance of the package allows you to easily calculate the maximum allowable ambient operating temperature. The thermal resistance of the 14-pin plastic package is 83.3°C/W, and the maximum power dissipation is 800mW at 70°C. The maximum allowable operating temperature is The total power loss Pd of the chip is +150°C. It consists of three parts: the load-induced loss PL, the static loss Pq, and the dynamic loss Pt. For a point-to-point load, the resistive load-induced loss is the duty cycle. , load voltage, load current function, load power loss is: Pl = DV0 / L, where D is the duty cycle of the signal, V0 is the load voltage, 11 is the load current chip State power consumption: Pq = Vs, where Vs is the supply voltage, /h is the quiescent current when all outputs are low, and /L is the static current of the chip when all outputs are high. Approximately expressed as: Pt = / Vs (10 1 DC servo motor drive circuit TC4469 most commonly used to drive a full-bridge drive circuit composed of four MOSFET power switch tube, the basic principle of the circuit shown in the circuit of the power supply is +5 ~15V, in order to prevent the working voltage from exceeding +18V, an 18V zener diode is connected in parallel with the 14 pin of the integrated circuit.2 feet of the integrated circuit are used to control the steering of the servo motor, and when the 2 pin is low, the motor is transmitting. When pin 2 is at a high level, the motor reverses the integrated circuit's 518 pins and the two pins are connected in parallel to send a pulse width modulation signal (PWM). Changing the duty cycle of the PWM signal can change the speed of the motor. The high end of the full bridge circuit is The motor control circuit is shown as follows: The circuit is simple, reliable, easy to use, can control the speed of the DC motor continuously and bi-directionally adjustable, and has a current limiting function to prevent the load current from being used to damage the MOS-FETs circuit on the bridge. The ICM7555 integrated circuit is a commonly used CMOS bipolar time base circuit, which constitutes a pulse width modulation (PWM) circuit.The operating frequency of the pulse width modulation circuit is fixed at 20 kHz, and the modulation can be changed by adjusting the center tap position of the 100-potentiometer. The output pulse width of the device allows the pulse width duty cycle to vary from 2% to 98%. The TC4469 driver input in the circuit requires the input of two control signals: the PWM signal and the motor rotation direction control signal. 2 Determine the direction of rotation of the motor. If the TC4469's pin 2 is high, the motor rotates in the positive direction. Then when the pin 2 is low, the motor is reversed. The high and low levels on the pin 2 can be switched by using a switch. TC4469 Logic Input The control signal comes from pin 3 of the ICM7555. The logic input control signal is internally converted by the driver and converted to four output signals to drive one MOSFET full-bridge circuit. Full-bridge circuit consists of four MOSFETs power transistors. Two high-end power transistors on the bridge The P-channel MOSFETs are used, while the low-end two power transistors use the N-channel MOSFETs. The low-end two power transistors have their sources connected in parallel to a 0.18. The motor current sense resistor current sense resistor converts the armature current into a voltage and is applied to pin 4 of the ICM7555 via a milk resistor and transistor 2N3904 to function as an overcurrent shutdown protection when the motor operating current exceeds the threshold value. The voltage on the current sense resistor turns on the transistor, and pin 4 of the ICM7555 is low. When the 3 pin has no control pulse output, the pin 4 of the ICM7555 is high, and the pin 3 has the control pulse output. Page) TC4469 can directly drive two-phase stepper motor, no need to connect external components, the principle of the circuit shown in the control circuit has two input signals, respectively A and B; stepper motor two sets of windings are connected to the drive Output pins 1213 and 1011, each stepping pulse can rotate the stepper motor 7.5 = input signal of the driver The control terminal AB can interface with the PIC17C756AMCU and then be controlled by the PC via the RS-232 serial communication interface.
4.3 Three-phase Brushless Motor Driving The brushless motor requires two TC4469s. The schematic circuit is as shown. One is used to drive the high-end three MOSFETs of the three-phase bridge, and the other is used to drive the low-end of the three-phase bridge. 3 items loss, using the loss analysis method to calculate the motor output power, efficiency, power factor 5 test results analysis When the fan inlet air flap fully open, the superimposed motor input power is 19.04kW, input current is 325A, output power It is 16.94kW and the output speed is 5864r/min. The condition of the motor and the fan is basically normal. The calculation of the motor output power from the wind pressure and efficiency of the fan is basically consistent with the test results of the Xi'an Jiaotong University's motor laboratory.
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