9/22

IMPROVED SENSORLESS CONTROL WITH THE ST62 MCU FOR UNIVERSAL MOTOR

Figure 5. A low cost 8-bit micro-controller ST6220, a rail-to-rail operational

amplifier TS912, a triac and a small value sense resistor make the

heart of this sensorless speed regulated drive

The triac is controlled by pins PA0/PA1/PA2 of the micro. They are in parallel in order

to get enough current to trigger the triac. The 100 ohm resistor R11 limits the current

in the triac gate.

Two push-buttons are provided on pins PB5 and PB6 of the micro for the user inter-

face. Pushing one speeds up the motor, pushing the other slows it down. Alterna-

tively, it is possible to replace this push-button interface by a potentiometer R8, which

could be measured by the internal ADC. Both are shown on Figure 5, buttons and po-

tentiometer, but the attached software only implements the push-buttons.

Finally, Figure 5 shows an output of the micro-controller labeled RS232 (together with

the VDD supply). In the attached software, some routines are provided to help in the

application development and motor characterization. They allow to connect the motor

control board to the serial port COM1 of a personal computer. While the motor is run-

ning, the personal computer displays in a graphical form motor data such as meas-

ured current and firing delay, allowing easy interpretation and measurement. Of

course, it is necessary to use opto-isolated components to connect the computer to

the motor drive. This connection to a personal computer is described in annex 3.

BTB 08 600 CW

470 uF

10v

5.6V

8 MHz

2x33pF

VDD

TIMER

OSCIN

OSCOUT

NMI

TEST

NRESET

PB7

PB6

PB5

VSS

PA0

PA1

PA2

PA3

PB0

PB1

PB2

PB3

PB4

ST6220

HWD

VDD

RS232

390

0.5W

0.1uF

220 V

zero cross.

0.22u

1 k

22 k

750

TS912AI

6

5

8

4

7

2.7 k

68 n

1N4148

470 nF

400V

MOTOR

0.22 / 3 W

1nF

R1

R2

R3

R4

R5

R6

R7

R8

R9

R10

R11

C1

C2

C3

C4

C5

C6

100

VDD