Application description

AN414

10/14

Doc ID 1876 Rev 2

Figure 8 shows the measured performance of the power limitation. To modify the power limit

target, the look-up table can easily be modified. When the motor load changes, the motor

current varies. The ST6265C MCU measures this current and limits the motor voltage if

necessary.

Figure 8.

Motor power limitation performance

3.5

Program highlights

The total program takes 400 bytes of memory space, plus 1024 bytes for the tables. One

timer remains free, and 2500 bytes remain available on the ST6260C / ST6265C for

additional software or enlargement of the look-up tables.

It is possible, for example, to drive an LCD display by software, to execute pre-programmed

sequences of motor speeds, current limitations, etc. The EEPROM also remains available,

for example, to store user adjustments which must be saved when the power is off.

The line voltage compensation algorithm must be executed at high speed, as already

explained, while the power limitation algorithm can be executed less often. Therefore, the

complete program executes seven line compensations for each power limitation. The line

voltage is compensated every 380 micro-seconds while the power is sensed and limited

only every 3 milliseconds.

100

200

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400

500

100

150

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250

Vmotor

Imotor (A)

Power

0

50

0

0

1

2345

6

Vmotor (V)

Power (W)

MS19695V1