Universal motor drive

AN392

4/11

Doc ID 1863 Rev 2

1.4

Software

All operating features are contained in a 700 byte program. So more than 1 byte of ROM is

available for additional features.

A look-up table relating delay time to the power requirement contains 64 different levels. The

conduction time of the TRIAC can vary from 1.7 ms to 6.7 ms for a 60 Hz application and

from 2 ms to 8 ms to a 50 Hz application. The user can easily adjust the minimum and

maximum power levels because the corresponding delay times are slowly changing at the

top and bottom of the table.

It is recommended that all MCU inputs be filtered so that an input is validated only if it

remains constant for 15 s or more so that passive filter components can be saved. The

mains supply carries disturbances (glitches, telecommand signals, ...) which could disturb

the TRIAC drive. For this reason, a mains voltage zero crossing is only validated if it occurs

during a window of time (1.7 ms each 16.6 ms for 60 Hz operation and 2 ms each 200 ms for

50 Hz operation) selected by the internal timer of the MCU. This block acts as a filter and

again eliminates external components (Figure 3).

This circuit can be used in the following applications:

●

Vacuum regulation in a vacuum cleaner

●

Speed control in a food processor

●

Speed regulation with torque limiting in a drill

●

Unbalance detection in a washing machine

●

Washing machine door opener with remote control

Figure 3.

Major steps of the software

Line synchronization

Sensor acquisition

Power level requirement

Delay time td1 in timer

Calculation next delay

TRIAC firing

Delay time td2 in timer

Calculation next delay

Read version

Initialization

TRIAC firing

Window for zero

crossing mains

RESET