AN392

Practical results

Doc ID 1863 Rev 2

7/11

2.5

Software

The software for a light dimmer can be the same as for motor drive. The major difference

concerns the mains disturbances rejection in order to prevent lamp flickering. The timing is

carried out internally by the MCU timer. The mains period can be calculated internally by the

MCU to detect the mains frequency. But this mains frequency must not be disturbed by

noise coming from the line, as the mains synchronization signal is received every cycle.

3

Practical results

Figure 5 presents the current and voltage in a TRIAC driving a universal motor.

Figure 5.

Universal motor drive: TRIAC current and voltage

TRIAC current IT : 5 A/div

2 ms/div

TRIAC voltage VT: 250 V/div

IT

VT