Doc ID 15772 Rev 2

3/14

AN2991

Single-phase induction motor drive topologies

14

Figure 2. Two Triac topology

1.2

Semiconductor rating

1.2.1

Start capacitor voltage

The start capacitor and the auxiliary winding form a resonant R-L-C circuit. The capacitor

added to the mains voltage up to the capacitor complete discharge. This results in high

voltages across the Triac (see Figure 3). Even for a 220-240 V application, 700 V

semiconductors must then be chosen.

Figure 3. Voltage across Triac after turn off (612 V maximum)

C

VAC

1

PTC

2

T(°C) Klixon

Run ACST

Start ACST

Vc

Irun

Vrun

612 V