AN2777

Vacuum cleaner requirements

Doc ID 14748 Rev 1

9/13

3.2

Inrush current

Inrush current also causes significant stress on TRIACs, especially if the motor is turned on

in full wave mode. Today, with the electromagnetic standard applied to limit light flickering

due to appliance inrush currents (IEC 61000-3-3 standard), most vacuum cleaners feature a

microcontroller which implements a soft-start function. A full-cycle start-up thus occurs only

with wrong triggering by the microcontroller.

Figure 9 gives the measured inrush current of a 2000 W motor started in full-cycle mode,

with a 264 V rms line voltage (worst case for a 220-240 V line). The inrush current can reach

up to 70 A. This level is well below the maximum peak current allowed for the T1235H-6

Figure 9 also gives the calculated junction temperature for this device in a TO220AB

insulated package. The initial device temperature is 60 °C, as it could occur in the

application if the motor has already operated before a new start-up. Dissipated power is

be seen that the junction temperature remains below 150 °C during this start-up. The

operation is then totally safe for the device.

Figure 9.

Junction temperature and current at start-up (2000 W, 230 V motor,

T1235H-6I TRIAC)

3.3

Turn-off requirement

(

➁, as defined in Equation 1).

-100

-50

0

50

100

150

200

-0.05

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

Current (A) and Temperature (°C)

IT

Tj

time (s)