AN441

Typical examples of inrush current reduction

Doc ID 3579 Rev 3

11/16

Figure 10 show an example of Triac switching on a 2200 W universal motor with or without

soft start. The difference is very clear, the current reaches a peak current up to 60 A without

soft start while it reaches 10 A with soft start. This current reduction has a direct impact in

the AC switch maximum junction temperature as shown in Figure 11 with a T1050H Triac.

The use of soft start at motor start-up allows:

●

Lower junction temperature

–

Better temperature operation margin leading to increased lifetime for the AC

switch

–

Use of lower AC switch range

●

Lower peak load current

–

Lower load current stress, so appliance reliability increases

Figure 11.

Junction temperature rise for Triac T1050H for universal motor

124.2 °C

Without soft start

With soft start

78 °C

Time (s)

T (°C)

j

0

0.8

0.6

0.4

0.2

80

130

120

100

65

T1

j a

T2

j a