AN441

AC switch control with an inductive load

Doc ID 3579 Rev 3

5/16

Figure 4.

Last turn-off polarity influence on the next turn on

2

AC switch control with an inductive load

2.1

Latching current

through terminals A2 and A1), to keep the device conducting when the gate signal is

removed. Diagram a in Figure 5 shows a bad Triac turn on due to too short gate pulse width

and Diagram b in Figure 5 shows a good Triac turn on. The pulse width is sufficiently large

so that the current i(t) reach the latching current. See Application note AN303 for more

information.

For inductive loads, as the current rate of increase is limited by the inductance, care has to

Figure 5.

Latching current of the AC switch

8.75 A

A

1.16 A

B

i(t)

t

t

i(t)

I

t

t

b

a

i(t)

I

I

t

t

i(t)

I

t

t