AN2716

STCC08 description

Doc ID 14460 Rev 2

13/28

1.5.2

AC switch state detection after IN signal removal

When the IN signal is removed (to turn on or off the AC switch), a parasitic detection of the

AC switch state exists up to the next AC load current zero (see Figure 11 for AC inductive

load case). As the AVF signal remains at a low-level state when the control is removed

Figure 11.

Parasitic detection for inductive load

To ensure a correct detection of the AC switch state and to take into account the AC switch

failed in diode mode, when the IN control is removed and whatever the AC load used, the

AVF reading must be carried out according to Equation 7. For example, with F = 50 Hz, the

AVF signal can be read after 20 ms when the IN control has been removed.

Equation 7

Note:

Overall, the AVF signal should be read during several AC line cycles to avoid an incorrect

interpretation of the AC switch state.

AVF

IAC

VLine

IACT

-IACT

ILoad

IN

Parasitic detection

t (s)

t (s)

t (s)

t (s)

Delay

t

F

t

min

Delay

1

_

>