AN2716 datasheet(23/28 Pages) STMICROELECTRONICS

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AN2716

Timing definitions

Doc ID 14460 Rev 2

23/28

define the

φAC phase shift. If RAC = 0 Ω, the rms IAC current and φAC phase shift are equal

respectively to rms ILoad current (ILoad_RMS) and φLoad phase shift of the AC load. If

RAC ≠ 0 Ω, the rms IAC current (IAC_RMS) and φAC phase shift depend on the value of the

resistor RAC and the AC load impedance. In this case, and according to Fresnel's diagram,

the maximum

φAC phase shift is defined by Equation 15 and Equation 16.

Equation 15

Equation 16

For example, in the worst case, if the minimum rms current (ILoad_min) and the maximum

φLoad phase shift of the AC load are respectively 0.1 A and 90°, the maximum φAC phase

shift is about 1.26 °. This phase shift is very low and can be neglected as most AC loads

have rms current higher than 0.1 A and phase shift lower than 90°. With RAC = RShunt

= 300 k

Ω and F = 50 Hz, t1_max and t2_min are respectively 1.7 ms and 8.3 ms.

Figure 19.

Fresnel’s diagram

Note:

If the AC load is a resistor, or is disconnected, the IAC current is in phase with the AC line

(

φAC = 0).

The STCC08 AVF signal should be read after the AC line peak voltage and before the t2

time to detect all AC switch states for most home appliance loads.

()

Load

rms

Load

rms

Line

sin

() ⎟

⎟

⎠

⎞

⎜

⎝

⎛

Load_max

rms_min

Load

rms_max

AC_max

Arc

sin

R . I

Load_RMS

AC = 0)

2 . p .f . L . I

Load_RMS

(R + R

AC).IAC_RMS

2 .

π .f . L .I

AC_RMS

Line_RMS

Load

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