Datasheet

Application information L6599
28/36
Figure 33. Line sensing function: internal block diagram and timing diagram
With reference to Figure 33 the following relationships can be established for the ON
(Vin
ON
) and OFF (Vin
OFF
) thresholds of the input voltage:
which, solved for R
H
and R
L
, yield:
While the line undervoltage is active there is no PWM activity, thus the V
CC
voltage (if not
supplied by another source) continuously oscillates between the start-up and the UVLO
thresholds, as shown in the timing diagram of Figure 33.
As an additional measure of safety (e.g. in case the low-side resistor is open or missing, or
in non-power factor corrected systems in case of abnormally high input voltage) if the
Vin
ON
1.25–
R
H
----------------------------------
15 10
6–
1.25
R
H
-----------+⋅=
Vin
OFF
1.25–
R
H
-------------------------------------
1.25
R
H
-----------=
R
H
Vin
ON
Vin
OFF
–
15 10
6–
⋅
------------------------------------------=
R
L
R
H
1.25
Vin
OFF
1.25–
-------------------------------------
⋅=