AN10881
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© NXP B.V. 2011. All rights reserved.
Application note
Rev. 2 — 26 September 2011
42 of 102
NXP Semiconductors
AN10881
TEA1713 resonant power supply control IC with PFC
7.6.1 Undervoltage or brownout protection level
The AC input voltage is measured via R1 and R2. Each resistor alternately senses half
the sine cycle and as a result, both resistors have the same value.
A typical resistor value of 2 M
can be applied for R1and R2 to keep the bleeder loss low.
The average voltage sensed is calculated as follows:
(16)
The SNSMAINS brownout protection (RMS) voltage level is calculated with
(17)
(18)
Example:
Required: V
BO
= 66 V (AC), with:
•
V
SNSMAINS(UVP)
= 0.89 V
•
R1 = R2 = 2 M
R
V
= 1 M
(19)
(20)
R3 = 560 k
, R4 = 47 k
The time constant for a recommended time constant of 150 ms, with C4 = 3300 nF:
7.6.2 Discharging the mains input capacitor
There is often an application requirement to discharge the X capacitors in the EMC input
filtering within a certain time. The replacement values of R1, R2, R3 and R4 determine the
resistance required for discharging the X capacitors in the input filtering. The replacement
value can be calculated with
(21)
V
AC
average
2 2
----------
V
AC
rms
=
R
v
R1
R2
R1
R2
+
--------------------
=
V
BO
2
2 2
----------
V
SNSMAINS UVP
R
v
R3
+
R4
-------------------
1
+
=
V
BO
2
2 2
----------
0.89
R
v
R3
+
R4
-------------------
1
+
=
66
1.9771
1
M
R3
+
R4
----------------------------
1
+
=
t
SNSMAINS
R4
C4
47
k
3300
nF
155
ms
=
=
=
R
disch
e
arg
R1
R2
R3
R4
+
R2
R3
R4
+
+
--------------------------------------
+
=
