
L6561
4/13
3
OVER VOLTAGE PROTECTION OVP
The output voltage is expected to be kept by the operation of the PFC circuit close to its nominal value.
This is set by the ratio of the two external resistors R1 and R2 (see fig. 5), taking into consideration that
the non inverting input of the error amplifier is biased inside the L6561 at 2.5V.
In steady state conditions, the current through R1 and R2 is:
and, if the external compensation network is made only with a capacitor Ccomp, the current through Ccomp
equals zero.When the output voltage increases abruptly the current through R1 becomes:
Since the current through R2 does not change,
IR1 must flow through the capacitor Ccomp and enter the
error amplifier.
This current is monitored inside the L6561 and when reaches about 37
A the output voltage of the multi-
plier is forced to decrease, thus reducing the energy drawn from the mains. If the current exceeds 40
A,
the OVP protection is triggered (Dynamic OVP), and the external power transistor is switched off until the
current falls approximately below 10
A.
However, if the overvoltage persists, an internal comparator (Static OVP) confirms the OVP condition
keeping the external power switch turned off (see fig. 4).Finally, the overvoltage that triggers the OVP
function is:
Vout = R1 40A.
Typical values for R1, R2 and C are shown in the application circuits. The overvoltage can be set indepen-
VZCD
5
Lower Clamp Voltage
IZCD = -3mA
0.3
0.65
1
V
IZCD
5
Sink Bias Current
1V
≤ VZCD ≤ 4.5V
2
A
IZCD
5
Source Current Capability
-3
-10
mA
IZCD
5
Sink Current Capability
3
10
mA
VDIS
5
Disable threshold
150
200
250
mV
IZCD
5
Restart Current After Disable
VZCD < Vdis; VCC > VCCOFF
-100
-200
-300
A
OUTPUT SECTION
VGD
7
Dropout Voltage
IGDsource = 200mA
1.2
2
V
IGDsource = 20mA
0.7
1
V
IGDsink = 200mA
1.5
V
IGDsink = 20mA
0.3
V
tr
7
Output Voltage Rise Time
CL = 1nF
40
100
ns
tf
7
Output Voltage Fall Time
CL = 1nF
40
100
ns
IGD off
7
IGD Sink Current
VCC =3.5V VGD = 1V
5
10
-
mA
OUTPUT OVERVOLTAGE SECTION
IOVP
2
OVP Triggering Current
35
40
45
A
Static OVP Threshold
2.1
2.25
2.4
V
RESTART TIMER
tSTART
Start Timer
70
150
400
s
Table 5. Electrical Characteristics (continued)
(VCC = 14.5V; Tamb = -25°C to 125°C;unless otherwise specified)
Symbol
Pin
Parameter
Test Condition
Min.
Typ.
Max.
Unit
I
R1sc
V
out
2.5
–
R1
--------------------------
I
R2
2.5V
R2
------------
==
=
I
R1
V
outsc
V
out
2.5
–
+
R1
-----------------------------------------------------
I
R1sc
I
R1
+
==