OVER VOLTAGEPROTECTION 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 R
1 and R2 (see fig. 2), taking into con-
sideration that the non inverting input of the error
amplifier isbiased inside the L6561at 2.5V.
In steady state conditions, the current throughR1
and R2 is:
I
R1sc
=
V
out
− 2.5
R1
= I
R2
=
2.5V
R2
and, if the external compensation network is
made only with a capacitor C
comp
, the current
throughC
comp equalszero.
When the output voltage increases abruptly the
current throughR1 becomes:
I
R1
=
V
outsc
+∆V
OUT
− 2.5
R1
=
I
R1sc
+∆
I
R1
Since the current through R2 does not change,
∆
I
R1
must flow through the capacitor C
comp
and
enter theerror amplifier.
Thiscurrentis monitoredinsidethe L6561andwhen
reachesabout37µA the outputvoltageof themulti-
plieris forcedto decrease,thusreducing theenergy
drawn from the mains . If the current exceeds 40µA,
the OVP protectionis triggered(Dynami cOVP),and
the externalpowertransistoris switched offuntilthe
currentfallsapproximatelybelow10µA.
However, if the overvoltage persists, an internal
comparator(Static OVP) confirms theOVP condition keeping the external power switch turned off
(see fig.1).
Finally, the overvoltage that triggers the OVP
functionis:
∆
Vout = R
1 ⋅
40µA.
Typical values for R
1,R2and C are shown in the
applicationcircuits. Theovervoltagecanbe setindependentlyfrom the average outputvoltage.The precision in setting the overvoltage threshold is 7% of
ELECTRICALCHARACTERISTICS
(continued)
ZERO CURRENT DETECTOR
Symbol Pin Parameter Test Condition Min. Typ. Max. Unit
V
ZCD
5 Input Threshold Voltage
Rising Edge
(1) 2.1 V
Hysteresis (1) 0.3 0.5 0.7 V
V
ZCD
5 Upper Clamp Voltage IZCD =20µA 4.5 5.1 5.9 V
V
ZCD
5 Upper Clamp Voltage I
ZCD
= 3mA 4.7 5.2 6.1 V
V
ZCD
5 Lower Clamp Voltage I
ZCD
= –3mA 0.3 0.65 1 V
I
ZCD
5 Sink Bias Current 1V≤V
ZCD
≤
4.5V 2
µ
A
I
ZCD
5 Source Current Capability -3 -10 mA
I
ZCD
5 Sink CurrentCapability 3 10 mA
V
DIS
5 Disable threshold 150 200 250 mV
I
ZCD
5 Restart Current After Disable V
ZCD
< Vdis; VCC>V
CCOFF
-100 -200 -300 µA
OUTPUT SECTION
V
GD
7 Dropout Voltage I
GDsource
= 200mA 1.2 2 V
I
GDsource
= 20mA 0.7 1 V
I
GDsink
= 200mA 1.5 V
I
GDsink = 20mA 0.3 V
t
r 7 Output VoltageRise Time CL = 1nF 40 100 ns
t
f 7 Output Voltage Fall Time CL = 1nF 40 100 ns
I
GD off
7IGDSink Current VCC=3.5V VGD= 1V 5 10 - mA
OUTPUT OVERVOLTAGE SECTION
I
OVP
2 OVP Triggering Current 35 40 45 µA
Static OVP Threshold 2.1 2.25 2.4 V
RESTART TIMER
t
START
Start Timer 70 150 400 µs
(1) Parameter guaranteed by design, not testedin production.
L6561
4/11