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 C
comp
, the current through C
comp
equals zero.When the output voltage increases abruptly the current through R1 becomes:
Since the current through R2 does not change, ∆I
R1
must flow through the capacitor C
comp
and enter the
error amplifier.
This current is monitored inside the L6561 and when reaches about 37µA the output voltage of the multi-
plier is forced to decrease, thus reducing the energy drawn from the mains. If the current exceeds 40µA,
the OVP protection is triggered (Dynamic OVP), and the external power transistor is switched off until the
current falls approximately below 10µA.
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:
∆V
out
= R
1
· 40µA.
Typical values for R
1
, R
2
and C are shown in the application circuits. The overvoltage can be set indepen-
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 µA
I
ZCD
5 Source Current Capability -3 -10 mA
I
ZCD
5 Sink Current Capability 3 10 mA
V
DIS
5 Disable threshold 150 200 250 mV
I
ZCD
5 Restart Current After Disable V
ZCD
< V
dis
; V
CC
> 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 Voltage Rise Time C
L
= 1nF 40 100 ns
t
f
7 Output Voltage Fall Time C
L
= 1nF 40 100 ns
I
GD off
7 IGD Sink Current V
CC
=3.5V V
GD
= 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
Table 5. Electrical Characteristics (continued)
(V
CC
= 14.5V; T
amb
= -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
∆+==
