NCP1380 ON Semiconductor, NCP1380 Datasheet - Page 22

• Manufacturer Part Number: NCP1380
• Description: Quasi-Resonant Current Mode Controller
• Manufacturer: ON Semiconductor

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the signal on ZCD pin (pin 1). Indeed, a negative voltage
applied on this pin directly affects the internal voltage
reference setting the maximum peak current (Figure 40).
winding voltage becomes a negative voltage proportional to
needed to bypass R
on−time, we obtain the following relationship:
Where:
N
/ N
V
V
using Equation 2. While selecting the value for R
must be careful not choosing a too low value for this resistor
in order to have enough voltage for zero−crossing detection
during the off−time. We recommend having at least 8 V on
ZCD pin, the maximum voltage being 10 V.
follows:
R
p,aux
in
OPP
ZCD
The over power compensation is achieved by monitoring
When the power MOSFET is turned−on, the auxiliary
To ensure optimal zero−crossing detection, a diode is
If we apply the resistor divider law on the pin 1 during the
By selecting a value for R
During the off−time, ZCD pin voltage can be expressed as
We can thus deduce the relationship between R
p
is the DC input voltage
:
is the negative OPP voltage
is the auxiliary to primary turn ration: N
R
V
ZCD
ZCD
R
R
R
) R
opl
ZCD
+
opl
opu
R
opu
Au x
+
ZCD
during the off−time.
V
+ *
R
aux
) R
opl
opl
* V
Rz cd
N
, we can easily deduce R
opl
V
p,aux
ZCD
Ropu
Ropl
d
V
* V
aux
V
V
Figure 40. Over Power Compensation Circuit
in
OPP
* V
ZCD
* V
OVER POWER COMPENSATION
ZCD/OPP
d
OPP
1
p,aux
DRV
opl
opl
(eq. 2)
= N
(eq. 3)
(eq. 4)
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ESD
protection
, we
and
opu
aux
Vt h
CS
22
the input voltage. As the auxiliary winding is already
connected to ZCD pin for the valley detection, by selecting
the right values for R
over power compensation.
Design example:
V
V
N
If we want at least 8 V on ZCD pin, we have:
We can choose: R
peak current by 37.5% at high line (370 Vdc). The
corresponding OPP voltage is:
Using Equation 2, we have:
Thus,
leakage blanking
aux
R
d
p,aux
For the over power compensation, we need to decrease the
R
= 0.6 V
ZCD
Tblank
opu
V IL IMIT
= 18 V
R
= 0.18
+
−
) R
+ 221
opt
V
OPP
opu
OPP
Ropl
R
+
R
+ *
ZCD
+ 0.375
opl
ZCD
−0.18
* R
+
+
N
opu
= 1 kW and R
p,aux
ZCD
V
18 * 0.6 * 8
aux
and R
( −0.3 )
370 * ( −0.3 )
V
+ 221
V
* V
lin
V
OPP
8
IpFlag
V
ILIM
* V
Demag
opl
ZCD
d
* V
+ −300 mV
, we can easily perform
OPP
opl
1k * 1k + 220 kW
[ 1.2
ZCD
= 1 kW.
+ 221
(eq. 5)
(eq. 6)
(eq. 7)
(eq. 8)