NCP1382 ON Semiconductor, NCP1382 Datasheet - Page 15

• Manufacturer Part Number: NCP1382
• Description: Quasi Resonant Current Mode Controller Featuring Pfc Go To Standby Function
• Manufacturer: ON Semiconductor

100 W specification when we enter the high line region. To
cope with this problem, we need to compensate the
controller in such a way that its peak capability gets reduced
at higher input voltages. How much do we need to
compensate the peak excursion? We can find the answer by
calculating DI
= 400 V. With our previous numbers, DI
therefore need to instruct the controller to reduce its peak
excursion by 588 mA at high line. Otherwise speaking, if we
think in voltages, the CS pin excursion shall drop from 0.8 V
(at low line, the maximum peak is 0.8 / R
necessary static voltage. Suppose that the BO network
divides the bulk voltage by 400 (V
V
have 1 V on the BO pin. due to the transconductance
amplifier of a 80 mS gm, it will turn into a 80 mA offset
current. To get our 147 mV, we just divide it by 80 mA:
R
the peak current is affected by the variable offset:
Figure 21 graph. The output power is slightly above what we
in
offset
P O (V in ) :+
To CS Comp.
As one can observe, the output power runs out of the initial
We can now calculate our R
We can now update Equation 4 with Equation 5, where
If we now plot the compensated curve, we obtain
). Therefore, in presence of a 400 V input voltage, we will
Figure 20. A Transconductance Amplifiers
= V
Transforms the BO Voltage into a Current
Comp.
To BO
offset
80 mS
G1
P
0.8
R S
= I
/ V
(h@(V in @(V out )V F )))
)
PLL
inHL
-
+
V in
L P
- I
@ t P * V in @ a @ g m @ R offset
2
x a . g
PHL
, with V
m
offset
@ V out ) V F )
= 1.8 kW.
BO
BO
CS
resistor to generate the
inLL
= a . V
= 200 V and V
S
V
) to (3.2 - 0.588).
P
bulk
= 588 mA. We
R
offset
in
V in
= 0.0025 x
N
NCP1381, NCP1382
R
sense
(eq. 5)
http://onsemi.com
inHL
15
0.25 = 653 mV at high line. Figure 19 shows the situation at
both line levels. A possible solution lies in offsetting the
current floor by the necessary value, which is, in our case,
0.8 - 0.653 = 147 mV. The traditional way of doing this goes
through the wiring of a high value resistor to the bulk
capacitor. This unfortunately dissipates heat. The
NCP1381/82 offers a more elegant option since it
transforms the voltage available from the Brown-out pin
into a fixed current, routed to the CS pin. That way, we can
calculate a resistor value which, once inserted in series with
current sense voltage image, will create our necessary offset.
Figure 20 shows this internal connection:
were originally shooting for and the total power excursion
is now kept within 15 W.
Overvoltage Protection
made by sensing the plateau voltage at the switch turn-off.
However, a sampling delay is introduced to avoid
considering
demagnetization pin goes above V
goes high. If this condition is maintained when the sampling
pulse arrives, then a fault is latched. Figure 22 shows the
arrangement and Figure 23 portrays a typical waveform.
Once latched, the controller stops all driving pulses and V
is clamped to 6 V. Reset occurs when the user unplugs the
converter from the mains and V
The NCP1381/82 features an overvoltage protection
105
100
Figure 21. The Compensated Converter Output
95
90
200
Power Response to Input Variations
the
250
V
leakage
in
, VOLTAGE (V)
300
inductance.
CC
demlatch
reduces below 4 V.
, the comparator
350
When
400
the
CC