NCP1381 ONSEMI [ON Semiconductor], NCP1381 Datasheet - Page 8

• Manufacturer Part Number: NCP1381
• Description: Low−Standby High Performance PWM Controller
• Manufacturer: ONSEMI [ON Semiconductor]

Startup Resistor Calculation
calculation of the startup element. Suppose that we have the
following information:
VCC
VCC
I
Startup duration below 2 s at minimum input voltage.
Input voltage from 85 VAC to 265 VAC.
Standby power below 500 mW.
CC2
For the sake of the example, we will go through the
1. From a startup DV of 15 − 10 = 5 V and a 4 mA
2. If we want a startup below 2 s, then the charging
ON
OFF
= 4 mA, given by the selected MOSFET Q
total consumption, we can obtain the necessary
V
the feedback loop is closed within 10ms: CV
4 m x 10 m / 5 = 8 mF or 22 mF for the normalized
value if we account for the natural dispersion.
current flowing inside the V
= 15 V.
CC
= 10 V.
capacitor to keep enough voltage, assuming
Figure 5. A Typical Startup Sequence Followed by a Faulty Condition
CC
capacitor must be
g
.
http://onsemi.com
CC
=
NCP1381
8
In latched mode, an internal zener diode is activated and
clamps V
zener is relaxed and the circuit can startup again.
Please note that in fault mode the V
priority and stops the pulses anytime V
minimum operating level VCC
3. The minimum input voltage is 85 x 1.414 = 120 V.
4. From this value, we can calculate the dissipated
above: I
the 15 mA of I
above 180 mA.
Then, R
< 580 kW.
power at high line: P
= 242 mW.
CC
to around 6 V. When V
startup
charge
> 15 x 22 u / 2 > 165 mA. If we add
CC1
should be below (120 − 15) / 180 m
, the total startup current shall be
startup
OFF
= (265 x 1.414)
.
CC
CC
goes below 4 V, this
comparator has the
CC
falls below its
2
/ 580 k