ncp1251 ON Semiconductor, ncp1251 Datasheet - Page 3

• Manufacturer Part Number: ncp1251
• Description: Ncp1251 Current-mode Pwm Controller For Off-line Power Supplies
• Manufacturer: ON Semiconductor

OP P
FB
CS
RFB
Vlatch
vdd
VDD
Vskip
/ 4.2
Vfold
OVP
gone?
Frequency
modulation
LEB
Frequency
foldback
Figure 2. Internal Circuit Architecture
Up
RST
4
R
S
600 ns time
constant
counter
Q
Q
250 mV
peak current
freeze
Rramp
Power on
reset
http://onsemi.com
VOPP
vd d
The soft-start is activated during:
- the startup sequence
- the auto-recovery burst mode
1 ms
blanking
3
65/
100 kHz
clock
power
on reset
+
IpFlag
V FB < 1.05 V ? s e t p o in t = 250 mV
Vcc and logic
management
Vlimit
Vlimit + VOPP
S
R
hiccup
20 ms time
constant
Q
Q
4 ms
SS
IpFlag
UVLO
VOVP
Clamp
GND
Drv
Vcc