HV
to PFC’s VCC
+
NCP1231
OVP
BO/OVP
1
8
SS
2
7
3
6
4
5
NCP1231
Ramp
+
Vout
GND
GND
Figure 1. Typical Application Example
PIN FUNCTION DESCRIPTION
Pin No. Pin Name
Function
Pin Description
1
PFC VCC Directly powers the PFC This pin is a direct connection to the VCC pin (Pin 6) via a low impedance switch.
front−end stage
In standby and during the startup sequence, the switch is open and the PFC VCC
is shutdown. As soon as the aux. winding is stabilized, Pin 1 connects to the VCC
pin and provides bias to the PFC controller. It goes down in standby and fault
conditions.
2
FB
Feedback Signal
An optocoupler collector pulls this pin low to regulate. When the current setpoint
falls below 25% of the maximum peak, the controller skips cycles.
3
CS
Current Sense
This pin incorporates two different functions: the standard sense function and an
internal ramp compensation signal.
4
GND
IC Ground
−
5
DRV
Driver Output
With a drive capability of +500 mA / −800 mA, the NCP1231 can drive large Qg
MOSFETs.
6
VCC
VCC Input
The controller accepts voltages up to 18 V and features a UVLO of 7.7 V typical.
7
SS
To provide an internal This pin provides three different functions, via a capacitor to ground, saw tooth
(Soft−Start) ramp timing for different signal whose function is to create a soft−start, frequency dithering and 100 msec
usages
fault timer.
8
BO/OVP Brown−Out and OVP
By connecting this pin to a resistive divider, the controller ensures operation at a
safe mains level. If an external event brings this pin above 4 V, the controller is
permanently latched−off.
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