ncp1231d65r2g ON Semiconductor, ncp1231d65r2g Datasheet - Page 18

• Manufacturer Part Number: ncp1231d65r2g
• Description: Lowstandby Power High Performance Pwm Controller
• Manufacturer: ON Semiconductor

Overvoltage Protection
protection on Pin 8. Figure 39 shows the internal component
configuration inside the chip. When the voltage on Pin 8 is
above 4.2 V then an OVP signal permanently latches off the
controller; all output drive pulses are stopped and the Vcc Pin
6 ramps up and down between Vccon and Vccmin until the
user unplugs the converter power allows Vcc to drop below
Vccreset (4.0 V). By bringing Vcc down to the reset voltage
(around 4.0 V), the latch is released and the IC can restart.
BrownïOut Protection
supply for being over stressed when the main input power
drops below the typical universal input range of 85ï265 Vac.
When this occurs, the controller stops the drive output and
waits for normal power to resume. Hysteresis is used on the
The NCP1231 combines an over and underïvoltage
A BrownïOut (BO) protection feature prevents the power
By arranging two comparators on the same pin, both
OVP and under voltage sensing can be implemented.
Latchoff
Figure 41. An Internal Ramp is used to Introduce Frequency Jittering on the Oscillator Saw Tooth
from
PWM
to Dr
62.4 kHz
Brown
Out
Figure 42.
OVP
+
ï
0.5 / 0.23
+
+
Internal Ramp
4V
65 kHz
8
http://onsemi.com
NCP1231
4 ms
18
67.6 kHz
BO comparators because the voltage on the bulk energy
storage capacitor ripple voltage is affected by the input
voltage and output power level. For this reason when BO
comparator toggles, the internal reference changes from
input ac voltage in back within the normal operating range
and the voltage on the bulk energy storage capacitor is back
to normal range, the controller resume normal operation.
drive output is disabled. This level is dependent on the ripple
voltage on Pin 8. A capacitor can be added between Pin 8 and
ground to select the amount of ripple voltage. The larger the
capacitor, the lower the ripple voltage, the greater the
amount of hysteresis.
Thermal Protection
integrated circuit in the event that the maximum junction
temperature is exceeded. When activated (160 qC typically)
the controller turns off the PWM Drive Output. When this
occurs, Vcc will drop (the rate is dependent on the NCP1231
loading and the size of the Vcc capacitor) because the
controller is no longer delivering drive pulses to the
auxiliary winding charging up the Vcc capacitor. When Vcc
drops below 4.0 volts and the Vccreset circuit is activated,
the controller will restart. If the user is using a fixed bias
supply (the bias supply is provided from a source other than
from an auxiliary winding, refer to the typical application )
and Vcc is not allow to drop below 4.0 volts under a thermal
shutdown condition, the NCP1231 will not restart. This
feature is provided to prevent catastrophic failure from
accidentally overheating the device.
500 mV to 230 mV. This effect is not latched, as soon as the
The lower threshold (VBLow) is the level at which the
An internal Thermal Shutdown is provided to protect the
Internal Sawtooth