ncp1234ad100r2g ON Semiconductor, ncp1234ad100r2g Datasheet - Page 20

• Manufacturer Part Number: ncp1234ad100r2g
• Description: Ncp1234 Fixed Frequency Current Mode Controller For Flyback Converters
• Manufacturer: ON Semiconductor

protection, an offset proportional to the input voltage is
added on the CS signal by turning on an internal current
source: by adding an external resistor in series between the
sense resistor and the CS pin, a voltage offset is created
across it by the current. The compensation can be adjusted
by changing the value of the resistor.
sense signal is small, i.e. in light load conditions, where it
input, and its output is periodically sampled and reset, in
order to follow closely the input voltage variations. The
sample and reset events are given by the V
comparator used for sampling detection for the AC line
To compensate this and have an accurate overpower
But this offset is unwanted to appear when the current
A 3 bit A/D converter with the peak detector senses the ac
I
LIMIT
HV
FB
I
P
Figure 34. Line Compensation for True Overpower Protection
Figure 35. Schematic Overpower Compensation Circuit
High
Line
V
HVstop
Peak Detector
Converter
V
A/D 3 bit
FB (OPC)
+
t
delay
HVsample
http://onsemi.com
Watch
(32 ms)
Dog
20
Register
would be in the same order of magnitude. Therefore the
compensation current is only added when the FB voltage is
higher than V
voltage, there is needed an additional circuitry to read or at
least closely estimate the actual voltage on the bulk
capacitor.
input. If only the DC high voltage input is used, no reset
signal is generated by the V
watch dog is used to generate the sampling events for
sampling the DC input high voltage line.
t
3 bit
delay
However, because the HV pin can be connected to an ac
To CS
Block
Low
Line
T
LEB
blanking
FB(OPCE)
I ctrl
time
compensated
I Generator
.
I
P
to be
HVsample
CS
condition and the 32 ms