AND8031 Datasheet, PDF (4/12 Pages) ON Semiconductor – Isolated Precision Regulation of a Single 1.8 Volt Output from a Universal Line Input

AND8031/D
36
16
Extended
Range with
PNP
6.0
3.75
3.2
2.5
2.15
1.95
1.6
TL431
TLV431
NCP100
Figure 6. Power Supply Output Voltage Range
Comparison for Programmable Precision References
Figure 5 illustrates an additional 1.0 uF capacitor, C3,
which is required for normal operation of the NCP100.
Bandwidth concerns are raised when a capacitor is placed
from the cathode to anode of the precision reference. Since
the PNP transistor is used to drive the optocoupler, the
cathode current of the NCP100 is amplified by the beta of the
transistor therefore minimizing the effects of C3. R3 is a
factor in the overall gain of the feedback network and R4
limits the current into the diode of the optocoupler. The
roll–off frequency of the feedback network is related to R1
and C2 only. Figure 7 shows the circuit schematic, the gain
and the phase of the TLV431 and the NCP100 with and
without the PNP.
V_out
R_OSC
V_out
R_OSC
R3
R1
C2
C3
U1
R2
GND
Q1
C3
R4
R3
R1
C2
U1
R2
GND
Figure 7. Schematics for Gain and Phase Comparison of TLV431 and NCP100
Note: C3 only for NCP100
70
Gain
60
Phase
50
40
180
90
0
–90
–180
10
100
1k
10 k
100 k
Frequency (Hz)
Figure 8. TLV431 with PNP
40
Phase
30
20
Gain
10
0
–10
–20
–30
180
90
0
–90
–180
10
100
1k
10 k
100 k
Frequency (Hz)
Figure 9. TLV431 without PNP
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