AND8112 Datasheet, PDF (10/12 Pages) ON Semiconductor – A Quasi-Resonant SPICE Model Eases Feedback Loop Designs

AND8112/D
V3
120
AC =
dem
R_prim
0.5
9
V_Coil
R1
1k ₄
FreeRun
1
8
fb ₂
7
3
6
4
5
X1
FreeRunDT
t_off(min) = 1 m
V_drain
3
Simplified simulation of a
NCP1207−based board
X4
I_out
XFMR−AUX
RATIO_POW = −0.06
RATIO_AUX = −0.06
D1
MBR20100CT
L3
2.2 m
R5
10 m
21
11
I_coil
L_prim
13
12
V_out
Resr1
15
60 m
1.2 m
14
R7
5
31 _R6
100
I_Diode
dem
C6
C_out1
1 mF
I_C = 16.5
150 m
16 C1
220 m
L_leak
100 p
I_C = 16.5
1p
V_out
7
V1
X3
PSW1
6
+
24
X2
PSW1
1
R_sense
0.5
I_D
C_reso
10 p
I_Reso
Feedback
fb
C5
1n
V_out
R_led
1k
17
X5
SFH615AGR
18
D4
BV = 15.6
Figure 12. This Simplified Transient Model Will Help to Check the Averaged Results
16.88
Real World Confrontation
Even if the above paragraph gives us the assumption that
our model sticks to reality quite well, nothing replaces a real
16.86
board measurement with a network analyzer. However, on
the NCP1207, the collector of the optocoupler is directly
16.84
internally pulled−up to a reference via a resistor, it thus
becomes difficult to open the loop via the series transformer
method. We thus went back to a simple open−loop
16.82
Cycle−by−Cycle V_out
16.80
Averaged V_out
configuration where a DC source fixes the expected
operating point. It does not cause any problem in our case
since the overall gain V_control to V_out is low. The AC
injection is then made via a 1000 mF capacitor. Figure 15
2.57 m 3.11 m 3.65 m 4.19 m 4.73 m
Figure 13. Audio Susceptibility with a Line Step
(200 to 350 V)0
depicts the adopted configuration on the bench, but also
replicated on the averaged model.
1
8
16.95
Averaged V_out
16.85
D = 20 mV
16.75
16.65 ^{Cycle−by−Cycle V}out
C1
1000 m
3
V_stim
AC = 1
2
7
3
6
4₄
5
5
R3
NCP1207
1k
1
V_bias
1.57
Figure 15.
R_sense
16.55
2.48 m 3.04 m 3.60 m 4.16 m 4.72 m
Figure 14. 0 and Load Step Response
Comparison Between Models (50 W to 0.5 W)
The AC measurement is obtained once the proper
operating point is reached by adjusting V_bias. The gain being
low, there is no problem of output runaway as long as V_bias
is slowly increased.
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