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TL431 with dynamic elements, behavior with two instances

I've copied Christophe Basso's TL431 model into Multisim.  The model works well, reflecting gain/phase as seen in Christophe's book "Switch Mode Power Supplies"  However, when there is another instance of the component in the same schematic, unexpected results occur. When the simulation first is run, the output voltage is correct @3.3V.  If I place another TL431 I get what is illustrated in the snapshot.33_B.gif


Nodes 1=REF, 2=Anode, 3=Cathode.  The model:


.subckt TL431 1 2 3

C1 3 20 43p
Q1 3 20 10 QN3904
R1 10 7 240
R2 7 2 6600
Q2 3 7 2 QN3904 50
D1 1 3  D4mod
D2 2 3 D2mod
V1 5 2 DC=2.49
R4 3 0 1e12
D3 2 20 D3mod
C2 2 7 1n
G2 2 20 5 1 -250e-6
.model QN3904 NPN AF=1.0 BF=300 BR=7.5 CJC=3.5pf
+IKF=0.025 IS=1.4e-14 ISE=3e-13 KF=9e-16 NE=1.5
+RC=2.4 TF=4E-10 TR=21E-9 VAF=100 XTB=1.5
.model D3mod D N=0.01
.model D2mod D BV=36 CJO=4E-12 IS=7E-9 M=0.45 N=1.3
+RS=40 TT=6E-9 VJ=0.6V
.model D4mod D BV=100V CJO=4E-12 IS=7E-9 M=0.45
+N=2 RS=0.8 TT=6E-9 VJ=0.6V


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Message 1 of 6


Hi Jackinnj,


By placing a component on the work area, even though it's not connected to the circuit it will be part of the netlist and can affect the simulation.  It can alter how the SPICE calculates the circuit and there may be common ground inside the model which means  unconnected component is not part of the circuit.


Tien P.

National Instruments
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Message 2 of 6

How do I add TL431 in multisim
Please explain me step by step procedure

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Message 3 of 6

Hi Dexter,


You can refer to this knowledge base:



Tien P.

National Instruments
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Message 4 of 6

dexterboot - 

There should be several TL431 components from TI under Power->Voltage reference.


I attached a file with Christophe Basso's version of the TL431. 

National Instruments
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Message 5 of 6

please attach your circuit so that we can investigate.



National Instruments
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Message 6 of 6