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What are some tips for modeling optocouplers for Pspice?
8 w6 G" n) B/ l/ ]1 TThough Model Editor does not provide a template for either an optocoupler or for a phototransistor, it can beused create components of these models. For example,you can use Model Editor to model the electricalcharacteristics of the input LED of an optocoupler." R; i+ g7 B M6 l# e' Y9 v
In the case of the optocoupler,you need to create a model for a LED input,and also for a single BJTphototransistor output optocoupler.4 _/ M* b: s) K3 { H
1.LED
, [ Y8 F! \" K$ n8 v9 Z& T( I4 h) NTo model LED input, fit the forward current vs. voltage curve of the LED, and the LED capacitance curve toa PSpice diode. These curves are available in datasheets.
0 z2 Y* q) l1 z, b( F2.CTR curve fit
7 Y8 L0 @8 M' h* S0 G: ^Use Mathcad or Excel to fit the CTR curve to a polynomial. A polynomial which may work is of the formA*exp(B+Cx).
! j3 c. g! w2 T. x0 nIn the sample model shown below, the Gpcg source models the CTR curve. In this case, two regions were fitseparately, the region If<=10mA and the region If>10mA, where If is the LED forward current. The outputcurrent of the Gpcg source is the phototransistor collector current.
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