All bipolar transistor and Darlington models are based on SPICE's modified Gummel-Poon model. A typical model for a single transistor is shown as follows:
*Zetex FMMT493A SPICE Model v1.0 Last Revised 30/3/06 * .MODEL FMMT493A NPN IS =6E-14 NF =0.99 BF =1100 IKF=1.1 +NK=0.7 VAF=270 ISE=0.3E-14 NE =1.26 NR =0.98 BR =70 IKR=0.5 +VAR=27 ISC=1.2e-13 NC =1.2 RB =0.2 RE =0.08 RC =0.08 RCO=8 +GAMMA=5E-9 CJC=15.9E-12 MJC=0.4 VJC=0.51 CJE=108E-12 +MJE=0.35 VJE=0.7 TF =0.8E-9 TR =55e-9 XTB=1.4 QUASIMOD=1 *
In the bipolar model:
Some standard bipolar transistor SPICE models may not include a parameter that allows BF, the hFE parameter, to vary with temperature. If XTB is absent it defaults to zero, e.g. no temperature dependence. If hFE temperature effects are of interest and XTB is not modeled then the following values may be used to provide an estimate or a starting point for further investigation:
It is suggested that the appropriate datasheet hFE profile is examined, and a SPICE test circuit created that simulates the device in question and generates a set of hFE curves. Two or three such iterations should normally be sufficient to define a value for XTB in each case.
Please remember that these notes are only a rough guide as to the effect of model parameters. Also, many of the parameters are interdependent so adjusting one parameter can affect many device characteristics.
At Diodes, we have tried to make the models perform as closely to actual samples as possible but some compromises are forced which can result in simulation errors under some circumstances. The main areas of error observed so far have been:
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