Models

I’m using a 2N4265 NPN BJT in my circuit. The circuit seems to run fine, but I was looking at the model parameters for this BJT and the BF is specified at 1.13172K. That seems way too high in comparison to the data sheet values of hFE. What am I missing here?

In SPICE, many of the parameters in the model statement are curve fitting parameters. These often don’t have a direct correlation to the data sheet values. For a BJT, the Beta vs Ic curve is actually calculated using four parameters: BF, NE, ISE, and IKF. The ISE and NE parameters model the additional base current that reduces the beta at low base-emitter voltages. The IKF parameter models the high-current reduction in beta.

To see the actual beta curve in Micro-Cap, use the Plot feature in the Attribute dialog box. Choose to plot the DC Current Gain and it will display the beta curve for that transistor model.