I was just trying to simulate a simple transistor circuit as common emitter in Proteus 8. However the I observe that the base-emitter voltage (Vbe) of the transistor 2N2222 is showing as 1.36v instead of 0.7v. This is a huge difference. Is there anything wrong with the attached circuit? Also Vce is 2.82v and I am not sure whether it is in saturation or not.

enter image description here

Below the the text script of the transistor model.



I tried using different transistors and found that this behavior occurs for transistors of LISA model. It is found working fine for transistors of SPICE model e.g. 2N222A, PN2222, BC548C etc. But still why LISA model does not give 0.7v for Vbe?


1 Answer 1


No, something is quite wrong with the model or simulator. You'd normally expect 600-800mV at the base under those conditions. 1.36V is way too high. Your circuit looks fine. Maybe try a different transistor.

I'd also expect the transistor to be saturated so Vce should be much less than 1V.

You can also try LTspice, a free download.

  • \$\begingroup\$ Agreed. I'd add about \$80\:\text{mV}\$ to the estimate because the Ohmic base resistance and the base current (BJT is saturated.) But that 2N2222 model is off by quite a bit, anyway. \$\endgroup\$
    – jonk
    Apr 20, 2019 at 9:57
  • \$\begingroup\$ Why is it too high? On the datasheet (from ST), it says 2N2222 goes to 1.3 V on 150 mA of IC current. Isn't it normal to go on those values if it says so in the datasheet? (Unless I didn't understand it - if I'm getting it wrong, please correct me) I was thinking those 0.7 V would be some "defaul", but different transistors had different VBE voltages. \$\endgroup\$
    – Edw590
    Dec 9, 2020 at 3:49
  • \$\begingroup\$ @DADi590 Typical voltages (what a model will usually present): i.imgur.com/oLhSPFk.png \$\endgroup\$ Dec 9, 2020 at 3:54
  • \$\begingroup\$ Thank you for the reply. What if we don't have a graph for a transistor? (I didn't find any for 2N2222 - is that one for 2N2222?) The one I mentioned says 2.6 V for 500 mA. Should I still assume 0.7 V as the active region VBE in that case? It's very distant from 2.6 V. If I had a graph would be easier, but I don't find any for this one. \$\endgroup\$
    – Edw590
    Dec 9, 2020 at 4:26

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