--- In LTspice@..., John Woodgate <jmw@...> wrote:
In message <kt8hbj+5vsb@...>, dated Tue, 30 Jul 2013,
jean_claudeabeille <jean_claudeabeille@...> writes:
Is anyboby here who can explain me how to calculate Ib in this circuit
: Draft2.asc. I found no formula(s) on the web while LTSpice knows.
Thanks.
You can't find a formula on the Web, even though there is one, because
it's not a practical thing. The base current is exponentially dependent
on the base voltage and the junction temperature. LTspice assumes values
in the exponential equation, but the slightest change can make a huge
difference to the current. Every individual transistor will give a
different result.
You simply don't use bipolar transistors with a fixed DC voltage between
base and emitter.
--
OOO - Own Opinions Only. With best wishes. See www.jmwa.demon.co.uk
Why is the stapler always empty just when you want it?
John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK
John,
The equation Helmut gave is an excellent approximation for the relationship between Vbe and Ib. It is used in ever circuit with a BJT that anyone simulates; in other words, it is a fundamentally important relationship in BJT analysis.
Rick
