From (11 it is visible that in the mode of a deep cut-off current of a collector has the minimum value equal to current of p - n - the transition displaced in the opposite direction. Current of the emitter has an opposite sign and much less current of a collector, as. Therefore in many cases it is considered equal :.
In the real transistor except thermal currents through transitions generation currents — recombinations, currents and currents of leak proceed. Therefore, are, as a rule, unknown. On transistors usually give values of the return currents of p in specifications - n - transitions. defined as current of the corresponding transition at not connected conclusion of other transition.
Emitter and collector p-n - transitions of the transistor are similar to p-n - transition of the diode. At separate connection of tension to each transition their volt-ampere is defined as well as in case of the diode. However if - transitions to put tension to one of p-n, and conclusions of other p-n - transition to close among themselves , the current proceeding through p-n - transition to which tension is attached, the of nonbasic carriers of a charge in base will increase because of change. Then:
where - thermal current of emitter p-n - transition, measured at the of base and a collector closed ; - thermal current of collector p-n - transition, measured at nakorotko conclusions of a and the emitter.
If p - n - transition is displaced in the opposite direction, instead of thermal current it is possible to substitute value of the return current, i.e. to consider, as. As a first approximation it can be done and at direct shift of p - n - transition. Thus for silicon transistors instead of it is necessary to substitute where the coefficient of m considers influence of currents of real transition (m = 2-. Taking into account this equation (1, (1 often write down in other look which is more convenient for calculation of chains with real transistors:
which shows, in how many time should be changed for receiving the same change of current what gives change of tension. The minus sign means that for providing = const of an increment of tension have to have opposite polarity. The coefficient is rather small () therefore at practical calculations on emitter often neglect influence of collector tension.