A.C. Emitter Resistance
A.C. Emitter Resistance-The ac or dynamic resistance of emitter-base junction diode of a transistor is called ac emitter resistance. It is defined as the change in base-emitter voltage divided by change in corresponding emitter current [See Fig. 1]
i.e. Rac =VBE/VE I For instance, suppose an ac base voltage change of 1 mV produces an ac emitter current change of 50 µA. Then emitter diode has an ac resistance of
Rac =1mV/50 µA=20 Ω
Formula For AC Emitter Resistance
It can be show mathematically that the ac resistance of emitter diode is give by ;
Rac= 25mV/ IE
where IE = dc emitter current (= VE/RE) at Q point
Note the significance of this formula. A.C. Emitter Resistance-It implies that ac emitter resistance can be finnd simply by substituting the quiescent value of emitter current into the equation. There is no need to have the characteristics available. It is important to keep in mind that this formula is accurate only for small signal operation. It is a usual practice to represent ac emitter resistance by re′.
∴ re ′ = 25mV/ IE
The subscript e indicates emitter. The lower case r is use to indicate an ac resistance. The prime shows that it is an internal resistance.
আমাদের অন্যান্য পোষ্টসমূহ:
BCS Preliminary: All Bcs Question, Answer and Solve.
আমাদের অন্য ওয়েবসাইট দেখার জন্য এখানে ক্লিক করূন