1. BJT structure note: this is a current of electrons (npn case) and so the conventional current flows from collector to emitter. heavily doped ~ 10^15 provides the carriers lightly doped ~ 10^8lightly doped ~ 10^6

2. BJT characteristics

4. BJT modes of operation ModeEBJCBJ CutoffReverse Forward activeForwardReverse Reverse activeReverseForward SaturationForward

5. Cutoff: In cutoff, both junctions reverse biased. There is very little current flow, which corresponds to a logical "off", or an open switch. Forward-active (or simply, active): The emitter-base junction is forward biased and the base-collector junction is reverse biased. Most bipolar transistors are designed to afford the greatest common-emitter current gain, βf in forward-active mode. If this is the case, the collector-emitter current is approximately proportional to the base current, but many times larger, for small base current variations.proportional Reverse-active (or inverse-active or inverted): By reversing the biasing conditions of the forward-active region, a bipolar transistor goes into reverse-active mode. In this mode, the emitter and collector regions switch roles. Since most BJTs are designed to maximise current gain in forward-active mode, the βf in inverted mode is several times smaller. This transistor mode is seldom used. The reverse bias breakdown voltage to the base may be an order of magnitude lower in this region. Saturation: With both junctions forward-biased, a BJT is in saturation mode and facilitates current conduction from the emitter to the collector. This mode corresponds to a logical "on", or a closed switch. BJT modes of operation

6. BJT structure (active) current of electrons for npn transistor – conventional current flows from collector to emitter. B C E IEIEIEIE ICICICIC IBIBIBIB - + V BE V CB - + +- V CE

7. BJT equations (active)  = Common-base current gain (0.9-0.999; typical 0.99)

8. BJT equations (active)  = Common-emitter current gain (10-1000; typical 50-200)

9. BJT equations (active)  = Common-emitter current gain (10-1000; typical 50-200)  = Common-base current gain (0.9-0.999; typical 0.99)

10. BJT large signal models (forward active)

11. BJT large signal models (reverse) Common-base current gain (0.1-0.5) BJT transistor is not a symmetrical device

12. BJT Ebers-Moll (EM) model

13. BJT structure The npn transistor has beta=100 and exhibits an Ic=1mA at V BE =0.7V. Design the circuit so that a current of 2mA flows through collector and a voltage of +5V appears at the collector.

14. BJT equations The voltage at the emitter was measured and found to be -0.7V. If beta=50, find I E, I B, I C and V C.

15. BJT equations A given npn transistor has beta=100. Determine the region of operation if: a)I B =50uA and I C =3mA b)I B =50uA and V CE =5V c)V BE =-2V and V CE =-1V

16. BJT equations R B =200kΩ, R C =1kΩ, V CC =15V, beta=100. Solve for I C and V CE

17. BJT equations R B =200kΩ, R C =1kΩ, V CC =15V, beta=100. Solve for I C and V CE