Presentation for professional english lesson transistors What is a Transistor?

Diodes and Bias

• Diode: simple P-N junction.
• Forward Bias: allows current to flow from P to N.
• Reverse Bias: no current allowed to flow from N to P.
• Breakdown Voltage: sufficient N to P voltage of a Zener Diode will allow for current to flow in this direction.

3 adjacent regions of doped Si (each connected to a lead):

• 3 adjacent regions of doped Si (each connected to a lead):
• Base. (thin layer,less doped).
• Collector.
• Emitter.
• 2 types of BJT:
• npn.
• pnp.
• Most common: npn (focus on it).

Bipolar Junction Transistor (BJT)

npn bipolar junction transistor

pnp bipolar junction transistor

Developed by Shockley (1949)

1 thin layer of p-type, sandwiched between 2 layers of n-type.

• 1 thin layer of p-type, sandwiched between 2 layers of n-type.
• N-type of emitter: more heavily doped than collector.
• With VC>VB>VE:
• Base-Emitter junction forward biased, Base-Collector reverse biased.
• Electrons diffuse from Emitter to Base (from n to p).
• There’s a depletion layer on the Base-Collector junction no flow of e- allowed.
• BUT the Base is thin and Emitter region is n+ (heavily doped)  electrons have enough momentum to cross the Base into the Collector.
• The small base current IB controls a large current IC

BJT NPN Transistor