Bipolar Ref. Book: Electron
Devices and Circuit
Junction Theory - Robert L.
Boylestad and Louis
Transistor Nashelsky
(BJT)
,Transistors
• Invented in 1948 by John Bardeen, Walter Brattain and
William Shockley at Bell Lab
• Transistors have replaced Vacuum tubes
• Transistors offer several advantages
• No heating is required, hence no delays and need
less power
• Small in size and light in weight
• Require very low operating voltages
• Consume less power and are operationally efficient
• Long life and essentially no aging effect
• Shock resistant
,Transistor Construction
⚫ Bipolar Junction Transistor is a 3-layer
semiconductor device consisting of
Either two “n” and one “p” type layers of
material – npn Transistor n p n
Or two “p” and one “n” type layers of
material - pnp Transistor
⚫ Transistor has 3 regions: Base (B), Emitter (E), Collector (C)
Emitter emits or injects electrons (for npn) or holes (for pnp) into base.
Base passes most of these charge carriers (electrons/holes) to collector.
Collector gathers charge carriers from the base.
First Junction is called Emitter-Base Junction and 2nd junction is called Collector-Base
Junction.
⚫ Width: Width of Emitter & Collector regions is much greater than the base region.
⚫ Ratio of the total width to width of the center layer is 150:1. Collector is physically larger
than emitter region due too heat dissipation requirements.
⚫ Doping: ⚫ Base is lightly doped as compared to outer layers (1:10 or less) resulting in less
conductivity (more resistance).
⚫ Emitter is heavily doped.
⚫ Doping of Collector is in between the heavy doping of emitter and light
doping of base.
, Transistor - Symbol
⚫ Bipolar Junction Transistor: Symbols used
for representing npn and pnp transistors are
as shown. In npn transistor, emitter has an
outward pointing arrowhead.
npn
⚫ In pnp transistor emitter has an inward
pointing arrowhead.
⚫ All current directions refer to conventional
(hole) flow rather than electron flow. Thus
arrows in all electronic symbols have a
direction defined by this convention.
⚫ Therefore, the arrow in the diode symbol is
defined by the direction of conduction/
conventional current.
⚫ In a BJT (Bipolar Junction Transistor) pnp
device holes and electrons participate in
the injection process into the oppositely
polarized material.
Devices and Circuit
Junction Theory - Robert L.
Boylestad and Louis
Transistor Nashelsky
(BJT)
,Transistors
• Invented in 1948 by John Bardeen, Walter Brattain and
William Shockley at Bell Lab
• Transistors have replaced Vacuum tubes
• Transistors offer several advantages
• No heating is required, hence no delays and need
less power
• Small in size and light in weight
• Require very low operating voltages
• Consume less power and are operationally efficient
• Long life and essentially no aging effect
• Shock resistant
,Transistor Construction
⚫ Bipolar Junction Transistor is a 3-layer
semiconductor device consisting of
Either two “n” and one “p” type layers of
material – npn Transistor n p n
Or two “p” and one “n” type layers of
material - pnp Transistor
⚫ Transistor has 3 regions: Base (B), Emitter (E), Collector (C)
Emitter emits or injects electrons (for npn) or holes (for pnp) into base.
Base passes most of these charge carriers (electrons/holes) to collector.
Collector gathers charge carriers from the base.
First Junction is called Emitter-Base Junction and 2nd junction is called Collector-Base
Junction.
⚫ Width: Width of Emitter & Collector regions is much greater than the base region.
⚫ Ratio of the total width to width of the center layer is 150:1. Collector is physically larger
than emitter region due too heat dissipation requirements.
⚫ Doping: ⚫ Base is lightly doped as compared to outer layers (1:10 or less) resulting in less
conductivity (more resistance).
⚫ Emitter is heavily doped.
⚫ Doping of Collector is in between the heavy doping of emitter and light
doping of base.
, Transistor - Symbol
⚫ Bipolar Junction Transistor: Symbols used
for representing npn and pnp transistors are
as shown. In npn transistor, emitter has an
outward pointing arrowhead.
npn
⚫ In pnp transistor emitter has an inward
pointing arrowhead.
⚫ All current directions refer to conventional
(hole) flow rather than electron flow. Thus
arrows in all electronic symbols have a
direction defined by this convention.
⚫ Therefore, the arrow in the diode symbol is
defined by the direction of conduction/
conventional current.
⚫ In a BJT (Bipolar Junction Transistor) pnp
device holes and electrons participate in
the injection process into the oppositely
polarized material.
