Bipolar Transistor Review

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Bipolar Transistor Review

• Transistors are three terminal devices that acts
  like electrically controlled switches or
  amplifier controls.
• It has either NPN or PNP configuration.
• An npn bipolar transistor uses a small input
  current and positive voltage at its base

• (relative to its emitter) to control a much
  larger collector-to-emitter current
• Conversely, a pnp transistor uses a small output
  base current and negative base voltage (relative
  to its emitter) to control a larger
  emitter-to-collector current.

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Bipolar Transistor Review
Types of Bipolar Transistor
Used to amplify low level signals. Gain is 10 to
500. IC max 80 to 600ma, operating frequency 1 to
300Mhz
Used primarily as switches. Gain is 10 to 200.
Max IC rating 10 to 1000mA. Max switching rates
between 10 to 2000MhZ
Used to amplify high frequency signals. Gain is
10 to 500 IC max 10 to 600mA, max operating
frequency 2000Mhz
Used in high power amplifiers or power supplies.
They have heat sinks. Power rating 10 to 300W.
Gain is 10 to 500 IC max 1 to 100 A, operating
frequency 1 to 100Mhz
Two transistors in one which has more stability
at high current levels. Gain is much larger than
a single transistor
Light sensitive transistors. When base exposed to
light it flows a base current which operates the
transistor.
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Bipolar Transistor Review

• An npn bipolar transistor is made by sandwiching
  a thin slice of p-type semiconductor between two
  n-type semiconductors.
• When no voltage is applied at the transistor
  base electrons in the emitter are prevented from
  passing to the collector side because of the
  depletion regionat the p-n junction.

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Bipolar Transistor Review

• When a positive voltage is applied to the base of
  an npn transistor, the pn junction between the
  base and emitter is forward biased.
• Electron enters into the very thin base region
  from the emitter.
• This process is a trick by which most of the
  electrons are driven into the collector region
  and hence heavy current flows from emitter to
  collector region.
• The amount of emitter-to-collector current can be
  varied by varying the base current.

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Bipolar Transistor Review

• The figure shows a typical characteristic curve
  for a bipolar transistor.
• It describes the effects the base current IB and
  the emitter-to-collector voltage VEC have on the
  emitter/collect currents IE and IC.
• IE is practically equal to IC

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Bipolar Transistor Review

• Saturation Region It is the region of operation
  where the maximum collector current flows and the
  transistor works like a closed switch from
  collector to emitter.
• Cutoff Region It refers to the region of
  operation near the voltages axis of the
  collector characteristic curve where the
  transistor acts like an open switch. Only a very
  small leakage current flows in this mode of
  operation.
• Active mode/region It describes transistor
  operation in the region to the right of
  saturation and above cutoff, where a near-linear
  relationship exists between terminal currents
  (IB, IC, IE).
• Bias Bias refers to the specific dc terminal
  voltages and current of the transistor to set a
  desired point of active-mode operation or
  quiescent point (Q-point)

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Bipolar Transistor Review

• Formulae

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Bipolar Transistor Review
9
RC
RB
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Relay Driver
12V
120Vac
RB