Transistor
Transistor

A three-terminal Semiconductor device that controls or amplifies Current, acts as an electrically controlled switch.

Bipolar Junction Transistor
MOSFET

Bipolar Junction Transistor
Bipolar Junction Transistor

A Transistor that is controlled with Current.

Bipolar Junction Transistor-1762474692345.svg > invert

Properties

Breakdown

  • base-emitter breakdown occurs when Emitter voltage is much higher than base voltage, use protection Diode

Bipolar Junction Transistor-1760709670456.png > invert

BJT Rules

  • polarity: must be greater than
  • junctions:
    • base-emitter is a forward biased diode, enabling a larger current through collector and emitter
    • base-collector is a reverse biased diode
  • max ratings: , , and have a max rating
  • when above are obeyed,

Design Considerations

  • choose a larger base current than necessary since is low at low
  • use suppression diode when switching an inductive load

Common Emitter
Common Emitter

A BJT configuration where output is taken from the emitter, providing Voltage buffering (high Input Impedance and low Output Impedance).

\usepackage{circuitikz}
\begin{document}
\begin{circuitikz}[american, thick]

\draw (0,0) node[npn] (Q1) {};
\draw (Q1.B) to[short, -o] ++(-1,0) node[anchor=east]{$V_{in}$};
\draw (Q1.C) -- ++(0,1) node[tground]{} node[anchor=south]{$V_{DD}$};
\draw (Q1.E) -- ++(0,0) to[R, l=$R$] ++(0,-2) node[ground]{};
\draw (Q1.E) to[short, -o] ++(1,0) node[anchor=west]{$V_{out}$};

\end{circuitikz}
\end{document}

Properties

  • Also called emitter follower since output (emitter) tracks input (base)
  • can source Current through BJT and sink Current through R

Analysis

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