Semiconductor Fundamentals Unit 2 – Diodes and Half-Wave Rectification
NEW TERMS AND WORDS
barrier voltage - the voltage potential required for current flow through the depletion region of a
diode junction. The barrier voltage must be overcome by the forward bias voltage before current
can flow in a diode.
forward voltage drop (VF) - the condition that exists when the cathode of a diode is negative
with respect to its anode, and forward current flows.
forward biased - the condition that exists when the cathode of a diode is negative with respect to
its anode, and forward current flows.
reverse biased - the condition that exists when the anode of a diode is negative with respect to
the cathode.
pulsating dc - the rectifier output pulses of one polarity that corresponds to half-cycles of the
rectifier ac input voltage when the diode is forward biased.
ripple - the pulsations appearing in the output voltage of a rectifier circuit.
half-wave rectification - rectification in which output current flows only during half-cycles of
the ac input.
characteristic curve - a graphic representation of diode current flow versus diode voltage drop.
leakage current - the very small current that flows through a reverse biased diode.
minority carriers - free electrons in P type material, and holes (positive charges) in N type
material. Minority carriers are caused by the presence of tiny quantities of natural impurities in
the base semiconductor material. They are responsible for most reverse (leakage) current through
a semiconductor.
breakdown voltage - the reverse voltage that causes a diode to conduct heavily and destructively
in the "wrong" direction. Diodes should be selected to have a breakdown voltage greater than
any normally applied reverse voltage.
dynamic forward resistance (rF) - the apparent resistance of a conducting diode; calculated from
a measured change in diode voltage drop divided by a measured change in current.
rectification - the process of converting an alternating current into a pulsating direct current.
reverse recovery time (tRR) - the time required for a diode to stop conducting after forward bias is
removed. Reverse recovery time is due primarily to stored charges.
stored charges - positive and negative charges temporarily existing in a forward biased
semiconductor due to current flow. Stored charges reduce the efficiency of common
semiconductors at high frequencies because they increase the time required for a junction to
switch from the forward to reverse biased state.
EQUIPMENT REQUIRED
F.A.C.E.T. base unit
SEMICONDUCTOR DEVICES circuit board
Multimeter
Oscilloscope, dual trace
Generator, sine wave