Transcript experiment_VII

Schedule
• Last Lab today
• No class next week
• “makeup” following week. A great time to
come in and practice for the exam
• Exam on May 10. see my web site for old
exams. I don’t believe in creativity in lab
exams.
Lab #7: Diode and Rectifier Circuits
• learn what diode is
• learn some simple circuits that use diodes
•Energy levels of electrons in
atoms are quantized (1s, 2s, 2p,
etc)
Diode
•When these atoms are brought
together in crystals, these
energy levels become energy
bands with gaps between them.
• The distributions of electron
energies depends on the
temperature. The highest
possible energy when T=0 is
called the Fermi Energy (EF).
• some materials can be made
into semi conductors by adding
small amounts of impurities. ptype (one fewer valence e than
Si) and n-type (one more
valence than Si).
• semi conductors do not
conduct at T=0.
1 eV
Diode
104 – 106 V/cm, 0.3-0.6 V
Electrons migrate from n to the holes in p, giving a net
charge to each side (neg on p side, pos on n side)
In steady state, there are conduction electrons who have
enough thermal energy to go over the potential barrier and
make a (positive) current from p to n. There is an equal and
opposite current of electrons that get enough thermal energy
to break their bonds in the p region, go up into the conduction
band, and then slide down the barrier back to the n region.
Diode
+
-
Here, the external bias aids the
electrons trying to go from n-p
and you get a net current in the
p to n direction.
-
+
Here, the external voltage stops the
electrons going from n to p. The
ones going from p-n can still go and
you get a (small) net current from n
to p (the prob to get enough thermal
energy to break the bond is
unchanged)
I  I 0 (e
qV / kT
 1)
Diode
symbol
Idealized I vs V
Realistic I vs V
I  I 0 (e
qV / kT
 1)
Half-wave rectifier
Full wave rectifier
RC differentiator
See pg 36
For t>>RC. Voltage
across resistor is
derivative of VIN
frequency to voltage converter
Hints
• lab begins pg 70
• no error analysis this lab
• IV.A. Do 10 measurements
• IV.A be careful. RMS, not peak-to-peak
• IV.A. Try pulling/pushing the amplitude knob on the scope. You should be
able to go up to about 7.5V and down to 0.1 V.
• IV.A fit the upper points to a straight line, extrapolate the line down to the
lower points. Include a graph with all the points and the line extrapolated from
the high voltage points.
• IV.B. take measurements for 3 different generator voltages and compare
ratios of gen to vload for the various quantities for the 3 generator voltages
• IV.C. Be careful! Not the normal cap
• IV.C. USE CURSORS NOT MEASURE
• IV.C take at least 8 points
Hints
• skip V-A, V-B, and V-C