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Lectures 27+28
A little more about power
Beginning amplifiers+opamps
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View Full Document DC power supplies
+
V1

I
1
+
V2

•
V1 = 120V*cos(60Hz·2
π
t)
•
Transformer steps down voltage from wall
voltage by N.
•
Full wave rectifier converts to DC (see
lecture 7+8), with drop of 2V
TO
= 1.4V (V
TO
= 0.7V)
– When V2> Vout+2V
TO
, D2, D3 turn on,
charge C
– When V2< Vout2V
TO
, D1, D4 turn on,
charge C
– Otherwise, R discharges C
•
So Vout ~ 120V/N2V
TO
•
“ripple” set by R, C.
•
Can power dc devices, charge batteries
+
Vout

D1
D2
D3
D4
15
10
5
0
5
10
15
0
2
4
6
8
10
12
time
V o lta g e
V2
V2
Vout
Amplifiers
•
Use amplifiers to make signals
bigger
•
Ideally, treat this as a voltage
controlled voltage source with
gain Av.
•
A sense for how this might be
done:
– Start with a voltage controlled
conductance: this is a good
model of:
• Some transistors
• Synapses
– Load with big resistor+ battery
•
Key points:
– Battery voltage+ DC current
needed
– Always have an output
impedance
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This note was uploaded on 11/21/2011 for the course ECE 2100 taught by Professor Kelley/seyler during the Spring '05 term at Cornell University (Engineering School).
 Spring '05
 KELLEY/SEYLER
 Amplifier

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