SP.764, Practical Electronics Dr. James A. Bales

Lecture 2: Switches, Rectifiers and Generators

Topics:

1) Homework Review

2) Switches

3) Bridge Rectifiers

4) AC vs. DC

5) Function Generators and Oscilloscopes

Homework Review:

Homework 1: Voltage dividers

VVOUT 18=K1

K9

V20+

OUTVVIRV == 2011

VVIRV OUT 022 ==

+= 212

RRRVV INOUT

Vkk

kV 1891

120 =

+=

K1

K9

V20

OUTV

11 IRV =

22 IRV =( )22

2 20R

VVRVI OUT ==

221

20RV

RV

RV OUTOUT +=

+=

211

1120RR

VRV

OUT111

1 0RV

RV

RVI OUTOUT ===

+= 21120RR

RVVOUT

V2=

SP.764, Practical Electronics Lecture 2 Dr. James A. Bales Page 2 of 4

Homework 2: Diodes

There are two diodes that will be used in class:

Zener diodes: If you put a negative voltage across a Zener diode, it has a second turn-on point. The slope of the I-V curve of the second turn-on point

is even more abrupt than the slope of the I-V curve of the first turn-on point.

You can tail the breakdown voltage from a couple of volts to hundreds of

volts. A Zener diode is used in reverse bias to clamp and hold the voltage.

The name Zener diode comes from a Physics term called the Zener effect,

which is not even related to the Zener diode at all. However, the Zener diode

does exhibit the Avalanche effect.

Silicon diodes: These diodes do not emit light. Have same functionality as other diodes. Their forward voltages are really small (~0.6-0.7 volts).

Diodes dont have resistance. If the voltage is below a diodes forward voltage, then

the element looks like an open circuit. If the voltage is below the forward voltage,

the element behaves as a short circuit.

V5+

VVF 4=

1R 2R

VVF 2=

( ) == 15020

251 mA

VVR

( ) == 5020

452 mA

VVR

SP.764, Practical Electronics Lecture 2 Dr. James A. Bales Page 3 of 4

If RL is such that VOUT = 1V, there is no current flow through the diode. The diode

conducts (turns on) when VOUT hits RL.

One gets VOUT = 2V when RL = 220 ohms.

Now, try RL = 330 ohms. The voltage divider predicts VOUT = 2.5V. BUT the diode

clamps at 2.0V! The diode will steal any necessary current to stay at 2V. The bigger

RL is, the more current passes through the diode.

V5+

LR

V2= 220LR

< 220LR

> 220LR

mAIII 9321 =+=

( ) mAVVI 9330

251 =

=

V5+

330

LRVVF 2=

1I

2I3I

SP.764, Practical Electronics Lecture 2 Dr. James A. Bales Page 4 of 4

AC vs. DC

One can implement a simple DC to AC converter with a switch configuration like the

following:

With switch to one position:

VA - VB = 9V

With switch on the other position:

VB - VA = -9V

+

+-

-A

B

V9

V9

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