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Electronics
reduced
to
it's
simplest
form
is
the
flow
of
electrons
are
either
on or off, or they vary between on and off. These two methods of
controlling electricity are known as digital and analog electronics. A
light switch turns a light on and off (digital) and a light dimmer
turns a light to any point from off to on (analog). A computer is a
digital device that contains may on / off switches.
The
flow
of
electricity
is
either
direct
current
(DC)
or
alternating
current
(AC).
A battery is an example of DC, and the power in your house is AC.
AC has advantages in power distribution. DC has power losses in the
long transmission lines that AC can reduce. More on this later,
first lets talk about the common parts used to control electricity.
This
is
very
important

complicated
circuits
are
made
from
many
simple
subcircuits
wired
together to perform complicated functions.
CircuitMaker
for
students
is
a
schematic
capture
and
simulation
program
and
is
included
free on the Pilot Pro plans DVD or you can find it on the web. The
program is to large to fit on my domain.
Common
formulas:
E=Volts (electromotive force), R=Ohms (resistance), I=amps (current),
P=Watts (power)
Common
components used in electronics:
Resistors (Ohms)  oppose current by producing a voltage drop, converts
Voltage to a current.
Capacitor (Farads)  stores electrons, blocks DC and passes AC
Coil (Henry) passes DC and blocks AC
Transformer  changes voltage to a higher or lower value and changes
the current inversely
Transistor  turns electron flow off and on,
or varies the flow from off to on.
Diode  blocks the flow of
electrons in one direction. The arrow points in the positive direction.
A anode +, K cathode .
LED  light admitting diode
Always read the data sheets on components for more information.
Resistors
Values can be changed by add components in parallel or series.
The smaller resistor in the parallel circuit dominates the total value.
The larger resistor in the series circuit dominates the total value.
Resistor
used as a current sense.
A resistor limits current and drops Voltage and can be used as a
current to Voltage converter using Ohms law  I=V/R.
The color code value for resistors:
color

Value 
For memorization  Tolerance 
Black 
0 
Bad 

Brown  1 
Boys 
+ 1% 
Red  2 
Rape 
+ 2% 
Orange 
3 
Our 
+ 0.05% 
Yellow 
4 
Young 

Green 
5 
Girls 
+ 0.5% 
Blue 
6 
But 
+ 0.25% 
Violet 
7 
Violet 
+ 0.1% 
Gray 
8 
Gives 

White 
9 
Willingly 

Gold 
+ 5% 

Silver 
+ 10% 

None 
+ 20% 
Time
constants
Time constants: For resistor/capacitor  Vt = E (1e *
(t/RC)). For resistor/inductor (time for current to reach full
value)  It = E/R * (1e * (t*R/L)). Where R is in ohms, C
is in farads, L is in Henries, t is in seconds, and e is in the natural
log base 2.71828.
One time constant (R*C) is equal to 63.2% of the final value.
After the second time constant an additional 63.2% of the remaining
charge or current will be reached (63%, 86%, 95%, 98%, 99%). The
same is true for discharge. Three to five time constants are need
to get close to full charge or current.
RC time constant
Capacitor values
cap marking = size in pF
105 = 1,000,000pF or 1000nF or 1uF
104 = 100,000pF or 100nF or 0.1uF
103 = 10,000pF or 10nF or 0.01uF
102 = 1,000pF or 1nF or 0.001uF
101 = 100pF or 0.1nF or 0.0001uF
pF = picoFarad, nF = nanoFarad, uF = microFarad
Driving
an LED
LEDs or light admitting diodes drop about 2 Volts before they conduct.
Check the specification sheet for Vf (forward Voltage) and max current.
This LED is rated at 1.7 Volts before it will start to turn on and can
use 0.04 amps of current. We need to have a resistor that will limit
current to no more than 40 ma or the LED will burn out and fail. Ohms
law says R=E/I, we need to subtract the LED Voltage drop from the
calculation so R=(91.7)/0.04 = 182.5. Round this up to a standard
resistor value you get 200 Ohms. If the LED specs are not known then
try using Vf = 2V and LED I = 0.02 amps as ball park ratings.
Changing
Voltage levels
Wrong
Right Voltage divider
Vout = Vin*(R2/(R1+R2)) = 10*(10k/(10k+10k)) = 10*0.5 = 5V
The down sides are this supply is current limited and Vout changes as
Vin changes.
Voltage
reference
D1=5.1V Zener diode, R1 = (Vin min  Vz) / (Imax) = (105.1) /
(0.01) = 490 round up to 499 standard value.
Zener diodes have a reverse voltage breakdown point. This Zener Voltage
point depends on the diode part number.
Standard resistor values can be found in a Digikey or Mouser catalog.
Voltage
Regulator
D1=5.6V
Zener
diodes
are
designed
to
be
hooked
up
backwards
because
they
start
to
conduct
at
a
specific
reverse
Voltage.
The
resistor
limits current through the diode and transistor base. The transistor
drops about 0.4V through the base  emitter junction. The transistor is
wired as a Voltage follower or common collector. With the transistor
added the output can supply more current. This transistor can supply
about 200ma of current.
Integrator
The integrator
is used
for a signal delay or low pass filter. If the RC time constant is a
10th (1/10) the period of the signal then it has a high amplitude. If
the RC time constant is 10 time the period of the signal then it acts
like a first order filter.
The signal period is 1/1000Hz = 0.001, the RC time constant is
30000*0.0000000047 = 0.000141. The RC time constant is set at 1/10 that
of the signal period.
Here the
RC time constant (R = 100K, C = 1uF) is set at 10 times that of the
signal period. the RC
time constant is 100000*0.0000001 = 0.01. This looks like a low pass
filter.
Differentiator
The differentiator is used as a trigger or high pass filter. If
the RC time constant is a 10th (1/10) the period of the signal then it
has a high amplitude. If the RC time constant is 10 time the period of
the signal then it acts like a first order filter.
The
signal period is 1/1000Hz = 0.001, the RC time constant is
30000*0.0000000047 = 0.000141. The RC time constant is set at 1/10 that
of the signal period.
Here the RC time constant (R = 100K, C = 1uF) is set at 10 times that of the signal period. the RC time constant is 100000*0.0000001 = 0.01. This looks like a high pass filter.
The
integrator
and differentiator
circuits
above
are
made
from
a
RC
Voltage
divider
circuit.
The
capacitor
is
like
a
variable
resistor
and
it's
value
is
base
on the frequency passing thought it. This is called capacitive
reactance. The formula for capacitive
reactance is Xc
=
1/(2*Pi*frequency(Hz)*Capacitance(F)).
Reactance for caps and inductors
*Voltage and current phase rule of thumb:
Voltage leads current in an inductor by 90 degrees
Current leads Voltage in a capacitor by 90 degrees
Triangle
to sine converter
Diodes are one way valves. The diodes start to turn on at about 0.7V
(forward Voltage drop). When the diodes conducts the resister drops
some Voltage and limits current. Silicon diodes drop about 0.7V,
germanium diodes drop about 0.2V. The resistor also limits current
through the diodes. To much current will destroy the diodes.
Diode
Curve trace
Here is the curve trace of a diode. This shows the Voltage /
current response of a forward biased diode. The current through the
diode is monitored as a DC sweep of the Voltage from 0.25V to 1.5V.
Curve tracer
OPEN
SHORT
RESISTOR
DIODE
ZENER
CAPACITOR
EMITTER BASE
EMITTER COLLECTOR
Sinusoidal Voltage and current
Effective Voltage = 0.707 * Peak [Also know as Root Mean Square (RMS)]
 do this in the reverse order (square, mean, root) to get an RMS
number.
Half cycle average = 0.637 * Peak
Peak Voltage = 1.414 * effective
Effective Voltage = 1.11 * average
Transistor
configuration (bipolar)
letter
Meaning
For memorization
BEC common
Bob eats carols
PVI gain
Pretty veal in
ABG alpha, beta,
gamma a big garage
LMH input impedance
liking mostly her
HML output impedance
hot moist loins

NPN  negative, positive, negative  (Not Pointing iN)
PNP  positive, negative, positive
* Bipolar transistors
are current controlled devices. FET transistors or Voltage controlled.
* A transistor is said to be in its active mode if it is operating
somewhere between fully on (saturated) and fully off (cutoff).
* Base current tends to regulate collector current. By regulate, it is
meant that no more collector current may exist than what is allowed by
the base current.
* The ratio between collector current and base current is called "Beta"
(β) or "hfe". hfe varies and is not a good parameter.
* β ratios are different for every transistor, and they tend to change
for different operating conditions.
* The Vbe (Voltage across the base and emitter diode junction) is about
0.6 to 0.8V.
*Vcc is collector Voltage, Vee is emitter Voltage referring to NPN type
Transistor calculations
The transistor above has a hfe of 100 and we want 20mA and 5V at
the collector.
hfe = Icollector / Ibase and Ib = Ic / hfe, Vbe = 0.7V
Ib = 20mA / 100 = 0.2mA
+12V  IbRb  0.7V = 0 so Rb = (V  Vbe) / I or Rb = (12V  0.7V) /
0.0002A = 56,500 Ohms
AND
+12V  IcRc  5V = 0 so Rc = (V  Vce) / I or Rc = (12V  5V)
/ 0.02A = 350 Ohms
Transistor as a
switch
The
Gnd out Vc is ~ (about) 0.05 to 0.2V at saturation.
Common emitter circuit for a 200ma load and hfe = 100.
Ibase = Icollector / hfe (0.002 = 0.200 / 100)
R2 = V1  Base Emitter V drop / Ibase (5650 = 12 
0.7 / 0.002) Round R2 down to the standard 5.6k, 5% value due to the
drop in gain or hfe.
This switch is an inverter. When the base is high the output is low or
sinks current.
As the the transistor goes into saturation (full on) the hfe rating
drops off (gain decreases).
Protect the collector from going lower than the base with a reverse
diode to ground at the collector, as in AC loads. Or a diode reversed
biased across an inductor load.
Emitter follower
The emitter follower or Voltage
follower output follows the input minus the Vbe Voltage drop of about
0.7V. The advantage of this circuit is you can buffer the driver signal
from the load. This circuit has current gain and can source low
impedance loads.
ΔIe = ΔVb / R1
ΔIb = 1 / (hfe +1) * ΔIe = ΔVb / R(hfe + 1)
Rin = (hfe + 1) * R1 + R2
Transistor as an
amplifier
More on the way