patâs electronics lecture
TRANSCRIPT
-
8/3/2019 Pat s Electronics Lecture
1/68
Pats Electronics Lecture
basics
-
8/3/2019 Pat s Electronics Lecture
2/68
Water Analogy (helped me)
Does somekind of work
Watersource
Pressure pusheswater through pipe
Flow
(Water drain= return)
Laptag MILL andSWEATSHOP
Currentreturn
Current flow
Does usefulwork
Battery
-
8/3/2019 Pat s Electronics Lecture
3/68
Water Analogy, contd
Water Pressure(the higher the pressurethe more water flows)
Voltage(The higher the voltagethe more current flows)
Water Flow Rate(e.g. gallons per
minute)
Current(which is actually charge
flow rate: 1 coulomb/sec= 1 ampere)
-
8/3/2019 Pat s Electronics Lecture
4/68
Work
In both pictures, potential energy isconverted to work, where
Work =
Kinetic energy
Heat
Some other kind of potential energy
Physics note: Total Energy is conserved
-
8/3/2019 Pat s Electronics Lecture
5/68
Whats Happening
Electric charges can flow in conductors
Like charges repel
Unlike charges attract
Battery
+ + + +
- - - - -
Because of the chemistryinside the battery, there is
a voltage set up acrossthe terminals
-
8/3/2019 Pat s Electronics Lecture
6/68
Whats Happening
Electric charges can flow in conductors
Like charges repel
Unlike charges attract
Battery
- -- -
- - -- - - -
+ + ++ + +
+ ++ +
If we connect wires, theyalso become charged up
-
8/3/2019 Pat s Electronics Lecture
7/68
Whats Happening
Electric charges can flow in conductors
Like charges repel
Unlike charges attract
Battery
+ charges
+ charges
-
8/3/2019 Pat s Electronics Lecture
8/68
Whats really happening
Electrons are flowing out of bottom ofbattery, around to the top
Since they are negative, the direction ofthe current flow (by convention) isopposite their physical movement
It is MUCH EASIER to think of positivecharges flowing, even though they areslightly fictitious
-
8/3/2019 Pat s Electronics Lecture
9/68
Typical Elements of a circuit
Wires
Voltage Sources
Electronic Components Resistors
Capacitors
Inductors Modular circuits (e.g. amplifiers)
Occasionally diodes and transistors
-
8/3/2019 Pat s Electronics Lecture
10/68
Wires
These are good conductors, withpractically unimpeded flow of current
Electrons in metal form a kind of plasma
Any flowing current creates a magneticfield (which btw can be used to measurethe current)
Size is measured by AWG, American
Wire Gauge, since the 1850s
-
8/3/2019 Pat s Electronics Lecture
11/68
Interesting note on AWG
The gauge number is similar to decibelmeasurement for sound
20 steps in AWG is (almost) a factor of 10in wire diameter
For instance, #1 AWG wire is ~ 10x thediameter of #20 AWG
We typically use #20 to #24 for circuits
-
8/3/2019 Pat s Electronics Lecture
12/68
Voltage
(the Electrical version of pressure)
Measured with a meter, if time variation isslow enough
Measured with a scope and typically ascope probe if fast time variation
Hazards: HIGH VOLTAGE CAN KILL YOU
(actually its the current through your heart)
-
8/3/2019 Pat s Electronics Lecture
13/68
Pressure is not exactly Voltage
One difference: voltage is alwaysmeasured between two points (e.g. ameter has a common probe and a
measurement probe. The reason for this goes back to the
attraction of charges,
Still a very good analogy, though
meterVoltsFieldElectric distance
in voltagechange
-
8/3/2019 Pat s Electronics Lecture
14/68
Water flow is not exactly Electricalcurrent
Water can flow even when there is not an(obvious) return path
-
8/3/2019 Pat s Electronics Lecture
15/68
2 hazards we will encounter
1: DO NOT USE A SCOPE OR METERTO MEASURE THE AC LINE VOLTAGE!!!
(what is AC voltage? We will cover this)
WHY?
THE METER CAN LITERALLY EXPLODE
You might kill a $10,000 scope
Use a Wiggy instead
-
8/3/2019 Pat s Electronics Lecture
16/68
2d hazard: Death
High voltages in our lab can kill you.
Best case scenario: you accidentally touch a high voltage terminal, and currentstarts to flow through your arm. If this current is much larger than your nerveimpulses, you can no longer pull your arm away, because your muscles dont
receive the command. It hurts. You begin to think about how dumb you were tohave one hand resting on ground while you poked around with the other one.Next, some guy who also didnt listen grabs onto you to try to pull you away.
Current flows through him, too, so he is useless. Finally someone who paidattention to this lecture finds a non-conducting hook and saves both victims.
Worst case: sufficient current finds its way through your heart to stop it, too.
-
8/3/2019 Pat s Electronics Lecture
17/68
High Current
This can also be dangerous:
wires can heat up, and cause fires.
Circuit elements (wires) can literally explode ifa lot of energy is dumped into them quickly
More subtly, interrupting a high current cangive a high-voltage transient!!! Of all the
hazards, this is the only one I personally hadexperience with that actually did kill a guy.
(We will get to the reason for this.)
-
8/3/2019 Pat s Electronics Lecture
18/68
Resistors Resistors impede the flow of electrical
current
Like a pin-hole for water flow
Watersource
Constriction in piperesists the water flow need more pressure to get the same flow pressure after the constriction is lower
High pressure
Lower pressure
Similarly, there is a voltage drop across a resistor whencurrent flows throu h it.
-
8/3/2019 Pat s Electronics Lecture
19/68
Resistors
Symbol
Measured in ohms:
A resistance of 1 ohm will let 1 Amp of currentflow for a voltage drop of 1 Volt (across theresistor).
Ampere
Volt11
-
8/3/2019 Pat s Electronics Lecture
20/68
Ohms Law
IRV
RVI
I
V
R
-
8/3/2019 Pat s Electronics Lecture
21/68
Computing resistance
Resistance
Where (rho) is the resistivity of the material
L is the length
A is the area
A
LR
length L
Area A
=
-
8/3/2019 Pat s Electronics Lecture
22/68
Some Resistivities
Material Resistivity
Copper m 8107.1
Carbon m 5102
Silicon m 600
Water m 5108.1
Glass m 1010
Teflon m 2210
-
8/3/2019 Pat s Electronics Lecture
23/68
Resistor Marking
Color Code
First 2 bands = digits
3d band = power of 10 4th band = tolerance: gold 5%, silver 10%, none 20%
E.g. brown black red is
= 1 0 00
= (a one followed by a zero followed by 2 zeros)Other Notes:
3d band = gold: divide by 10
3d band = silver: divide by 100
01
2
3
4
5
6
78
9
-
8/3/2019 Pat s Electronics Lecture
24/68
Remember
Black = 0 (no color)
White = 9 (all colors)
Grey is close to white, so make it 8 Brown = ? Might as well be 1
The rest correspond to the spectrum
ROYGBV (You may have heard of this guy: Roy G. Biv)Red = 2etc.
-
8/3/2019 Pat s Electronics Lecture
25/68
From http://www.token.com.tw/resistor/image/color-code.jpg
-
8/3/2019 Pat s Electronics Lecture
26/68
Simple Circuit Diagrams 1
1 Voltage Source (e.g. battery)
1 resistor
Given a 9 V battery, and a 1000 ohm resistor, whatcurrent will flow?
-
8/3/2019 Pat s Electronics Lecture
27/68
Simple Circuit Diagrams 2
Resistors in series:
-
8/3/2019 Pat s Electronics Lecture
28/68
Simple Circuit Diagrams 3
Resistors in parallel:
-
8/3/2019 Pat s Electronics Lecture
29/68
Convenient formulas:
Series resistors:
Parallel resistors:
21 RRRtotal
21
21
RR
RRRtotal
Note: it may help to think about the construction of a resistor
-
8/3/2019 Pat s Electronics Lecture
30/68
Another circuit
-
8/3/2019 Pat s Electronics Lecture
31/68
think about what happens in this
arrangement:
Watersource
High pressure
Lower pressure
-
8/3/2019 Pat s Electronics Lecture
32/68
What about this one?
Hint: symmetry helps
-
8/3/2019 Pat s Electronics Lecture
33/68
Other useful components
Inductors
Capacitors
Diodes Integrated Circuits (e.g. RF amplifier)
MOSFETs
Occasionally transistors Rarely vacuum tubes
-
8/3/2019 Pat s Electronics Lecture
34/68
Electrical Power
Power is rate of dissipation of energy
Also rate of getting work done
CurrentVoltageP
Energy is conserved, so if we are notstoring any energy:
Power in = Power out + heat dissipatedas losses
-
8/3/2019 Pat s Electronics Lecture
35/68
AC Voltage, Current
AC stands for alternatingcurrent
Nevertheless people still talk
about AC current coming outof the wall.
The voltage alternates: if youhad a really fast meter, youwould see the polarityreversing 60 times a second*
* Or just use an oscilloscope, BUT DONT HOOK IT UP DIRECTLY
-
8/3/2019 Pat s Electronics Lecture
36/68
Water analogy:
2 buckets on a see-saw
Watersource/sink
Watersource/sink
-
8/3/2019 Pat s Electronics Lecture
37/68
Water analogy:
2 buckets on a see-saw
Watersource/sink
Watersource/sink
-
8/3/2019 Pat s Electronics Lecture
38/68
Why AC?
See War of Currents on wikipedia Edison wanted DC
Tesla wanted AC
No good way to transform DC to a differentvoltage (at least in 1900) Transmission requires high current
Must generate near point of load
AC can be transformed up to high voltage, lowcurrent, for transmission, then back to saferlevels (110 V) near point of load
-
8/3/2019 Pat s Electronics Lecture
39/68
AC Outlet: 110 V (rms)
Ground
Low side,or neutral
High side,or line
In an AC line cord, standard colors are: Green for ground, White for neutral, and Black for line
NOTE: in most AC wiring, BLACK is the hot, or high voltage, side
-
8/3/2019 Pat s Electronics Lecture
40/68
AC Voltage Measurement
Level is quoted as
Peak-to-peak (least ambiguous)
Peak
RMS = root mean square, which is the average valueof the square of the voltage. This is what a typicalhandheld voltmeter reads on the AC setting.
110 V is the RMS value, peak is around 160 V,or 2110
-
8/3/2019 Pat s Electronics Lecture
41/68
Transformer
2 sets of windings, with their magnetic fields coupled. Use iron to channel the field from one set to another Step up or down the voltage according to the turns
ratio
p
s
in
out
N
N
V
V
primary
winding
secondary
winding
-
8/3/2019 Pat s Electronics Lecture
42/68
Transformers, conts
ps NVV primary
secondary
#
#
turns
turnsN
ps IN
I1
where
ssppppin IVI
NNVIVP
1
Also
Note: Power is conserved:
-
8/3/2019 Pat s Electronics Lecture
43/68
Capacitors
Symbols:
Let AC through, but not DC; another way of saying thisis that they tend to keep the voltage across themconstant
Have an impedance (not a resistance because theydont dissipate any power)
CfZ
2
1||
-
8/3/2019 Pat s Electronics Lecture
44/68
2 conductors separated by a physical space
Capacitor construction
dAC 0 d
A
C, in Farads, is a measure ofhow much charge can bestored for a given voltage
meterFarad120 108.8
-
8/3/2019 Pat s Electronics Lecture
45/68
Water Model
Water balloons in a sealed oil-filledenclosure:
-
8/3/2019 Pat s Electronics Lecture
46/68
Water Model
Water balloons in a sealed oil-filledenclosure:
-
8/3/2019 Pat s Electronics Lecture
47/68
Water Model
Water balloons in a sealed oil-filledenclosure:
-
8/3/2019 Pat s Electronics Lecture
48/68
Water Model
Water balloons in a sealed oil-filledenclosure:
-
8/3/2019 Pat s Electronics Lecture
49/68
Capacitors, contd
Often the gap is filled with a dielectric materialto increase the capacitance; using an insulatoralso allows the gap to shrink, d0, but voltagestays the same without breakdown.
All dielectrics have a safe operating voltage,which is given as the voltage rating Sometimes the dielectric can only be charged in
one direction: the capacitor is polarized, orelectrolytic advantage is higher capacitance
Ugly fact that we will not worry about: mostdielectrics change their value as they are biasedto higher voltages!
-
8/3/2019 Pat s Electronics Lecture
50/68
Inductors
Symbol
Let DC through, but not AC; another way of saying thisis that it tends to keep the current flowing through it ata constant level
Have an impedance (not a resistance because theydont dissipate any power)
LfZ 2||
-
8/3/2019 Pat s Electronics Lecture
51/68
Inductor Construction
Any coil of wire
Sometimes iron is added to
increase the magneticstored energy, whichincreases the inductance
-
8/3/2019 Pat s Electronics Lecture
52/68
Inductance
N
A
turns#
Area
Length
ANL
2
0
Why N2?
Current flowing through the windings produces a magneticfield; more turns produces more field, proportional to thenumber of turns in a given length.
Each turn then picks up voltage from the changing magneticfield; with the turns in series the voltage adds, so the total is
proportional to the total number of turns.
-
8/3/2019 Pat s Electronics Lecture
53/68
Example circuit
Initially the switch is open, so no current is flowing
Close the switch: the inductor tends to keep thesame current flowing, which is zero.
Eventually the inductor looks like a wire, so thecurrent is given by Ohms law: I= VR
-
8/3/2019 Pat s Electronics Lecture
54/68
Water analog: heavy paddle-wheel
Flow
2. Paddle-wheel has heavy flywheelattached so it is hard to spin up,but once it is spinning it tends to
keep going
Valve
1. Once valve isopened, paddle-wheelbegins to spin
3. Eventually the paddle-wheel gets up to speed, and the flow
is limited by the resistance in the line
A th i it th d f hi h
-
8/3/2019 Pat s Electronics Lecture
55/68
Another circuit: the dangers of highcurrent
Initially the switch is open, so some current flows,such that I= V R
Close the switch: current starts to increase
Suppose the current builds up to 100x its initialvalue, then the switch is opened: what happens?
Inductor tries to keep the same current flowing, so
initially V = 100x the battery voltage
-
8/3/2019 Pat s Electronics Lecture
56/68
Generating high pressure due to current flow
Flow
Suppose valve is initially closed
Valve
Paddle-wheel is spinning slowly
Then we open the valve for some amount of time, letting theflow build up (paddle-wheel spins faster)
-
8/3/2019 Pat s Electronics Lecture
57/68
Generating high pressure due to current flow
Flow
Then valve is closed again
Valve
Paddle-wheel spins up
Flow throughthis leg stops
Flow transfers to
this leg
The pressure ahead of the resistance goes up, since thepaddle-wheel keeps spinning; eventually slows down to
steady state
-
8/3/2019 Pat s Electronics Lecture
58/68
Diodes
Symbol:
Function: only let current flow one direction
Convert AC to DC useful for power supplies,
detecting radio signals,
Pos Neg
-
8/3/2019 Pat s Electronics Lecture
59/68
Water Analog of a diode
A flap inside a pipe
flow: no flow:
-
8/3/2019 Pat s Electronics Lecture
60/68
SOLDERING
Solder works by forming a solution of the metalsbeing joined in the liquid solder.
So the solder needs to be hot enough to flow,BUT
Too much heat traveling up the leads willdestroy semiconductors!
The work pieces rather than the soldering ironmust melt the solder
When done, the two conductors being solderedshould look wetted
-
8/3/2019 Pat s Electronics Lecture
61/68
Solder wire
Has flux inside. Flux is a wax-like goothat has a few percent acid, for cleaningthe oxide layer from wires being soldered.For plumbing, the same thing happens except the flux is usually applied separately.
And you cant use lead solder anymore. And usually a torch is used instead of an iron.
-
8/3/2019 Pat s Electronics Lecture
62/68
Soldering Hints
Liquid solder conducts heat better than a dry tip,so it helps to put a dab of solder onto the tipbefore soldering. The associated flux can alsohelp clean up the tip.
It helps to tin the leads being solderedindividually before actually trying to solder themtogether.
The smoke comes from burning flux, not lead,but still probably not healthy to breathe it in.
Dont hold solder in mouth.
-
8/3/2019 Pat s Electronics Lecture
63/68
Soldering Irons - experience
Temperature regulated ones are crucial
Tips are special if you decide that youwant a sharper tip, you can sand the tip
down to a point, but it will dissolve a littlebit each time you use it and disappearbefore too long.
-
8/3/2019 Pat s Electronics Lecture
64/68
Solder joint cross section
From http://www.emeraldinsight.com/fig/2170250306001.png
-
8/3/2019 Pat s Electronics Lecture
65/68
Making a Circuit Board
1. Generate a layout, using some kind of PCB software. There areprograms that are free but that I know very little about (we use a badbut expensive tool, which is not even sold anymore):
Eagle, from http://www.cadsoftusa.com/
Kicad, from http://www.lis.inpg.fr/realise_au_lis/kicad/
Top Bottom
For our process, we generate a positive image: colored parts
(which print as black) will be copper, white parts no copper.
http://www.cadsoftusa.com/http://www.lis.inpg.fr/realise_au_lis/kicad/http://www.lis.inpg.fr/realise_au_lis/kicad/http://www.cadsoftusa.com/ -
8/3/2019 Pat s Electronics Lecture
66/68
Circuit Board, contd
2. Use laser printer to print layout (also calledartwork) on a transparency
3. Align top and bottom, and tape them together.
4. Slip a pre-sensitized board between them.
Top transparency
Bottom transparency
Circuit board, has copper on both sides,covered with photo-resist.
-
8/3/2019 Pat s Electronics Lecture
67/68
Circuit Board, etching
5. Expose in UV box for 5 minutes. The UV goesthrough the clear parts of the transparency, and doessomething to the photoresist.
6. Soak board in developer this washes off theexposed photoresist. (Dilute the developer solution 1part developer to 10 parts water.)
7. Rinse developer off using water8. Etch in Ferric Chloride solution. The
photoresist that is still on the copper prevents the
copper from being etched, at least for a while. Etchingusually completes in 15-45 minutes, depending on howold the solution is. You never know, so you need tokeep an eye on the progress.
-
8/3/2019 Pat s Electronics Lecture
68/68
Circuit board fab cautions and notes:
The ferric chloride solution will irritate your skinafter a few minutes, so a little is OK butgenerally you should rinse it off.
It will also eat holes in your clothes, if it gets on
them and dries there. ( mysterious little holesnext time you wear them) There is an aquarium heater and a bubbler in
the ferric chloride tank, to help speed things upremember to turn it off.
Dont pourferric chloride down the copper drainpipes.