Pat’s Electronics Lecture

1. Pat’s Electronics Lecture basics

2. Current flow Battery Water source Does useful “work” Pressure pushes water through pipe Current return Laptag MILL and SWEATSHOP Flow Does some kind of work (Water drain = “return”) Water Analogy (helped me…)

3. Water Analogy, cont’d

4. “Work” • In both pictures, potential energy is converted to “work”, where • Work = • Kinetic energy • Heat • Some other kind of potential energy • Physics note: Total Energy is conserved

5. + + + + Battery - - - - - What’s Happening • Electric charges can flow in conductors • Like charges repel • Unlike charges attract Because of the chemistry inside the battery, there is a voltage set up across the terminals

6. Battery What’s Happening • Electric charges can flow in conductors • Like charges repel • Unlike charges attract + + + + + + + + + + If we connect wires, they also become charged up - - - - - - - - - - -

7. Battery What’s Happening • Electric charges can flow in conductors • Like charges repel • Unlike charges attract + charges + charges

8. What’s really happening • Electrons are flowing out of bottom of battery, around to the top • Since they are negative, the direction of the current flow (by convention) is opposite their physical movement • It is MUCH EASIER to think of positive charges flowing, even though they are slightly fictitious

9. Typical Elements of a circuit • Wires • Voltage Sources • Electronic Components • Resistors • Capacitors • Inductors • Modular circuits (e.g. amplifiers) • Occasionally diodes and transistors

10. Wires • These are good conductors, with practically unimpeded flow of current • Electrons in metal form a kind of plasma • Any flowing current creates a magnetic field (which btw can be used to measure the current) • Size is measured by “AWG”, American Wire Gauge, since the 1850s

11. Interesting note on AWG • The gauge number is similar to decibel measurement for sound • 20 steps in AWG is (almost) a factor of 10 in wire diameter • For instance, #1 AWG wire is ~ 10x the diameter of #20 AWG • We typically use #20 to #24 for circuits

12. Voltage • (the Electrical version of pressure) • Measured with a meter, if time variation is slow enough • Measured with a scope and typically a scope probe if fast time variation • Hazards: • HIGH VOLTAGE CAN KILL YOU • (actually it’s the current through your heart…)

13. Pressure is not exactly Voltage • One difference: voltage is always measured between two points (e.g. a meter 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

14. Water flow is not exactly Electrical current • Water can flow even when there is not an (obvious) return path

15. 2 hazards we will encounter • 1: DO NOT USE A SCOPE OR METER TO 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

16. 2d hazard: Death • High voltages in our lab can kill you. Best case scenario: you accidentally touch a high voltage terminal, and current starts to flow through your arm. If this current is much larger than your nerve impulses, you can no longer pull your arm away, because your muscles don’t receive the command. It hurts. You begin to think about how dumb you were to have one hand resting on ground while you poked around with the other one. Next, some guy who also didn’t listen grabs onto you to try to pull you away. Current flows through him, too, so he is useless. Finally someone who paid attention 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.

17. High Current • This can also be dangerous: • wires can heat up, and cause fires. • Circuit elements (wires) can literally explode if a lot of energy is dumped into them quickly • More subtly, interrupting a high current can give a high-voltage transient!!! Of all the hazards, this is the only one I personally had experience with that actually did kill a guy. (We will get to the reason for this.)

18. Resistors • Resistors impede the flow of electrical current • Like a pin-hole for water flow Water source High pressure Lower pressure • Constriction in pipe • resists the water flow  • need more pressure to get the same flow • pressure after the constriction is lower Similarly, there is a voltage drop across a resistor when current flows through it.

19. Resistors • Symbol • Measured in ohms: A resistance of 1 ohm will let 1 Amp of current flow for a voltage drop of 1 Volt (across the resistor).

20. Ohm’s Law

21. Area A length L Computing resistance • Resistance Where ρ (rho) is the “resistivity” of the material L is the length A is the area =

22. Some Resistivities

23. 0 1 2 3 4 5 6 7 8 9 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

24. 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 = 2…etc.

25. From http://www.token.com.tw/resistor/image/color-code.jpg

26. Simple Circuit Diagrams 1 • 1 Voltage Source (e.g. battery) • 1 resistor Given a 9 V battery, and a 1000 ohm resistor, what current will flow?

27. Simple Circuit Diagrams 2 • Resistors in series:

28. Simple Circuit Diagrams 3 • Resistors in parallel:

29. Convenient formulas: • Series resistors: • Parallel resistors: Note: it may help to think about the construction of a resistor

30. Another circuit

31. Water source High pressure Lower pressure …think about what happens in this arrangement:

32. What about this one? Hint: symmetry helps

33. Other useful components • Inductors • Capacitors • Diodes • Integrated Circuits (e.g. RF amplifier) • MOSFETs • Occasionally transistors • Rarely vacuum tubes

34. Electrical Power • Power is rate of dissipation of energy • Also rate of getting work done • Energy is conserved, so if we are not storing any energy: Power in = Power out + heat dissipated as losses

35. AC Voltage, Current • AC stands for alternating current • Nevertheless people still talk about “AC current” coming out of the wall. • The voltage alternates: if you had a really fast meter, you would see the polarity reversing 60 times a second* * Or just use an oscilloscope, BUT DON”T HOOK IT UP DIRECTLY

36. Water source/sink Water source/sink Water analogy: • 2 buckets on a see-saw

37. Water source/sink Water source/sink Water analogy: • 2 buckets on a see-saw

38. Why AC? • See “War of Currents” on wikipedia • Edison wanted DC • Tesla wanted AC • No good way to transform DC to a different voltage (at least in 1900) • Transmission requires high current • Must generate near point of load • AC can be transformed up to high voltage, low current, for transmission, then back to safer levels (110 V) near point of load

39. AC Outlet: 110 V (rms) Low side, or neutral High side, or line Ground 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

40. AC Voltage Measurement Level is quoted as • Peak-to-peak (least ambiguous) • Peak • RMS = root mean square, which is the average value of the square of the voltage. This is what a typical handheld voltmeter reads on the AC setting. • 110 V is the RMS value, peak is around 160 V, or

41. 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 “primary” winding “secondary” winding

42. Transformers, cont’s where Also Note: Power is conserved:

43. Capacitors • Symbols: • Let AC through, but not DC; another way of saying this is that they tend to keep the voltage across them constant • Have an impedance (not a resistance because they don’t dissipate any power)

44. Capacitor construction 2 conductors separated by a physical space d A C, in Farads, is a measure of how much charge can be stored for a given voltage

45. Water Model • Water balloons in a sealed oil-filled enclosure:

46. Water Model • Water balloons in a sealed oil-filled enclosure:

47. Water Model • Water balloons in a sealed oil-filled enclosure:

48. Water Model • Water balloons in a sealed oil-filled enclosure:

49. Capacitors, cont’d • Often the gap is filled with a “dielectric” material to increase the capacitance; using an insulator also allows the gap to shrink, d  0, but voltage stays 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, or electrolytic – advantage is higher capacitance • Ugly fact that we will not worry about: most dielectrics change their value as they are biased to higher voltages!

50. Inductors • Symbol • Let DC through, but not AC; another way of saying this is that it tends to keep the current flowing through it at a constant level • Have an impedance (not a resistance because they don’t dissipate any power)