SAFETY PART 1

1. SAFETY PART 1 CHAPTER 2 CHAPTER 2

2. OBJECTIVES In this chapter you will learn • Why employers are so safety conscious and why you should be, too. • How your eyes, ears, nose, throat, and skin are susceptible to harm from laboratory accidents. • What electrical shock is, and how it can affect your heart. • How today's solid-state circuits are safer than those of the vacuum tube era. CHAPTER 2

3. How to avoid danger while working on electrical circuits. • How to handle toxic and hazardous chemicals safely. • How hand tools can be more dangerous than power tools. • How to avoid safety problems when working with power tools. • How to protect your voltage-sensitive projects from the "static electricity monster." • What first-aid steps to take if an accident occurs in the laboratory. • About environmental concerns with regard to product design and development. CHAPTER 2

4. SAFETY: WHO CARES? Who cares about safety? Well, your employer for sure and, we hope, you too. For your employer, safety is primarily an economic and legal issue; for you, it is a personal and, when your colleagues are involved, a moral concern. CHAPTER 2

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6. BODY PARTS SUSCEPTIBLE TO DAMAGE The human body is a fragile thing. It is easily cut, bruised, burned, irritated, shocked, and poisoned. External organs associated with our five senses and internal organs vital to our very lives are susceptible to injury in the school or workplace. CHAPTER 2

7. COVERING YOUR FIVE SENSES Although bionics is the current rage, and electronics has contributed mightily to its development, most would agree that the real thing is still the best. To keep our eyes, ears, nose, throat, and skin safe from harm, we must first see how they can be hurt when exposed to hazardous conditions. CHAPTER 2

8. AT THE HEART OF THE MATTER • Of all the internal organs, the heart is certainly the most vital. If it stops, even for only 4 to 6 minutes, death can result. Many factors can cause the heart to stop beating. Here, however, only the most rele­ • vant one-electrocution, or electrical shock-is considered. Let's see just what electrical shock is and how it can destroy the heart. CHAPTER 2

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11. HOW MUCH CURRENT IS ENOUGH TO KILL? One way to increase current flow is to reduce circuit resistance. Body resistance may be quite high if skin moisture is low and there are no cuts or abrasions at the point of electrical contact. In such cases, little current will flow and only a mild shock may result. Nonetheless, if any of these fac­tors is reversed, resistance will be lowered and large amounts of current can result. If the path for current flow is through the chest, the heart can re­ceive a lethal dose of current, an electrical shock. The heart will then most likely go into fibrillation (rapid, irregular muscle contraction) and stop beating. CHAPTER 2

12. A mere 1 to 20 milliamperes (mA) can cause a painful sensation; at 30 mA, breathing may stop; and 100 to 300 mA is enough to cause electrocu­tion. Clearly, even small amounts of unwanted current through the body can be very dangerous to your health. CHAPTER 2

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14. WHERE THE DANGER LIES It is time to look at where in the school laboratory or workplace the danger to your safety lies. Problem areas and practical solutions will be identified. Although specific advice in the form of “do's and don's” will be given, keep in mind that maintaining a safe working environment isn't complicated. It involves just four simple rules: CHAPTER 2

15. 1. Keep your work area neat and orderly. Being able to see what you have and what you are doing will eliminate many problems. 2. Be alert and attentive at all times. Distractions of any kind can only leave you open to risk. 3. Know the correct safety procedures. If you are not sure how to operate safely a piece of test equipment, a tool, or any machinery, ask your instructor. There is a safe way to do everything. Learn what it is and do it. 4. If an accident does occur, know what action wetake. Be familiar with the basic first-aid measures that could mean the difference between a quick re­covery and a serious medical complication. CHAPTER 2

16. The Do's • Do work with one hand behind your back while testing live circuits. In that way if you complete the path for current flow, at least it won't be through your heart. • Do use an isolation transformer while working on ac-powered equipment. This device isolates the powered equipment from the power source, adding a strong measure of safety. • Do make sure that all capacitors (components that store an electrical charge) are discharged before beginning troubleshooting. Use an insulated screwdriver to short out capacitor leads. • Do use three-conductor grounded line cords and polarized plugs with ac-operated equipment. Both items reduce the danger from short-circuited chassis. • Do keep your fingers out of live chassis. Test all circuits with a voltmeter or specially designed test lamps. CHAPTER 2

17. The Don't • Don't install or remove any electronic compo­nents while the circuit is connected to a power source. Following this procedure will protect you as well as the component. • Don't over fuse. Using a fuse with a higher rating than is recommended only defeats the fuse's purpose. • Don't work with wet hands. As noted earlier, if body resistance goes down, current flow goes up. Even sweat can moisten the hands enough to cause excessive current flow. • D Don't cut wires carrying electricity. Again, it isn't just the ac line cord that is lethal (Capable of causing death ). Assume all wires carry enough current to harm you. • Don't disconnect electrical devices from the wall outlet by pulling on the line cord; pull the plug handle. CHAPTER 2

18. SUMMARY Congratulations again-assuming, of course, that you did indeed read this chapter on safety. We dealt. general terms, discussing first just why it is so important to care about safety. Then, after looking at the body parts are susceptible to harm, we focused on where the dangers lie. We examined the risks related to electrical shock, toxic and hazardous chemicals, and misuse of hand and power tools, the dangers of static electricity to projects, and industry wide environmental concerns. In the coming chapters you will be full reminded of what is presented here. You will also read about additional safety precautions when the pieces of equipment and construction procedures are introduced. Now, before you rush on to Chapter ( don't forget to take the safety test in Appendix A). CHAPTER 2

19. VOLTAGE REGULATORSPART 2 CHAPTER 2 CHAPTER 2

20. OBJECTIVES • Describe the basic concept of voltage regulation • Discuss the principles of series, shunt, and switching voltage regulation • Discuss IC voltage regulators and some of their applications CHAPTER 2

21. INTRODUCTION The purpose of voltage of regulation is to maintain a precise voltage output from a power supply despite load and input voltage variations. There are basically two categories: linear and switching. As with many systems discrete device circuits are being replaced with integrated circuits. We will discuss a few of the IC type regulators. CHAPTER 2

22. VOLTAGE REGULATION Line regulation is the maintenance of a specific output voltage despite changes in input voltage. How well a regulator performs line regulation can be determined by the formula below. CHAPTER 2

23. VOLTAGE REGULATION Load regulation is the maintenance of a precise output voltage despite changes in load resistance. How well a regulator performs load regulation can be determined by the formula below. No-load (NL) Full-load (FL). Load Regulation = (VNL - VFL)/VFL)) 100% CHAPTER 2

24. BASIC SERIES REGULATORS With series regulation the control element is in series with the input and output. CHAPTER 2

25. BASIC SERIES REGULATORS The Zener diode sets the reference voltage for the non-inverting input of the op-amp. Any changes in the output are fed back to the inverting input of the op-amp. The difference voltage output of the op-amp biases the transistor to correct the output voltage for the overall circuit. The output of this regulator can be determined by the formula below. VOUT (1 + (R2/R3) )VREF CHAPTER 2

26. BASIC SERIES REGULATORS Overload protection for a series regulator protects the control element in the case of a short or an unusually heavy load (low RL). Q2 is biased by the voltage drop across R4. When load current exceeds the predetermined level Q2 diverts current from the base of Q1 cause Q1 to conduct less. The load current maximum can be determined by the formula below. IL(max) = .7V/R4 CHAPTER 2

27. BASIC SERIES REGULATORS fold-back current limiting allows operation up to peak load current. with a shorted output the current is dropped to a lower value (folded back). vr4=vr5 + vbe must be overcome before q2 conducts to limit current. CHAPTER 2

28. BASIC SHUNT REGULATORS In shunt regulation the control element is in parallel with the load. CHAPTER 2

29. BASIC SHUNT REGULATORS The shunt regulator is similar in design to the series. With attempted changes in output voltage, Q1 is biased to conduct more or less. This dynamic collector-emitter resistance and R1 act as a voltage divider network that maintains a specific voltage across the load. R1 limits current in the case of a short. CHAPTER 2

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31. BASIC SWITCHING REGULATORS The switching regulator is more efficient than the linear series or shunt type. This type regulator is ideal for high current applications since less power is dissipated. Voltage regulation in a switching regulator is achieved by the on and off action limiting the amount of current flow based on the varying line and load conditions. With switching regulators 90% efficiencies can be achieved. CHAPTER 2

32. BASIC SWITCHING REGULATORS With the step-down (output is less than the input) configuration the control element Q1 is pulsed on and off at variable rate based on the load current. The pulsations are filtered out by the LC filter. CHAPTER 2

33. BASIC SWITCHING REGULATORS The step-up configuration works much the same as the step-down. The difference is in the placement of the inductor and the fact that Q1 is shunt configured. During the time when Q1 is off the VL adds to VC stepping the voltage up by some amount. CHAPTER 2

34. BASIC SWITCHING REGULATORS With the voltage-inverter configuration the output voltage output is of opposite polarity of the input. This is achieved by VL forward biasing reverse biased diode during the off times producing current and charging the capacitor for voltage production during the off times. With switching regulators 90% efficiencies can be achieved. CHAPTER 2

35. IC REGULATORS Regulation circuits in integrated circuit form are widely used. There operation is no different but they are treated as a single device with associated components. These are generally three terminal devices that provide a positive or negative output. Some types are have variable voltage outputs. CHAPTER 2

36. IC REGULATORS A typical 7800 series voltage regulator is used for positive voltages. The 7900 series are negative voltage regulators. These voltage regulators when used with heatsinks can safely produce current values of 1A and greater. The capacitors act as line filtration. CHAPTER 2

37. IC REGULATORS Adjustable IC regulators are available with either positive or negative output. They can be set to produce a specific voltage by way of an external reference voltage divider network. Switching regulators are also available in IC form. CHAPTER 2

38. IC REGULATORS To increase the current capability of an IC regulator an external pass transistor can be used. CHAPTER 2

39. IC REGULATORS A current limiting circuit similar to the one discussed earlier can be used to protect the external pass transistor. CHAPTER 2

40. SUMMARY Voltage regulators keep a constant dc output despite input voltage or load changes The two basic categories of voltage regulators are linear and switching The two types of linear are series and shunt. The three types of switching are step-up, step-down, and inverting. Switching regulators are more efficient than linear making them ideal for low voltage high current applications. CHAPTER 2

41. IC regulators are available with fixed positive or negative output voltages or variable negative or positive output voltages. Both linear and switching type regulators are available in IC form. Current capacity of a voltage regulator can be increased with an external pass transistor. CHAPTER 2

42. EXAMPLES EXAMPLE 1: When the input to the particular voltage regulator decreases by 5V, the output decreases by 0.25 V. The nominal output is 15 V. Determine the line regulation in %/V. CHAPTER 2

43. SOLUTION The line regulation as a percentage change per volts is: CHAPTER 2

44. EXAMPLE 2: Determine the output voltage for the regulator in the following figure. CHAPTER 2

45. SOLUTION VREF = 5.1, the Zener voltage. The regulated output voltage is therefore: CHAPTER 2

46. EXAMPLE 3: Determine the minimum and maximum output voltages for the voltage regulator in the following figure. Assume IADJ = 50 A. CHAPTER 2

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48. SOLUTION When R2 is set at its minimum of 0 ohm. When R2 is set at its maximum of 5kohm. CHAPTER 2

49. EXAMPLE 4: What value of R1 is necessary in a 7805 regulator to provide a constant current of 0.5 A to a variable load that can be adjusted from 1 ohm to 10 ohm. CHAPTER 2

50. R1=10 Ohm CHAPTER 2