WEBVTT 00:00.640 --> 00:04.400 When designing hardware, especially for portable gadgets or embedded systems. 00:04.400 --> 00:08.680 One of the biggest concerns is power efficiency. 00:10.040 --> 00:10.720 But why? 00:11.120 --> 00:19.960 Because if a device is powered by a battery, it needs to use as little energy as possible to last longer, 00:20.000 --> 00:24.560 stay cooler, and work reliably without failure. 00:24.760 --> 00:37.480 So basically, in circuits, heat equals inefficiency, and power consumption in a circuit isn't random. 00:37.480 --> 00:42.240 It follows the behavior of three key electromagnetic properties. 00:43.360 --> 00:45.080 The one is resistance. 00:49.040 --> 00:52.480 Capacitance and inductance. 00:53.720 --> 01:01.440 And among this, resistance plays the major role in consuming the electrical energy and turning it Into 01:01.600 --> 01:06.160 heat, which is essentially wasted energy. 01:06.640 --> 01:08.360 Now let's first understand how. 01:08.680 --> 01:11.680 Two important terms that form the foundation of this topic. 01:12.440 --> 01:13.880 The first is energy. 01:15.240 --> 01:19.040 Energy is basically the ability to do work. 01:19.120 --> 01:22.880 Now in electrical systems it is measured in joules. 01:24.240 --> 01:30.840 And the power is the rate at which energy is consumed or transformed. 01:30.840 --> 01:46.920 It is measured in watts or uppercase W, where basically the one watt equals to one joule per second. 01:48.280 --> 01:51.360 So one joule second. 01:52.560 --> 01:58.720 Now think of it this way if energy is how much work you can do. 01:59.040 --> 02:02.440 The power is how fast you do it. 02:03.680 --> 02:06.400 Now let's understand the stored energy in batteries. 02:06.960 --> 02:18.960 So imagine you have a backup battery and labeled as 240 watt hour. 02:20.160 --> 02:22.600 So what does this mean practically? 02:23.320 --> 02:33.600 So it basically means it can deliver 240W of power steadily for one hours. 02:33.880 --> 02:42.320 So if we want to convert watt hours into joules, which we need to do that to understand the total energy 02:42.360 --> 02:46.560 stored, we multiply by the number of seconds in an hour. 02:46.920 --> 03:05.600 So basically 240 watt hours multiplied by 3600 seconds Hours and it will be basically equal to 03:07.120 --> 03:10.240 864,000 03:11.560 --> 03:12.240 joules. 03:13.280 --> 03:20.080 Now this means the battery stores 864,000 joules of energy. 03:21.520 --> 03:35.600 And to put it another way, that's basically enough to power a 60 watt device continuously for 4 hours 03:35.600 --> 03:54.040 or 120 watt device for two hours, or 240 watt device for one hours, or 480 watt device for 30 minutes. 03:55.400 --> 04:04.560 That's basically how the battery labeling works in electronics. 04:04.560 --> 04:09.320 We calculate power using a simple but powerful formula. 04:10.720 --> 04:16.560 P equals v and I. 04:18.000 --> 04:19.880 This is power. 04:21.200 --> 04:27.160 Remember power is watts, V is voltage. 04:28.920 --> 04:37.960 Basically is V and I is current through the component in amperes. 04:39.360 --> 04:45.120 Now this tells us exactly how much electrical energy is being used at any moment. 04:45.400 --> 04:48.560 Now, because of the official definitions of voltage and current. 04:48.920 --> 04:52.480 This is also defines what a what actually is. 04:53.200 --> 04:57.880 So one watt equals one volt. 04:57.920 --> 05:01.680 Multiply by one amperes. 05:02.960 --> 05:10.360 In other words, one that is one volt times one ampere. 05:10.720 --> 05:20.080 So in a circuit, if we have ten amps or let's actually use our phone charger, right. 05:20.920 --> 05:30.900 If your phone charger is ten watts delivers ten watts of power, it will be basically probably five 05:30.900 --> 05:35.280 volts multiplied by two amperes. 05:35.560 --> 05:38.720 Now go and read your chargers. 05:40.800 --> 05:41.560 Rates. 05:42.480 --> 05:49.240 So here I have 33W of charger. 05:51.280 --> 05:53.240 It also charge 15W. 05:53.440 --> 06:04.340 So it is written here that 15W is basically five volts multiplied by three ampere so it delivers five 06:04.340 --> 06:05.920 volts at three amperes current. 06:07.200 --> 06:18.440 So if I, if I and I have 33W some shame phone charger I have here, it says 33W which is fast charging 06:19.480 --> 06:23.200 and it delivers 33W. 06:24.640 --> 06:28.880 Fast output is 11V and three amperes. 06:28.880 --> 06:29.320 Yeah. 06:29.360 --> 06:35.760 It delivers 33W using 11V, volts and three amperes. 06:36.520 --> 06:43.320 Now go and read the power efficiency of other electronic components. 06:43.320 --> 06:44.320 It is interesting. 06:45.080 --> 06:45.720 Believe me. 06:47.160 --> 06:50.720 Now we have learned about this. 06:52.200 --> 06:52.480 Yeah. 06:52.560 --> 06:58.000 And you also learned about the passive components in our previous lectures, including capacitors, 06:58.000 --> 06:58.960 inductors. 06:59.520 --> 07:05.320 You will also learn about the resistors here as well, which is an important component. 07:06.440 --> 07:11.360 Also important topic to understand how CPUs central processing units work. 07:12.640 --> 07:13.080 Yeah. 07:13.400 --> 07:20.320 Now let's break down each type of passive component behaves with respect to energy use. 07:20.960 --> 07:24.400 So basically the capacitors. 07:26.440 --> 07:35.880 When charging, a capacitor lets the current flow temporarily and once fully charged, it blocks DC 07:35.880 --> 07:37.200 current completely. 07:37.360 --> 07:40.960 And at that point it consumes almost almost no power. 07:41.280 --> 07:46.120 But not zero power because not component. 07:46.160 --> 07:49.960 No, there's no component that is 100% power efficient. 07:50.680 --> 07:58.600 And it also stores energy in an electric field between its place and for the inductors or inductance, 08:00.000 --> 08:02.930 we have what an In inductance. 08:02.970 --> 08:06.570 At first, they resist changes in current. 08:06.930 --> 08:15.250 After the current stabilizes, the voltage across them drops to near zero, and in a steady state DC 08:15.250 --> 08:20.370 conditions, they also consume very, very little power, but again, not zero. 08:21.370 --> 08:24.850 Now this their energy in magnetic field. 08:26.170 --> 08:27.890 And also we have the resistors. 08:29.690 --> 08:34.290 Resistors basically always always allow current to flow. 08:34.730 --> 08:36.610 Resistors do not store energy. 08:36.730 --> 08:46.730 And resistors continuously convert electrical energy into heat which is basically heat is basic means 08:46.730 --> 08:49.770 inefficiency in electrical circuits. 08:51.130 --> 08:59.730 Now these in simple DC circuits only resistors are responsible for continuous power consumption. 09:00.770 --> 09:05.330 These are not 100% percent efficient and not compare. 09:05.330 --> 09:12.530 But compared to this, capacitors, resistors, capacitors and inductors consume little power. 09:12.530 --> 09:18.650 But resistors basically turns your energy into heat. 09:19.930 --> 09:24.770 Now let's dig deeper into how resistors dissipate power. 09:25.370 --> 09:32.290 Now we will start from the basic power formula we have learned so far. 09:33.610 --> 09:35.290 You will use this formula a lot. 09:36.290 --> 09:37.850 Multiply by I. 09:38.410 --> 09:48.050 Now this is let's substitute the Ohm's law which remember Ohm's law was v equals I multiplied by r. 09:49.650 --> 09:57.730 So basically what we will do is p equals I multiplied by I r p. 09:57.930 --> 10:11.850 And this is equals to power Our two and R, or alternatively, what we can get is we can substitute 10:12.570 --> 10:23.850 I and V and we will get I, v, I and p v power R. 10:25.290 --> 10:27.650 And the important takeaway from this formula is. 10:30.170 --> 10:37.330 Power increases with the square of the current, and power also increases with the square of the voltage 10:37.970 --> 10:38.450 here. 10:39.730 --> 10:45.690 Now this explains why modern electronics often aim to reduce current levels, because even a small increase 10:45.690 --> 10:48.570 can cause a large increase in heat and energy loss. 10:49.850 --> 10:55.690 And the real world considerations is in real circuits, non component is perfectly ideal. 10:55.730 --> 11:04.330 As I said capacitors have a small internal resistance known as e S. 11:04.490 --> 11:04.810 R. 11:05.130 --> 11:07.730 This basically means equivalent series resistance. 11:08.450 --> 11:16.610 Resistors have a bit of inductance due to their physical structure, and inductors have some unintended 11:16.610 --> 11:17.570 capacitance. 11:18.050 --> 11:23.530 And at high frequencies, like those used in a wireless communication or modern processors, these secondary 11:23.530 --> 11:29.210 effects becomes very important here because the CPUs are so fast, right? 11:30.530 --> 11:33.290 So when you design circuits, you need to account for these effects. 11:33.290 --> 11:37.090 So make sure everything works correctly efficiently and stays cool. 11:38.290 --> 11:44.810 Now that we have discussed passive components, it's time to meet the real hero of modern electronics 11:45.450 --> 11:47.290 the transistors. 11:48.650 --> 11:51.690 Now, transistors are not a passive components. 11:52.970 --> 11:57.610 They are active components, meaning they can control the flow of electrical current electronically. 11:58.650 --> 12:04.250 So you may ask here why are they important. 12:04.450 --> 12:08.650 Now they can act as switches that turn on and off rapidly. 12:09.330 --> 12:17.170 They can act as amplifiers that boost signals, and they are the building blocks of all modern logic 12:17.450 --> 12:18.490 circuits today. 12:18.810 --> 12:24.330 Now, without transistors, we will not have computers, smartphones, or any modern digital technology. 12:25.490 --> 12:31.090 And before transistors, early computers used a mechanical switches to build logic circuits. 12:31.410 --> 12:38.090 Now let's walk you through a simple mechanical not gate using a push button switches. 12:38.130 --> 12:38.810 Now we have. 12:38.810 --> 12:44.890 The two switches are wired in series between 5V and 0V. 12:45.570 --> 12:51.090 Now the top switch is normally closed and the bottom switch is normally open. 12:51.930 --> 13:01.610 And when x equals zero, which basically means no buttons pressed, the top switch stays closed and 13:01.610 --> 13:09.010 the bottom switch stays open and the output is going to be five volts. 13:09.210 --> 13:10.530 This is logic one. 13:10.530 --> 13:22.690 And when the x is one the top switch opens which x equals one basically pressed. 13:24.130 --> 13:27.370 And yeah the bottom switch stays. 13:29.370 --> 13:34.250 Bottom switch closes and the output is zero volts. 13:35.610 --> 13:39.730 So a not gate made from two push button switches. 13:41.530 --> 13:43.170 The circuit inverts the input. 13:43.450 --> 13:47.690 It acts exactly like a not gate in a digital logic. 13:48.290 --> 13:51.210 However, mechanical systems had a major drawbacks. 13:51.210 --> 13:56.770 They were slow, they wore out over time, and they were large and bulky. 13:57.130 --> 14:02.650 Now, clearly a better solution was needed and the solution was electronic transistors. 14:04.090 --> 14:06.730 Transistors completely changed the game here. 14:06.730 --> 14:17.250 So modern transistors, which had a switch on or off in a billionth of a seconds or nanoseconds, and 14:17.250 --> 14:25.970 modern transistors are so small that millions of them fit on a single CPU or chip, and they use extremely 14:26.010 --> 14:29.330 like extremely low amounts of power. 14:29.570 --> 14:35.970 They allow digital logic to be implemented faster, smaller, and more efficiently than ever before, 14:36.210 --> 14:44.770 and voltage levels are typically five volts or sometimes 3.3V or 1.8V. 14:44.810 --> 14:50.370 Now, if you go to your computer's Bios, uh, in the CPU setting, you can see these voltages. 14:50.370 --> 14:50.850 Exactly. 14:50.850 --> 14:53.890 These voltages, uh, what these are. 14:53.930 --> 15:03.090 So this in modern transistors, these voltages basically mean one and zero volt basically means zero 15:04.530 --> 15:12.050 And by switching between these two states electronically in a very fast, very, very, very fast transistors 15:12.050 --> 15:17.210 performs all the calculation and data processing that make digital devices work. 15:18.650 --> 15:23.810 So what you will learn in next lectures is in the next lecture, we will explore the two critical types 15:23.810 --> 15:26.770 of transistors used in digital circuits. 15:27.290 --> 15:42.210 Uh mosfet mos fet basically means uh metal oxide semiconductor field effect transistors and CMOs, which 15:42.210 --> 15:46.770 is complementary metal oxide semiconductor. 15:47.570 --> 15:53.850 Now, these technologies enabled today's computers and smartphones to be fast, small, and energy efficient. 15:54.370 --> 15:57.130 Now, uh, thank you for watching this, uh, lecture. 15:58.210 --> 16:04.650 And get ready to dive into the world of modern transistors, which is a very interesting topic here.