During 6th grade science we had a chapter on Simple Machines, and my textbook listed a common lever as an example, the sort that can be used to make work easier. Its illustration showed a stick perched atop a triangular shaped stone, appearing very much like a teeter-totter in the playground. A man was pushing down on one end of the stick to move a large boulder with the other end. Staring at it I thought to myself, “That doesn’t look like a machine to me. Where are its gears?” That day I learned about more than just levers, I learned to expect the unexpected when it comes to machines.
Last time we learned that under patent law the machine referred to in federal statute 35 USC § 101 includes any physical device consisting of two or more parts which dynamically interact with each other. We looked at how a purely mechanical machine, such as a diesel engine, has moving parts that are mechanically linked to dynamically interact when the engine runs. Now, lets move on to less obvious examples of what constitutes a machine.
Would you expect a modern electronic memory stick to be a machine? Probably not. But, under patent law it is. It’s an electronic device, and as such it’s made up of multiple parts, including integrated circuit chips, resistors, diodes, and capacitors, all of which are soldered to a printed circuit board where they interact with one another. They do so electrically, through changing current flow, rather than through physical movement of parts as in our diesel engine.
A transformer is an example of another type of machine. An electrical machine. Its fixed parts, including wire coils and steel cores, interact dynamically both electrically and magnetically in order to change voltage and current flow.
Electromechanical, the most complex of all machine types, includes the kitchen appliances in your home. They consist of both fixed and moving parts, along with all the dynamic interactions of mechanical, electronic, and electrical machines.
Next time we’ll continue our discussion on the second hurtle presented by 35 USC § 101, where we’ll discuss what is meant by article of manufacture.
Posts Tagged ‘capacitor’
| Back in the early 1970s my dad, a notorious tightwad, coughed up several hundred dollars to buy his first portable color television. That was a small fortune back then. The TV was massive, standing at 24 inches wide, 18 inches high, and 24 inches deep, and weighing in at about 50 pounds. I think the only thing that made this behemoth “portable” was the fact that it had a carrying handle on top.
A major reason for our old TV being so big and clunky was of course due to limitations in technology of the time. Many large, heavy, and expensive electronic components were needed to make it work, requiring a lot of space for the circuitry. By comparison, modern flat screen televisions and other electronic devices are small and compact because advances in technology enable them to work with far fewer electronic components. These components are also smaller, lighter, and cheaper.
Last time we looked at the components of a simple unregulated power supply to see how it converts 120 volts alternating current (VAC) to 12 volts direct current (VDC). We discovered that the output voltage of the supply is totally dependent on the design of the transformer, because the transformer in our example can only produce one voltage, 12 VDC. This of course limits the supply’s usefulness in that it is unable to power multiple electronic devices requiring two or more voltages, such as we’ll be discussing a bit further down.
Now let’s illustrate this power supply limitation by revisiting our microprocessor control circuit example which we introduced in a previous article in this series on transistors.
In Figure 1 we have to decide what kind of power to supply to the circuit, but we have a problem. Sure, the unregulated power supply that we just discussed is up to the task of providing the 12 VDC needed to supply power for the buzzer, light, and electric relay. But let’s not forget about powering the microprocessor chip. It needs only 5 VDC to operate and will get damaged and malfunction on the higher 12 VDC the current power supply provides. Our power supply just isn’t equipped to provide the two voltages required by the circuit.
We could try and get around this problem by adding a second unregulated power supply with a transformer designed to convert 120 VAC to 5 VAC. But, reminiscent of the circuitry in my dad’s clunky old portable color TV, the second power supply would require substantially more space in order to accommodate an additional transformer, diode bridge, and capacitor. Another thing to consider is that transformers aren’t cheap, and they tend to have some heft to them due to their iron cores, so more cost and weight would be added to the circuit as well. For these reasons the use of a second power supply is a poor option.
Next time we’ll look at how adding a transistor voltage regulator circuit to the supply results in cost, size, and weight savings. It also results in a more flexible and dependable output voltage.
| Back when television had barely escaped the confines of black and white transmission there was a men’s clothing store commercial whose slogan still sticks in my mind, “Large and small, we fit them all.” It’s a nice concept, but unfortunately the same doesn’t always apply to electronic power supplies.
Last time we learned that when the electrical resistance changes on an unregulated power supply its output voltage changes proportionately. This makes it unsuitable for powering devices like microprocessor chips, which require an unchanging voltage to operate properly. Now let’s look at another shortcoming of unregulated power supplies, that being how one supply can’t fit both large and small voltage requirements.
Figure 1 shows the components of a simple unregulated power supply.
The diagram illustrates the voltage changes taking place as electric current passes through the supply’s four components, which ultimately results in the conversion of 120 volts alternating current (VAC) into 12 volts direct current (VDC).
First the transformer converts the 120 VAC from the wall outlet to the 12 volts required by most electronic devices. These voltages are shown at Points A and B. The voltage being put out by the transformer results in waves of energy which alternate between a positive maximum value, then to zero, and finally to a maximum negative value.
But we want our power supply to produce 12 VDC. By VDC, I mean voltage that never falls to zero and stays at a positive 12 volts direct current consistently. This is when the diode bridge and capacitor come into play. The diode bridge consists of four electronic components, the diodes, which are connected together to form a bridge and uses semiconductor technology to transform negative voltage from the transformer into positive. The result is a series of 12 volt peaks as shown at Point C.
But we still have the problem of zero voltage gaps between each peak. You see, over time the voltage at Point C of Figure 1 keeps fluctuating between 0 volts and positive 12 volts, and this is not suitable to power most electronics, which require a steady VDC current.
We can get around this problem by feeding voltage from the diode bridge into the capacitor. When we do that, we eliminate the zero voltage gaps between the peaks. This happens when the capacitor charges up with electrical energy as the voltage from the diode bridge nears the top of a peak. Then, as voltage begins its dive back to zero the capacitor discharges its electrical energy to fill in the gaps between peaks. In other words it acts as a kind of reserve battery. The result is the rippled voltage pattern observed at Point D. With the current gaps filled in, the voltage is now a steady VDC.
The output voltage of the unregulated power supply is totally dependant on the design of the transformer, which in this case is designed to convert 120 volts into 12 volts. This limits the power supply’s usefulness because it can only supply one output voltage, that being 12 VDC. This voltage may be insufficient for some electronics, like those often found in microprocessor controlled devices where voltages can range between 1.5 and 24 volts.
Next time we’ll illustrate this limitation by revisiting our microprocessor control circuit example and trying to fit this unregulated power supply into it.
| Electrical voltage flow and water flow have a lot in common. They’re both affected by fluctuations in supply, fluctuations which can adversely impact both performance and equipment integrity. Take for example a sprinkler that fails to cover a designated section of lawn due to heavy neighborhood demand. Everybody wants to water on the weekend when it’s been 90 degrees all week, and low water pressure is the result. There are times when it’s hard to get a glass of water. By contrast in the winter months, when water demands tend to be lower, water supplies are plentiful. This scenario of varying water pressure is analogous to what sometimes occurs within electric circuits.
In my previous blog article on wall warts, I described the operation of a simple power supply consisting of a transformer, diode bridge, and capacitor. Together, these components converted 120 volts alternating current (VAC) to 12 volts direct current (VDC). The wall wart power supply is fine for many applications, however it is unregulated, meaning if there are any sudden surges in power, such as spikes or dips caused by lightning strikes or other disturbances on the electric utility system, there could be problems.
Take for example a power supply that is used in conjunction with sensitive digital logic chips, like the one used in my x-ray film processor design shown in my last blog article. These chips are designed to run optimally on a constant voltage, like 5 VDC, and when that doesn’t happen input signals can fail to register with the computer program and cause a variety of problems, such as output signals turning on and off at will. In the film processor the drive motor may start at the wrong time or get stuck in an on modality. If power surges are high enough, microprocessor chips can get damaged, compromising the entire working unit.
The output voltage of an unregulated power supply can also vary in response to power demand, just as when sprinklers don’t have sufficient water flow to cover a section of lawn. Demand for power can change within a circuit when electrical components like relays, lights, and buzzers are turned on and off by digital logic chips.
Next time we’ll take a look at a basic concept of electrical engineering known as “Ohm’s Law” and how it governs the variable output voltage response of unregulated power supplies.
| What do wall warts, aka AC wall adapters, and microwave ovens have in common? Well, in previous blogs discussing microwaves, we saw how a microwave oven’s high voltage circuitry uses a transformer, diode, and capacitor to effectively convert AC voltage into DC voltage. Wall warts do much the same thing and in very much the same way.
If you will recall from our discussion of microwave ovens in the past few weeks, the transformer in a high voltage circuit transforms 120 volts into a much higher voltage, say 4000 volts, in order to make things work. The diode and capacitor within both the microwave and the wall wart are key to facilitating this magical act, but in the wall wart it happens at a much lower voltage, about 12 volts.
Last week we began exploring the inner workings of the wall wart. We discovered how its transformer converts the 120 volts emanating from your average wall outlet to the 12 volts required by most electronic devices. These voltages are shown at Points A and B in Figure 1 below. The fact that the voltage being put out results in waves of energy which alternate between a positive maximum value, zero, and a negative maximum value, makes it an unacceptable power source for most electronic devices. They require voltage that doesn’t alternate, and this is where the wall wart’s diode bridge and capacitor come into play.
Figure 1 – The Workings of the Wall Wart Transformer
The wall wart’s diode bridge consists of four electronic components, namely the diodes, which are connected together. This diode bridge goes a bit further than the single diode present in a microwave oven, because it doesn’t merely eliminate negative aspects of alternating voltage. It actually transforms negative voltage into positive voltage. The result is a series of 12 volt peaks as shown at Point C of Figure 1. In fact, we end up with twice as many voltage peaks, and this is important, as you’ll see below.
We still have the problem of zero voltage gaps to address. You see, over time the voltage at Point C of Figure 1 keeps changing between 0 volts and positive 12 volts. This can lead to problems, because many electronic devices require a consistent voltage of greater than zero to operate properly. For example, a light emitting diode (LED) might develop an annoying flicker, or you might end up hearing an irritating hum while listening to the radio. These annoyances are virtually eliminated by feeding voltage from the diode bridge into the capacitor, which gets rid of the zero voltage gaps between the voltage peaks.
Like a microwave’s capacitor, the one within a wall wart charges up with electrical energy as the voltage from the diode bridge nears the top of a peak. Then, as voltage begins its dive back to a zero value, the capacitor discharges its electrical energy to fill in the gaps between peaks. The result is the rippled voltage pattern at Point D of Figure 1. With the gaps filled in, the voltage is at, or close enough to, the 12 volts required to keep an electronic device operating properly when it is connected to the wall wart’s low voltage power cord.
Well, that’s it for our look at the wall warts that power our myriad of electronic devices. Next time we’ll switch to a totally topic and look at some of the basics of food manufacturing equipment design.
What would a cop show be without a crime scene, or better yet the obligatory dissection at the morgue? Forensic doctors performing autopsies have become commonplace, the clues they provide indispensable. Forensic engineers such as myself do much of the same thing, working our way backwards through time by dissecting industrial equipment and consumer products left in the wake of fires, injuries, and deaths.
Let’s do some forensic dissecting now to see what’s in a wall wart and how it works. The inside of a basic wall wart is shown in Figure 1.
Figure 1 - Inside The Wall Wart
You’ll note that a wall wart has four main components: a transformer, diode bridge, capacitor, and a printed circuit board (PCB). The PCB is constructed of plastic resin upon which is mounted copper strips. This makes a rigid platform base upon which electronic components are attached, namely the transformer, diode bridge, and capacitor. These components are soldered to the PCB, tying them together both mechanically and electrically. Now let’s see how the components of the wall wart work together to change the 120 volts coming from your standard wall outlet into the 12 volts needed to power a typical electronic device. We’ll use an instrument known as an oscilloscope to help us visualize what’s going on. See Figure 2.
Figure 2 – The Workings of the Wall Wart Transformer
What is depicted in the graph above is the oscilloscope’s ability to receive an electronic signal, measure it, graph it, and then display it on a screen. This enables us to see how the signal changes over time. At Point A, which represents the wall wart plugged into a wall outlet, the voltage alternates between positive 120 volts and negative 120 volts upon entering the wall wart, which will now act as a transformer.
The wall wart transformer then does as its name suggests, it transforms the 120 volts coming from the outlet into the 12 volts shown at Point B. You will note that this lower voltage also alternates between positive and negative values, just as the original 120 volts emanating from the wall outlet did. In one of my earlier blogs I explained that transformers only work when the electricity passing through them alternates over time. (Click here for a refresher: Transformers ) High voltage alternating electricity in one transformer coil creates magnetic fields that induce alternating electricity at a different voltage in a second transformer coil. So when you put alternating voltage into the transformer, you get alternating voltage out. But that’s not the end of the story. Many electronic devices operate on voltage that doesn’t alternate. What then? Will our handy wall wart still be able to bridge the electrical gap to fill our needs?
Next time we’ll see how the diode bridge and capacitor come into play to deal with the alternating voltage from the transformer in a manner eerily similar to a microwave oven’s high voltage circuit.
Ever been jolted with electric current? Like the time you’d just gotten out of the shower and went to plug in a lamp with damp hands? So what do you think the voltage was that caused that nasty biting feeling that resulted from your momentary lapse in good judgment?
Once, while operating a subway car at a railroad museum at which I was a member, I was inadvertently “electrocuted.” I went to turn on the lights inside the car, and unbeknownst to me the light switch was faulty. When I touched it I instantly became connected to the car’s 600 volt lighting circuit. With just a split second of contact the current passed through the tip of my right index finger, along my right arm, down the right side of my body, and out the tip of my big toe, finally exiting into the metal railcar’s body. The current actually burned a hole where it had exited through my boot. The experience was both frightening and painful, but fortunately did not result in any real injury. I was lucky that the current had bypassed my heart, because if it hadn’t, I might not be alive today.
That was 600 volts. Now imagine being jolted by the 4000 volts present in a microwave oven’s internal high voltage circuitry.
Last week we discovered how the high voltage circuit in a microwave oven converts the ordinary, everyday 120 volts alternating current (AC) present in our homes into a much higher voltage approximating direct current (DC). This is done by an internal component known as the capacitor. The capacitor is capable of storing large amounts of electrical energy, and this can result in microwave ovens presenting a danger even when unplugged.
A microwave oven capacitor is shown in Figure 1. If you happened to touch its wire terminals while it’s still charged, its power can rapidly discharge high voltage electrical current throughout your body. The electrical current from the capacitor can even stop your heart from beating, and this is exactly what caused the demise of a person featured on a soon to be released Discovery Channel program, Curious and Unusual Deaths. While being interviewed as an expert for the program, I was asked to explain this rather unique phenomenon of latent stored energy, and how it may present a threat.
Figure 1 – A Microwave Oven Capacitor
Remember, a microwave oven capacitor can remain charged with dangerous electrical energy for hours, even days, after the microwave oven plug is pulled from the wall outlet. The bottom line here is that you should not attempt to fix your microwave oven, unless you are trained and certified to do so.
Next week we’ll switch to a different topic, namely an electrical device known as a “wall wart.” That’s the black plastic adapter you plug into electrical outlets to power your cell phones, laptops, and other small electronics.
| The world of electricity is full of mysteries and often unanticipated outcomes, and if you’ve been reading along with my blog series you have been able to appreciate and come to some understanding of a fair number of them. This week’s installment will be no exception.
Last week we looked briefly at the high voltage circuit within a microwave oven. We discovered that the circuit contains a transformer that raises 120 volts alternating current (AC) to a much higher voltage, around 4000 volts AC. The circuit then transforms the AC into direct current (DC) with the help of electronic components known as a diode and capacitor. Let’s take a closer look at how the diode and capacitor work together to make AC into DC.
Let’s follow an AC wave with the aid of a device called an oscilloscope. An oscilloscope takes in an electronic signal, measures it, graphs it, and shows it on a display screen so you can see how the signal changes over time. An AC wave is shown in Figure 1 as it would appear on an oscilloscope.
Figure 1 – Alternating Current Wave
You can see that each wave cycle starts with a zero value, climbs to a positive maximum value, then back to zero, and finally back down to a maximum negative value. The current keeps alternating between positive and negative polarity, hence the name “alternating current.”
Within the microwave oven’s high voltage circuitry the transformer does the job of changing, or transforming if you will, 120 volts AC into 4000 volts AC. This high voltage is needed to make electrons leave the cathode in the magnetron and move them towards the anode to generate microwaves.
But we’re not done with the transformation process yet. The magnetron requires DC to operate, not AC. DC current remains constant over time, maintaining a consistent positive value as shown in Figure 2. It is this type of consistency that the magnetron needs to operate.
Figure 2 – Direct Current
The microwave’s diode and capacitor work together to convert the 4000 volts AC into something which resembles 4000 volts DC. First the diode acts like a one-way valve, passing the flow of positive electric current and blocking the flow of negative current. It effectively chops off the negative part of the AC wave, leaving only positive peaks, as shown in Figure 3.
Figure 3 – The Diode Chops Off The Negative Part of the AC Wave
Between the peaks are gaps where there is zero current, and this is when the capacitor comes into play. Capacitors are similar to batteries because they can be charged with electrical energy and then discharge that energy when needed. Unlike a battery, the capacitor charges and discharges very quickly, within a fraction of a second.
Within the circuitry of a microwave oven the capacitor charges up at the top of each peak in Figure 3, then, when the current drops to zero inside the gaps the capacitor comes into play, discharging its electrical energy into the high voltage circuit. The result is an elimination of the zero current gaps. The capacitor acts as a reserve energy supply to fill in the gaps between the peaks and keep current continually flowing to the magnetron. We have now witnessed a mock DC current situation being created, and the result is shown in Figure 4.
Figure 4 – The Capacitor Discharges to Fill In The Gaps Between Peaks
The output of this approximated DC current looks like a sawtooth pattern instead of the straight line of a true DC current shown in Figure 2. This ripple pattern is evidence of the “hoax” that has been played with the AC current. The net result is that the modified AC current, thanks to the introduction of the diode and energy storing capacitor, has made an effective enough approximation of DC current to allow our magnetron to get to work jostling electrons loose from the cathode and putting our microwave oven into action.
You now have a basic understanding of how to turn AC into an effective approximation of DC current. Next week we’ll find out how this high voltage circuit can prove to be lethal, even when the microwave oven is unplugged.
| My mom was a female do-it-yourselfer. Toaster on the blink? Garbage disposal grind to a halt? She’d take them apart and start investigating why. Putting safety first, she always pulled the plug on electrical appliances before working on them. Little did she know that this safety precaution would not be enough in the case of a microwave oven. Let’s see how even an unplugged microwave can prove to be a lethal weapon and, yes, we’re going to have to get technical.
Last week we talked about the magnetron and how it needs thousands of volts to operate. To get this high of a voltage out of a 120 volt wall outlet–the voltage that most kitchen outlets provide–the microwave oven is equipped with electrical circuitry containing three important components: a transformer, a diode, and a capacitor, and just like the third rail of an electric railway system these items are to be avoided. If you decide to take your microwave oven apart and you come into contact with high voltage that is still present, you run the risk of injury or even death. But how can high voltage be present when it’s unplugged? Read on.
First we need to understand how the 120 volts emitting from your wall outlet becomes the 4000 volts required to power a microwave’s magnetron. This change takes place thanks to a near magical act performed by AC, or alternating current. In the case of our microwave components, specifically its diode and capacitor, AC is made to effectively mimic the power of DC, or direct current, the type of current a magnetron needs. This transformation is made possible through the storage of electrical energy within the microwave’s capacitor.
Next week we’ll examine in detail how this transformation from AC to DC current takes place, as seen through a device called an oscilloscope.