## Posts Tagged ‘Ohm’s Law’

### Transistors – Voltage Regulation Part XIV

Monday, October 22nd, 2012### Transistors – Voltage Regulation Part XIII

Monday, October 15th, 2012
Last time we learned how the Zener diode, an excellent negotiator of current, is involved in a constant trade off, exchanging current for voltage so as to maintain a constant voltage. It draws as much current through it as is required to maintain a consistent voltage value across its leads, essentially acting as voltage regulator in order to protect sensitive electronic components from power fluctuations. Now let’s revisit our example power supply circuit and see how Ohm’s Law is used to determine the amount of electric current, ## Figure 1
If you’ll recall, Ohm’s Law states that current flowing through a resistor is equal to the voltage across the resistor divided by its electrical resistance. In our example that would be R. In fact, the voltage across _{Limiting}R is the difference between the voltages at each of its ends._{Limiting} Applying this knowledge to our circuit, the voltage on one end is V. According to Ohm’s Law the equation which allows us to solve for _{Zener}I is written as:_{PS}
V – _{Unregulated}V) ÷ _{Zener}R_{Limiting} And if we have a situation where V, such as when the voltage of an unregulated power supply like a battery equals the Zener voltage of a Zener diode, then the equation becomes:_{Zener }( V) = 0_{Zener }And if this is true, then the following is also true:
R= 0_{Limiting} In other words, this equation tells us that if V, then the current _{Zener}I will cease to flow from_{PS} the unregulated portion of the circuit towards the Zener diode and the external supply circuit. Put another way, in order for I to flow and the circuit to work, _{PS}V must be greater than _{Unregulated}V._{Zener} Next week we’ll continue our discussion and see why the resistor ____________________________________________ |

### Transistors – Voltage Regulation Part XII

Sunday, October 7th, 2012
Let’s continue our discussion with regard to the example circuit discussed last time and see how the Zener diode works in tandem with the limiting resistor to control current flow and hold the output voltage at a constant level. ## Figure 1
To recap our discussion from last week, the unregulated power supply portion of the circuit in Figure 1 generates an unregulated voltage, V and converts it into a steady output voltage, _{Unregulated}V. Because these output terminals are connected to the ends of the Zener diode, _{Output}V is equal to the voltage put out by it, denoted as _{Output}V._{Zener} The Zener diode, an excellent negotiator of current, is essentially involved in a constant trade off, substituting electric current that originates in the unregulated power supply portion of the circuit for voltage, I, through it as it needs, its objective being to keep _{Z}V at a constant level, and it will continue to provide this constant output, despite the fact that V_{Output} varies considerably._{Unregulated} So, where does the current I, that is, the current flowing from the unregulated power supply area, as shown in Figure 1. _{PS}
I splits off from _{Z}I and continues on to the Zener diode, while current _{PS}I splits off from I on its way to the total internal resistance, _{PS}R, in the external supply circuit. _{Total} What this means is that when you add I together, you get I. Mathematically speaking this is represented as:_{PS}
= I_{Z} + I Why solve for I, _{PS}V, _{Unregulated}V, and _{Zener}R relate to each other with regard to the Zener diode. _{Limiting}____________________________________________ |

### Transistors – Voltage Regulation Part VI

Sunday, August 26th, 2012 Believe it or not as a kid in grade school I used to hate math, particularly algebra. None of my teachers were able to decipher its complexities and render it comprehensible to me or the majority of my classmates. Then in high school everything changed. I had Mr. Coleman for freshman algebra, and he had a way of making it both understandable and fun, in a challenging kind of way. With 40 years of teaching under his belt, Mr. Coleman knew exactly how to convey the required information in an understandable manner, and to this day I find his insights useful in solving engineering calculations.
Last time we began our discussion on Ohm’s Law and how it may be applied to our example circuit to solve for the electrical current flowing through it. Let’s continue our discussion to see how the Law applies to only one part of the circuit. Then, we’ll use a little algebra to show how the output voltage of an unregulated power supply is affected by changes in ## Figure 1
To help us see things more clearly, in Figure 1 we’ll cover up the inside workings of the unregulated power supply side of the circuit and concentrate on the external supply part of the circuit alone. Since Ris the same as the power supply output voltage, _{Total }V._{Output} In my previous article, we learned that according to Ohm’s Law, the current flowing through a resistance is equal to the voltage applied to it, divided by the resistance. The fact that I, flowing through :_{ }R_{Total}
Now let’s pull the cover off of the unregulated power supply again to see what’s going on within the circuit as a whole. ## Figure 2
In Figure 2 we can see that the current,
We can combine the above two equations for R, _{Internal}R, and _{Total}V:_{DC}
Then, by rearranging terms and applying the cross multiplication principle of algebra we can solve for R_{Total:}
This equation tells us that although V will fluctuate when _{Output}R does. This fact is demonstrated in our equation when we make use of algebra. That is to say, when a term changes on one side of the equation, it causes the other side of the equation to change as well. In this case, when _{Total}R changes, it causes _{Total}V to change in proportion to the fixed values of _{Output}V and _{DC}R._{Internal}Next time we’ll look at another shortcoming of unregulated power supplies, more specifically, how one supply can’t power multiple electrical circuits comprised of different voltages. ____________________________________________ |

### Transistors – Voltage Regulation Part V

Sunday, August 19th, 2012 I’m sure you’ve seen the television commercials warning about harmful interactions between prescription medications. By the same token electronic circuitry can also be adversely affected by certain combinations of electrical components, as we’ll discuss in today’s blog.
Last time we R increases, the electrical current, _{Total}I, decreases, and when R decreases, _{Total}I increases. In contrast to this increasing/decreasing activity of the total resistance Rdoesn’t fluctuate. Let’s explore Ohm’s Law further to see how the static effect of _{Internal}, Rcombines with the changing resistance present in _{Internal }R to adversely affect the unregulated power supply output voltage, _{Total}V, causing it to fluctuate._{Output}## Figure 1
In Figure 1 R are operating in series, meaning they are connected together like sausage links. In this configuration their two resistances add together as if they were one larger resistor. _{Internal} Generally speaking, Ohm’s Law sets out that the current,
In the case of the circuit represented in Figure 1, the resistors R are connected in series within the circuit, so their resistances must be added together to arrive at a total power demand. Voltage is applied to these two resistors by the same voltage source, _{Total}V. So, for the circuit as a whole Ohm’s Law would be written as:_{DC}
But, Ohm’s Law can also be applied to individual parts within the circuit, just as it can be applied to a single kitchen appliance being operated on a circuit shared with other appliances. Let’s see how this applies to our example circuit’s ____________________________________________ |

### Transistors – Voltage Regulation Part IV

Sunday, August 12th, 2012 We’ve all popped a circuit breaker sometime in our lives, often the result of making too heavy of an electrical demand in a single area of the house to which that circuit is dedicated. Like when you’re making dinner and operating the microwave, toaster, mixer, blender, food processor, and television simultaneously. The demand for current on a single circuit can be taxed to the max, causing it to pop the circuit breaker and requiring that trip to the electrical box to flip the switch back on.
Last time we began our discussion on unregulated power supplies and how they’re affected by power demands within their circuits. Our schematic shows there are two basic aspects to the circuit, namely, its direct current source, or R. Now let’s connect the power supply output terminals to an external supply circuit through which electrical current will be provided to peripheral devices, much like all the kitchen gadgets mentioned above._{Internal}## Figure 1
The external supply circuit shown in Figure 1 contains various electronic components, including electric relays, lights, and buzzers, and each of these has its own internal resistance. Combined, their total resistance is Current, notated as
I can change, that is, increase or decrease, depending on how many components the microprocessor has turned on or off within the external supply circuit at any given time. When R increases, electrical current, _{Total}I, decreases. When R decreases, electrical current _{Total}I increases. Next time we’ll continue our discussion on Ohm’s Law, introduced last week, to show how the static effect of R to_{Total} adversely affect an unregulated power supply’s output voltage.____________________________________________ |

### Transistors – Voltage Regulation Part II

Sunday, July 29th, 2012 I joined the Boy Scouts of America as a high schooler, mainly so I could participate in their Explorer Scout program and learn about electronics. I will forever be grateful to the Western Electric engineers who volunteered their personal time to stay after work and help me and my fellow Scouts build electronic projects. The neatest part of the whole experience was when I built my first regulated power supply with their assistance inside their lab. But in order to appreciate the beauty of a regulated power supply we must first understand the shortcomings of an unregulated one, which we’ll begin to do here.
Last time we began to discuss how the output voltage of an unregulated power supply can vary in response to power demand, just as when sprinklers don’t have sufficient water flow to cover a section of lawn. Let’s explore this concept further. ## Figure 1
Figure 1 shows a very basic representation of a microprocessor control system that operates three components, an electric relay (shown in the blue box), buzzer, and light. These three components have a certain degree of internal electrical resistance, annotated as R, and _{B}R respectively. This is because they are made of materials with inherent imperfections which tend to resist the flow of electric current. Imperfections such as these are unavoidable in any electronic device made by humans, due to impurities within metals and irregularities in molecular structure. When the three components are activated by the microprocessor chip via field effect transistors, denoted as FET 1, 2 and 3 in the diagram, their resistances are connected to the supply circuit._{L} In other words, R, and _{B}R create a combined level of resistance in the supply circuit by their connectivity to it. If a single component were to be removed from the circuit, its internal resistance would also be removed, resulting in a commensurate decrease in total resistance. The greater the total resistance, the more restriction there is to current flow, denoted as _{L}I. The greater the resistance, the more I is caused to decrease. In contrast, if there is less total resistance, I increases. The result of changing current flow resistance is that it causes the unregulated power supply output voltage to change. This is all due to an interesting phenomenon known as
where, Next time we’ll apply Ohm’s Law to a simplified unregulated power supply circuit schematic. In so doing we’ll discover the mathematical explanation to the change in current flow and accompanying change in power supply output voltage we’ve been discussing. ____________________________________________ |

### Transistors – Voltage Regulation

Sunday, July 22nd, 2012 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.
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