## Posts Tagged ‘circuit’

### Transistors – Voltage Regulation, Final Chapter

Monday, November 19th, 2012### Transistors – Voltage Regulation Part XVII

Monday, November 12th, 2012### Transistors – Voltage Regulation Part XVI

Monday, November 5th, 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 XI

Monday, October 1st, 2012
Without limits on our roadways things would get quickly out of hand. Imagine speeding down an unfamiliar highway and suddenly coming upon a sharp curve. With no speed limit sign to warn you to reduce speed, you could lose control of your car. Limits are useful in many situations, including within electronic circuits to keep them from getting damaged, as we’ll see in a moment.
Last time we introduced the Zener diode and the fact that it performs as a voltage regulator, enabling devices connected to it to have smooth, uninterrupted operation at a constant voltage. Let’s see how it works. ## Figure 1
In Figure 1 we have an unregulated power supply circuit introduced in a previous article in this series. We learned that this power supply’s major shortcoming is that its output voltage, V._{DC} It also varies with changes in, R changes when components are turned on and off by microprocessor and digital logic chips. When _{Total}V is not constant, those chips can malfunction, causing the device to operate erratically or not at all._{Output}But we can easily address this problem by adding a Zener diode voltage regulator between the unregulated power supply and the external supply circuit. See the green portion of Figure 2. ## Figure 2
Our power supply now consists of a Zener diode and a limiting resistor, I, flowing through the Zener diode. Without this limiting resistor, _{Z}I could get high enough to damage the diode, resulting in system failure._{Z}Next time we’ll 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. ____________________________________________ |

### Transistors – Voltage Regulation Part VIII

Sunday, September 9th, 2012 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. ## Figure 1
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. ____________________________________________ |

### 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.____________________________________________ |