## Posts Tagged ‘output terminals’

### Transistors – Voltage Regulation Part XV

Sunday, October 28th, 2012### 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 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.____________________________________________ |