Transistor Biasing: Through one of my previous articles you must have acquired good knowledge regarding transistors. But the base of a transistor is quite vulnerable to high currents, so a resistor is incorporated to limit the current and provide a safe biasing voltage.
The value of the base resistor of a transistor may be calculated through the below-given formula:. A resistor when placed in series with the LEDs regulates a proper flow of current through them. To calculate the value of a series LED resistor, the following formula may be used:. In Timing Circuits: The timing components used in timer and oscillator circuits always incorporate a resistor and a capacitor. Here the time taken to charge or discharge a capacitor constitutes the basic time pulse or trigger for the circuit.
A resistor is effectively used to control this charging and discharging process and its value is varied to obtain different time intervals. Surge Protection: The initial switch ON of a power supply may at times inflict a dangerous voltage surge into an electronic circuit, damaging its critical components.
A resistor when introduced in series with the supply terminals of the circuit helps in checking the sudden rise in voltage and averting possible harm. These resistors are generally of low values so that the overall performance of the circuit is not affected. The above basic examples must have provided you sufficient knowledge regarding the use of resistors in electronic circuits and helped you to understand what is the function of a resistor.
For further information, feel free to add your comments comments need moderation and may take time to appear. Q1: How many types of resistors are there based on the type of materials used? A: There are many kinds of resistors based on the type of material used to make the resistor: 1. Wirewound WW Resistors 2. Resistors are made from materials like copper or carbon, which make it difficult for the electrical charges to flow through a circuit. The most common type of resistor is a carbon resistor, which is a general purpose resistor, best suited for lower-powered circuits.
Some other common resistor types include the film resistor and the wire-wound resistor. Resistors are essential to many electoral circuits, and they can be applied to a myriad of different applications. Protect against voltage spikes. Resistors also protect components against voltage spikes. Components that are sensitive to a high electrical current, like LED lights, will be damaged if there is not a resistor to control the flow of the electrical current.
In addition, fuses and circuit breakers can also be used to protect your electrical circuit against voltage spikes. Provide the proper voltage. Resistors ensure components receive the proper voltage by creating a voltage drop, and they can protect a component from voltage spikes. Each component in an electrical circuit, like a light or a switch, requires a specific voltage. If a component in your circuit requires less voltage than the rest of your circuit, a resistor will create a voltage drop to ensure the component does not receive too much voltage.
The resistor will create a voltage drop by slowing down, or resisting, the electrons as they try to flow through the resistor. Similarly, placing a length of wire conductor near a positive charge will cause a charge gradient across the length of wire.
The charge at any point on the wire can be calculated using its distance from the source charge and known attributes of the material used in the wire. Positive charge owing to the absence of electrons will appear farther away from the positive source charge, while negative charge owing to the collection and surplus of electrons will form closer to the source charge.
Because of the electric field, a "potential difference" will appear between two points on the conductor. This is how an electric field generates voltage in a circuit. Voltage is defined as electric potential difference between two points in an electric field. Eventually, the charge distribution along the length of wire will reach "equilibrium" with the electric field.
This doesn't mean charge stops moving remember Brownian motion ; only that the "net" or "average" movement of charge approaches zero. Let's make up a galvanic or voltaic cell power source. Useful mnemonic: " an ion" is " an ion" is " A N egative ion". This movement goes towards the cathode. Note: Earlier we said that positive charge is the "absence" of electrons. Cations positive ions are positive because stripping away electrons results in a net positive atomic charge owing to the protons in the nucleus.
These cations are mobile in the galvanic cell's solution, but as you can see, the ions do not travel through the conductive bridge connecting the two sides of the cell. That is, only electrons move through the conductor. Based on the fact that positive cations move and accumulate towards the cathode, we label it negative positive charges are attracted to negative.
Conversely, because electrons move towards and accumulate at the anode, we label it positive negative charges are attracted to positive. This is because conventional current follows the flow of positive charge and cations, not negative charge. This is because current is defined as the flow of virtual positive charge through a cross-sectional area. Electrons always flow opposite to current by convention.
What makes this galvanic cell non-ideal is that eventually the chemical process generating the electric field through the conductor and causing electrons and charge to flow will come to equilibrium. This is because ion buildup at the anode and cathode will prevent the reaction from proceeding any further. Assume you're on a hill and you have some arbitrary path down the hill constructed with cardboard walls.
Let's say you roll a tennis ball down this path with cardboard walls. The tennis ball will follow the path. Now let's say you have an escalator at the bottom of the hill. Like a Rube Goldberg machine, the escalator scoops up tennis balls you roll down the path, then drops them off at the start of the path at the top of the hill.
Now, let's say you almost completely saturate the entire path escalator included with tennis balls. Just a long line of tennis balls. Because we didn't completely saturate the path, there are still gaps and spaces for the tennis balls to move. A tennis ball that is carried up the escalator bumps into another ball, which bumps into another ball which The tennis balls going down the path on the hill gain energy owing to the potential difference in gravity.
They bounce into each other until finally, another ball is loaded onto the escalator. Let's call the tennis balls our electrons. If we follow the flow of electrons down the hill, through our fake cardboard "circuit", then up the magical escalator "power source", we notice something:.
The "gaps" between tennis balls are moving in the exact opposite direction of the tennis balls back up the hill and down the escalator and they are moving much faster. The balls are naturally moving from high potential to low potential, but at a relatively slow speed. Then they are moved back to a high potential using the escalator. The bottom of the escalator is effectively the negative terminal of a battery, or the cathode in the galvanic cell we were discussing earlier.
The top of the escalator is effectively the positive terminal of a battery, or the anode in a galvanic cell. The positive terminal has a higher electric potential. By definition, it is: the amount of charge that passes through a cross-sectional area per second units: Coulombs per second. Current density is the amount of charge flowing through a unit of area units: Coulombs per meter-squared.
If you have a tennis ball launcher spitting positively charged balls through a doorway, the number of balls it gets through the door per second determines its "current". How fast those balls are moving or how much kinetic energy they have when they hit a wall is the "voltage". Think of it like this: there are a fixed number of electrons and protons. In an electrical circuit, matter is neither created nor destroyed In the tennis-ball escalator example, the balls were just going in a loop.
The number of balls remained fixed. What happens is that charge loses potential. Ideal voltage sources give charge its electric potential back. Let's take that conservation of charge principle.
A similar analogy can be applied to the flow of water. If we have a river system down a mountain that branches, each branch is analogous to an electric "node". The amount of water that flows into a branch must be equal to the amount of water flowing out of the branch by the conservation principle: water charge is neither created nor destroyed.
However, the amount of water that flows down a particular branch is dependent on how much "resistance" that branch puts up. For example, if Branch A is extremely narrow, Branch B is extremely wide, and both branches are the same depth, then Branch B naturally has the larger cross-sectional area. This means Branch B puts up less resistance and a larger volume of water can flow through it in a single unit of time.
Because of the conservation principle, all charge into a node must flow out. There is no "unused" current because current isn't used. There is no change in current in a single series circuit.
However, different amounts of current can flow down different branches in an electrical node in a parallel circuit depending on the resistances of the different branches.
Technically, the LED and resistor s don't "use" current, because there is no drop in current the amount of charge passing through the LED or resistor s in a unit of time. This is because of the conservation of charge applied to a series circuit: there is no loss in charge throughout the circuit, hence no drop in current. The amount of current charge is determined by the behavior of the LED and resistor s as described by their i-v curves.
Here's a basic LED circuit. If you do not meet the activation voltage, practically no current will flow. Refer to the LED i-v curves linked below. If you attempt to push current in the direction opposite the LEDs polarity, you will be operating the LED in a "reverse-bias" mode in which almost no current passes through. The normal operating mode of an LED is forward-bias mode.
Beyond a certain point in reverse-bias mode, the LED "breaks down". Check out the i-v graph of a diode. LEDs are actually PN junctions p-doped and n-doped silicon squashed together. Based on Fermi levels of the doped silicon which is contingent on the electron band-gaps of the doped material the electrons require a very specific amount of activation energy to jump to another energy level.
This is also why LED lighting seems so "artificial": natural light contains a relatively homogeneous mix of a broad spectrum of frequencies; LEDs emit combinations of very specific frequencies of light.
The energy levels also explain why the voltage drop across an LED or other diodes is effectively "fixed" even as more current goes through it. Examine the i-v curve for an LED or other diode: beyond the activation voltage, the current increases a LOT for a small increase in voltage. In essence, the LED will attempt to let as much current flow through it as it possibly can, until it physically deteriorates.
Yep, Kirchoff's voltage law is that the sum of all voltage drops in a loop around a circuit is zero. In a simple series circuit, there is only one loop. Connecting the terminals of a battery together results in a large current discharged at the voltage of the battery.
That voltage is dissipated through the battery's internal resistance and the conductor wire in the form of heat -- because even conductors have some resistance. This is why shorted batteries get super hot. That heat can adversely affect a chemical cell's composition until it blows up. Here's the rhetoric: imagine there's this amazing concert. All your favorite bands are going to be there.
It's going to be a smashing good time. Let's say the event organizers have no concept of reality. So they make the entry fee to this amazing concert almost completely free. They put it in an extremely accessible area. In fact, they're so disorganized, they don't even care if they oversell and there aren't enough seats for everyone who buys tickets. Pretty quickly, this amazing concert turns into a total disaster. People are sitting on each other, spilling beer everywhere; fights are breaking out, the restrooms are jammed, the groupies are freaking everyone out, and you can barely hear the music above all the commotion.
Think of your LED as that amazing concert. In this dumb example, "resistance" translates into "cost of entry". By simple economic principles, raising the cost of the concert decreases the number of people who will attend. Similarly, raising the resistance in a circuit prevents charge and subsequently current from going through.
This means your LED concert doesn't get completely wrecked by all the people charge. What's the quickest way to gain understanding of basic electricity? Just focus on "hot button" issues like the following. Fix your mental concepts, and everything snaps into place and makes sense. Conductors are materials which are composed of "movable electricity.
Beware of the widespread incorrect definition of conductors:. Wires are like pre-filled hoses, where the electrons of the metal are like water already inside the hose. In metals, the atoms' own electrons are constantly jumping around and 'orbiting' all throughout the entire metal bulk.
All metals contain a 'sea' of movable fluid-like electricity. So, if we hook some metal wires in a circle, we've created a kind of concealed drive-belt or flywheel. Once the loop is formed, the circular "electricity belt" is free to move inside the metal. If we grab and wiggle our wire circle, we'll actually produce a tiny electric current by inertia, just as if the wire was a hose full of water.
Search: Tolman effect. The path for current is a complete circle, including the power supply. Power supplies don't supply any electrons.
In other words, the circle has no beginning. It's a loop, like a movable flywheel. The movable electrons are contributed by the wires themselves. Power supplies are just electricity-pumps. The path for current is through the power supply and back out.
A power supply is just another part of the closed loop. Electric currents are fairly slow flows. But, like wheels and drive-belts, when we push upon one part of the wheel, the entire wheel moves as a unit. We can use a rubber drive-belt to instantly transfer mechanical energy. We can use a closed loop of electricity to instantly transfer electrical energy to any part of the loop. Yet the loop itself doesn't move at the speed of light! The loop itself moves slow. And for AC systems, the loop moves back and forth while the energy moves continuously forward.
Big hint: the faster the electrons, the higher the amps. Zero amperes? That's when the wires' own electrons come to a halt. Another hint: electrical energy is waves, and electrons are the "medium" along which the waves travel. The medium wiggles back and forth, while the wave propagates fast forward. Or, the medium jerks backwards, moving slowly, while the wave moves forward extremely rapidly.
In other words, no single "electricity" exists, since there were always two separate things moving inside circuits: the slow circular currents of electrons, and the fast one-way propagation of electromagnetic energy. They move with two entirely different speeds in circuits, and while currents flow in loops, the energy flows one-way from a source to a consumer.
Batteries don't store electricity. They don't store electric charge. They don't even store electrical energy. Instead, batteries only store chemical "fuel" in the form of uncorroded metals such as Lithium, Zinc, Lead, etc. But then, how can batteries work? Easy: a battery is a chemically-powered charge-pump. As their metal plates corrode, chemical energy is released and they pump electricity through themselves.
The path for current is through the battery and back out again. Pumps aren't used for storing the stuff being pumped! And, battery 'capacity' is just the quantity of chemical fuel inside. A certain amount of fuel is able to pump a certain total quantity of electrons before the fuel is used up. It's a bit like rating your gas tank in miles of travel, rather than in gallons.
Gas tanks don't store miles, and batteries don't store electricity! Rechargable batteries? That's when we forcibly run them backwards, so their internal "exhaust products" get converted back into fuel: corrosion compounds get turned back into metal again.
Resistors don't consume electricity. When a light bulb is turned on, its own electrons begin moving, as new electrons enter one end of the filament, yet at the same time other electrons are leaving the far end. The filament is part of a complete ring of electrons which move like a drive-belt. The heating effect is a kind of friction, as when you push your thumb against the rim of a rotating tire. Your thumb isn't consuming rubber, instead it's just heated up frictionally, and light bulbs don't consume electrons, they just "rub upon" the moving electrons, and heat up frictionally.
So, resistors are just friction devices. The path for electrons is through, and no electrons are consumed or lost.
Note that the faster the electrons, the higher the amperes, and the greater the heating. There is no 'rest' of the current. Current is used as much as needed. See it as there is no brake at how fast the electrons can run. If there is no resistor, the LED will use the electrons in the fastest 'speed' possible.
Since this is too much, the LED will burn sooner or later. I don't know the reason why it drops, probably the internal mechanism of the LED causes some voltage to be used. This means the remainder does have less voltage left. And yes, it will continue until nothing is left.
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