If you have embarked upon electronics projects in the past, there is a good chance you have already encountered this common component and soldered into your circuit without second thought. Diodes are valuable in electronics and serve a variety of purposes, which will be highlighted in upcoming steps.
First, what is a diode?
A diode is a semiconducting device, that allows current to flow in one direction but not the other.
A semiconductor is a kind of material, in this case silicon or germanium, whose electrical properties lie between those of conductors (metals) and insulators (glass, rubber). Consider conduction: its is a measure of the relative ease of which electrons move through a material. For example, electrons move easily through a piece of metal wire. You can change the behavior of a pure material, like silicon, and turn it into a semiconductor by doping. In doping, you mix a small amount of an impurity into the pure crystalline structure.
The kinds of impurities added to pure silicon can be classified as N-type or P-type.
Diodes are made from two differently doped layers of semiconductor material that form a PN junction. The P-type material has a surplus of positive charge carriers (holes) and the N type, a surplus of electrons. Between these layers, where the P-type and N-type materials meet, holes and electrons combine, with excees electrons combining with excess holes to cancel each other out, so a thin layer is created that has neither positive nor negative charge carriers present. This is called the depletion layer.
There are no charge carriers in this depletion layer and no current can flow across it. But when a voltage is applied across the junction however, so that the P-type anode is made positive and the N-type cathode negative, the positive holes are attracted across the depletion layer towards the negative cathode, also the negative electrons are attracted towards the positive anode and current flows.
Think of a diode as a one-way street for electricity. When the diode is in forward bias, the diode allows traffic, or current, to flow from the anode, towards the cathode leg. In a reverse bias current is blocked so there is no flow of electricity through the circuit. When current is flowing through a diode, the voltage on the positive leg is higher than on the negative leg, this is called the diode's forward voltage drop. The severity of the voltage drop is a function of the semiconductor material that the diode is made from. When the voltage across the diode is positive, a lot of current can flow once the voltage becomes large enough. When the voltage across the diode is negative, virtually no current flows.
First, what is a diode?
A diode is a semiconducting device, that allows current to flow in one direction but not the other.
A semiconductor is a kind of material, in this case silicon or germanium, whose electrical properties lie between those of conductors (metals) and insulators (glass, rubber). Consider conduction: its is a measure of the relative ease of which electrons move through a material. For example, electrons move easily through a piece of metal wire. You can change the behavior of a pure material, like silicon, and turn it into a semiconductor by doping. In doping, you mix a small amount of an impurity into the pure crystalline structure.
The kinds of impurities added to pure silicon can be classified as N-type or P-type.
- N-type: With N-type doping, phosphorus or arsenic is added, in parts per billion, to the silicon in small quantities. Phosphorus and arsenic both have five outer electrons, so they are displaced when they get into the silicon lattice. The fifth electron has nothing to bond to, so it's free to move around. It takes only a very small quantity of the impurity to create enough free electrons to allow an electric current to flow through the silicon. Electrons have a negative charge, hence the name N-type.
- P-type - In P-type doping, boron or gallium is added to the pure silicon. Those elements each have three outer electrons. When mixed into the silicon structure, they form "holes" in the lattice where a silicon electron has nothing to bond to. The absence of an electron creates the effect of a positive charge, hence the name P-type. Holes can conduct current. A hole happily accepts an electron from a neighbor, moving the hole over a space.
Diodes are made from two differently doped layers of semiconductor material that form a PN junction. The P-type material has a surplus of positive charge carriers (holes) and the N type, a surplus of electrons. Between these layers, where the P-type and N-type materials meet, holes and electrons combine, with excees electrons combining with excess holes to cancel each other out, so a thin layer is created that has neither positive nor negative charge carriers present. This is called the depletion layer.
There are no charge carriers in this depletion layer and no current can flow across it. But when a voltage is applied across the junction however, so that the P-type anode is made positive and the N-type cathode negative, the positive holes are attracted across the depletion layer towards the negative cathode, also the negative electrons are attracted towards the positive anode and current flows.
Think of a diode as a one-way street for electricity. When the diode is in forward bias, the diode allows traffic, or current, to flow from the anode, towards the cathode leg. In a reverse bias current is blocked so there is no flow of electricity through the circuit. When current is flowing through a diode, the voltage on the positive leg is higher than on the negative leg, this is called the diode's forward voltage drop. The severity of the voltage drop is a function of the semiconductor material that the diode is made from. When the voltage across the diode is positive, a lot of current can flow once the voltage becomes large enough. When the voltage across the diode is negative, virtually no current flows.
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Signing UpStep 1: Different uses for different Diodes.
There are many different kinds of diodes, and each one serves a different purpose as an electronic component.
A Light Emitting Diode or LED is probably the most well known and most easily identified. The LED emits visible light when electrons jump across the PN junction.The resulting light is referred to as electroluminescence.
Photodiodes conduct only when they are exposed to light. These can be useful in making projects with a light activated switch, so that a circuit in only active in the presence of light.
Zener diodes are designed to conduct in the reverse direction, only when something called the breakdown voltage is reached will the circuit conduct. These are dialed to precise tolerances, see the section on Zener Diodes in step 3.
Rectifier diodes are designed to stop electricity from flowing in the wrong direction. Diodes are sometimes known as rectifiers for their use to rectify alternating current electricity into direct current, by removing the negative portion of the current.
Schottky diodes are designed to turn on and off very rapidly when the breakdown voltage is reached, responding quickly in digital circuits. When current flows through a diode there is a very small voltage drop across the terminals. Silicon diodes have a voltage drop, or loss; a Schottky diode voltage drop is significantly less. This lower voltage drop enables higher switching speed and better system efficiency.
Diodes can be used in a number of ways, like to protect a current-sensitive circuit. A device that uses batteries will likely contain a diode that protects it when battery is inserted improperly. The diode will stop the reversed current from traveling from the battery to the rest of the circuit-- thus, the diode protects the sensitive electronics inside the your circuit.
In the next few steps, you will find information about some of the most commonly used kinds of diodes.
A Light Emitting Diode or LED is probably the most well known and most easily identified. The LED emits visible light when electrons jump across the PN junction.The resulting light is referred to as electroluminescence.
Photodiodes conduct only when they are exposed to light. These can be useful in making projects with a light activated switch, so that a circuit in only active in the presence of light.
Zener diodes are designed to conduct in the reverse direction, only when something called the breakdown voltage is reached will the circuit conduct. These are dialed to precise tolerances, see the section on Zener Diodes in step 3.
Rectifier diodes are designed to stop electricity from flowing in the wrong direction. Diodes are sometimes known as rectifiers for their use to rectify alternating current electricity into direct current, by removing the negative portion of the current.
Schottky diodes are designed to turn on and off very rapidly when the breakdown voltage is reached, responding quickly in digital circuits. When current flows through a diode there is a very small voltage drop across the terminals. Silicon diodes have a voltage drop, or loss; a Schottky diode voltage drop is significantly less. This lower voltage drop enables higher switching speed and better system efficiency.
Diodes can be used in a number of ways, like to protect a current-sensitive circuit. A device that uses batteries will likely contain a diode that protects it when battery is inserted improperly. The diode will stop the reversed current from traveling from the battery to the rest of the circuit-- thus, the diode protects the sensitive electronics inside the your circuit.
In the next few steps, you will find information about some of the most commonly used kinds of diodes.
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The LED here probably has a built-in resistor designed for 5 volt operation.
I want to know so if I decide to wire some up to a 12 or 24 volt system, I'll have an idea as to how many I should (or can) put in series and what size and wattage resistor I should use.
Can you help?
Sorry I can't really be more specific. You can get an apparent brighter LED by pulsing it at say 50 Hz or higher, and keeping the duty cycle down but while lit, driving it at many times its current, keeping the average heat down.
Hope this helps.
de Bob VE3SUY
Dan
Thank you, AuderyObscura, your contribution is great and I am thankful to you.
We look forward to reading more from you.
1) if any of the leds are reversed it will not light nor will the led in series with it ( unless you break down the reversed led as with a zeener )
2 the graphic has 1 ohm printed should be 1k ohm as the text says, also color code looks a bit like 10k, but I may be wrong on that one.
Right now, I don't have time to put such a device together. I still have to buy a battery and charger at Batteries Plus here in the local area of KCMO.
I went through engineering school, but I just don't have the time. I am working on an all electric car that will beat all production cars. I am only building one. I just got the electric motor to run my high powered hydrostatic drive system. This car is so advanced compared to most vehicles, but now GM and others are catching up with parts like magnetic suspension. I am also using a magnetic clutch that acts like a full time regenerative system. There is so much more to this project. I can't go into details right now, I am sure some special interest groups won't let me divulge either.
I have ruined several adjustable 12 volt car power adapters after miscalculating the resistance of several LED's in series for a lighting project.
Remember from then that you may have to recalculate your power needs, especially if you have either a very low current power supply - or a lot of LED's on a higher power supply!
In any project, always have a multimeter to hand to check your values and do not hesistate to have Ohm's law written down somewhere so you can check that you are calculating values the right way!
Cheers,
Daniel
I have a small solar panel that I want to charge a battery with. I was given a diode to keep the battery from discharging.
Can you tell me by the marking on the diode which direction is the permited flow and which direction the flow is stopped?
Thanks.
Otherwise, great 'ible! Very clear.