What is Diode: Definition and 567 Discussions

A diode is a two-terminal electronic component that conducts current primarily in one direction (asymmetric conductance); it has low (ideally zero) resistance in one direction, and high (ideally infinite) resistance in the other. A diode vacuum tube or thermionic diode is a vacuum tube with two electrodes, a heated cathode and a plate, in which electrons can flow in only one direction, from cathode to plate. A semiconductor diode, the most commonly used type today, is a crystalline piece of semiconductor material with a p–n junction connected to two electrical terminals. Semiconductor diodes were the first semiconductor electronic devices. The discovery of asymmetric electrical conduction across the contact between a crystalline mineral and a metal was made by German physicist Ferdinand Braun in 1874. Today, most diodes are made of silicon, but other semiconducting materials such as gallium arsenide and germanium are also used.

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  1. X

    Why Does the Bottom Diode Short First in a Multi-Diode Circuit?

    http://img38.imageshack.us/img38/6127/88280233.jpg I circled the given answer. The problem asks for I and V. I guess the bottom diode shorts first and then that makes the top two diodes be open circuited. Is there any good explanation on why the circuit behaves like that? I guess it comes...
  2. Q

    Solve Simple Diode Problem: Voltage Drop @ 300K

    Homework Statement You have a series circuit consisting of a dc power supply, a 90 ohm resistor and a diode. If the measured current in the circuit is 136 mA, and the saturation current for the diode is 0.006 mA, what is the voltage drop across the diode? Assume the diode temperature is 300...
  3. M

    Simple Diode Qs: +3v/+1v & 3mA/4mA - Max

    Homework Statement Here is a link to two figures I drew from a book I am using http://www.flickr.com/photos/96575810@N00/4339202724/sizes/o/ These figures are assuming ideal diodes (no voltage drop, no resistance). In this example, on the left hand circuit, the voltage is listed as +3v...
  4. N

    Diode Rectification: Estimating Shutoff Time After Peak Voltage

    1. The question. Suppose that the input frequency into a full-wave diode bridge rectifier is 60Hz, and suppose that the RC time constant of the network filter capacitor and the load resistance is 10ms. Estimate the time after the peak input voltage when the diode shuts off. The circuit looks...
  5. L

    Understanding Zener Diode Load Currents and Regulation

    I have to answer this question in front of the class tomorrow. Been struggling all weekend with no joy. Question: Determine the minimum and maximum loads currents for which the zener diode on the figure below will maintain regulation. What is the minimum RL that can be used. Vz=12v...
  6. A

    Capacitance of a forward biased diode

    How does a forward biased p-n junction display capacitive effect? I understand that a reverse biased diode can exhibit capacitance with the depletion region acting as a dielectric, but in a forward biased junction, depletion region does not exist,so how does it show capacitive behaviour?
  7. Q

    Batteries in parallel with a diode

    I was wondering what the effects are if any if I connect a 17V DC source in parallel with a 9 V battery but the 9 V battery has a diode that prevents current from flowing into it. Thanks
  8. G

    Forward Bias Effects on PN Junction Diodes

    Hello, Here is my question: If we have a regular PN junction diode, which is forward biased we will observe the effect "injection", we will have more minority carriers than normal near the PN junction. I would like to ask you whether this "injection" is observed during the whole period...
  9. M

    Can a Diode Protect a Transistor from High Voltage?

    i want to protect my transistor(working in saturation) from high incoming voltage... can a diode be used to protect it from the high voltage?
  10. N

    How Much Power Can a 20A Diode Dissipate in Normal vs. Abnormal Conditions?

    Question requires a definition and typical values during normal/abnormal operation (Power dissipation of 20A Diode with 1V across it) Have got definition no problems, but am struggling with typical values. Power dissipated would be in watts, but in order to provide that you would need...
  11. D

    Diode characteristics/dealing with infinity

    New to the forum, I'll say "Hi," first :) Homework Statement Have a physics assignment to hand in. Very simple experiment - increase the voltage in a circuit and measure the current/voltage across the diode in forward and reverse. The problem comes with dealing with infinity in some of the...
  12. R

    Is My Diode Becoming Too Hot? Troubleshooting Advice Needed

    Dear Experts,o:) I have recently soldered some diodes to maintain a constant voltage. This i learned from this nice forum. But when using it, the diode can become quite warm. My doubt is, when diodes become warm to touch, like about 60 degrees celsius , is it something wrong with the...
  13. S

    Voltage Drop in Diode: Exploring Causes & Amplifier Doubts

    the depletion region is resposible for voltage drop all that is fine but in forward bias there is no depletion region hence there can be no voltage drop but it is mentioned in my book that the voltage will drop by .7 volt how come this can happen also i have many doubts in transistor...
  14. G

    Measuring the Boltmann constant by the IV curve of a diode

    So the current through a diode as a function of applied voltage is: I = I0 [ exp( V q / KB T) - 1 ] where V is the voltage (independent variable), q is the charge of the electron (constant), T is temperature (constant over each trial), I0 is some parameter that's measured to be really tiny (I...
  15. A

    Compact Diode Options for Small Circuit Designs | 1N4148 Alternatives"

    guys I'm looking for general purpose diode like 1N4148. it should be small.(smaller than 1n4148). surface mount solution is not going to work as they are very expensive. I'm working on a circuit and need to use parts small as possible. i use 1/8w resistors and 1n4148 as diodes as they are...
  16. A

    What Is the Slope Resistance of a Zener Diode?

    what is the mean of "slope resistance" of zener diode? Its parallel to diod or series?
  17. J

    Engineering Simple Diode Circuit Analysis: Homework Help and Solutions

    Homework Statement Attached is the homework problem I'm having difficulty with. I need to sketch vout for the circuit, assuming the diode ON voltage is 0.6 V. I'm stuck at how to begin this problem. Homework Equations The Attempt at a Solution It's only the 2nd week of class so...
  18. A

    5 Methods to use a transistor as Diode.

    Homework Statement List at least five methods by which a transistor can be used as a diode. Homework Equations N/A The Attempt at a Solution I know three configurations viz. Collector Emitter Short, Collector Base short and Base emitter Short.. What would be the remaining two...
  19. Y

    Engineering Solving Diode Resistor Circuit Homework

    Homework Statement Find Voltage/Current across each diode: ----R--- |...| V...D |... | ----R--- Repeat 50x until...
  20. E

    How the diode will act in these situations in transition period

    http://i30.tinypic.com/2i2r9i.gif
  21. M

    How to Choose the Right Diode Model for Your Project?

    I am just beginning to learn about diodes and I was wondering if there are any tips to making the correct guess for the diode model. For our class, we use a model that consists of four regions instead of the simple on/off model. basically to figure out what the diode is doing, we insert the...
  22. P

    Half-Wave Rectifier Average Diode Current

    http://img12.imageshack.us/img12/7084/helpphg.jpg In the image shown above, how is the average diode current calculated? This is an old homework assignment and I'm taking notes. I would appreciate any help. Thank you.
  23. A

    Solving Diode Bridge Current with AC-to-DC Circuit

    Hello, I made a circuit to convert AC to DC. It looks like this. http://openbookproject.net/electricCircuits/Semi/03267.png My output DC voltage is around 5 volts. Could someone please explain to me how I could figure out the current running through each of the phases at a given time given a...
  24. P

    Understanding Diode Output Behavior in an AC Circuit

    This post is similar to the one that I made the other day. There are two problems that I am having trouble understanding. The link is below: http://img510.imageshack.us/img510/4396/diodeproblem.jpg They are numbered 4-5 (Ignore 3) . Once again I know the predictions are correct , because I did...
  25. P

    Understanding Reverse Bias Diode Output Voltage

    The link provided shows two cases of reverse bias Diodes. From my understanding a reverse bias diode is supposed to block the voltage from reaching the output. So from the following picture wouldn't both of the outputs be 0v. I know that the answers in the diagram are correct because I did them...
  26. S

    Solving Basic Diode Circuit: Voltage Across Diodes @ 1mA

    Homework Statement Given a basic circuit of a voltage source and two diodes in series: D1 is .7v @ 10mA D2 is .6v @ .1mA If I is 1mA, What is the voltage across the two diodes? Homework Equations VT~.026 Vt= 60log (I(t)/Is I1 produces V1 I2 produces V2 so V2 = V1 + 60(mV)[log...
  27. LydiaAC

    Point Contact Diode: Rectification Properties Explained

    Hello everybody: It is known that point contact diodes were an antecedent of PN junction diodes. I have read that they got their rectification properties from the fact that the metal in the point doped the semiconductor and formed a PN junction. However, it is known that you can rectify with...
  28. S

    Solve Ideal Diode Problem: V & I Calculation

    Hi, I am stuck trying to work out a problem involving two ideal diodes. http://img200.imageshack.us/img200/668/idealdiodev.jpg I need to find V and I. Aswell as which diode is on and off. I have tried to solve it by assuming d1 is on and hence V is 0 but i can't get the right...
  29. N

    Capacitor and diode curcit for ac to dc voltage

    http://img42.imageshack.us/img42/2461/49889005.th.jpg My question is, why does the dc voltage vary with time in this way? Ply it is something to do with the diode allowing current to flow when it has 0.7V or more across it, allowing the capacitor to charge, and when the voltage drops to...
  30. R

    Calculating AC and DC Resistance of a Silicon Diode in 300K

    Diode ac and dc resistance? here is my question ...saturation current of a silicon diode is 2uA.and forward current is 20mA...i want to find out the AC and DC resistances of the diode in 300k... so i know that , I(forward)=I(saturate)[exp(eV/nKT)-1] ..so by differentiating both sides...
  31. F

    Solving a Diode Circuit with Varying Resistances

    Homework Statement A diode with reverse saturation current of 1pA and an ideality factor of 1.15 is connected in series with a resistance of 200ohms and connected to a 5V DC supply voltage. Find the current flowing in the diode at a temperature of 290K? How does the current change when a...
  32. D

    Understanding the Role of Series Resistors in Piece-Wise Linear Diode Models

    I am NOT trying to solve this as a homework problem, I'm just trying to dig out basic concepts that I'm missing when using this battery+resistance diode model.I'm having trouble seeing why, when solving for current, KCL equation does NOT work out as: 1) I= (0-Va)/rd 2) I=(Va-(-5))/R...
  33. 0

    Simple Derivation Of Diode Equation

    I am looking for the simplest possible derivation of the diode equation. I need it to reference to it in my advanced higher project. Basically I have to dissect it. I unfortunately don't know how to derive it and I can't find one simple enough to use. This is what I am trying to end up with...
  34. N

    What is the voltage drop across a diode when it is reverse biased?

    Hi guys, I have a very simple question but which is messing with my mind. I'm trying to figure out the voltage drop across a diode when it is reverse biased, and I'm just not getting anywhere. Can someone please take a look at the attached image and explain to me what the voltage drop across...
  35. B

    Small signal approximation diode model

    hello all I am new here so i don't know if this is the correct place for this topic so sorry for any inconvenience caused. this is my question: Use the small-signal model of the diode to predict the output voltages for the input voltages given. Plot a graph of | vout(t) | based on the small...
  36. E

    Can Zener Diodes Maintain a Constant Voltage Regardless of Applied Voltage?

    I have trouble getting my head around Zener Diodes. If you reverse bias them, and apply a current, it will not conduct until the applied voltage reaches the Zener Voltage. Am I to understand that no matter how much voltage (within reason) you apply to the diode, its output voltage will always...
  37. M

    Why no current in reverse-biased diode?

    I try to understand why, really, there is no current (except for leakage) when a diode is reverse-biased. I studied several texts, and no one really explains, like for instance this otherwise very pedagogic http://en.wikipedia.org/wiki/P-n_junction#Reverse-bias". How I think: The negative...
  38. ¡

    Flyback Diode Implementation/Sizing w/ Relays/Switches

    I searched but had no luck. Sorry if this kind of thing has been answered a bunch. I'm designing a circuit for my car. If you want to know more just ask and I will explain. I want to know when I need to use diodes to protect stuff. I have attached a wiring diagram. I know I need diodes D1...
  39. M

    How come when you reverse a diode the current/voltage? is zero?

    Hi I have been looking through my book, and even online for the answer because I don't understand why this happens, but I can't find the proper answer anywhere...can someone help me? Thanks.
  40. M

    How come when you reverse a diode the current/voltage? is zero?

    Hi I have been looking through my book, and even online for the answer because I don't understand why this happens, but I can't find the proper answer anywhere...can someone help me? Thanks.
  41. N

    Derivation of voltage for vacuum diode space charge region

    I have found the 1D differential equation relating voltage and position for a vacuum diode in the space charge region, which is \frac{d^2V}{dx^2} = constant * V^{-1/2} and I know the solution to be V(x) = V_0 \left(\frac{x}{d}\right)^{4/3} which is found by multiplying both...
  42. T

    Help: Design Resistor & Diode Pair Branch for Voltage Control

    Homework Statement Design a “smart” branch with resistors and a diode pair such that the branch resistance drops if the voltage applied on the two ends of the branch is too high, and vice versa, (i.e., the branch resistance increases if the voltage applied on the two ends of the branch is...
  43. U

    Forward Biasing a Diode: Explained

    There are a lot of resources out there which mention that when a diode is forward biased the majority carriers at the n-type material will move to the p-type material "through" the holes therefore the holes will move from the p-type region to the n-type region. However, this doesn't make any...
  44. F

    Ideal diode questions final soon help

    Ideal diode questions final soon urgent help its actually an example in my book (sedra and smith, 5th ed) which i fail to understand completely! Question: the question is : Assuming the diodes to be ideal find V and I in the circuits. I obviously went through the example but it totally...
  45. G

    Can Transistors Be Used as Zener Diodes?

    Can anyone explain about or point me to any articles about using transistors as zener diodes ? Why not just use zeners, and what connections (c-b short or e-b short) and their pros and cons ?
  46. R

    Solving Zener Diode Problems: 1N5226BT/R 3.3V, Zz = 28 ohms

    I am using 1N5226BT/R zener diodes (3.3 Vz, Zz = 28 ohms) and am having trouble getting a constant voltage source... Silly me, I designed a circuit assuming zener diodes would act ideally... According to the datasheet the minimum voltage reverse breakdown voltage would be 3.1 V. Here's what...
  47. J

    IV curve of a BD-5 tunnel diode

    Hi All Anyone know where I might find the IV curve for a General Electric BD-5 tunnel diode? I have found a few short datasheets for the BD series, but I really need a curve. Does anyone know where to find such a thing? Or should I just get the SourceMeter out and make one myself...
  48. R

    Pulsing a diode laser with very long pulses and very low repetition rates

    Greetings, I am an electronic engineer doing some research on high power laser diodes. The problem I try to solve needs ~2300W of optical peak power coming from a high power laser diode. The pulses must be with very long (30ms) at very low repetition rates (2Hz). So,the duty cycle is...
  49. L

    Pn Junction Diode: Electrons, Holes, and Immobile Ions

    folks, when a pn junction diode is formed, electrons in the n type and holes in the p type diffuse. agreed. then how immobile ions are formed at the vicinity of the junction leading to depletion region? how these immobile ions prevent further diffusion? it is being said electrons and holes...
  50. T

    Transistors and Diode Test

    Homework Statement Explain why the BC junction will give a smaller voltage drop, and will thus have a higher voltage measured then a BE Junction. Homework Equations N/A The Attempt at a Solution Okay, hopefully this is the right section to post this in. See, I have read the book...
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