# Diode Definition and 53 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. ### Understanding a heat sensor circuit?

What I understand is that the β parameter of the npn transistor is temperature dependent. Increasing the temperature increases the collector current and hence the LED turns ON. But I don't understand the resistor arrangement.Also I can see that the diode is keeping the Base-Emitter junction in...
2. ### Calculate the voltage across a resistor using Thevenin's Theorem

I'm thinking I should apply Thevenin's Theorem to find the voltage, but I need to find I_D in order to be able to calculate U_S.
3. ### How to find the voltage threshold at which diode switches states?

I've attached pictures with the circuit and part of the attempted solution. I've replaced the diode with its offset model and obtained the equivalent circuit in the 2nd picture. After applying KVL, I've obtained that u_l=−u_D−i_D*R. Since U_D0 is greater than 0, I've deduced that the diode must...
4. ### B Logarithmic IV graphs of diodes

Hello there, I've been working through a task (that doesn't have an answer sheet or explanation) in which we plot I against V for three different diodes. Each has a different threshold voltage and displays the usual charcteristic curve. The final question is this: "It is suggested that the...
5. ### Fundamentals of the PN Junction

Unbiased circuit (no driving voltage source) ************** Fig 1 The N-type material has a tendency to donate electrons to the P-type (i.e. absorb holes from) across the PN junction via diffusion current exclusively within the conduction band of both materials. It does so after those...
6. ### B P-N junction Semiconductors

I'm new to semiconductors. While I was studying types of biasing in semiconductors, here's what I read - 'In forward biasing, the width of the depletion region is reduced.' Here's what I thought - Since the potential barrier is reduced in the junction due to external potential, the diffusion...
7. ### Engineering DC bias current and small-signal resistance

We are given that ##i_D = 8\cdot 10^{-12} (e^{v_D/20m} - 1)## Hence ##i_D' = e^{50 v_D}/2500000000## and ##i_D'' = e^{50 v_D}/50000000## Then I have that ##\delta i_D \approx\frac{ e^{50 v_D}}{2500000000} \cdot \delta v_D = \delta v_D / 5## Cancelling ##\delta v_D## from boh sides and solving...
8. ### What is the design methodology of a Heatsink for a high-power diode?

In reference of Ned Mohan's book, I have designed a heatsink, firstly natural convection taken into account, but laboratory test results and theoretical calculations are not matching. The test results: For 40 A (means 62 W), 30 Celsius ambient temp, it raised up 51 Celsius. So, Rs-a =...
9. ### Novice question about Relays, Capacitors, and Diodes

Hello, In regards to this relay, TQ2SA-1.5V Panasonic 2 Form C AS Single side stable, 1.5VDC 2A DPDT NON-LATCHING SMD Relay Link to Relay PDF 1 of Relay PDF 2 of Relay (specifically pages 5-6) is attached at the bottom as a pdf file. I was previously told that I would need to wire a IN4001...
10. ### Using a generator to charge 2 batteries

My project is to create a circuit for a stroller that can store the mechanical work into electrical while moving around and with the push of a switch, use the electrically stored energy to assist the movement of the stroller. I’ve tried capacitors but it ended up not being enough voltage and I...
11. ### Ohmic Resistance in diodes

Well I was just wondering how ohmic resistance works in a diode . I mean lets take forward bias mode.In forward bias mode electrons are diffused from the n type region to the p type region.The depletion layer still exists but is very narrow.So according to Drude model of ohmic resistance...
12. ### B Semiconductors confusion

Assume we have a diode . We connenct the negative terminal of the battery(anode) to the n type region and we connect the positive terminal of the battery to the p type region of the battery.The net force forces electrons to start flowing from the n type region to the p type region.As long as we...
13. ### Semiconductor physics: Voltage below forward voltage

Assume we have a diode closed circuit.We connect the p type region of the diode to the positive terminal of the battery(cathode).We connect the n type region of the diode to the negative terminal of the battery(anode).The voltage of the battery is 0.3V .The diode%s intristic se miconductor is...
14. ### Diode operation from reverse bias to zero bias

Assume we have a closed diode circuit .We connect the n type region of the diode to the positive terminal of the battery.We connect the p type region of the diode to the negative terminal of the battery.The depletion layer is increased.Now we open the circuit.Why the diode returns to its zero...
15. ### Load resistance in voltage regulator

Homework Statement [/B] I want to find the minimum resistance ##R_L## so as to maintain ##V_z##(voltage of the zener corresponding to the minimum current ##I_{z_0}##) across the same resistor ##R_L##. Homework Equations ##V_z##(voltage of the zener corresponding to the minimum current...
16. ### Vacuum diode electron flow

Dear Sirs I have been going through the "radiotron designers handbook", but I can't seem to find the answer to the doubt I have about the electron flow of the source Vp. Kindly consider the below two circuits, the difference is the polarity of Vf. Question: In both circuits, the electrons...
17. ### Engineering What is the output voltage of this ideal diode circuit?

Homework Statement Given the following circuit: what is the positive and negative peak values of Vo? vi has a frequency of 1kHz, peak of 5V, and is a sine wave. Homework Equations x(t) = Vsin(2(pi)*f*t) KCL, KVL, etc. The Attempt at a Solution [/B] I made Vi to be 5sin(2(pi)1000t) during...
18. ### Semiconductor substrate/Al_Comsol

I have a semiconductor substrate and a metal. The metal is coated on substrate then a voltage applied. how can i simulate this in Comsol software.
19. ### Pn junction under forward bias

If two batteries are connected such that positive terminal of one is in contact with negative terminal of other then we add the potentials so the potential will then be their sum. Similarly if a battery is connected to a pn junction diode such that positive terminal is connected to negative...
20. ### A Interface states in a PIN diode

Is the equation used to determine the density of interface states in schottky diodes from capacitance- frequency data applicable to PIN junctions?
21. ### Electronics diode modelling

Homework Statement It's simple problem but I get stuck while calculating the VD. Currents and voltages in the circuit are required. So V, VD and I Homework Equations The Attempt at a Solution Since VA<VK I would assume that diode is OFF and then the diode can be represented by break. Upon...
22. ### Diode Question: need to understand why my approach is wrong

Homework Statement A screenshot of the problem: imgur link: https://i.imgur.com/ljtoclm.png Homework Equations The Attempt at a Solution My first attempt at the solution was this: imgur link: https://i.imgur.com/TJcvOzy.jpg However, I have access to the worked solution, and it is...
23. H

### Motorcycle starter safety circuit

I don't know if it's the same for a car but bikes uses a starter relay to set off a starter motor which cranks the engine. Bikes have a side stand for you to lean the bike against when stationary. In case the rider tries to start the bike with side stand deployed (could cause crash if forget to...
24. ### Electrical DIY solar power system

Hello, I've been building my own solar panel system and throughout this process I've accumulated a lot of questions. If anyone could help answer them I would greatly appreciate it! First I'll start off explaining what I have. A polycrystalline solar panel 17V 2.2A and a mono crystalline panel...
25. ### I Determining Appropriate Focal Length

So I'm working on a project where we're deciding a new lens to use for our laser diode. I need to determine the appropriate focal length based on the equation: 1/ƒ = 1/μ + 1/σ where ƒ is our focal length, μ is the distance from the lens to image and σ is distance from lens to object. For the...
26. ### Bridge rectifier transfer function

Homework Statement I am asked to decide which one of these is the transfer function of a bridge rectifier I was thinking D, but my friend says D is for when there is only one diode. Can anyone explain what the right choice is and why? This is not homework, rather preparation for my final.
27. ### B Existence of depletion layer in contact surface

in a P-N junction diode, in an equilibrium state, a depletion layer forms in the surface of contact of N type and P type. But the problem is, this layer is formed by diffusion of electron to a lower electron density zone. Why does it always have to form right in the contactt surface? when...
28. ### Calculating Q points for diodes

Homework Statement In Figure Q22, the empirical junction diode equation is : (eqn is in the picture attached) for both diodes D1 and D2, where VT = 26 mV at room temperature, n = 1, IS = 3.5 x 10-14 A, R1 = 600 Ω, R2 = 300 Ω, R3 = 200 Ω, VS = 9 V. Calculate the Q-points ID = _____ mA and VD =...
29. ### Finding the forward current of diode

Homework Statement A Si diode is operated at the room temperature (27 °C). For a forward current of 1 mA, the voltage VD is found to be 0.9 V. If the VD is 1 V, the forward current = _____ mA. Given that nVT = 26 mV The answer is 46.81 Homework Equations Shockley diode equation? The Attempt...
30. ### Ideal diode question

Homework Statement I am trying to prepare for an exam that is tomorrow, my professor gave sample questions but did not give us any solutions or answers. I have trouble with this question: Homework Equations The Attempt at a Solution I don't know what to do. I would maybe try to figure out...
31. ### Assumptions with diodes

Homework Statement I am working on this problem, where I need to find I and V Homework Equations The Attempt at a Solution I know the right answer will be when D1(left) is off and D2(right) is on, we went over the solution in class. I wanted to do the 4 assumptions just to try to...
32. ### Confusion about how KCL and KVL are used for diode circuits

Homework Statement This is just one of the example problems in my book which is already solved for me, but I don't really understand their solution which I'll post here: They start out with assuming Vin is very negative, which makes D1 turn on and makes Vout=VD,on+Vin. THen they solve for...
33. ### Diodes & rectifiers

Homework Statement I am practicing problems like this: where Vs=10V, R=2kohm, they say it is like a battery + ideal diode with VD=0.7V I have to sketch the transfer characteristic Vo=f(Vs) and draw the waveform of Vo(t) Homework Equations The Attempt at a Solution I am really unsure how to...
34. ### How did Roentgen rectify current in the first x-ray?

Hi, I was studying Roentgen (and Crookes tubes) and realized that they used spark gap generators which sent out bursts of AC current. However, Crookes tubes work with one end being the cathode and one the anode. They did this before diodes so how did they ensure that one side was negative and...
35. ### B Half/full wave Rectification

Why RMS values change during half wave rectification, full wave rectification? And why does RMS value remain constant during smoothing?
36. ### Diode aging characteristics

Hi, Does anyone know if there are such characteristics that are tell tale signs of diode degradation? I'm not sure if diodes fail short or open, I'd have thought open, but I'm not sure. I was wondering if as a diode gets old the forward bias voltage might increase? Or the diode power loss per...
37. ### I-V characteristics of a diode

I was doing an experiment to plot the IV characteristics of a diode. I connected a resistor, diode and milli ammeter in series. I connected a voltmeter across the diode. I measured the diode voltage and diode current. When i changed the resistor, I got a different set of diode voltage readings...
38. ### Engineering Zener voltage controlled circuit design

Homework Statement Homework Equations V0=Vsrz/Rs+rz+VzoRs/Rs+rz-ILrzRs/rz+Rs The Attempt at a Solution I formulated 4 cases for voltage inputs of 11 and 13.6 V and 0 to 100 mA. The zener current has to be between 3 and 30mA or 103 and 133mA. How can the current be maintained in thes two...
39. ### Amplifying a Photodiode using an OpAmp

Dear electrical engineers, Here a question from a serious electronics n00b =D. I tried to build a system as shown in the image. I have a photodiode which gives me a clock signal in the range of 200 to 500mV. Frequency will be in the range of 100 to 1000 Hz. I would like to amplify this...
40. ### PIV full-wave Bridge Rectifier

Homework Statement Part C of the problem below. I have the solution but I don't follow the logic. Homework Equations Turns ratio: Vp/Vs = Np / Ns KVL I do not think I need any elaborate formulas to solve this. The Attempt at a Solution Solution Provided by instructor: I am confused why...
41. ### Light bulb & Diode: linear or non-linear elements.

Homework Statement These questions are related to an experiment where we had to record the current for varying values of potential difference (10 readings), then repeat the process with the applied potential difference was reversed a) Why is the resistance of a light bulb not constant? b) Does...

I was wondering, does the lifetime of a diode depend on how long it takes for all the free P electrons to transfer over to the p holes? In other words, do the electrons that fall into the p holes ever return to the n side?
43. ### How can the neutral regions in a diode have constant potential?

Homework Statement It is said that the potential in the neutral regions of a PN junction diode is CONSTANT. Homework Equations V=Q/4ΠΣr The Attempt at a Solution It is said in all textbooks to ASSUME that the electric field in the neutral regions as zero. Two aspects confuse me. 1. What...
44. ### KVL loop in BJT biasing

Please help how Ve is calculated what i think is that it should be: -Ve=-Vee+IeRe; How Ve is taken positive please someone draw equivalent circuit for same
45. ### What happens when collector-base voltage is 0 in transistor?

Hello I'm now studying current mirror and have a question about replacement of diode to transistor as shown in the attached image. The upper image is original current mirror circuit shown in study document. Collector current IC is very similar to current through Rbias thus current to load can...
46. ### Determine the reverse saturation current for the diode

Determine the reverse saturation current for the diode below, given that VS = 5V, R = 360Ω produces a diode current of 10mA. Use h = 1.3 and VT = kT/q = 25mV. I believe this is the formula needed. Id = Is(e^(VD/(h*25mV))-1) The problem I had was I've done several questions similar to this but...
47. ### AXIS P1355 Camera I/O + relay to turn on light/garage door

here is the manual http://www.axis.com/en/files/manuals/um_p1355_49956_en_1303.pdf [Broken] see page 61 Notes: i have seen this thread https://www.physicsforums.com/threads/axis-camera-with-i-o-and-relay-to-turn-on-lights.538043/ but this camera is a bit different i think as it has digital...
48. ### Electric Field in Capacitors and Diodes

Hello, Capacitor When a capacitor is connected to a voltage source, electrons will move from one plate and accumulate in the other in accordance to Q=CV. Due to the imbalance of charges (positive and negative ions) between the plates, an electric field exists that flow in the direction of the...
49. ### Why do the free electrons in the N-type want to diffuse?

I'm trying to understand how a diode works and for this I've used(among other resources) the book written by Albert Malvino, Electronic Principles. Everywhere I read about this topic, it says that when the N-type and P-type semiconductors are joined together, the free electrons from the N-type...
50. ### Is CFL an inductive load?

As far as I know, Compact Fluorescent Lamp (CFL) is an inductive load. I understand that inductive load doesn't allow an immediate change in current. When the circuit was initially open (through open switch) then became close, the inductive load was energized. So opening again the circuit after...