Questions tagged [diodes]

Diodes are semiconductor components made from a P-type and N-type silicon material, that allows current to only flow in one direction.

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66
votes
7answers
228k views

What is “forward” and “reverse” voltage when working with diodes?

What is the difference between "forward" and "reverse" voltages when working with diodes and LEDs? I realize this question is answered elsewhere on the interwebs such as wikipedia, but I am looking ...
57
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9answers
35k views

Why can't two series-connected diodes act as a BJT?

Another form of the question is: will joining two diodes with wires (pn-np) make a transistor-equivalent? I read that they are not equivalent, but why?
48
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2answers
8k views

Why do some diodes have a glass package?

Put simply, why do some diodes such as most Zeners and Schottky diodes have a glass package as opposed to the more traditional plastic package? Is it ease of manufacturing, thermal properties, or ...
41
votes
5answers
13k views

For a lower voltage drop one could use Schottky diodes, but what are the disadvantages of Schottky's?

In other words, why don't we always use Schottky diodes if they are so much better? What diode properties do Schottky diodes have that makes them unfit for certain applications?
41
votes
4answers
105k views

How to choose a flyback diode for a relay?

A diode is put in parallel with a relay coil (with opposite polarity) to prevent damage to other components when the relay is turned off. Here's an example schematic I found online: I'm planning on ...
40
votes
8answers
8k views

Why isn't there a potential difference across a disconnected diode?

I know this question sounds silly, as if there was a potential difference a current would be created when the terminals are connected together and this would mean energy has come from somewhere. The ...
39
votes
11answers
35k views

Is paralleling diodes a bad idea?

I'm trying to repair an 800W power supply (see my previous question on this.) One thing that gets me is that the design has two schottky diode packages (in TO-220) in parallel. I was always told this ...
36
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6answers
46k views

How do I model an LED with SPICE?

What diode modifiers are used in practice to model LEDs with SPICE (Berkeley v.3f5)? These are available to me: ...
36
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2answers
2k views

How does current get into a diode?

I think I understand more or less how an ordinary semiconductor diode works: Crystal doped differently in different regions, carrier depletion where they meet, bla bla bla. However, actual diodes ...
34
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9answers
104k views

What is the reverse recovery time in a diode?

What is the reverse recovery time in a diode?
33
votes
2answers
67k views

Purpose of the diode and capacitor in this motor circuit

I'm hooking up a small DC motor to an arduino using an NPN transistor using the following diagrams I found online: The circuit works, and I'm successfully able to make the motor run. Now, I'm ...
28
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7answers
6k views

What's the purpose of these two diodes in this circuit?

What's to point of using these two diodes? Can't you just replace them with a resistor?
26
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4answers
39k views

Common types of diodes to keep around

I'm working on stocking my home workshop with frequently used parts so I can spend more time tinkering and less time watching my mailbox. What are the differences between different kinds of diodes? ...
26
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3answers
17k views

How to decide between a TVS or Zener diode for overvoltage protection?

I'll leave my specific circuit out of this for a more broad question: What criteria does one use when deciding whether to use a Zener diode or a transient voltage suppressor, for overvoltage ...
24
votes
4answers
4k views

Why does an LED have to be a diode?

I know LED stands for Light Emitting Diode; but why does this component need to be a diode to emit light? My question assumes that the "leds" we see everywhere (for lighting, screens, etc) are ...
24
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5answers
14k views

Why don't relays incorporate flyback diodes?

Warning: this may be an extremely naive question (if so, please enlighten me). Many applications of relays require a flyback diode to protect against inductive voltage. I'm unable to find any relay ...
22
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5answers
25k views

When/why would you use a Zener diode as a flywheel diode (on the coil of a relay)?

I have just been cogitating on the tutorial at http://www.electronics-tutorials.ws/io/io_5.html, and in the discussion of flywheel diodes it includes this sentence without further elaboration: As ...
22
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7answers
36k views

Correct use of Flyback or Snubber diode across Motor or Transistor?

From seeing a few schematics where the flyback or snubber diode has been placed across the transistor C-E terminals (Right Configuration), instead of what I typically seen as the the flyback being ...
22
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2answers
2k views

Half-wave diode rectifier - is textbook wrong?

I've noticed that in all resources on diodes and rectifiers, they show the output voltage as the positive half-wave of the input signal. However, that seems wrong. I understand that there's a voltage ...
21
votes
7answers
12k views

Why is the diode forward voltage constant?

When you have a diode with a certain barrier voltage (e.g., 0.7 V for Si) and you apply a voltage higher than this barrier potential, why does the voltage across the diode remain at 0.7V? I ...
21
votes
4answers
28k views

How diodes protect H-bridge DC motor driver?

I don't really understand how these diodes in this circuit and similar circuits (like driving a relay circuit) protects the controller circuit from the energy stored by the inductance of the coil. I ...
21
votes
3answers
4k views

Compensating the forward voltage drop of a diode signal rectifier

I am reading Arts of Electronics and they are showing this circuit: It says that D1 compensates for D2's forward drop by providing 0.6V of bias. I don't understand this circuit at all. Is the +5V an ...
21
votes
1answer
17k views

Understanding an 'ideal' diode made from a p-channel MOSFET and PNP transistors

The Raspberry Pi B+ models have a protection circuit between the USB connector and the 5V net on the board. They recommend putting a similar protection circuity on a Pi HAT before 'backpowering' the ...
19
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5answers
3k views

Why does my multimeter show a wrong voltage over a large resistor?

I am having a hard time answering one particular question about our experiment.. In our experiment, R1 and R2 were set to 1Meg each and later to 10k... I understand the need for R1 and R2 a bit. ...
19
votes
5answers
16k views

Lowest voltage drop diode possible

I am harvesting energy from an NFC device using a tuned antenna on my PCB. Though this method I am able to generate about 3.05V. I would like to charge a super capacitor using the power harvested from ...
19
votes
2answers
43k views

Difference between a rectifier diode and signal diode

Can somebody please explain to me the differences between a signal diode and rectifier diode in terms of their electrical characteristics and their Lissajous patterns? I know that Shockley's equation ...
18
votes
12answers
12k views

Does a diode really follow Ohm's Law?

Does a diode really follow Ohm's Law? Ohm's law states that the current through a conductor between two points is directly proportional to the voltage across the two points. Introducing the ...
18
votes
5answers
31k views

Is full wave rectifier better than half wave one?

I am curious if there are practical differences between a DC power supply based on a half wave rectifier or a full wave rectifier. I mean I have a few small DC power supply units which should give ...
18
votes
2answers
3k views

Why did they use ultrafast diodes in a 50 or 60 Hz bridge?

This is again from an HP power supply (PSU). The incoming 230 V is rectified into 340 VDC and is fed to a switched-mode supply. The odd thing here is that the manual for that unit, HP6023A, ...
18
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5answers
107k views

Diodes in parallel or series

I am wondering what the effects are of putting diodes in parallel or putting them in series. (like current capabilities, voltage capabilities etc.) Let's say I have a datasheet of a diode. What ...
17
votes
7answers
47k views

Using a diode to ensure current flows in only one direction, without causing a voltage drop

To power my microcontroller (ATmega8), I am using a ~5.4V voltage source. I want to ensure that I don't accidentally connect the voltage source in reverse, and figured a diode would be a nice way to ...
17
votes
7answers
27k views

Can a diode fail to open position?

I know a diode can short out and fail closed. Is it possible for a diode to fail in the open position, and what would cause this to happen?
17
votes
5answers
84k views

What is the difference between 1N4001 and 1N4007 other than their maximum reverse voltage?

I compared 1N400x diodes here. As far as I see, all of their properties are same other than their maximum reverse voltages. Their maximum current recovery time reverse leakage current capacitance ...
17
votes
3answers
3k views

Full-bridge converter rectifier kicks

I'm in the process of building an 8kW isolated DC/DC converter, full-bridge topology. I'm seeing some interesting phenomena on the diodes. When each diode becomes reverse-biased, a voltage spike ...
17
votes
6answers
2k views

“Standard” components…?

In class we are designing a few different circuits and it uses some diodes and opamps. Everything is fine on paper and everything makes sense. These are only ever refereed to as a "diode" or "opamp". ...
17
votes
2answers
11k views

Uses for a Double Diode?

Can anyone tell me what a 'double diode' is used for? For example, a BAV99. I'm not sure of the correct name for it and so can't find it in any of my reference books. I've come across one in a circuit,...
16
votes
2answers
3k views

How does a zener diode and a resistor regulate voltage?

I'm having trouble understanding the simple voltage regulator that can be built using a zener diode (from section 2.04 in the Art of Electronics). I know that it would be better to use amplifiers, et ...
15
votes
2answers
2k views

Why doesn't my multimeter show the correct Zener reverse voltage?

I have a 3.3V Zener diode, brand new from a reputable source. When I set my Fluke 101 multimeter to diode test mode, and put the black lead next to the dark bar on the diode and red on opposite side, ...
15
votes
5answers
2k views

Are varicaps (capacity diodes) obsolete?

I have read that varicaps (capacity diodes) are a "modern" alternative to variable capacitors. In several electronics books only positive properties of varicaps are mentioned. But several major ...
15
votes
4answers
32k views

How does a diode clamping circuit protect against overvoltage and ESD?

I always see this circuit when talking about overvoltage or ESD protection (does this circuit accomplish both, or just one?): However, I don't understand how it works. Say I put in 20V at Vpin. So ...
15
votes
4answers
2k views

How do I calculate the current in parallel branches?

I've been playing around with an Arduino for a while now, and while I know just enough about simple circuits to get little projects up and running, I still don't know enough to figure out what's going ...
15
votes
2answers
30k views

Differences between TVS diode and Zener diodes, in diagrams and in practice?

I have been looking at circuit protection using TVS and Zener diodes. I have seen the following symbols used to represent TVS diodes in circuit diagrams: simulate this circuit – Schematic ...
15
votes
1answer
9k views

What are the disadvantages of using a diode bridge for DC polarity?

As far as I understand, diode bridges are mainly used to convert AC into DC, but one can also use them just to ensure an expected DC output polarity for arbitrary DC input polarity. I have some small ...
15
votes
1answer
22k views

What is the difference between “reverse stand off voltage” and “breakdown voltage” on a TVS?

On a transient voltage suppressor, let's take a unidirectional Fairchild P6KE11A for example, what is the main difference between reverse stand off voltage (\$V_{RWM}\$) and breakdown voltage (\$V_{BR}...
14
votes
4answers
8k views

Building a passive ethernet hub with anti-parallel diodes

I've found several guides online on how to build a passive ethernet hub, the design is always the same: I'm wondering what each of the 2 anti-parallel diodes do? For both positive and negative ...
13
votes
5answers
3k views

Diode not behaving as short circuit

I recently started to play with online circuit simulator and in a very simple circuit I can't understand the behavior I have a voltage source connected through a current limiting resistor to a diode ...
13
votes
3answers
1k views

Forward drop of diode vs forward drop of LED

It is always said that forward voltage drop in the diode is around 0.7 volts. LED also being a diode, why does it have a greater forward voltage drop of around 3 Volts? What is the model of LED that ...
13
votes
3answers
1k views

Zener diodes in glass axial package - not inherently shielded from photoelectric effect?

I discovered today that a glass packaged axial leaded 5V Zener diode will become a source of about 0.450 Volts when the glass package is held in the beam of a low-power purple (405nm) laser pointer. ...
13
votes
5answers
23k views

What happens after a zener diode breaks down?

I've strapped a 6V zener diode across the 5V/GND rails of my circuit, and I want to know what will happen if my supply were to somehow fail pass 12V straight to the rest of my board. The zener will ...
13
votes
2answers
2k views

Can anyone tell me what is the purpose of diodes at the output of a chip?

I am new to engineering, and now I am puzzled. My friend bought the product and he gave me the circuit diagram. But I don't know the purpose of diodes D10-D17. Can anyone give me an answer?