Following some rather poor advice given to one person on Instructables, the advice not coming from anyone on instructables of course, I thought I would give a few tips and help on some parts of electronic. I will try and keep it simple and so those who often say they like electronics but as one person put it, was rubbish at it, will be able to understand a bit more and enjoy making some projects safely.

As with many things there is a lot to learn so let’s have a look at basics.
I want to have a look at diodes, in particular the light emitting diode or LED.

Step 1: The Diode

A diode is a device which, when a voltage is put on its wires in one way will let a current flow but if the connections are reversed the current will be blocked. It is a valve. If we compare it to a water valve, the pressure of the water is the volts and the water is the current. So the diode is like a non return water valve.
There are many types of diode, signal diode, power diode, schottky diode, zener diode, avalanche diode, laser diode and of course the light emitting diode.

Step 2: Diode Data

All electronic components come with what looks like a complicated data sheet and it is this that lets people design circuits which will work and also be safe and not blow up. In the case of diodes there are some things which are important.
The maximum forward current, this is usually given as a symbol ‘If max’ although there may be other symbols. This is the maximum current or amps that the diode can take without it melting. When current flows through a diode it gets warm. The more current the hotter it gets until it melts. Bye bye diode. Now if say the maximum current for a particular diode is 2 amps, that is If max is 2A that does not mean that 2.1 amps will immediately blow it up. However over time it will get hot and MAY fail. Certainly is say you pass 3 amps it will fail as it gradually gets hot. So look at If max

There is another similar thing ‘If avg’. That is average forward current. This is always less than If max. So over a period of time, say If avg is 1.8A and If max is 2A and for some time the forward current is 1.9A and some 1.7A things may be OK. But if the forward current is always 1.9A then you are heading for trouble.

Another important thing is the maximum voltage the diode can block. Remember a diode only lets current flow in one direction and current flows when a voltage is applied. But if the voltage you put is in the direction that the diode blocks current is too high it ‘punctures’ the diode and that is instant death. The number you are looking for is the piv or peak inverse voltage. It is vital you never apply a voltage any higher than this in the blocking direction of the diode. Here in the UK the mains is 230volts rms. That means the peak of the mains is about 320 mains, don’t worry why at the moment just accept it. So If I put a diode in a circuit that is connected to the mains I would chose one with a piv of at least 400v

If you can look at pdf files here is the full data for a popular range of diodes.

Step 3: Getting It All Together

Let’s look at part of the data sheet for a popular diode the 1N4001
DC part no.: 1N4001
Maximum recurrent peak reverse voltage* : 50 V
Maximum DC blocking voltage: 50
Maximum average forward rectified current 1.0 A
Maximum overload surge 8.3ms single half sine-wave: 50 A

This shows that the maximum reverse voltage can be 50 volts. The average forward current is 1 amp and the maximum pulse if you like of current is 50 amps which cannot last longer than 8.3 milli seconds.
There are other things in the data for this diode but these are the important ones, after that you might have to look at the rest.

So that’s it for a bit about diodes, this is my first instructible so I would appreciate any comments bad or good or any questions. In a short time I will look at LED’s and then answer a question I have been given.
<p>Nice. This answered a lot of my questions surrounding the tech info I need to purchase the correct diode.</p>
I don't understand what you mean by &quot;the peak of the mains is about 320 mains.&quot; UK mains voltage is 230v with a tolerance of +\-10% eg 216-253v.
OK. The UK mains is as you say 230v but it is ac or alternating current. The voltage raises positively then descends to zero and continues negatively then increases back to zero and starts again. The path is a sine wave. The quoted 230v it's the voltage equivalent as if the voltage was static. That is dc. So the average voltage is 230v. This means at times the mains is at zero volts, at other times it is over 230 volts. The result is the same as if it were static at 230v. This is termed 230v rms or root mean square. To calculate the peak voltage, take the rms i.e. 230 in this case and divide by 0.7 which gives 328. I would choose a component which would be able to operate continuously at least 400v to cope with the peaks of 328v. Hope this helps, if you want further clarification I will try to help further.
<p>Thank you for taking the time to reply. I get it now. </p><p>The quoted 230v is basically an <strong>average</strong> over a given time. The peaks will go higher than 230v or lower than -230v in one cycle</p><p>Vrms = Vp / sq root of 2 (1.4) </p>
<p>Here is a graphic of RMS and peak to peak</p><p><a href="http://www.sengpielaudio.com/SpannungSpitzeEffektiv02.gif" rel="nofollow">http://www.sengpielaudio.com/SpannungSpitzeEffekti...</a></p><p>I know it helps me visualize what is going on. The time, and area of RMS is the most significant value. Which is not to say that peak to peak isn't occurring but it just isn't as important I suppose. Kind of like when they throw out the high, and low scores judging athletic events? Something like that I guess.</p>
Sorry, after reading my own post at just gone midnight I see a mistake in the theory. The calculation of peak voltage should read rms x 1.4 = peak that is 230 x 1.4 = 322v. Sorry about that.

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