Why is this circuit not rectifying?

[David-Baratheon]

I set up this half-wave rectifier to test out multisim. It should be cutting off the signal in one directon. Any idea why it isn't doing that?

[aa232004]

hello,

look , I am sorry but there is nothing wrong with MS, your cuircut is wrong.

you must connect resistor of some realistic value in serial with diode.

I'd suggest to read some basic book about how electronic works.

good luck

Michael

[David-Baratheon]

I have a degree in electronics. I know how electronic circuitry works.

The diode should only allow current in one direction. The resistor you usually see in circuit books represents the electronic load that would be receiving the DC voltage.

It does also have the additional functionality of limiting current, and I have just realised that MultiSIM actually has components that fail when certain criteria is met such as overheating.

In this case, it is most likely the breakdown voltage of the diode that is causing the failure. I need a diode that can still block current in one direction at UK mains voltage levels. How do I spec the diode to ensure it will prevent voltage breakdown at 230V R.M.S?

[aa232004]

Hello,

Look, if you do know electronics,why you have a problem with just 1 component  circuit

just go ahead and use your knowledge. and skip following.

but  - just in case  - if you decide  that your knowledge is not deep enough - read following -

first  -  I 'd suggest  to you to remember that -

major function of resistor is to limit current. and create voltage across it's terminals when that current flows through that resistor.

second -

in your original circuit everything works just fine. you just do not know what to expect from such circuit and how to measure it.

according to Kirchhoff's voltage law (KVL)  -  The directed sum of the electrical potential differences (voltage) around any closed network is zero - ALWAYS.

so what you see on scope screen is the source's  voltage. no problems at all.

ii you install current meter in series with your diode you will see that diode does it's job  - getting open and closed, but current getting damn high, up to few KA,

and why is that - because you did not put the resistor.

there is the second circuit attached - that one with resistor - I guess that is what you expected to see.

back to diode selection -

you have to figured out 2 major things - max reverse voltage and max direct current of that diode

reverse voltage- convert source RMS voltage to P-P , divide it by 2 and add 30..50 % - and that is reverse voltage of your diode should be.

direct curent  - depends on application - you have to calculate it your self.

good luck

Michael

[David-Baratheon]

Ok but how do I search for components based on spec? i can only see how to search by family or search for names.

[aa232004]

Hello

now you hit the right nail on the head - as much as I know it is impossible in MS.

you have to go and check one by one which is pretty annoyng.

another option is  to go to DoGIKey.com or octopart.com  and find diodes that fit your needs and then look for the same diode in MS DB.

 and BTW, thanks for bringing that situation up - I am going to ask NI to include that fiture  in next version.

good luck

Michael

[David-Baratheon]

Ok yes that will be a good feature. The only trouble with searching for components from a supplier is the MultiSIM libraries are fairly small, so won't necessarily have whatever I find. 

Are more of the components likely to be found in digikey?

Also, is there a way to input my own components, or will suppliers provide any sort of files so I can inport their components to MultiSIM?

Yes please do put the suggestion forward. If I am trying to rectify UK mains voltage then the diode needs to have a fairly high reverse breakdown voltage, so making this circuit will be quite difficult unless I use a really high current limiting resistor.