Author Topic: How much current does it take to switch a diode?  (Read 3809 times)

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Re: How much current does it take to switch a diode?
« Reply #8 on: December 17, 2011, 14:38:25 pm »
I'm not asking about the specs of diodes,but the operation of the diodes.I know what my diodes are,and the mur1550 or 1560's won't work at the frequecies I'm running.Any of the diodes I've tried just don't seem to be doing anything.If I take the diode out, it will still produce the exact same signals when in resonance.They just do't block the way Stan says.

My set up is using so little power,that I don't think that there is any current going through the coils that can turn on the diodes to make it block.

Understand what I'm saying?
Don
Hi Don,

If I may ask,
do you use your home build 3" resonance cell isolated in Delrin replica? Or other tubes connected?
Does your VIC core material has about 2000 ui? No? maybe the (B)EMF current induced from the chokes (magnetic fields) is too weak to bounce on the diode and to the cell and restrict amps.

Br,
Webmug

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Re: How much current does it take to switch a diode?
« Reply #9 on: December 17, 2011, 15:40:30 pm »
HMS,
My setup is pulling around 200-300ma into the primary.I will test across my diode as you have,and see what I get.

Webmug,
I'm using my delrin cover tube set,that's all I have.
I'd have to look up the cores ui,I don't know it off hand.
The core is a Ferroxcube U core,the largest one they make.The legs are @ 3/4 inch in diameter.
The chokes are in the 10-11 Henries ech,very high.

I'm going to make some new chokes with larger gauge wire and just a couple  hundred turns,to see if more current will help.I'll also try the same idea with the primary and secondary.

Don

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Re: How much current does it take to switch a diode?
« Reply #10 on: December 17, 2011, 17:02:55 pm »
(http://upload.wikimedia.org/wikipedia/commons/thumb/a/a5/Diode-IV-Curve.svg/500px-Diode-IV-Curve.svg.png)

Ohm's Law for a diode, relates the current through the diode to the voltage across it, by an exponential relationship, the 0.7 volts is just an approximation, and it really depends on where on that curve you are.

With a reverse voltage then the current should be zero, but really it is just a minimal value so the circuit should be "off"

The next question is how and when do you reverse bias that diode in the circuit, at what point in the pulse train? It is reverse biased when the voltage on the secondary is lower than the voltage on the choke at the end that connects to the diode.

But since voltage is relative it becomes more unclear, you have to choose a reference for the circuit, which may or may not be grounded on the secondary side.

I think a differential probe across the diode would be a useful step.

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Re: How much current does it take to switch a diode?
« Reply #11 on: December 18, 2011, 23:19:53 pm »
yea current can only pass in the forward bias direction. If you try to pass current in reverse bias, you will cause an avalanche effect and damage the diode. This is why in my video where I explain how the the LC circuit operates, I saw that due to the diode you will have only the positive phase current flowing through the circuit. The diode also keeps the positive phase of the L2 choke from reaching the secondary. Another thing to remember is that positive voltage is lacking electrons and a negative voltage has an abundance of electrons. While keeping this in mind, think of how a a transistor operates. You have a P material sandwiched between two N materials to form a NPN transistor. In Stephens radio interviews he says the cell acts much like a transistor, you have the two plate (N material) and the water in the middle (P material). That is something for you guys to think about ;)