How much current does it take to switch a diode?
Started by unknown · · 12 posts
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#1 · date not recorded
In all of my testing,I keep seeing the same effect.The blocking diode doesn't seem to be doing anything,as far as blocking goes.
From what I've read,diodes limit CURRENT FLOW to one direction only.
So the question becomes, If we are restricting too much current with our choke coils,will the diode even work?
How much current does a diode need to switch on and block current from flowing in the reverse direction?
In my testing the signals going into and out of any diode I test is the same signal.No blocking effect.
Any thoughts on these questions.
Don
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#2 · date not recorded
Don, I'd have to double check to be sure but I think diodes
are switched by a difference in potential (.7V) and not
current flow.
In the wfc vic the secondary coil is the same size as each
choke. All hit resonance at the same frequency and all
coils produce ac. So if you place a probe at ether side of
the diode you'll see the ac from the nearest coil.
Your right about the diode limiting current to one direction,
but in the vic there are 2 kinds of current flow. One is line
current which is the current which flows through all
components. The other is due to the coils equivalent circuit
which is a parallel lc circuit. So all coils have a circulating
current which is where the ac comes from.
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#3 ·
If my memory serves me,it would take on average .7 volts for the diode to let voltage through,or more than that amount.
But I'm pretty sure that diodes are current limiting only in one direction and not voltage.
I may be wrong
Don -
#4 ·
what are the specs of the diode/s? Maybe we can find a spec sheet online? -
#5 ·
I don't think I ever found a place to buy the Mur1550 so I went with the MUR1560. Here is the data sheet for it, I don't know how close it is in comparison if you are using the 1550.
http://www.digchip.com/datasheets/parts/datasheet/161/MUR1560-pdf.php -
#6 ·
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 -
#7 ·
Don, If that's what you think the problem is, maybe you can do some tests to see if your right. Just see if you can change the wave form. Maybe you can lower your resonant frequency or increase your load or inrease your input voltage. Maybe if it's not to inconvenient you could wrap a primary with less turns and thicker wire -
#8 ·
Don
I'm seeing the same thing with my multisim replication. I get AC no matter which side of the diode I measure.
If I use an oscope to measure the Vdrop across the diode I see unipolar pulses. (no frequency doubling)
I should point out that my multisim replication has a somewhat high line current (over 20mA) and I'm getting the same results
so I don't think this is due to the small current that you mentioned. -
#9 · date not recorded
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.
Hi Don,
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
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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#10 · date not recorded
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 -
#11 · date not recorded
(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. -
#12 · date not recorded
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
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