hello all,

i was doing some basic tests with a schottky diode, without succes, so finally i've decided to ask for some help, since i'm sure missing something important about the theory.

I have put up a circuitry like in the picture attahced



I would try to rectify the reduced 125 Khz signal. Due to the 125 Khz frequency, i've decide to use a schottky diode (don't know if the choice is appropriate), so i was expecting to see in his cathode a only-positive pulsed half-wave. Instade i continue to see by oscilloscope a complete sinusoidal wave.

if any help,
many thanks, angelo

Attached Images

circuit.jpg (10.2 KB, 36 views)

 

What kind of diode are you using? Diode capacitance can cause this. If you are using a high-current diode (high capacitance), then you need a low-value resistor as a load. You apparently are using an oscilloscope. The input resistance is much too high.

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Ron

 

Yes, the input resistance of the scope is very high, like more than 1 Mohm. You need to load the right side of the diode with a resistor to get what you want. Resistor value should be much more than the values of those two on the left, but not nearly as high as 1 Mohm.

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RadioRon

 

If your Schottky diode can survive 38V then it should have the attenuator as its load like this:

Attached Images

Schottky rectifier.PNG (16.5 KB, 9 views)

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Uncle $crooge

 

Schottkys are fast, yes? Silicon-metal diode, no minority carriers to sweep out? Or is my semiconductor physics bad?

 

Big Schottkys have big junctions, and therefore lots of capacitance.

Attached Images

	MBRS320 capacitance.PNG (15.3 KB, 11 views)
	MBR1045 capacitance.PNG (19.8 KB, 10 views)

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Ron

 

Wow, I've never seen a Schottky that did 200V!

 

Nor I. I kind of need one.

 

Thanks all,

sorry for incomplete data, the diode i'm using now is 1N5819, but i eventually can buy another one i need in 5 minutes from my home.

Yesterday i've imagine something about it, looking some diagrams here and there, so i've try to load the right part with a 33K resistor, but i can't measure anything anymore at the cathode, 0 level always.

Thanks again,
Angelo

 

What are the values of your resistors, and why are you doing this?

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Ron

 

values of my voltage divider are 10M and 2,2M. Actually i'm just wandering how i can see the positive-only signal i was expecting, with negative part cutted by the diode, and then if possible to have a DC from this signal, using a capacitor.


angelo

 

A total of 12.2M is not a load. Try it with 10k in series with 2.2k.

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Uncle $crooge

 

200V... get them upto alot higher

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Nothing is impossible.
Once a problem is realised, the rest is just details

 

FWIW, I experimentally discovered my 1N5822's will actually do 50% more PIV than they're rated for. Failed short though - is that normal?

 

How about 6kV? Pie in the sky, of course.

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Ron