Schottky diode as rectifier

[spectrum]

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

 

[Roff]

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.

 

[RadioRon]

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.

 

[audioguru]

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

 

[Speakerguy]

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

 

[Roff]

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.

 

[Speakerguy]

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

 

[dknguyen]

Nor I. I kind of need one.

 

[spectrum]

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

 

[Roff]

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?

 

[spectrum]

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

 

[audioguru]

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

 

[Styx]

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

200V... get them upto alot higher

 

[Speakerguy]

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

 

[Roff]

How about **broken link removed**? Pie in the sky, of course.

Schottky diodes made on these epitaxial diamond films have breakdown voltages >6 kV, twelve times the highest breakdown voltage reported for any diamond diode and higher than any other semiconductor Schottky diode.

 

[Roff]

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

Yeah, they usually get longer.

 

[Speakerguy]

I should neg rep you for that

 

[Roff]

I should neg rep you for that

I know. I just couldn't resist.
I got a thanks and a balanced rep for this thread. What does a balanced rep mean? I suppose it is open to interpretation by the repper.

 

[Speakerguy]

No one ever pos reps me here And I've got almost 400 posts. Hrmph.

On my other forum I've got mad rep. I got +3 in one day in recognition for calling the Iowa caucuses dead on (it's a politics/religio-stuff forum, so I won't mention any more here).

But seriously, do Schottky's generally fail as a dead short? My power supply was current limiting at 12.5A at a few tenths of a volt after it went.

 

[Nigel Goodwin]

But seriously, do Schottky's generally fail as a dead short? My power supply was current limiting at 12.5A at a few tenths of a volt after it went.

Most diodes usually fail dead short, not just Schottky's.