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Matching diodes.
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Pehr



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PostPosted: Sun Dec 16, 2007 11:53 am    Post subject: Matching diodes.
Subject description: How to?
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The Yusynth Wavefolder requires 1N4148s matched in pairs. I know how to match transistors (I think), but how does one match diodes? Confused

Does anyone know? Wink

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Pehr



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PostPosted: Sun Dec 16, 2007 11:56 am    Post subject: Reply with quote  Mark this post and the followings unread

0k 0k, I should have googled before I wrote Embarassed hehe Smile

Ken Stone wrote:
To match diodes, try connecting them in series with a 10k resistor across 10 to 15 volts, and measuring for identical drops across the diodes themselves. It would be best to use the same supply and resistor for all measurements, and try to do all measurements at the same temperature. Avoid handling the diodes while testing them to prevent body heat changing their temperature.


EDIT: Why does one need matched diodes btw?

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yusynth



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PostPosted: Sun Dec 16, 2007 12:07 pm    Post subject: Reply with quote  Mark this post and the followings unread

If you have a modern DVM, you have a position to test diodes, the procedure then is to select the diodes that exhibits the same direct voltage drop down to the mV.

If you haven't that function in your DVM you can use a very simple circuit, a 9V battery a 68K resistor (for a current around 0.1mA) and the diode to be tested. Connect the diode in series with the resistor and the battery such that the diode is polarised in direct mode (conductive mode). Then measure the voltage drop of the diode.

By the way here the diodes need be matched such that the waveshaping be symetrical with respect to 0V. In the waveshaper each diode of the pair defines the local shape of the curve, one for the positive voltage and the other for the negative voltage, that's why they must be identical to achieve the very same shape.

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Last edited by yusynth on Sun Dec 16, 2007 12:57 pm; edited 2 times in total
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Pehr



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PostPosted: Sun Dec 16, 2007 12:37 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thanks for the answer Yves! Very Happy That explaines it.

I hope my DVM has that feature, otherwise I'll just measure the voltage drop.

Cheers Smile

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a.b.o.z.



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PostPosted: Wed Jun 04, 2008 3:19 am    Post subject:   Reply with quote  Mark this post and the followings unread

And, how to match capacitors?
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yusynth



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PostPosted: Wed Jun 04, 2008 3:35 am    Post subject: Reply with quote  Mark this post and the followings unread

With a capacimeter (function available on most of the multimeters, simply measure the value of the capacitors and select those within a given tolerance window.
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6079smith



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PostPosted: Wed Jun 04, 2008 5:25 am    Post subject: Reply with quote  Mark this post and the followings unread

I'm going to knock up a simple Wheatstone Bridge specifically to match passive components... something like this (scroll down to the appendix near the end).
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Funky40



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PostPosted: Wed Jun 04, 2008 8:15 am    Post subject: Reply with quote  Mark this post and the followings unread

6079smith wrote:
I'm going to knock up a simple Wheatstone Bridge specifically to match passive components... something like this (scroll down to the appendix near the end).

that's very interesting ! thanks
I would like to match Resistors to a tolerance of 0,01% .
Can this circuit do this ? ( it seems to me )
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a.b.o.z.



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PostPosted: Wed Jun 04, 2008 2:36 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thnx smith.
175 years old technology and still doing its job.
great.
I'm amazed!
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Peake



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PostPosted: Wed Jun 04, 2008 9:10 pm    Post subject: Reply with quote  Mark this post and the followings unread

Funky40 wrote:
I would like to match Resistors to a tolerance of 0,01% .
Can this circuit do this ? ( it seems to me )


If you wish to pay the price to simply purchase them:

http://precisionresistor.com/ultra-precision-resistors-hr-hva-hvs-hva-rx-series-c-25.html

"1% to 0.005%"

They're there if you want them Smile
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