How can I measure the piv of an unknown diode?

Thread Starter

whitehaired novice

Joined Jul 15, 2017
289
My previous electronic knowledge is about 60 years out of date. I have a vague memory of testing the piv of some diodes. I think I used a high voltage--probably 600 volts-- a high ohm resistor in series with the diode and --really vague here--an oscilloscope.

Surely the voltage must have been AC? Or may half wave rectified AC? I did not have access to a frequency generator and only had access to the 'scope for a short time. Could I have used my 1000 ohm/volt multimeter and not the scope?

Obviously, if I had a variable voltage supply which ran up to 600 volts (or more) I could series the diode with a 1 meg resistor and measure the voltage across the diode while increasing the voltage slowly till it breaks down. That would work but who has such a supply? Not most hobbiests.

Any instruction will be appreciated.
 

Janis59

Joined Aug 21, 2017
1,834
Just put in the serie some 1 MOhm resistor or larger, switch to the LATR and measure with oscilloscope a current.
 
Last edited by a moderator:
Obviously, if I had a variable voltage supply which ran up to 600 volts (or more) I could series the diode with a 1 meg resistor and measure the voltage across the diode while increasing the voltage slowly till it breaks down. That would work but who has such a supply? Not most hobbiests.
That would work. Your variable supply can be an isolated Variac (isolation xformer + Variac), rectifiers and a capacitor and a bleeder resistor.

See: www.hammondmfg.com/pdf/5c007.pdf

Breakdown is non-destructive if current limited.
 

Thread Starter

whitehaired novice

Joined Jul 15, 2017
289
It has occurred to me that I don't need a variable voltage. I can put a several megOhm resistor in series with, say a 600 volt low current supply and connect my diode (observing polarity) across the voltage, then measure the voltage across the diode. Care must be taken in connecting the diode because 600 volts hurts.

I have a good isolation transformer so I think I could double the 120 volts twice.

Any advice?
 

ebeowulf17

Joined Aug 12, 2014
3,307
Full wave rectified and filtered 120 VAC gets you 1.4*120*2 or about 336 VDC.

In any event simple curve tacers have been built using a transformer. One such device is: http://www.arrl.org/files/file/QEX_Next_Issue/May-June2017/Ferreora.pdf

Here's something to look at: http://www.valvewizard.co.uk/curvetracer.html
Are you sure about the last *2? I thought full wave rectified, filtered DC was 1.414 * VAC RMS value. Peak to peak readings involve the doubling, but I didn't think normal DC conversion did. So, I'd expect about 170VDC from 120VAC.
 

KL7AJ

Joined Nov 4, 2008
2,229
My previous electronic knowledge is about 60 years out of date. I have a vague memory of testing the piv of some diodes. I think I used a high voltage--probably 600 volts-- a high ohm resistor in series with the diode and --really vague here--an oscilloscope.

Surely the voltage must have been AC? Or may half wave rectified AC? I did not have access to a frequency generator and only had access to the 'scope for a short time. Could I have used my 1000 ohm/volt multimeter and not the scope?

Obviously, if I had a variable voltage supply which ran up to 600 volts (or more) I could series the diode with a 1 meg resistor and measure the voltage across the diode while increasing the voltage slowly till it breaks down. That would work but who has such a supply? Not most hobbiests.

Any instruction will be appreciated.
With or without destroying it?
 

Thread Starter

whitehaired novice

Joined Jul 15, 2017
289
KL7AG--nondestructive.
ebowulf17--I think KeepItSimple was using my doubling circuit. Actually I'm going to double twice for something around 600+
KeepItSimple--many thanks for the links. Though it is unlikely that I'll ever get my hands on a scope I did download the article about the Octopus.

Well, I do have one of those JYE scope kits but the Google machine indicates a very high failure rate and I'm pretty sure my hands are shakier than the average purchaser--so I am not holding out much hope. It is a single trace unit anyway, so no curve tracing, even if I get it working.
 
Are you sure about the last *2? I thought full wave rectified, filtered DC was 1.414 * VAC RMS value. Peak to peak readings involve the doubling, but I didn't think normal DC conversion did. So, I'd expect about 170VDC from 120VAC.
Your correct. A 5 day migraine has gotten in the way. I confused 120/240 auto-switching power supplies. In one case they half wave rectify (2400) input and the other full wave rectify to get the nominal 168V DC rail to start with. Ratings for that filter cap are around 350-400 V.

Thanks much (corrected in post)!
 

ebeowulf17

Joined Aug 12, 2014
3,307
Your correct. A 5 day migraine has gotten in the way. I confused 120/240 auto-switching power supplies. In one case they half wave rectify (2400) input and the other full wave rectify to get the nominal 168V DC rail to start with. Ratings for that filter cap are around 350-400 V.

Thanks much (corrected in post)!
Sorry about the migraine. Hope you feel better soon!
 
Top