Diode 1N4002: voltage drop

Thread Starter

Jan Luthe

Joined Jan 10, 2015
72
Generally what I see on 'spec' sheets for voltage drop is: "max 1 volt@1 amp".
In my circuit running at 1.2vdc, 50ma, I measure a votage drop of about 0.2v. Is this correct? Does voltage drop change with current?
 

GopherT

Joined Nov 23, 2012
7,983
Generally what I see on 'spec' sheets for voltage drop is: "max 1 volt@1 amp".
In my circuit running at 1.2vdc, 50ma, I measure a votage drop of about 0.2v. Is this correct? Does voltage drop change with current?
Yes, there is a V/I curve for diodes. Look at the datasheet. it is not linear.
 

Thread Starter

Jan Luthe

Joined Jan 10, 2015
72
Thanks GopherT. I'll try to find a data sheet. (when I said 'spec sheets' I meant the data that is listed on a site like digikey)
I looked at some data sheets and voltage drop seems to be about 0.6v @ 100ma. Would a measured voltage drop of 0.2v be reasonable for say 10ma?
 
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dl324

Joined Mar 30, 2015
8,918
I looked at some data sheets and voltage drop seems to be about 0.6v @ 100ma. Would a measured voltage drop of 0.2v be reasonable for say 10ma?
According to this from the attached datasheet; forward voltage would typically be 0.6V @ 10mA and 0.75V @ 100mA.
1n400xIV.jpg
 

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WBahn

Joined Mar 31, 2012
24,693
Thanks GopherT. I'll try to find a data sheet. (when I said 'spec sheets' I meant the data that is listed on a site like digikey)
I looked at some data sheets and voltage drop seems to be about 0.6v @ 100ma. Would a measured voltage drop of 0.2v be reasonable for say 10ma?
No, that is not reasonable at all.

For the Fairchild 1N4002 (https://www.fairchildsemi.com/datasheets/1N/1N4002.pdf), you see that the typical (as opposed to max) voltage at 100 mA is about 750 mV.

For diodes, a good rule of thumb is that the current changes by a factor of ten for a change in forward voltage of about 120 mV (this corresponds to an ideality factor of 2 near room temperature). As you can see from Figure 2, the voltage at 10 mA is about 600 mV, which is in pretty decent agreement with this rule of thumb.

As you can see, the current-voltage characteristic (on a semi-log plot) is roughly linear for lower currents. At higher currents other factors, such as parasitic resistances, start playing a more pronounced role.
 
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