Dear Sir/Madam,

Recently I bought a transistor tester, it helps me to check many unknown devices and show me the important information.

I tested with a LED and it reported Ir=4nA, C=23pF, what does it mean?

Best regards,

Kelvin.

 

Ir is Iᵣ, reverse current through the diode when it is reverse biased, that is hooked up "backwards".
C is capacitance, in this case 23 picofarads.

 

@Kelvin Lee

@Yaakov is totally correct! But just so u know, some ppl (and also datasheets) informally call reverse current _leakage current_
Also, cuz of parasitic effects, capacitance reading isn't vry useful w/o knowing test frequency (which should be specified in tester's manual otherwise u can just suss it out with TDO during test)

 

Ir is Iᵣ, reverse current through the diode when it is reverse biased, that is hooked up "backwards".
C is capacitance, in this case 23 picofarads.

Thanks Yaakov, what is the use of reverse current? Is it the same as the current need to light up the LED?

 

what is the use of reverse current?

'Use' is inapplicable in this context -- Ir is merely a characteristic of semiconductor junctions - noted as a current under a specified reverse bias EMF < Ebr...--- Not to be confused with Zener (i.e. post-breakdown) current!

Is it the same as the current need to light up the LED?

Illumination of an LED requires conduction under forward bias conditions! Typical I[fwd] falling in the range of 1-30 mA for discrete devices...

Best regards
HP

 

But just so u know, some ppl (and also datasheets) informally call reverse current _leakage current_

Correct! -- Such stems from the (IMO dubious) analogy of a semiconductor junction to a fluid-flow 'check valve'

Also, cuz of parasitic effects, capacitance reading isn't vry useful w/o knowing test frequency

Absolutely! Then too, wave-shape (i.e. harmonic profile) must be taken into account! @Kelvin Lee If/where the reactance values are important, please heed @Aleph(0)'s advice and have a 'gander' at the test frequency and waveform!

Best regards
HP

 

Recently I bought a transistor tester, it helps me to check many unknown devices and show me the important information.

Does the documentation indicate the current for the Vf determination, or the voltage for the reverse current value? Without that information, measurements are only good for making comparative assessments.

 

Illumination of an LED requires conduction under forward bias conditions!

Just out of curiosity, does a pn junction not emit any photons due to reverse leakage?

 

Also, cuz of parasitic effects, capacitance reading isn't vry useful w/o knowing test frequency

Also the test bias voltage will play a big role

 

Just out of curiosity, does a pn junction not emit any photons due to reverse leakage?

Possessed of PEs in the optical range? - I very much doubt it? -- Of course some --as a practical matter trivial-- resistive heating (with secondary IR emission) will occur - but that's hardly the point... Intriguing idea, Tho...


Re: Junction capacitance:

Also the test bias voltage will play a big role

Indeed! -- 'Tis the 'Varactor' (i.e. 'Wooldridge') effect come a callin' --- You getting this @Aleph(0)

Very best regards
HP

 

Just out of curiosity, does a pn junction not emit any photons due to reverse leakage?

When my son was in middle school, or maybe grade school, I was trying to get him interested in electronics. I was showing him how a curve tracer worked and was using some LEDs to show him how brightness and forward voltage were affected by current.

I distinctly remember observing light being emitted from a reversed biased LED. I thought it odd at the time and have since seen numerous references stating that photons aren't emitted under reverse bias/leakage. I'll have to do some more experiments.

 

I distinctly remember observing light being emitted from a reversed biased LED.

Interesting... Phosphorescence, perhaps?

I'll have to do some more experiments.

Please share your results with us!

With genuine intrigue!
Very best regards
HP