No Markings - Identify Part

[Sceadwian]

The cost of first class postage.

More than the part =)

 

[colin55]

Send me one, and I'll measure the reverse current for you.

This is something new in electronics that I have never learnt.
Please let me know what University you went to.

 

[DerStrom8]

I have absolutley no idea what a "1n148" is.

How do you think they test a diode to determine what its PIV is?

You know very well what he meant.

My bet is it being a 1n4148 or 1n914 (basically the same). I suppose it could be a zener, but there are ways to test that. The following is a simple way to check and see not only if it is a zener diode, but what voltage it is:

Measure the forward-biased voltage on the Zener diode using the diode function on a multimeter. Do this by putting the positive or red lead on the anode side of the diode, which is unmarked. Place the negative or black lead on the cathode side of the diode, which is marked by a stripe. A Zener is made from silicon, so an undamaged one will read 0.5 to 0.7 V when it is forward-biased.

Measure the reverse-biased voltage on the Zener diode by switching the multimeter probes. Place the positive lead on the marked or cathode side, and the negative lead on the unmarked or anode side. You should get a reading indicating infinite resistance or no current flow.

Attach the positive side of the 9-V battery to one side of a 200 ohm resistor and connect the other end of the resistor to the cathode side of the Zener diode, so that it will be reverse-biased. Then wire the remaining diode terminal to the negative side of the battery.

Place the multimeter on a DC voltage setting. Measure the voltage across the diode by placing a multimeter lead on each terminal. It should read the approximate zener voltage. Note that the voltage between the battery and ground remains at 9 V.

I hope this helps, Jason. Good luck!
Regards

 

[KeepItSimpleStupid]

I can measure to a 100 pA resolution at least. That's why I offered. Let's see you do that on your DVM. Power diodes will have a much higher leakage current.

Reverse current: The current that flows in the opposite direction. For a 1n4148, it's on the order of 25 nA.

Hey, I used to measure currents below 1 pA and set the system up to do so. Measuring the resistance of a piece of paper was a snap. It also depended on the amount of moisture in the paper. It's an insulator, true, but a measurable one. Resistivity of the paper would have been a bit harder, but I had available to me the equipment to do so.

Reverse current is Ir on this datasheet: **broken link removed**

My guess is, you've never read a datasheet before?

More reasons to believe that: The 1n4148 can stomach 200 mA continuous. A far cry from 3-4 mA.

As for reverse current: Must of been the solid state physics course or reading in grade school. Just not sure. Or was it working a a semiconductor research lab?

 

[colin55]

Reverse current is not going to differentiate a 1N4148 from a whole selection of diodes.

 

[Sceadwian]

Reverse current is not going to differentiate a 1N4148 from a whole selection of diodes.

Unless you decide to look at the leakage current and compare that to the PIV voltage at other currents. Just like a diode forward biased (moreso in fact) a diode reverse biased into conductance will exhibit drastically different curves depending on the current ranges you specify. Where is the line drawn, from what basis is standard?

I have no doubt your generalization is accurate for reverse bias testing but this must done with a 'high' voltage constant currents source.

 

[KeepItSimpleStupid]

50 nA minimum for a 1n4001 and 25 nA maximum for a 1n4148. Sure can help differentiate.

 

[colin55]

We started with trying to determine if a surface-mount diode was a 1N4148 or nearly equivant and ended up with someone trying to say it was a 1N4001.

 

[KeepItSimpleStupid]

There isn't a whole lot of difference between 20 V and 75V. There is a big difference with junction temperature. The 1n4148 is a very different diode from a zener, schotkey, rectifier and fast recovery rectifier.

It would't hurt to do:
1. Max forward current - Waste one for this test
2. Forward voltage
3. Forward breakdown voltage - It's non-destructive
4. Reverse breakdown voltage - Non-destructive
5. Leakage current.

This will easily answer:
1.Is it A ZENER and he voltage?
2. PRV providing you have a power supply with enough voltage
3. Is it a schotkey
4. Is it likely to be a 1n4148

Lets's add capacitance. I could do that too. Agilent U1733C Rectifiers will have a much lager capacitance than a regular diode.

 

[KeepItSimpleStupid]

Did I try to say it was an 1n4001? Nope. The likely candidates are zener, 1N4148 and/or 1N914.

I'm not kidding. Send me two, I'm < than 200 miles away and I'll see what I can come up with. One I'll toast finding the forward current.

 

[Sceadwian]

As I asked earlier, what currents define the breakdown and forward current voltages?

 

[KeepItSimpleStupid]

Leakage current depends mostly on junction temperature. That's easily monitored looking at Vf.

Leakage current makes the most sense near the PIV rating which is how the IN4001 is measured. The 1n4148 is a function of junction temp.

 

[KeepItSimpleStupid]

Breakdown voltage is a voltage phenomena. It is NON-DESTRUCTIVE if the current is limited. The diode itself will do most of the limiting.

What's a "forward current voltage"? Confused, big time.

 

[KeepItSimpleStupid]

OK, you meant current at a particular forward voltage. Obviously, if it's a rectifier, it has to be <=PRV, so assume it's at the PRV. I think that's a safe assumption. Reverse voltage is NON-DESTRUCTIVE and it's also the Zener voltage. The Zener should be much flatter, I would think.

I need to look at a datasheet.

 

[KeepItSimpleStupid]

The reverse leakage current for Zeners are fairly high: https://www.electro-tech-online.com/custompdfs/2012/04/1N4728-4764.pdf

So, anyway:

Low capacitance: Good possibility it's a 1n914/1N4148
High leakage even at 1V: likely a Zener diode

Let's leave out variactor diodes and high voltage diodes.

 

[Sceadwian]

Reverse voltage is NON-DESTRUCTIVE and it's also the Zener voltage.

Just a technical correction, avalanche breakdown and Zener breakdown are separate semi-conductor effects so this statement is not quiet right.

 

[KeepItSimpleStupid]

Yea, I know that. A technicality. All Avalanche diodes are called Zener diodes and both processes happen around 5.1 V. It's still non-destructive. Go find a diode labeled an "avalanche diode"? Ok, they exist: http://www.hitachi.eu/pdd/products/diodes/controlled_avalanche/index.html, but it's really the same mechanism causing PRV, just controlled.

Exceeding the Zener voltage does what? It regulates at the Zener voltage providing you limit the current. Same is true with the PRV. It's just not a tightly controlled parameter.

 

[Sceadwian]

but it's really the same mechanism causing PRV

The correction was a minor technicality but an important one, the statement in quotes above is absolutely false. Avalanche and Zener breakdown are discretely separate breakdown modes and behave differently, specifically avalanche breakdown exhibits hysteresis where zener breakdown does not. Anything under 5 volts is going to be dominated by the zener breakdown and anything over is going to exhibit more avalanche breakdown (in general) Avalanche breakdown is more prevalent in lightly doped semi conductors and zener breakdown is more prevalent in heavily doped junctions, and as temperature increases zener breakdown diminishes and avalanche gains.

I'm not sure how true zeners are constructed on a fabrication level for voltages over about 5 volts but I suspect they're actually multiple zeners in series, or are in fact not truly zener diodes but hybrids which is why there's so much interchangeability of the terms avalanche and zener. It's something I'd like to delve into deeper but it's not easy to come across fabrication masks of cmos devices and details of the doping of specific components. I'd imagine you'd have to be deep in the industry to have any true knowledge of what is commonly out there.

I would hazard a guess that the only true zener diodes out there are the ones that are under 5 volts

All Avalanche diodes are called Zener diodes and both processes happen around 5.1 V

This again is absolutely false, for the reasons stated above. Both processes can happen around 5.1 volts which one dominates is highly complicated and outside the scope of this discussion. It is simply important to note that the reasons for the breakdowns are different and move on, those that want to get into the physics a bit more can try to dig.

It's still non-destructive

This is mostly false, any zener or diode that exhibits breakdown over it's rated forward current will smoke, and possible sooner because the voltage will be higher at the same current so the dissipated power will be higher at the same current.

It's only non-destructive if something else limits the current, there is no inherent current limiting to either breakdown mode, being that your statement requires additional components to be in the circuit it is not appropriate to state about breakdown modes in general.

 

[KeepItSimpleStupid]

**broken link removed**

Doping controls the mechanism. Also note that both or non-destructive if the current is limited and I've been saying that all along Which is also what I remember from Solid State Physics.

This thread is starting to diverge into an argument that we both agree on, but isn't really relevant to making an educated guess of the diode type.

I'll still offer what I can because of the instrumentation I possess, namely the ability to measure small currents and capacitance. I also have a precision voltage source to 100 Volts.

 

[Sceadwian]

It's not an argument KISS, I believe we've both clarified every statement previously made to now be accurate and fully described, that's all I was trying to do. As a side note I would be curious as to what instrumentation you do have, I might take you up on that offer out of simple curiosity about some basic components. Feel free to start a new thread if you feel it appropriate (send me a private message if you do in case I miss it) or just post in here.