Electronics help... esp with a diode.

[The Chairman]

I am trying to measure a diode to find out what kind of diode it is. It looks like a Zener diode and when I measure one way I get an open. Reverse polarity and I get .426. I can post a picture of it, I guess, but I don't see any identifying marks on it.

On another note, I have a TES 2014 and want a manual for it. There are a number of features, including a transistor tester that I would love to understand a bit better. For that fact, what is the value of the diode I tested? The diode test is included in the ohms range. Is it measuring volts, ohms or what? No, I am not an electronics engineer, though I am trying to understand a few circuit fundamentals here.

 

[hongrace]

A diode is a one way valve for electric current. If you measure it in the ohm range, it will show an open circuit in one direction and a short circuit in the other. This is consistent with your test. Unlike a resistor, you can't measure a "value" of a diode. The spec of a diode is typically the current it can handled and the blocking voltage in the reverse direction.

 

[Wookie]

That's right. To put it in plumbing terms, it's a check valve. The ohm ratings are the size of the valve (ability to handle flow) and the spring tension (resistance to back flow). Some diodes have a gate, that is, a third terminal that allows you to open the diode on purpose and close it again when you want flow to stop. These are called Silicon Controlled Rectifiers, and you might set them up to run a very slow speed A/C motor from a normal A/C power source, so you don't have to deal with gearing. A control rod in a nuclear reactor is one such example. You want that control rod motor turning very slowly, but you don't want to deal with gears.

 

[lucca brassi]

http://www.falstad.com/circuit/e-index.html all electronics circuits (you need java ) look ''Diode I/V Curve''

basicaly you measuring voltage vs current in I. and III. quadrant ( right vs reverse polarity ) that's give you typical curve of diode

http://www.youtube.com/watch?v=JlZtn2PTuYo

 

[ianr33]

I am trying to measure a diode to find out what kind of diode it is. It looks like a Zener diode and when I measure one way I get an open. Reverse polarity and I get .426. I can post a picture of it, I guess, but I don't see any identifying marks on it.

Those numbers tell you the diode is O.K. ,nothing more. Without some identifying numbers on the diode you are pretty much screwed figuring out exactly what it is. These numbers are often very small. If it's a zener it will likely start with BZX

 

[Zung]

If you have access to a variable DC power supply, you can measure the breakdown voltage of any diodes, Zener or not. Just connect the (+) to the cathode through a resistor of about 100K and a milliampere meter and slowly increase the voltage until the current starts flowing.

But, given the price of a diode, Zener or not, salvaging is probably not worth the trouble.

 

[Jax]

On another note, I have a TES 2014 and want a manual for it. There are a number of features, including a transistor tester that I would love to understand a bit better. For that fact, what is the value of the diode I tested? The diode test is included in the ohms range. Is it measuring volts, ohms or what? No, I am not an electronics engineer, though I am trying to understand a few circuit fundamentals here.

TES Electrical Electronic CORP.

They do not list the TES 2014 on their site. You will have to try the "contact us" to find a manual.

 

[The Chairman]

I'm not trying to salvage the diode, but identify it.

Jax, yeah, I went to their contact screen last night and it only gave me an error.

 

[wedivebc]

Yeah an unmarked zener will need to be tested via a voltage supply and a resistor to limit current. Put a volt meter across the diode and apply a reversed bias voltage higher than the expected voltage of the zener. The voltage you read across the diode is the zener avalanche voltage. You don't need a variable supply.
Just make sure the resistor will not allow too much current to flow.

 

[Jax]

Pretty good discussion on identifying unknown Zeners: Build a Zener Diode Identifier : Identifying an Unknown Zener

Looks like fun to build the tester.