many greeting all members


I registered just now to this forum, I have basic knowledge in electronics.


I need to determine if items above are defective or not, using a dmm or a test circuit.

can anyone help me ?

thanks in advance

 

In most application you can use both of them interchangeably.

 

I need to determine if items above are defective or not, using a dmm or a test circuit.

Based upon experience, it is highly unlikely that your optocouplers are "defective" (damaged, maybe, but not defective).

More likely, you have a problem in your snubber circuit, assuming you are trying to drive an inductive load.

Can you be more specific as to why you might think the devices are defective? I may be able to help you if you do.

BTW, there is a huge problem with black-market forgeries, especially with these type of parts. Unscrupulous vendors will buy cheaper, less capable, parts and relabel them as the more expensive, capable parts. They will ultimately fail. In fact, Fairchild will not even be willing to help you until you prove you purchased the parts from an authorized distributor. If you did not, they are most likely fakes.

 

Based upon experience, it is highly unlikely that your optocouplers are "defective" (damaged, maybe, but not defective).

More likely, you have a problem in your snubber circuit, assuming you are trying to drive an inductive load.

Can you be more specific as to why you might think the devices are defective? I may be able to help you if you do.

BTW, there is a huge problem with black-market forgeries, especially with these type of parts. Unscrupulous vendors will buy cheaper, less capable, parts and relabel them as the more expensive, capable parts. They will ultimately fail. In fact, Fairchild will not even be willing to help you until you prove you purchased the parts from an authorized distributor. If you did not, they are most likely fakes.

sorry, I meant "damaged". I have the same circuit in big quantity, there is item above in this circuit. discussing with a person, he told me that them got damaged often, so I need to test them if it is in working conditions or not(not defective by producer), using a dmm or building suitable test circuit


I thank you very much for the help

 

Datasheets often show test circuits. Have you checked those?

 

sorry, I meant "damaged". I have the same circuit in big quantity, there is item above in this circuit. discussing with a person, he told me that them got damaged often, so I need to test them if it is in working conditions or not(not defective by producer), using a dmm or building suitable test circuit

There are many parameters that define the operation of an optocoupler. Some are static parameters, others are dynamic. Some are obvious (i.e. min LED current, max load current, etc.), others are a bit more subtle (i.e. dv/dt, di/dt, etc.). In many cases, a particular parameter may depend on on another (i.e. switching speed vs. led current), or may depend on the load.

Your original request for a test circuit is meaningless without an understanding of the parameter(s) you wish to measure/confirm. In fact, you already have a test circuit -- your application -- and it is failing!

Again, my guess is there is nothing wrong with the devices themselves. The problem is the application. To go any further, one would need some additional information:

1. What is driving the optocoupler?
2. What is the optocoupler driving?
3. What is the nature of the failure(s)?

This is a case where schematics would be infinitely useful, if you can provide them. Also, detailed specifications of the load, as well as the environment in which the application is to operate (i.e. source and voltage of A/C input, ambient operating temperature range) would be quite helpful.

I'll help you with #3. Generally, there are five modes of failure for an optocoupler:

1. Optocoupler fails to turn on;
2. Optocoupler fails to turn off;
3. Optocoupler turns on spontaneously (without input signal);
4. Optocoupler turns on half-wave only;
5. Optocoupler releases magic smoke.

Pick one, and then tell me the conditions under which the failure occurs.

 

hm, the problem seems to be complicated. I do not know which is the case of numbered points you professionally exposed. I do not know what have to do the ac power, because whole application is under -48vdc.

I have a lot of these items to determine if it is a good one or not. May be the problem is always the same, one of you described here.

in working condtion is hard to make measurements because the closed in rack and spaces are too small

 

hm, the problem seems to be complicated. I do not know which is the case of numbered points you professionally exposed. I do not know what have to do the ac power, because whole application is under -48vdc

Interesting that your app has a 400V OptoTRIAC for a low voltage DC application. Generally, these are used to control low current A/C devices, or to drive a higher power OptoTRIAC.

But, again, if you can find out the mode of failure, and possibly provide a portion of the schematic, it may be possible to determine the cause of failure.

 

here is the a part of the circuit:

 

In case you don't have the datasheet for the optocoupler, I have uploaded it to
http://www.rf-highvoltage.heliohost.org/spec-sheets/MOC304x.pdf