Transient-voltage-suppression question

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Tom

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Transient-voltage-suppression question
June 14, 2020 - 7:07am

Hello All,

A friend brought me a defective motor system by which the motor was variably driven and in the circuit was a triac. It was open. Upon close inspection there is what appears to be a tvs transient voltage suppresion device in series with the gate! It's about impossible to get any identification info off the device but the pc board has a double diode symbol which looks like two diodes facing each other with a common cathode bar. The other end of the "diode" goes to a capacitor and a relay contact. There is a 3 ohm resistor that is open and a blown npn transistor also. 

I've looked allot for any circuit where a tvs is in series with a componant but could not find any. Does anyone know why this type of device would be in series with a part like this? 

If it is truly not a tvs, then maybe the pc board silkscreen is wrong and this is just an open diode, with its cathode connected to that gate. 

What's the consensus about this?

 

Thanks!

Tom

Sourav Gupta's picture

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Provide the schematic diagram

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Tom

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Hello,

I tried to post a link to the schematic but it was flagged for aproval, which has not yet happened.

I don't know how to post the jpg here.

Tom

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You can add the image using IMCE tool in comment tool box or uplod in some jpeg hosting website and provide the link.

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motor driver2.jpg

Thanks! The parts in the red are those that failed. The part named "DB" is the one that I can't identify. As I mentioned, the silkscreen shows the symbol for a TVS but I can't understand how that part could work in series when it it's normaly in parallel. So I'm thinking it is actually a diode. I can't read the number/letters off it because they are to badly rubbed away. This part has failed open. Thanks for your help!

Debashis Das's picture

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Hi Tom, In the circuit, the 3ohm resistor is called a fusible resistor, Its not a fuse but it will blow up if anything goes wrong with the circuit. Thus fusible resistor.

The part TR is a TRIAC which is mainly used to control the AC voltage. The 150R resistor and the .1uF capacitor forms a snubber network.

The DB in the schematic called a DIAC.The name comes form DIode AC switch, its used to assist even triggering of a TRIAC.

The Transistor control the relay thus it switches the TRIAC circuit ON/OFF.

tinekastil2's picture

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I had a question about portable internet. I'm not even sure if that's the right term but basically I'll be moving into my cousins empty apartment for a month. There's no internet because she's been gone for so long, is there anyway to create like a hotspot that I can use to do work?

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Please make a separate post for this.

Sourav Gupta's picture

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Well to know the DIAC rating the TRIAC partnumber is required. What is the TRIAC partnumber?