Monitoring scr gate pulse

Thread Starter

Richardm1978

Joined Jun 3, 2022
6
Hi guys,
New here so bare with me.
I want to monitor gate pulses of an SCR, however I keep blowing up devices.... I remember something about ringing from my electronics apprenticeship, but literally have long forgotten it.
Basically how do I monitor the gate pulses of an anti parallel SCR package?
Thanks in advance
Richard
 

Ramussons

Joined May 3, 2013
1,271
Unless one main terminal of the SCR is Grounded, you will have to use a scope that is floating (not earthed) or use a Pulse Transformer for isolation.
Are you referring to a Triac as Anti Parallel SCR package?
 

AlbertHall

Joined Jun 4, 2014
12,071
Unless one main terminal of the SCR is Grounded, you will have to use a scope that is floating (not earthed)
You can also achieve this with a two channel 'scope which has an A-B function on the two channels. Then connect one probe to the gate and the other to the cathode/MT1 and the 'scope will dieplay the difference.

One possible problem with this is if the voltages on theses ponts are large it can overload the scope inputs and distort the waveform.
 

Thread Starter

Richardm1978

Joined Jun 3, 2022
6
Hello, thanks for replying.
It is a powerex ND431225.
I. Trying to see what the gate voltage is as I don't believe it is high enough for gate latching quickly and it keeps cooking.
 

Ramussons

Joined May 3, 2013
1,271
You can also achieve this with a two channel 'scope which has an A-B function on the two channels. Then connect one probe to the gate and the other to the cathode/MT1 and the 'scope will dieplay the difference.

One possible problem with this is if the voltages on theses ponts are large it can overload the scope inputs and distort the waveform.
Yes, BUT the scope Ground is an issue that must be considered.
 

Thread Starter

Richardm1978

Joined Jun 3, 2022
6
I can tell you the gate trigger is derived from 24vdc.... but I have no other info on it. I would expect around 3 to 5 volts dc to make the gate latch quickly. But before it blew up I measured 2v only. Ig can be up to 10v according to the spec sheet. Its been years since I did real scope work. I decided to leave and serve my country for a few decades lol. But coming back into it as I enjoy power electronics
 

Ramussons

Joined May 3, 2013
1,271
I can tell you the gate trigger is derived from 24vdc.... but I have no other info on it. I would expect around 3 to 5 volts dc to make the gate latch quickly. But before it blew up I measured 2v only. Ig can be up to 10v according to the spec sheet. Its been years since I did real scope work. I decided to leave and serve my country for a few decades lol. But coming back into it as I enjoy power electronics
Can we have a schematic please?
 

Thread Starter

Richardm1978

Joined Jun 3, 2022
6
I don't have one to give you. I just need best practical guidance on testing the gate pulse. I am assuming A-B with "ground" being the 0v side... I mean people test these pulses all of the time but finding practical guidance is hard. I am sorry I have less than all of the info here... but I can't remember these things from so long ago.
 

Ramussons

Joined May 3, 2013
1,271
I don't have one to give you. I just need best practical guidance on testing the gate pulse. I am assuming A-B with "ground" being the 0v side... I mean people test these pulses all of the time but finding practical guidance is hard. I am sorry I have less than all of the info here... but I can't remember these things from so long ago.
Even for a bench top test, you need to have a schematic.
The Powerex needs to wired up.
Supply needs to be given.
There has to be a load.
The gate needs a trigger.
How can you do all this without a schematic?
 

Thread Starter

Richardm1978

Joined Jun 3, 2022
6
It's already built and I am coming in after the fact. Literally, the gate signals I am not able to provide Info on. I'm not trying to be difficult, I am testing an as built with no info about the gate triggering system. And I just asked for the most practical guidance for testing any gate pulse in general.
If you forget the type of SCR, how would you go about testing a gate pulse? Please and thank you.
 

Ramussons

Joined May 3, 2013
1,271
It's already built and I am coming in after the fact. Literally, the gate signals I am not able to provide Info on. I'm not trying to be difficult, I am testing an as built with no info about the gate triggering system. And I just asked for the most practical guidance for testing any gate pulse in general.
If you forget the type of SCR, how would you go about testing a gate pulse? Please and thank you.
Follow post #3.
 
Top