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Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
Self_Defenestrate didn't explain fully why you should exchange the positions of the SCR and the load. The problem is that when you trigger the SCR, the load voltage appears on the cathode. This will cause part of the load current to flow backwards from cathode to gate and through the triggering circuit back into the 12v supply, probably destroying the SCR gate.
Registered Member #32
Joined: Sat Feb 04 2006, 08:58AM
Location: Australia
Posts: 549
It might be a good idea not to leave the SCR gate "floating". Stick 1M or something between the gate and ground. Easy to do and reduces the risk of accidental triggering a little.
[Edit: yeah, I actually had sensitive gate SCRs in mind.]
Banned Registered Member #110
Joined: Fri Feb 10 2006, 12:23AM
Location: Banned City
Posts: 85
It is a good idea not to leave a gate open. However, when it comes to SCRs, the gate has an internal pull down resistance to cathode. Not just a resistance, but a rather low value resistance ranging from 30 to 300 ohms. Hence why a 5v to 12v pulse signal applied to gate looks like a 1v to 3v pulse when seen in scope due to this inherently large voltage divider nature of an SCR gate. Sensitive gate SCRs have weak to no pull downs. Whenever a datasheet is either not available or does not specifiy the pull down resistance, use meter to find out the value.
Registered Member #295
Joined: Tue Mar 07 2006, 06:59PM
Location:
Posts: 23
Just out of curiosity why did you chose to use an isolated DC - DC converter? i'm not very familiar with this arrangement so i'd like to learn more, forgive the questions.
Registered Member #120
Joined: Fri Feb 10 2006, 07:07AM
Location: Westchester New York
Posts: 83
I just want to have my trigger isolated from the SCR and the circuit i would be using to operate things with. Basically it makes me feel safer and not as though I want to press the trigger button with rubber gloves. All the DC - DC converter is, is just a isolation transformer.
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SCR triggering
