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  #1  
Old 03-21-2012, 02:38 AM
qtlj657 qtlj657 is offline
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Question the circuit of SCR with 0-180 degree firing angle



it's about SCR with 0-180 degree firing angle circuit.
i can't figure out the function of the two 1N4004 Diode

Last edited by qtlj657; 03-21-2012 at 03:01 AM.
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Old 03-21-2012, 10:49 AM
jimkeith jimkeith is offline
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This is a very curious circuit--at first, I did not believe that it would even work.

Then I looked up the specs on the 2N5064 --it is a sensitive gate SCR with 200ua gate sensitivity.

The circuit is a real mind-bender.

How it works is the capacitor gets charged negatively via the 1N4001 that points up--the 1N4001 that points right keeps current from flowing reverse out of the SCR gate. The delay occurs as the capacitor must charge to a positive voltage before there is gate current. It appears that there may be much 'dead range' in the 2.5M pot as settings above about 100K will not provide sufficient gate current to trigger the SCR--unless, of course, the actual Igt is much lower than spec, and that is possible.
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Old 03-21-2012, 01:33 PM
qtlj657 qtlj657 is offline
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actually. it works.. i did work it out in the lab.

it's a lab about comparing two SCR circuit, one is 0-90 degree firing angle and the other is 0-180..



what you say is just i wonder.

in the lab i adjusted the rheostat all the time.. is it the reason the capacitor got charged?

i think the right hand side 1N4004 is blocking the possible negative current from the Cathode flowing back to gate.
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Old 03-22-2012, 01:44 AM
jimkeith jimkeith is offline
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Quote:
Originally Posted by qtlj657 View Post
in the lab i adjusted the rheostat all the time.. is it the reason the capacitor got charged?

i think the right hand side 1N4004 is blocking the possible negative current from the Cathode flowing back to gate.
Do not understand your first question.
Yes, this the 1N4004 prevents negative gate current--and negative load current.

Last edited by jimkeith; 03-22-2012 at 03:33 AM.
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