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Flyback circut resistor question

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Flyback circut resistor question

Unread postAuthor: sandman » Mon Oct 08, 2007 8:39 pm

WARNING: If do not know much about electronics then find a different topic to post in, this is for people that understand electronics well

as soon as i get some desoldering braid i will be harvesting a flyback for ignition, but i do not have the exact resistors that the wiki suggests

the wiki and other sources suggest about a 5w 220 ohm for R1 and about a 1w 27 ohm for R2
the resistors i have are:
2 10w 10 ohm resistors
1 5w
1 7W

various 1w resistors in the TV that as soon as i can figure out what they are ill post

so i would like some suggestions on which resistors i should use for R1.
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Unread postAuthor: Killjoy » Mon Oct 08, 2007 9:25 pm

first:
Are the 5w and 7w resistors also 10 ohms?
and what values for the 1w resistors do you have?

If none of the 1w resistors you have will work, then you can combine them till they equal 27 ohms or around there (a couple ohms off shouldn;t matter). Basically since all your resistors are 1w or greater, you can just combine them (connect them in series) and add their values so that the total value equals roughly 27 ohms.
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Unread postAuthor: sandman » Tue Oct 09, 2007 3:04 pm

sry i for got to type that in, the 5w is 1 ohm and the 7w is 2.7K ohms, and i gave a pic of some of the 1w resistor in the TV, and as soon as i figure out how to post more pics there are bout 7 other risistors
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Unread postAuthor: sandman » Wed Oct 10, 2007 9:07 pm

bump :)
as i got the desoldering braid tonight tomoro ill be taking the flyback out so any suggestions on what to use for the big resistor, i think i get the 1w one figured out
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Unread postAuthor: Killjoy » Thu Oct 11, 2007 12:40 am

I can't really help until you give a little more information on what resistors you do have. Still, if you don't have the exact value you can just add resisotrs to get the right value.

What are you planning for the 1w resisotor?
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Unread postAuthor: jimmy101 » Thu Oct 11, 2007 12:21 pm

Like kiljoy said, add (series) the resistors to increase the value.
Rtotal=R1+R2

Or, parrallel the resistors to decrease the value. For two resistors in parallel;
Rtotal=(R1R2)/(R1+R2)
So a 50 ohm and a 100 ohm in parallel gives (50)(100)/(50+100) = 33 ohm

I would suspect that the flyback circuit isn't all that picky about the resistor values. You can proably get away with larger value resistors if that is all you have. Smaller resistors may overload the transistor and fry it.

You can use lower power rated resistors if the circuit won't be operated for more than a second or so at a time. In a TV, the flyback circuit operates continously, hence the fairly large wattage rating on the resistors to handle the large amount of heat they generate.

As a rough estimate, if you are only operating the circuit 1 second in every ten then you can use a resistor with 1/10 the wattage rating. At 1 second every couple minutes you might be able to use 1/4 watt resistors instead of 10 watt ones.
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ok new problem

Unread postAuthor: sandman » Tue Oct 16, 2007 8:32 pm

ok, the best i could do was a 27 ohm 1W resistor which is close to the right value, and 2.7K ohm 7W resistor which is like 10 times what it was supposed to be but oh well.

So, right now i have everything jumpered up on my desk trying to find the right coil polarity by trial and error as the wiki article suggests and i have gone through all the possibilities twice and i never got it to whine as it says it will so im looking to you guys again :)
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jimmy should recognize that bag of resistors in the upper left corner :P

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ok new problem

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