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Old 19th September 2012, 04:28 PM   #21
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wow jackinnj that is a mess.
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Old 20th September 2012, 07:41 AM   #22
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by AudioSan View Post
i don't know about you. but over here i have never had more then about 2-3% variation on mains.
I too see a range that regularly moves between limits of +-2% to +4%.

I have never actually measured the voltage when at the extremes of our 216Vac to 254Vac.

But that does not create a reason for not designing for worst case that can happen.
I would not design for supply voltages outside that range, even though they would be a worse case.
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Old 20th September 2012, 10:30 AM   #23
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andrew. try the same calculation for worst case when you are within the 1A limit, say LM7812.
1A. 22V transformer. 30.8V DC thats 18.8V drop.
-6% regulation makes 20.75VAC and 29VDC. so 17V drop
or in worst case. 22V transformer +6%. so 32.6V DC. thats 20.6V drop.
so at 1A and 22V transformer. we look at dissipation between. 17W and 20.6W atleast.
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Old 20th September 2012, 05:13 PM   #24
AndrewT is offline AndrewT  Scotland
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I don't need to try another calculation.
I automatically do the same procedure for any circuit I want to build.

It is you that seems to have overlooked variations in operating conditions.

You try for your data, before you build, then you might not be so tempted to advise bad design, or non design to other builders.
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Old 20th September 2012, 05:37 PM   #25
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as long as the device can handle the current. and the sinks can handle the worst case dissipation, then it will run good.
my sinks can handle well above 10W dissipation.
but i do want to see a TO-220 sink that can handle the 20W dissipation that one will have with 20V drop and 1A current. (wich is within specs of the device)
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