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Old 17th June 2010, 06:55 PM   #1521
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Originally Posted by Malka07 View Post
Thanks Again Andrew and Regiregi22,

Correct me if im wrong, but my understanding is that when resistors are used in parralel, there wattage is added on, so for example a 68r(1 watt)//68r(1 watt)//15r(5 watt) would be equivalent to a 10r(7 watt) resistor???

However im not sure if i correct in this understanding

Alon
With these exact values, you will have a nearly equal disposition. The 15r one is nearly 5 times lower in value than the others (5x15=75), so it will burn 5 times more power. Being the others 1w and this one 5w, you have them almost matched. They will result in a 10r equivalent resistor, with a 7w ratting. I think you'll be fine.

Am I wrong in something?
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Old 17th June 2010, 06:57 PM   #1522
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I beleive they will all dissapate equally I believe, making it effectively a 3Watt max combo.
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Old 17th June 2010, 07:00 PM   #1523
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I beleive they will all dissapate equally I believe, making it effectively a 3Watt max combo.
They won't, just because they have different values, so they will pass different currents.
It's easy: Power is Current times Voltage. So, having all of them the same voltage applied, what will vary is current. Then, P=VxI, will give you higher wattage consumption.
Just ohm's law.
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Old 17th June 2010, 08:07 PM   #1524
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Alon,

The power will still be distributed accordingly with the most on the lower resistance as more current is passed.
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Old 18th June 2010, 08:42 AM   #1525
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the best formula for this comparison is P=V^2/R
find the power dissipated by any single resistor across the 2.04V of the CCS.
then total the dissipations for total losses.
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Old 18th June 2010, 08:55 AM   #1526
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I just wanted to confirm my understanding of what I've read with regards to potentiometer values. Back in post #138 it was said the sweet spot was a 20K pot, but anything between 15K and 25K would work without having to change the 220K resistor value.

Is a 20K pot still considered to be good? I'm looking at pairing the B1 with a ladder attenuator and if a 20K pot is still good then it opens up my choices with regards to sourcing (buy or build myself rather than just building).

Thanks
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Old 18th June 2010, 09:44 AM   #1527
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20k is good.
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Old 18th June 2010, 09:47 AM   #1528
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Thanks.
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Old 18th June 2010, 10:03 AM   #1529
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Originally Posted by westers151 View Post
I just wanted to confirm my understanding of what I've read with regards to potentiometer values. Back in post #138 it was said the sweet spot was a 20K pot, but anything between 15K and 25K would work without having to change the 220K resistor value.

Is a 20K pot still considered to be good? I'm looking at pairing the B1 with a ladder attenuator and if a 20K pot is still good then it opens up my choices with regards to sourcing (buy or build myself rather than just building).

Thanks
yeah, 20k is still alright. Time has passed by, but the design itself remains the same
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Old 18th June 2010, 10:43 PM   #1530
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Hello,

in BOM a 2x12V 50VA transformer is indicated.

Can a 2x12V 30VA R-Core one be suitable?

Thanks in advance
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