Power conversions

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Villemus
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Power conversions

Post by Villemus » Thu Aug 30, 2018 6:43 pm

Can anyone help me out. Does anyone one know what formulas to use to figure out what the conversion is from going to a 12V 850ma DC to 5v DC. Or from a 5V 2.5A to 3.3v. I'm trying to figure out what amperage I'll get when using the lower voltage rail.

Thanks in advance,

codeman0624
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Re: Power conversions

Post by codeman0624 » Fri Aug 31, 2018 5:48 am

Villemus wrote:
Thu Aug 30, 2018 6:43 pm
Can anyone help me out. Does anyone one know what formulas to use to figure out what the conversion is from going to a 12V 850ma DC to 5v DC. Or from a 5V 2.5A to 3.3v. I'm trying to figure out what amperage I'll get when using the lower voltage rail.

Thanks in advance,
It depends on what method you are using to convert your higher voltage to a lower voltage. If you are using a linear regulator (easiest way) then the current does not change, the current at the lower voltage is the same as at the higher voltage.

If you are using a switching scheme, then power is conserved, with some adjustment for regulator efficiency. So current out at your lower voltage is:
low current = ((high voltage * high current)/low voltage) * efficiency

So for example with your 12V scheme, and 90% efficiency, you would have:
5V current = ((12V * 0.85A)/5V)*0.9 = 1.83A of available current at 5V

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Re: Power conversions

Post by Villemus » Fri Aug 31, 2018 10:57 am

Thanks for the thorough explanation. what I'm trying to do, is fix my old NES. I lost the AC adaptor, and I've read a lot of places that you're better off switching to a 12V power supply for a more universal connection since the 7805 voltage regulator can handle up to 18V. I'm still doing research, but I wanted to see if I would have to account for the current since 10Vx1.3A=13W and 12Vx1.3=15.6W. The 5V to 3.3V was out of curiousity for a possible future project.

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Re: Power conversions

Post by Helder » Fri Aug 31, 2018 2:35 pm

Just get a 9v-12v DC adapter and NOT an AC one like the NES originally had. I use one used for my other system on the NES but I replaced the DC socket to be universal.
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