A little help needed in understanding DC power supplies

[Fahad Sadaqat]

Hi,

Actually, it's a pretty simple question that I wanted to ask. The DC power supplies which we often use in like labs or with some DC operated electronic equipment has its ratings written on it. For example, a DC adapter that I use with my internet modem has a rating of 12V 1A. The question is, that if I am to make a power supply by myself and I need to calculate the parameters, how exactly would I do that. The voltage calculation is pretty simple but what I am confused about is the current. How would I calculate the output current of the power supply that I want to make? If I were to make a power supply with 30 volts 5 Ampere output, how exactly would I figure out that the power supply has an output rating of 5 Amperes? Does it depend on the transformer rating that I am using for stepping down the voltage or load or both or some other thing?

Thank you.

 

[Bluejets]

Does it depend on the transformer rating that I am using for stepping down the voltage

That and any smoothing capacitors and /or chokes used.
In your example match voltage or near and then use max current so 12 * 5 = 60VA.(12V)
If I remember, most quote around 1000uF per amp output for capacitor sizing.

You say you understand the voltage so I won't comment there.

Just don't understand why would you want to build your own when one can buy an already proven design unit for much less than the cost of parts?

 

[Fahad Sadaqat]

Really appreciate the help. I don't really intend to make one but just wanted to understand the concept.

Thank you.

 

[davenn]

Really appreciate the help. I don't really intend to make one but just wanted to understand the concept.

Thank you.

OK and the current rating you see on a PSU is the max output for the supply ...
when building a PSU it would generally be designed to be able to supply more current that what will be normally drawn from it
that way it isn't always running at its limit

 

[Rayregula]

Texas instruments has a handy design tool here for power supplies and other useful stuff.
Just watch out for minimum component quantity's.