power supply spec definition help needed

Discussion in 'General Electronics Chat' started by minkey01, Dec 23, 2014.

  1. minkey01

    Thread Starter Member

    Jul 23, 2014
    177
    0
    Hi.

    I am trying to buy a dual output switching power supply. 5V and 24V.

    http://www.jameco.com/Jameco/Products/ProdDS/323380.pdf

    I understand all the specs except for one. Could someone explain to me what "INPUT AC Current typ." means? It is listed as .8A/115VAC. While the output DC says 2.2A and 1A. How can you have less amps in and more coming out?

    Sorry for my stupid question. I am sure it is something easy and obvious.

    Thanks!

    Happy Holidays.
     
  2. tindel

    Active Member

    Sep 16, 2012
    568
    193
    Switching power supplies are all about power conversion becoming efficient. POWER OUT cannot be greater than POWER IN.

    Watts = volts * amps

    So it looks like you have about 100 Watts into the converter...
     
  3. hvacpw

    New Member

    Dec 24, 2014
    1
    0
    A power supply is an electronic device that supplies electric energy to an electrical load. The primary function of a power supply is to convert one form of electrical energy to another and, as a result, power supplies are sometimes referred to as electric power converters. Some power supplies are discrete, stand-alone devices, whereas others are built into larger devices along with their loads. Examples of the latter include power supplies found in desktop computers and consumer electronics devices.
     
  4. ScottWang

    Moderator

    Aug 23, 2012
    4,856
    767
    The Power of AC part as:

    Win = Vin * Iin = 115V * 0.8A = 92 Wac
    Assuming eff(efficient) = 90%
    Wout = Win * Eff = 92Wac * 90% = 82.8 Wac

    The Power of DC part as:

    Wdc = Wac * Pi = 82.8Wac * 1.414 = 117.1 Wdc max

    The present Wout:
    Wdc = (5V * 2.2A) + (24V *1A) = 11W + 24W =35 Wdc
    So the rest power Pr = 117.1Wdc - 35Wdc = 82.1Wdc, the Wdc still have 82.1 Watts left.
     
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