# 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
185
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 Well-Known Member

Sep 16, 2012
593
199
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
5,478
864
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.