Converters or Transformers?

Question

In a convertor or a transformer, output Power = input Power OR (I out) (V out) = (I in) (V in)

But there are converters with the 120V and 15amps input which only produce 5amps and 12V output. How they work? I mean, Why this converters produce a power much less than the input power?

Actually, if the output voltage is 12V, the output current should be 150amps, but how they produce only 5 amps or even less?

Answer 1

The transformer isn't drawing 15 amps at 120V: if it's 100% efficient and has a full load attached to it, it's drawing 0.5 amps from the circuit. Actually, it's only drawing as much current as the components that are connected to it need: if you have a 12W (@12 volt) bulb, then it's drawing 1 amp @ 12 V, or 0.1 amps at 120V; the other 4 amps of capacity aren't being used.
The 15 amps is the maximum current that you can draw before blowing a fuse or tripping a circuit breaker, so you could plug 30 of those transformers into the wall.
The 5 amp transformer is only 5 amps, not because that's the most current they can draw from the house current, but because that's the most current they figure your computer needs; a 150 amp transformer needs to have much larger wiring to handle that much current.

Answer 2

Ok, first off and to be more accurate, output power + losses = input power. Transformers are not 100% efficient, tho they can be close to it, say generally about 90%. You could make one more efficient for a given load by adding more copper and steel, but you could get to the point where one to power a PC would be 99% efficient, but be the size of a desk and cost thousands of dollars.

About that converter you're talking about, are you sure that it actually DRAWS 15 amps (1800w) when outputting only 60w? That's only 3.33% efficiency! I'm trying to figure out how you could even build such a converter cheaper than you could one that was say 80-90% efficient. I mean, those watts have to be burning somewhere inside, and 1740 watts means a good fan and a hellacious heatsink.

Typical supplies built nowadays are generally in the 80 to 95% efficient range, and even old-school linears with hulking 60Hz transformers on the input were at least 70%. Where I work, we build battery chargers for forklifts, elec cars, etc that output up to 500 amps at 60v, at around 93% efficiency, supplied via 480v/3ph power.

Answer 3

Out put power= input power - losses. There are more power losses in a converter than a transformer. Transformers are very efficient, more than 96 percent, if I remember correctly.

Answer 4

i'm not sure what You recommend by employing push-pull, yet to me that's purely a DC to DC converter. See the area under. We used to apply this variety of situation, yet devoid of output rectifier, to grant AC from a DC grant.