Electronic – AC Adapter Input vs Output Power

acadapter

I have a laptop AC Adapter thats rated for 19.5v/3.34A DC output for a total of 65W. The input is rated at 100-240V/1.5A AC. My question is what is limiting the output to 65W? It seems like the input can support up to 100*1.5=150W minimum. I"m assuming you lose some in the AC to DC conversion, but 65W would be more than 50% loss. So, is the adapter able to support more than 65W or is there something here I'm missing?

Best Answer

I do power supply design for a living. When I specify that this circuit is rated for 19.5v/3.34A 65W, there could be so many reasons for this. Few arbitrary examples include:

-Transformer saturates at 70 VoltAmps (VA)
-The transistors I am using start breaking down after 21V and/or 4 Amps
-My linear voltage regulators start sinking too much heat due to high voltage differentials
-Capacitors start having huge ripple currents that they cannot handle (ESR losses)
-I am unable to meet compliance in powerfactor/emissions at higher power ratings

any many more possible things...

EDIT: As for the 1.5Amps input current, this is the maximum instantaneous current the adapter will pull from the input. It is NOT an RMS value.

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