I hope you all can explain this to me.
Let's assume we have an AC adapter with only a small number of parts, a step-down transformer and 1 to 4 diodes.
Let's assume that the primary of the adpater uses 0.1 amps at 120 volts. (I don't think it matters for the sake of this question how much the device itself uses. We can pretend that there are no losses and it has an output of 1 amp at 12 volts, and powers a device that uses the full amp. Or that the device uses less than that.)
So in this case when the device is on, it's consuming 12 watts from the power company. The primary of the AC adapter is using 12 watts.
Roughly, with an adapter of typical, simple, only 5 parts, design, how much in watts would the adapter use if the device were turned off, that is, if the secondary circuit of the adapter were open? The primary circuit would still be closed. The inductive impedance of the primary winding would go up -- it took me years to figure that out -- but I have no idea how much.
2) Yesterday, someone gave me a broken AC adapter used to power a Westell DSL modem. I broke it open and instead of the 5 or 6 parts such things used to have, this one had about 25 parts, including a small transformer and what looked like another winding on a metal core. Plus 3 big caps (one or more filter caps), I need more light and better glasses to count the diodes, one transistor, and something looking like a little glass fuse but with a white sandy body.Something this complicated must be smarter than earlier adapters. Does that mean it uses less current when the device intended to be powered is Off? Any idea how much a 25-part adapter like this uses when the devices is Off, assuming when it's On it uses 12 watts?
Thanks.