🚀 go-pugleaf

	re power supplies.

	As has already been stated the amp rating of a power supply (PSU)
	is the maximum rating. The actual current flow is always detemined
	by the load provided said supply can supply said load. If you
	attempt to take more than the rated current the supply woltage
	will drop below the specified tolerance band. That is if the
	PSU is 12V +- 10% with Imax of 2.5A and you attach a load of 3A
	the terminal voltage will fall below 10.8V (12V - 10%). Most 
	quality PSUs will however not allow you to do this and will
	current limit to prevent the PSU from overheating and failing.

	How much power is taken from the wall for a given load always
	depends on the efficiency of the power supply. A switching
	supply of 80% efficiency will take less power from the wall
	than a 50% linear supply. As follows


		Suppose the load takes 1A and the PSU is 12V

			Power consumed by load = 1A * 12V = 12W

			an 80% efficient PSU will consume

				12W * 0.2 W = 2.4W 

			a  50% efficient PSU will consume
	
				12W * 0.5 W = 6W

		Hence the 80% setup takes 14.4W from the wall
		while the 50% takes 18W.
	============================================================
 	Side note:- If you have the choice between two supplies that
			both can supply the load there are other
			factors to take into acount other than 
			efficiency.

	reliability:- Running a PSU at maximum load decreases the life
			expectancy of the unit.

	ripple and noise:- Running a psu at maximum load, will increase 
			the amount of ripple and or switching noise
			present at the terminals. This is because there
			is always a storage capacitor present which is
			being periodically discharged by the load. With
			small loads this discharge is less noticable.
			With audio and radio circuits this noise can be
			problematic.
	Physical size:- Like technology PSUs typically get  larger with
			Imax rating.

	Fault effects :- Running a 1A load with a 10A supply can be
			spectacular when a fault occurs. Smoke and flames.
			Use a fuse.
	===============================================================
 
			
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       >| "Only average people           | Trevor J German BSc    |<
       >|       never make mistakes."    | NCR, Waterloo, Ontario |<
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