Power supply consumption

I need to calculate the total power loss in my power supply to determine heat sinks and fans. Does a rule of thumb determine the typical power loss in rectifier bridge, capacitors and transformer? Maybe 10% power loss in transformer to the rated transformer power?

I guess a good rule of thumb is about 90% efficiency for transformer (maybe less for small ones) and 1.4 x average current for power dissipation in bridge rectifier. (Sorry that's two thumbs).

Dissipation in capacitor should be negligible unless you are talking about big power supplies or high ripple values.

You might use estimates for things like the transformer and rectifier however you'd be wise to understand the power losses in the switching or regulation circuitry - particularly at a variety of loads.

An example - if you were supplying 20 vdc from the rectifier/filter capacitor to a linear regulator and wanted to supply 12 vdc at 1 amp then the regulator would have to waste 8 vdc at 1 amp. Adjust this regulator down to an ouptut of 6 vdc at 1 amp and the power losses in the regulator would be 14 volts at 1 amp.

Don't worry about the transformer too much but the efficiencty will vary depending on the power rating and whether it's an E-core or torroid.

Assuming it's a linear regulator, the power loss in the rectifier and regulator is the voltage drop times the current.