AC -> DC using Bridge diode & Capacitor

[sdancer75]

Hi,



Watching this video I was wondering how a 9VAC simple converter can output a 15VDC since
9VAC X 1.4142Vrms = 12.72V.

It's because of the 25V capacitor maybe?

[MagicSmoker]

Measure the AC voltage going to the bridge - I bet it's over 10V* because the transformer is effectively unloaded. The voltage rating of the capacitor does not affect the voltage of a bridge rectifier (unless it is too low, at which point it will [eventually] fail short).


* - and probably over 11V, since there are two diode drops in series with the DC output at all times in a bridge rectifier.

[Zero999]

Yes, small transformers output a considerably higher voltage, than the rating when unloaded. Measure the AC voltage. It's got nothing to do with the voltage rating of the capacitor, which will only charge up to the peak AC voltage, minus the rectifier losses.

[Prehistoricman]

Yes, small transformers output a considerably higher voltage, than the rating when unloaded. Measure the AC voltage.

This property is known as the "regulation" of the transformer. In the case of these small ones, 20% is to be expected. That is, the output when unloaded is 20% above 9V.
10% can be expected from medium-size transformers.

I wouldn't recommend watching channels such as this. As you can see in the comments, nobody really knows what they're on about. The video doesn't teach you why the circuit works or go into any detail, hence why you have this question. Funny how these kinds of vids get so many views.