120 VAC

[Kevin Weddle]

The AC delivered to your house is apparently very sinusoidal. This is a claim I have read. So why a sine wave. Why not a triangle. It is because the sine wave has a low rate of change as it approaches the peak of the cycle. Sometimes the AC is low enough frequency dependent on your circuit, this is key.

  In general, we like to charge capacitors because they store energy. And in general, a capacitor will just pass a signal leaving it uncharged. Also, a signal will not develop across a capacitor at a higher frequency. So basically, they can either appear harmless, or they can charge.

So even though it may not matter when you consider that most supplies just have a diode and capacitor and that all the voltage does appear across the capacitor, that may not always be the case. You may be using the AC to power an RC circuit. It may be an RL load and therefore require a low frequency so that a signal will appear across the R.

Can you think of a case where you might want a higher frequency AC. A higher frequency might be good if you want to quickly recharge a capacitor. Then again a high frequency means greater signal loss across power lines. Any other ideas?

 

[audioguru2]

The AC delivered to your house is apparently very sinusoidal. This is a claim I have read. So why a sine wave. Why not a triangle?

The utility's mechanical generators produce a sine-wave so would you pay extra (double or triple?) for it to be converted to a triangle wave?
A triangle wave has many high frequency harmonics that probably won't pass through power transformers resulting in less voltage.

So even though it may not matter when you consider that most supplies just have a diode and capacitor and that all the voltage does appear across the capacitor

Capacitors are charged with DC, not AC. If the source impedance is low enough then a capacitor will fully charge to the peak voltage of the rectified input signal, minus the rectifier's forward voltage drop.

 

[Kevin Weddle]

Yeah, but even though the AC impedance of the capacitor is low, you still get all the voltage because there is not a divider. All the transformers output will end up across the capacitor. Well, I should say there is a small divider when you have a diode in there, but the diode can't drop a lot of voltage.