10-02-2014, 05:34 PM
If you conclude your reasoning at this point, then yes, I understand why you think that.
But take it a stage further:
If you sent that signal through a capacitor into an oscilloscope, you'd see a square wave. Agreed?
But capacitors only pass AC, right?
The capacitor has passed the AC component of the signal, removing the DC component in the process.
...
Another example to think about: looking at ripple on a DC power supply. I bet you've done this a fair few times...
Once again, you could argue that it's a purely DC signal because there is no reversal of current*. But no, you have an AC signal - perhaps 100mV - sitting on top of a DC offset of perhaps 12V.
How do you assess ripple on a power supply rail? You use a 'scope, set to AC at the input. As above, you are using a capacitor to remove the DC component so that you have the AC component in isolation.
As I said initially, this takes some thinking about. But it's worth it
Mark
* Actually, that's only true if the load is purely resistive.
But take it a stage further:
If you sent that signal through a capacitor into an oscilloscope, you'd see a square wave. Agreed?
But capacitors only pass AC, right?
The capacitor has passed the AC component of the signal, removing the DC component in the process.
...
Another example to think about: looking at ripple on a DC power supply. I bet you've done this a fair few times...
Once again, you could argue that it's a purely DC signal because there is no reversal of current*. But no, you have an AC signal - perhaps 100mV - sitting on top of a DC offset of perhaps 12V.
How do you assess ripple on a power supply rail? You use a 'scope, set to AC at the input. As above, you are using a capacitor to remove the DC component so that you have the AC component in isolation.
As I said initially, this takes some thinking about. But it's worth it
Mark
* Actually, that's only true if the load is purely resistive.
