Voltage Regulators - How do they know...?

Hi.

I have question about voltage regulators. How do they know what voltage to 'provide'. For example, a 78L05 gives 5v from a 9v-30v input (or something similar), or so I have heard.

If this is true, how does it know what voltage to drop it down to? I would have though it would need a reference point, the only reference point avilable being the input, which can vary. How does it accurately provide the right voltage?

Thanks

Tim

They use a zener diode inside such devices. Do a google search to learn more about zeners

well, just like with a zener diode, you can get one output voltage with an input voltage that is between a range.

internally, it is set up to put out 5V (7805).

oh, ok, hadn't thought of that.

thanks.

Tim