| ??? 12/01/09 16:30 Read: times Msg Score: +1 +1 Good Answer/Helpful |
#171345 - Ideal constant current source... Responding to: ???'s previous message |
Richard said:
Erik's assertion is that it's possible to generate a constant current without any input supply regulation. He implied that there's a current source that will provide a constant current despite the fact its input supply ranges randomly between 3 and 24 volts. That's where I challenged him to show us how it works. All he's referred to since then has been current sinks that are influenced considerably by the supply voltage. I just want to know what he means. But Erik ist right! An ideal constant current source is entirely independent of the supply voltage. A rather ideal constant current source can be built with the LM317, for instance, see at page 18 of this datasheet: http://cache.national.com/ds/LM/LM317.pdf Many constant current sources aren't ideal, though, but show slight shifts of current, when the supply voltage changes, by other words they show some non ideal line regulation performance. Then, there are these quasi constant current sources, which assume and need a regulated supply voltage. These often only contain a current limiting resistor to "guarantee" a constant current. Kai Klaas |
