News for hackers. Stuff that matters.

A comment on Ask HN: What's the purpose of the resistor in this circuit?.

Re:Ask HN: What's the purpose of the resistor in this circuit? by avishvak on Friday March 20, 2009 @08:13AM (#524798)
I request you to look at it differently from all the other posts. This resistor is a constant current sink. Albit a mediocre one. but its just a penny [a paisa in india] This thermister needs to sink a constant current in order to produce a temperature dependent voltage at its bottom leg. Normally, about a milliamp does the trick.

A resistor is a meiocre surrent sink because its own voltage drop is current dependent. these would be better choices [lot more expensive, but hugely more accurate] http://octopart.com/search?q=constant+current+sink

avishak, new delhi india

[ Parent | on HN ]
Re:Ask HN: What's the purpose of the resistor in this circuit? by mechanical_fish on Friday March 20, 2009 @09:03AM (#524831)
This is great! Another aspect of electronics that one must get used to is that there is usually more than one way to interpret every part of a circuit. And this current-sink point of view is quite useful -- as you point out, it immediately suggests a way to improve the circuit: Put in a better current sink, like a transistor.
[ Parent | on HN ]