tl431 constant current source

[blackjames]

hi, i recently tried a basic lm317 constant current circuit, and it worked well. i was wondering if a tl431 could be used instead for loads upto 0.1A. the datasheet shows that the internal circuit is similar to a lm317. what do u think? ive got about five, so i can blow a couple up and it dosent matter.

[digsys]

Hi James,
You can get simple answers like this fast just by googling - www.fairchildsemi.com/ds/TL/TL431A.pdf
If you check out their application circuits, you'll find both a CC source and sink. They are slightly more
complex than an LM317, requiring an extra transistor.

[Psi]

The TL431 is a shunt regulator.

It draws current (cathode/anode) when the reference input is above it's internal reference (2.5V).

The example circuits in the datasheet for current source/limit use this to turn off a transistor when the voltage across a current sense resistor gets above 2.5V.
You set the current by changing the sense resistor.

[oPossum]

The LM317L comes in a TO-92 package and works like the TO-220 package LM317, but is limited to 100 mA max.

Fixed regulators like the MCP1700/1702 and 78Lxx can also be used as current sources.

The LM317 is essentially a 1.25 volt fixed regulator that is adjusted by raising it's ground reference with a resistor divider. That technique works with many fixed voltage regulators as well.

[blackjames]

I asked the question because i was recycling old parts from some atx power supplys. I tried a 7808 cc and it worked well. Thanks guys