Constant Current Source LED Drive

This is a Constant Current Source LED Driver, When the LED driver Upper-NPN is driven by a voltage thru 4.7K the LED lights up. Assume that the Lower-NPN at bottom is absent. The current via LED and NPN is limited by R. 20mA may be ok 15mA even better. Or LED blows even transistor goes.

more LED light flashing

Read more source:
http://schematics.blogspot.com/2007/02/
constant-current-source-led-drive.html
Thank you.

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