Andy's Solar-bugs

B.E.A.M.
BEAM is an acronym standing for :
Biology, Electronics, Aesthetics and Mechanics
last updated June 26, 2002

White LED : constant current @20mA

Parts list :

1 White led	3v battery (used)	1 resistors : 33 ohms
1 : 4K7 resistor	2 : 2N3904

3 items :-)

Test drive the circuit on Breadboard June 26, 2002

Circuit is here

Current mirror

I=Vbe/Rs

with 2 AAA batteries (2*1.5V), measured 2.95V, loaded
Vbe : 573mV Rs : 33 ohms so I is 17.36mA

with 3 AAA batteries (3*1.5V), measured 4.26V, loaded
Vbe : 722mV Rs : 33 ohms so I is 21.88mA

with 4 AAA batteries (4*1.5V), measured 5.43V, loaded
Vbe : 732mV Rs : 33 ohms so I is 22.18mA

with 9V battery, measured 8.97V, loaded
Vbe : 727mV Rs : 33 ohms so I is 22.03mA

There is the way to drive white led : using constant current instead of constant voltage.