555 timer question

[lerxst88]

Sorry for the newbish question but I have a 555 timer hooked up designed to flash an LED.

a 555's max amp output is 200 milliamps and i just got this big-ass LED that runs on 400 milliamps so how can i make it work? I need a transistor im guessing but im not 100% sure on how to hook it up.

[brett]

Hi
to "drive" the LED, you'll want either a relay (slow switching and on-off switching) or an emitter-follower (fast switching and dimming or on-off switching). 
I'd go for an emitter-follower. 

Like this: http://en.wikipedia.org/wiki/Common_collector

When "on", the transistor is a low resistance path from the power supply, so connect a resistor between Vout and the LED (for 400mA use about a 22 ohm resistor).  Also, you'll need a power transistor, as 400mA will kill many small signal transistors.  BD139, TIP31, and MJE3055 are candidates.

cheers   

[lerxst88]

Genius!

Ill look for those transistors since i guess the 2N3904 and 2N2222s we have arent going to cut it.

Also to reveal what this is for! Im part of the build team for Illinois State's Solar Car and this is the circuit that will be flashing our strobe light that is mandated to be on top of all the cars! If anyone asks ill be sure to say that "brett from DIYStompboxes" helped!

[brett]

Best of luck with your project and for all of the other solar racers.  I hope they come a close second.

RE:  i guess the 2N3904 and 2N2222s we have arent going to cut it.

No, they are ok for nearly 100 milliamps, but 400 will kill them in a second.