hi
i'am looking for an ic for drive three 1watt white power led.(boost ic)
my input voltage is a li-ion battery with a voltage between 3.7 to 4.2
so output power of ic should be about 3-4 watt.
can you introduce a good ic to me?

 

Check out the Maxim IC's for this at
http://www.maximintegrated.com/products/power/hb-led-drivers/

 

Check out the Maxim IC's for this at
http://www.maximintegrated.com/products/power/hb-led-drivers/

i just find max77387.but this has two string and support 2 led in each string.but i have 3 led.
also this ic isn't available in my area.so can i use mosfet's circuits?
can you introduce me a simple circuit?

 

any help?
i need a mosfet's base circuit

 

Huh? The MOSFET, if present, is the most trivial part of a constant current driver as you need for LEDs.

What is your goal, to use a MOSFET or drive your LEDs? What are the specs of your LEDs? Where are you that you cannot get parts? Any other limitations we need to know of? (SMD OK? Thru-hole only? Dimmable?)

You'll get better feedback with better details.

 

OK
i have a li-ion battery with 3.7 to 4.2 voltage and 4800mAh of current.
i want drive two 3watt led's and led's need 3.6v and 680mA (3.6*0.68=2.448)
so i should use a step-up ic and i search market's in my area and find LM2577 FOR THIS
But i need a constant current for lm2577.i need fixed 680ma in output.
i want circuit of lm2577+constant current.

 

http://www.linear.com/products/step-up_(boost)_led_drivers
http://www.onsemi.com/PowerSolutions/parametrics.do?id=197
http://www.ti.com/lsds/ti/power-management/led-driver-products.page
http://www.rohm.com/web/global/search/parametric/-/search/Step-up (Boost) LED Drivers
http://www.st.com/web/catalog/sense_power/FM142/CL1854/SC1578