Hello everyone!

I am having some issues making my boost converter (TPS61085PWR) output the correct amount of current to 3 leds connected in series. I am using a 600mah 3.6v lipo battery to power the circuit. When the circuit is being powered from 3.6v, the boost converter is outputting ~11.5v, and the LED's are consuming ~.011A. When I increased the input voltage to 7.6v, the boost converter outputs ~11.6v, but the current goes up to .09A (where it should be).

TPS61085PWR Specs: http://www.mouser.com/ProductDetail...=sGAEpiMZZMtitjHzVIkrqX3TJ7GS2RvNwv6dhJ7aOSE=

Inductor Datasheet: http://www.mouser.com/ProductDetail...EpiMZZMsg%2by3WlYCkU3b8Zei%2b1OAi0lf8lVRnrEE=

LED Specs: http://www.mouser.com/ProductDetail/Cree-Inc/CLM4B-GKW-CWBYA693/?qs=3AcK5DacLbqCJqwggAponQ==

If anyone could give me some insight to this issue I would be forever grateful!

 

Also, I am running this converter in low-frequency mode (650kHz)

 

If you want to control the current through the LEDs then you need to use a converter in the constant-current mode, not constant-voltage.
LEDs are current devices and are very sensitive to any slight change is applied voltage.
They should never be operated from a voltage source without some means to control the current.

 

My plan was to use a resistor to limit the current. I have played around with different resistor values, but I just wanted to show that the converter is not outputting enough current with no means of current control. Perhaps I should use a different boost converter? (one with a constant current mode)

 

Try this:
Disconnect the cathode of D7 from ground and instead connect it to the FB pin. Remove R6 and change the value of R7 to 10 ohms. The current through the diodes will be 1.238 volts / R7. This gives 124 ma for 10 ohms.

 

Perhaps I should use a different boost converter? (one with a constant current mode)

That would be my recommendation if you want good efficiency (avoid the power loss in the resistor).

You could try using the tps61085 converter you have in the constant current mode.
If you put a resistor in series with the top of the LED chain to ground and connect the FB pin directly to that point (junction of the LEDs and the resistor), the current out should be 1.238V divided by the resistor value.

Edit: Richard beat me to it.