# Li-Ion battery for RGB strip

I am looking to power up my Teensy LC and my RGB strip from the same power supply, which is a 3.7V Li-Ion battery 3000mAh. The teensy can work perfectly fine with 3.7V.

The problem is when it comes to the RGB strip. Since I have about 40 LEDs, and it says that every LED takes 0.2W at 12V, I guess I will have around 0.7A current draw.

I looked up the internet for DC/DC converters, but they all have low output current. I need at least 0.7A and max 1A. Do you think I will have to boost to 3.7 to 5V and then 5V to 12 V ? Or is there another way ?

Thank you

• Or you could start with more cells and go the other way... Jun 5, 2017 at 18:12
• Yeah i thought about it, but i need it to be as portable as possible. It needs to fit in a small spot inside an instrument. So I can't add too much weight Jun 6, 2017 at 1:49

You haven't looked hard enough if you didn't find a 3.7V->12V step-up for >=1A.

I've built stronger things based on SMPS controller IC reference design circuits years ago. Since this is a design, and not a shopping recommendation site:

Try going to www.ti.com, use the (mobile) webbench power supply designer (it's on the home page), and design a 3.7 V -> 12 V converter. It works.

Also note that it's quite possible that you'd not want to use just any LED strip in this case – after all, they often contain series resistors themselves, which just wastes the voltage between the actual forward voltage of the LEDs and 12V. Meh.

With a bit of thought (generally: take a step-up controller, and instead of using a voltage divider to give the feedback voltage to achieve the a fixed output voltage, use a shunt resistor to achieve a fixed output current), you can design an actual constant-current LED driver instead of a constant-voltage voltage source, and get rid of the series resistors.

Also note that, depending on the currents, bijunction transistors as used in your block diagram (it's really not a schematic) might be suboptimal and you might want to go for MOSFETs, or just switch the step-up on and off (which requires controlling of some ENABLE pin or some secondary comparator, instead of actually low-side switching, and thus might be more effective and easier).

A voltage converter needs more power at its input for the heat it makes. 12V at 0.7A is 8.4W. The battery might need to supply 10W to the voltage converter. Then the battery charge will last for about 1.1 hours minus the current used by the teensy.