Building my own Buck driver, need some help

Flashlight Modding and DIY Parts
1

Hi there,

I need some help in building my own buck driver.

My goal: 3.5A-4A output for a single XML with high (>90%) efficiency on 2 * 18650.

I thought of using this buck regulator: AOZ1014. Datasheet: http://www.aosmd.com/pdfs/datasheet/AOZ1014DI.pdf

Looks like it has high efficiency, small size and a nice input/output range, I also think that it is very similar to AX2002/3 but with more current…

What do you think of that IC? Is that good, or is there any better option?

thanks.

2

That’s not the best choice for a foray into switching regulators…

First, there is no really easy way to dim (adjust output) using that part. You’d be relegated to complex adjustable resistor dividers on the FB pin or an external FET for anything other than full on.

Second, it’s not designed to be a current regulator. It CAN be a current regulator - but with the 0.8V FB pin comparator, you’d either have to drop 0.8V across a sense resistor (at 5A, that’s 4 Watts of heat) or again use complex circuits (op-amp or some such) to boost a smaller drop to 0.8V.

Do yourself a favor and pick a dedicated LED controller/regulator. It saves a lot of headaches.

PPtk

3

Ok thanks!

What ic you can recommend to drive 4a?

4

There are hundreds of choices. I would suggest perusing www.ti.com www.linear.com www.supertex.com

There are others… nxp, st, etc…

5

Do you absolutely have to build a driver?

If not, I’d suggest modding an existing driver such as this: http://intl-outdoor.com/xml-multicell-circuit-board-3a-55126v-p-361.html

by tweaking the sense resistor.

6

ok ill take a look at these.

about the above driver, do you know what microcontroller is used there? and what is the efficiency?

thanks

7

I don’t know for sure, but from the PWM frequency, I would guess it’s a PIC of some sort.

Most AVR ATTINY Parts have either a 4.8 Mhz or 9.6 Mhz internal oscillator which gives (friendly) 8 bit PWM Frequencies of
18.75Khz, 2.34Khz, 292Hz, 37.5Khz, 4.69Khz, and 586Hz

Whereas most PIC parts have a 4 Mhz internal oscillator which can be PLL multiplied by 4, giving (friendly) 8 bit PWM Frequencies of
62.5Khz, 15.625Khz, 7.8Khz, 3.9Khz,1.95Khz

That driver lists as having a 3.9Khz PWM Frequency, which you can see lines up nicely with a PIC not an AVR.

PPtk

8

I just tested this one: http://intl-outdoor.com/xml-multicell-circuit-board-35a-ouput-55126v-p-543.html on 3 batteries in series, 3 LED's in series and measures 3.6A, not bad.