Buck-Boost Drivers

The LT1270 is another good high current option and it requires fewer extra components than the LTC3785, but I don’t know which would work better for your purpose. I also wish there were more buck and boost drivers, but I’m not quite at the point where I’m confident in my design skills to start spending money on making drivers, and I don’t know how to program attiny13 or 85. And the inductor doesn’t have to be on a separate board, it could just be free floating.
Good luck.

I have updated the first post with links to some components that I think will help make this possible. Obviously everything needs to be as small as possible, so I am going with QFN and similar packages where possible. The MOSFET packages are tiny. Will make hand soldering difficult, but should be possible, hot air reflow is also possible.

As for cost, I know it will probably be more expensive than the FET/Linear drivers out there, but for me personally it is worth it. What would others around here be willing to pay for such a driver?

How much current is enough? I have been operating under the assumption that I want at least 5A to the emitter out of the driver, with 7A+ being the real goal. Obviously there will be some limits based on cell configurations, and it will be easier to get more power out of 2S+ configs. For 1S Boost mode though 6V/5A would be a good goal as that would at least fully drive an XHP70.

Loneoceans started work on one such driver but I haven’t seen him for a few weeks now. -Edit, he just updated that thread today.

how about using MCU controls the boost?

I use the 841 in these drivers: Mike C drivers: v8 series, ATtiny1634 based.

I like them, but I “upgraded” from 84A MU drivers so I didn’t need to re-design drivers because pin setup is identical. If you’re going from scratch you might want to look at the 1617. It’s very new though, so availability might be an issue.


I do have plans to experiment with using the MCU to directly control the switches of the regulator, I’m just not sure my programming and design skills will be enough to get good efficiency that way.

I like those drivers, good work! I am considering using the newer attiny MCUs, but will most likely go with the MSP430 if I require the MCU to read a current sense resistor due to the built in PGA and 16 bit ADC on that chip. 16 bit processing is nice too.

Looks like some interesting development going on there, wish I could read Russian! Looking at his schematic, is he just adding an extra switch in front of the boost regulator IC to make it a buck-boost?

Google translate isn’t very helpful on those types of discussions. It would also appear that that driver has max output current at 1A, so maybe the IC used in that one is not as interesting.

This is the old driver for the power button. Mosfet to turn off the power. The choice of LiIon 2.5V or LiFePo4 - 2.0V

IMHO dont need to do Buck :slight_smile:
Just do BOOST :slight_smile:
You can use 12V XHP 50.2 or 70.2 or new nichia…

Just for example, here’s what the scheme is doing now Tamagotchi
ZXCT1010 give you stable current

CSD17303Q5 + TS5A3159


1. TOP of the TOP :slight_smile:
CSD17303Q5 - Reverse Transfer Capacitance - 83pF, Input Capacitance - 2630pF, RDS (on) (3V)=2.7mΩ

2. CSD17311Q5 - Reverse Transfer Capacitance - 85pF, Input Capacitance - 3290pF, RDS (on) (3V)=2.3mΩ
3. CSD17306Q5A RDS (on) (3V)=4.2mΩ

4. CSD17556Q5B - Reverse Transfer Capacitance - 68pF, Input Capacitance - 5400pF, RDS (on) (4.5V)=1.5mΩ

long time ago))) good fet was
IRLHM620 - Reverse Transfer Capacitance - 620pF (its bad), Input Capacitance - 3620pF (its bad), RDS (on) (2.5V)=2.7mΩ
IRLH6224 - Reverse Transfer Capacitance - 770 pF, Input Capacitance - *3710*pF, RDS (on) (2.5V)=3.2mΩ

good litle fet
CSD13202Q2 - Reverse Transfer Capacitance - 43pF, Input Capacitance - 767pF, RDS (on) (2.5V)=9.1mΩ

and not so good :slight_smile:
IRLHS6242 - Reverse Transfer Capacitance - 180pF, Input Capacitance - 1110pF, RDS (on) (2.5V)=12.4mΩ (4.5V=9.4mΩ)

good inductors - Coilcraft | Mouser
XAL1060-222ME, XAL1010-222ME
XAL7030-272 etc
not so good, but I’m use it - VISHAY IHLP M11
IHLP-1212BZ- 11 IHLP2525CZER6R8 M11 … etc

I would really like to keep full buck-boost functionality, it would allow us to run 2S+ on a 3V LED to extend runtime which is a great feature to have IMO. For a pure buck or pure boost converter there are drivers out there. What I want is to be able to freely swap cell count, cell chemistry, and emitter VF without having to touch the driver.

If you look at the mosfets I have chosen they are a bit better in terms of capacitance, but have a higher RDSon resistance, but still low enough that I think it will be adequate (<20mohm). The main reason I chose them was the SC70-6 package, 2.05mm x 2.05mm square! I want footprints to be as small as possible so that this can potentially be miniaturized to 17mm.

This is good.
Reverse Transfer Capacitance has a huge impact on dynamic losses. Not only RDSon.

Google translation. Inferion is the developer of the meteor driver

Consider SEPIC as well - it will be easier to do low-side current sensing than with buck-boost where your output side is inverted. I use the LM3410 in a SEPIC configuration in the MELD3 drivers to run from primary CR123 or secondary cells, but it doesn’t have enough range to use multiple cells.

A 4A Buck-Boost-Driver for single Li-Ion cells would be nice. It would allow the use of the Osram Black Flat (very high Vf) in smaller lights. This would enable new throw records.

A wide input voltage driver needs adequately set cut-off points for battery over-discharge protection. A potential issue is voltage range overlapping for adjacent serial configurations, though in practice I only see this issue arising for 4S batteries and above. Possible cutoff points calculated over the 1S cut-off figure plus a small offset value times number off cells in series to reduce the chances of balancing issues. For 1Scut-off = 2.75V, offset = 0.1V, and n being the number of sections, this would be the general rule:

nS battery cut-off = n × (1Scut-off + (n - 1)offset)

The MCU would detect the input voltage and set the cutoff accordingly: 2.75 (1S), 5.7 (2S) or 8.85V (3S). Unobstrusive pre-cutoff warnings would also be advisable. Of course, this is just a good example. :-)


Originally posted on Thu, 05/11/2017 - 15:19; 1Scut-off value edition.


Reviving this old thread.

Are there any good buck boost drivers available for sale that could be used in flashlights?

I can’t seem to find any, as they are either buck or boost.

Given the multiple LED options in 6v and 12v LEDs, are there any recommended boost drivers ?


Buck and Boost Drivers, Testing, Modding, and Discussion (Pic Heavy)


What is the size you wish to have? Myself and some people on blf have build loneocean's gxb172 driver with success!

I am not yet sure on size requirements, working on a project with Clemence.
I will check in with him and see.

Does anyone know, do the common 1xAA drivers that work with li-ion as well as nimh/alkaline just have a separate linear channel for lithium, or does the input range for the buck/boost also cover lithium ion voltages?

I think most are just boost + linear stage (or the step-up converter runs in pass-through mode with Li cells), AFAIK there is no buck-boost chip in existence that goes down to 1xAA voltage levels. (2xAA, yes, TPS63000/TPS63020, but pointless since 2xLiIon voltage is way over maximum input voltage.)
Well the BW-ET1 has a step-up + a step-down converter in series but it’s a humongous driver for a 1xAA that wouldn’t fit in most other lights.

  • some may have a separate channel, something on the higher end like a ZL may have that, but I haven’t seen one yet.