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I need to power a control circuit from a variety of LiPo batteries 3-6S (12.6V to 25.2V). The control circuit can draw up to 100mA at 5V (atmega328p + other discrete components, LEDs, etc).

Choices I know about:

  • Voltage Regulator LM340T-5.0 stepping down any voltage up to 35V. The problem is power dissipation. Because the solution has very limited space, no heat-sink is available.
  • Buck/Step-Down Converter LMZM23600. 5-times more expensive and difficult to handle, due to strange packaging (pins on the bottom).

Is there any other straight-forward way to power control circuit from 3-6S battery ?

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  • \$\begingroup\$ electronics.stackexchange.com/search?q=oki dupe \$\endgroup\$ May 11, 2019 at 13:27
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    \$\begingroup\$ Search internet for "5V power module". If you want it as small as possible, you can expect QFN or BGA solutions which are very hard to hand solder. You probably need to find a bigger sized compromise. \$\endgroup\$
    – Huisman
    May 11, 2019 at 13:28
  • \$\begingroup\$ The cheap MC34063 might be a fine choice, if you can afford the PCB space. Also search for online calculators to figure out the component values easily. \$\endgroup\$
    – Indraneel
    May 11, 2019 at 13:34
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    \$\begingroup\$ I suggest you have a look at: digikey.com/en/product-highlight/r/recom-power/r78-series These are a "drop in" replacement for the 78xx voltage regulators but they are not linear regulators, they're buck converters. \$\endgroup\$ May 11, 2019 at 13:43
  • \$\begingroup\$ @Bimpelrekkie Absolutely perfect. A bit pricey, but I greatly appreciate your suggestion, since I had no idea this exists. \$\endgroup\$
    – Martin G
    May 11, 2019 at 18:03

2 Answers 2

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I suggest you have a look at these Recom or these Murata "drop in" replacement for the 78xx voltage regulators.

This is the Murata model:

enter image description here

These can be used as the 78xx linear regulators we all know but they are not linear regulators, they're buck converters designed to replace them.

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  • \$\begingroup\$ Murata's OKI-78SR series have a slightly smaller footprint than the one pictured above - more similar to a standard linear regulator itself. I've used these in a couple of my own projects. They are great little devices, even if more expensive than a regulator, and worth looking at if you cant deal with a lot of heat dissipation (these have basically zero!) and just want something you can solder in. \$\endgroup\$
    – Tom S
    May 11, 2019 at 21:20
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Look for XL6009 module on the internet. https://www.amazon.com/HiLetgo-Adjustable-DC3-0-30V-DC5-35V-Converter/dp/B07BNHR4HW/ref=mp_s_a_1_1_sspa?keywords=XL6009&qid=1557586948&s=gateway&sr=8-1-spons&psc=1

This module costs about $2/piece. It takes in 5-35V input and gives variable output. It costs a bit more than a linear regulator IC, but if you consider the cost of additional components like capacitors, connectors and PCB/vera board, it'll turn out that the linear regulator circuit will become costlier than the XL6009 module.

The lowest power dissipation you will get in linear regulator is (12.6-5)*0.1 i.e. 0.76W. The highest you can get is (25.2 - 5)*0.1 i.e. 2.02W. This much of heat can be dissipated via a heat sink easily. Its entirely upto you.

According to me, save yourself from the hassle of circuit design, component procurement, soldering, PCB fabrication, heat sinking etc. and buy the XL6009 module.

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  • \$\begingroup\$ Well, the design is quite small. I cannot fit the module there, but I will consider to make my own converter in my design, maybe the XL6009. Thanks \$\endgroup\$
    – Martin G
    May 11, 2019 at 18:06
  • \$\begingroup\$ You can even look at the miniature boost modules by Pololu rhydolabz.com/robotics-robotic-parts-c-155_164/… \$\endgroup\$ May 11, 2019 at 18:57
  • \$\begingroup\$ This is a fixed 3.3v variant. There is a 5v module too. Look for dealers in your area \$\endgroup\$ May 11, 2019 at 18:58

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