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DC-DC Converters vs Linear Regulators


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Looking for advice as software is my thing, I'm still pretty much new to hardware. 

 

It would seem that DC-DC Converters (Boost and Buck) would always be the preferred method to get the voltage you require as they are very low loss. Aren't regulators going to burn off a lot of wasted battery current? How do you guys deal with powering your battery operated projects for a long time at 3.3v? 

 

A project I'm wanting to work on is that I wanted to create a mesh network of cc2500's with attached water controlling solenoids and soil probes. Most solenoids are 9v or 12v, but i don't think a battery will last very long given the current required to keep it open.

 

But when I look at DC-DC converters, they are pretty expensive - Adafruit (who are always more expensive I know) sell a drop-in regulator replacement for $US15. Are there other parts that do as good a job? Or is this something one would just design into a board?

 

Any advice appreciated!

 

Richard

 

 

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 How do you guys deal with powering your battery operated projects for a long time at 3.3v? 

 

Lithium (CR2, CR123A), Li-Ion, or Lithium thionyl chloride batteries and carefully selected components that will tolerate the voltage range of the battery so no regulator is required. As a practical matter a LDO voltage regulator is typically required with Li-Ion because the max cell voltage is 4.2V and most 3.3V components won't tolerate that. Sometimes a carefully selected diode can be used instead of an LDO.

 

Switching regulators have various concerns such as cost, quiescent current, and actual efficiency (spec sheets promote the max not the typical).

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Options would include:

multiple battery packs, able to be routed in serial for high-voltage needs, and in parallel for low-voltage needs

or multiple battery packs wired in serial for high voltage, then down-convert to low volt for the MCU.

 

 

*disclaimer- I'm a noob and quite often, an idiot. Ignore me if I'm off base.

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Options would include:

multiple battery packs, able to be routed in serial for high-voltage needs, and in parallel for low-voltage needs

or multiple battery packs wired in serial for high voltage, then down-convert to low volt for the MCU.

 

 

*disclaimer- I'm a noob and quite often, an idiot. Ignore me if I'm off base.

 

Also from a noob, but:

 

I think tapping a subset of a series of batteries is discouraged. You end up draining cells at different rates, which causes problems.  (EEs could explain much better.)

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Are you going to spin a board(s) for this? I've used small buck regs from alpha & omega and a boost from semtech. The efficiently is much better than a LDO or a diode and allows you to increase voltage without more batteries. Some also disable themselves when there is a very light load. Depending, sometimes the internal discharge of the battery is the biggest drain on power.

 

For driving actuators like solenoids, hopefully the state that they will be in most of the time is undriven. So if there is a water valve to say water plants, it is on 1% of the time and off the rest. Then I would just use the uc to enable the boost reg when this actuator needs to be on.

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If its a small battery application, generally a SMPS isn't worth it. What ya gotta worry about is quiescent current usage such that you don't drain the battery over time. For general purpose, the MCP1702 is a nice, easy, flexible, low quiescent current LDO for battery applications. SMPS are super handy for 12-24V battery systems where you need more than 1A draw at a low voltage rail. It always depends on the application.

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I agree with username for the most part. Only caveat is the comment about a freshly charged lipo being 4.2 volts then to fully discharge, take it down to 2.5 volts, this is where the tps61200 comes in handy. I'd just be careful about the drop across the LDO after it falls out of regulation which it will over the discharge of the battery.

 

So many solutions, hard to choose. I think they all have merit.

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