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Topic: Running a voltage regulator below recommended input voltage. (Read 2 times) previous topic - next topic

Jack Christensen

A buck-boost regulator comes to mind. Haven't actually done one myself, but I've had good results with a small boost converter (MCP1640) in a circuit that requires right around 100mA at 5V. It can use two or three alkaline or NiMH AA cells. Haven't done a real good test yet, but it looks like two fresh alkaline cells should run it for at least 8 hours, three should give half again that. Makes a lot of sense to boost a lower voltage when it can be done at 90%+ efficiency, as opposed to knocking it down with a linear regulator and wasting power. A lot of the switching regulators these days don't require complex circuitry. Build it on a PC board, keep things close and traces short and you're off to the races.

I definitely would try to avoid the scenario of running a regulator (or most anything) out of spec.
MCP79411/12 RTC ... "One Million Ohms" ATtiny kit ... available at http://www.tindie.com/stores/JChristensen/


Nov 16, 2012, 10:22 pm Last Edit: Nov 16, 2012, 10:29 pm by John_S Reason: 1
That's a fantastic solution. I will definitely look into it. Based on the datasheet, the additional circuitry for the MCP1640 is minimal, and they even have a recommended PCB layout.

The only problem is this eliminates the external 12V option, but I can still have a linear regulator for that.
Or would anyone have an example of a switching regulator with a 2-12V input and 5V output?

Edit: Anyone have any comments about the MIC2570?

Jack Christensen

Nov 17, 2012, 12:18 am Last Edit: Nov 17, 2012, 12:20 am by Jack Christensen Reason: 1
Took a quick look at the MIC2570 datasheet, it's a boost regulator as is the MCP1640, I'm not 100% sure, but my initial assumption would be that the input voltage cannot exceed the output voltage (same as MCP1640). Other than that, it looks fine. TI makes some interesting buck-boost regulators, they're in very small surface mount packages though, if that's an issue.

Using a linear regulator on the 12V input also occurred to me. Feels a bit kludgey, but if the low efficiency is not an issue (and it might not be for a SLA, etc.) then that could work.

I have a small PC board which I use as a breadboard power supply that uses the MCP1640. Happy to share, if you're interested, PM me.
MCP79411/12 RTC ... "One Million Ohms" ATtiny kit ... available at http://www.tindie.com/stores/JChristensen/


^Do you think you could post a picture of your PCB layout?

I am a bit lost finding a suitable inductor. I don't understand saturation current or ESR. Could you link a suitable inductor that digikey supplies? I would like an SMD part, but I will be soldering by hand, so the leads can't be on the bottom.

For the capacitors would these work? http://www.digikey.ca/product-detail/en/C2012Y5V1A106Z/445-1371-1-ND/567608

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