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I have a circuit that runs 5V. I need to integrate a CO2 sensor that requires 6V. What would be the simplest, most cost effective way to do this? I need about 200ma for the sensor

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    \$\begingroup\$ Stock DC-DC boost regulator. 200mA wouldn't need very large discretes. \$\endgroup\$ Aug 30, 2012 at 3:55

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boardbite's TPS61040 is just one of many step-up converters which will do the job. But it costs 1.88 dollar in 1s at Digikey, while the cheapest I found is only 70 cent. That's the Semtech SC4503.

enter image description here

This is the typical application schematic from the datasheet. Again, this will be similar for many other step-up switchers. The SC4503's reference voltage is typically 1.25 V, so for 6 V out you have to set R1 to 190 kΩ. At 12 V out and 200 mA the SC4503 will have a 90 % efficiency, for 6 V you can expect a slightly higher value. It can supply more than 1 A of output current, so you'll have lots of headroom. Comes in a SOT23-5 package, and the 1.3 MHz switching frequency means you only need a small inductor.

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  • \$\begingroup\$ Nearly a third the cost, nice! May I ask which search/catalog you generally use for finding parts? Or is this Semtech part just from experience \$\endgroup\$
    – boardbite
    Aug 30, 2012 at 12:11
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    \$\begingroup\$ For me always Digikey. I haven't purchased much from them (I use them for information!), but their on-line selection tools are excellent; I use them all the time. Direct links to manufacturer's site for datasheets on all parts as well. Just throw in the right parameters, and sort by price. IIRC I have used Semtech parts in the past, but the advantage of a site like Digikey ensures availability (they have 10 000 in stock), however exotic the brand may be. \$\endgroup\$
    – stevenvh
    Aug 30, 2012 at 12:23
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The TPS61040 (from TI), among other adjustable-output step-up regulators, can accommodate 200 mA or more current draw at output voltage of 6V, from input voltage of 5V.

It is available in SOT23-5 package as well as 6-SON (similar to QFN), so you can start with a larger prototyping-friendly footprint, then move on to a smaller one for a final product.

Also, it's a fairly popular and inexpensive part, so you should have no trouble obtaining it. I think it costs a $1-2 in single-unit quantities.

I have used it before (for an LCD backlight application), and had good results with little layout effort (minimal number of peripheral parts, including a 10uH inductor).

Here is its datasheet.

If you can't get that one, frankly there are dozens of options out there; just look under stepup/boost regulators in Digikey or Mouser. I just find that particular one to be convenient and reliable.

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Check the acceptable voltage range for all your components. There's a good chance you can run both all of your logic AND the CO2 sensor at 5.5V, so you'd just need to adjust your primary supply.

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  • \$\begingroup\$ If a logic IC's datasheet mentions 5.5 V as maximum for Recommended Operation Conditions, that's already 10 % margin included on a nominal 5.0 V. If you operate at 5.5 V and have a 10 % tolerance on that you may meet/exceed Absolute Maximum Ratings. \$\endgroup\$
    – stevenvh
    Aug 30, 2012 at 18:47
  • \$\begingroup\$ @stevenvh Sure, but plenty of 5V devices list 4.5-6V as the allowable range, and plenty of 6V devices allow 5-7.5V, so 5.5V makes everyone happy even with 10% tolerance. \$\endgroup\$
    – Sparr
    Aug 30, 2012 at 18:56
  • \$\begingroup\$ In my experience that 6 V is often Absolute Maximum Ratings. Many users think that's maximum for normal operation, but it isn't. You should stay away from AMR. \$\endgroup\$
    – stevenvh
    Aug 30, 2012 at 18:59
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    \$\begingroup\$ also CO2 sensor requires 6v +/- .1v \$\endgroup\$
    – neufuture
    Sep 2, 2012 at 17:09

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