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I’m making a battery powered air quality sensor node using Adafruits Feather M0 LoRa MCU. I have a MH-Z19 carbon dioxide sensor that requires 5V (datasheet says 3.6 ~ 5.5 V DC, and average current draw < 18 mA). The M0 only provides 3.3V. There is a BAT pin which gives ~3.7V straight from the Li-Po battery, but it is apparently not enough for the MH-Z19. I also tried using a Pololu 5V step-up regulator (U1V10F5) after both the BAT and 3V pins on the MCU. It did not work at all with the 3V pin. It worked with the BAT pin, but only when the battery was pretty full. When the voltage dropped it first started making noises, and then stopped working.

So my current solution is using 3 AA batteries for just the MH-Z19. Now I want to shut the 3 AA battery and sensor circuit off when the MCU is in “sleep mode”. Shut it off like with a mechanical switch, except I want to control the switch using the MCU. Can I use load switches for this? Can they effectively stop the circuit so that the batteries power is not wasted. I guess I need something that defaults to not being shortened since the controller is going to sleep. Is this possible with a Load Switch?

I have been looking at these following Load Switches.

AP22802 from Diodes Inc.

TPD3S044DBVR from Texas Instruments

Would it be better to use something like a relay or a MOSFET?

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  • \$\begingroup\$ A MOSFET would be the easiest to control and use least switching power while having tiny leakage current. \$\endgroup\$ – TonyM Apr 24 '17 at 13:46
  • \$\begingroup\$ @TonyM Thanks. What kind of MOSFET would be suited for this? Would I only need the MOSFET? \$\endgroup\$ – Frode Apr 24 '17 at 14:09
  • \$\begingroup\$ How often will your sensor be switched on and for how long each time? Will you turn it on for 100 ms every 5 secs or something. \$\endgroup\$ – TonyM Apr 24 '17 at 18:10
  • \$\begingroup\$ @TonyM It will be switched on for 5-60 seconds somewhere between every minute and every fifth minute. \$\endgroup\$ – Frode Apr 25 '17 at 8:33
  • \$\begingroup\$ Then I'd go for @JWL 's answer below. (Don't forget to upvote and select as the answer if you do.) \$\endgroup\$ – TonyM Apr 25 '17 at 9:19
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So the TPD3S044 has a few D+ and D- protection and from your quick description it doesn't sound like you need that. Take a look at something a bit more simple like the tps22915 The switch is default off which is good for your low power mode and also has a relatively low Rdson.

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