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I recently built step up converter which work quite good. Now I would like to build a circuit which would enable this step up converter when battery voltage drops below 1.8V (Arduino BOD).

  • I need to keep in mind power consumption because of battery power

Now, I do not know what is the best method to do that.

I guess that couple of transistors would do the job but I do not know where to start. Also I dont know if it is optimal solution bacouse of battery power.

The EN pin is a logic-level input used to enable or disable device switching and lower quiescent current while disabled. A logic high (>70%of VIN) will enable the regulator output. A logic low (<20% of VIN) will ensure that the regulator is disabled.

So if I understand it correctly, I need "circuit" that will "bring" VIN on EN pin when VIN < 1.8 V.

Please give me some direction to start with this. Thank you.

EDIT 2017-03-07 I went search in direction mentioned in comments and found this video. Which I guess is good start.

p.s. Iam using MCP1625 which has enable pin.

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  • \$\begingroup\$ Basically its factory recommended design of MCP1625 discussed here electronics.stackexchange.com/questions/236184/…. \$\endgroup\$
    – MightyPolo
    Mar 6, 2017 at 14:23
  • \$\begingroup\$ The solution will include a reference, a divisor, and some type of comparator to drive the boost enable. If cost is not a concern, you can find all of this in a single IC which is targeted at this sort of application. \$\endgroup\$
    – M D
    Mar 6, 2017 at 14:24
  • \$\begingroup\$ How many cells in series are you using for this? 1 alkaline? \$\endgroup\$
    – Dejvid_no1
    Mar 6, 2017 at 14:58
  • \$\begingroup\$ @Dejvid_no1 right now in my prototype I went for CR123A because of its size. Alternatively I would use two AA bateries. \$\endgroup\$
    – MightyPolo
    Mar 7, 2017 at 9:21

2 Answers 2

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I'm guessing you won't be able to squeese out so much energy of the battery when it is almost empty.

Anyhow you could either use a low voltage comparator with a reference, like this:

enter image description here

Change the resistors accordingly for your application. You might want to invert the output with an NPN transistor and a pullup.

Or you could build something with transistors. I don't know if this actually works in the "real" world but it works in my LTSpice simulation:

enter image description here

Q1 holds EN low until VBAT reaches approximately 1.8 V when it releases EN to VBAT. The trip point can be adjusted by changing R5 and R4. R7 provides a bit of hysteresis around the trip point. I'm mediocre at designing transistor circuits so I would definitively go with the IC version.

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  • \$\begingroup\$ Thank you sir, this is what I was looking for. I use 3V battery and BOD is around 1.8 V. That is 60% of battery would be vasted. Transistor circuit is impressive, but I will go with IC. Thank you. \$\endgroup\$
    – MightyPolo
    Mar 7, 2017 at 14:12
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Could you not just use a comparator circuit to measure when the battery voltage drops below 1.8V, then have this toggle the EN pin?

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  • \$\begingroup\$ But how do I get reference for OA when voltage is changing in time.. Divider would return slightly different values each time. \$\endgroup\$
    – MightyPolo
    Mar 7, 2017 at 11:40
  • \$\begingroup\$ You can use a reference voltage chip, and have the divider set against that, or you can get some type of comparator chip with a built in low reference voltage. Seems the guy above me answered pretty extensively though, and that IC he mentioned will do the trick nicely! \$\endgroup\$
    – MCG
    Mar 8, 2017 at 8:35

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