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I am about to wire up some HIH-4000 humidity sensors to a project of mine. The datasheet suggests a maximum voltage of 5.8V in (minimum 4V).

If I am using a 4AA battery pack (non-rechargable), will I have to worry about the extra .2 volts going through the HIH-4000?

I know 4 AA batteries are theorized to produce ~6 volts and I will be using the 6 volts elsewhere in my circuit to run other things.

Here are my questions:

  1. Should I worry about resisting the extra .2V?
  2. If so, will a simple resistor work for the long term?
  3. Whether I use a resistor or I make a step down converter, should I step it down more, to around 5V?
  4. Will this extend the life of the HIH-4000?
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    \$\begingroup\$ Have you considered adding a simple silicon diode between the battery and the sensor to drop the supply by about 0.6V? Probably a good bit cheaper than a step down converter and less wasteful than a couple of resistors. \$\endgroup\$ – JIm Dearden Jun 6 '14 at 17:08
  • \$\begingroup\$ I have not. I'm pretty new to electronics so I'm learning as I go. I'll look into this. Thank you! \$\endgroup\$ – ntgCleaner Jun 6 '14 at 17:30
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Yes, you do need to worry about the extra .2V. Silicon vendors put some guard band in, so your device would likely work, but you could see erratic operation and you could experience reduced lifetime.

Jim's suggestion of putting a diode in series would work, but I would use a Schottky, since you only need .2V of drop it would give you longer run time.

You could also look at using a buck-boost converter to supply the 5V. That would let you get 5V out over the whole battery discharge curve and use more of the full energy of your battery. (Though by 0.9V the batteries are pretty much dead, so not sure how much extra run time that will give you or what voltage the rest of your circuit needs.)

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  • \$\begingroup\$ Very nice. I haven't heard of a Shottky diode. I looked into it and it seems like it will work very nicely. Thank you! \$\endgroup\$ – ntgCleaner Jun 6 '14 at 20:29

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