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Do I need a regulator? — Parallax Forums

Do I need a regulator?

CountMurphyCountMurphy Posts: 19
edited 2013-02-03 15:03 in Propeller 1
I'm somewhat new to working with hardware so please bear with me if this is really basic. I have this (https://www.sparkfun.com/products/731) battery which outputs 3.7 volts. Now since the prop takes 3.3V in, I assumed I needed an LDO regulator to give it stable power. The problem is I am having trouble finding a regulator that can work with such a small voltage difference. So my question is, is it safe to just plug the battery into my project with out regulating it? If not, what regulators do you guys use to bypass this issue?

Comments

  • Mike GreenMike Green Posts: 23,101
    edited 2013-01-31 22:25
    The problem is that the maximum supply voltage for the Propeller is 3.6V and the absolute maximum voltage is 4.0V. More than that may destroy the Propeller. The 3.7V of the battery is above the maximum supply voltage and battery voltages are notoriously not exactly what one believes they should be. It is not safe to use this battery directly with the Propeller. You should plan on dropping at least 0.4V of the battery voltage. An LM2936 LDO regulator has a maximum dropout voltage of 0.4V with typical dropout voltages much lower (0.1V-0.2V). I'm sure you could find other similar regulators. Another option would be to use a switching transistor, say a PNP transistor in the 3.7V lead and the base grounded through a resistor. A 2N3904 has a maximum saturation voltage of 0.4V at 50mA with a base current of 5mA for example.
  • jmgjmg Posts: 15,173
    edited 2013-01-31 22:27
    try this thread
    http://forums.parallax.com/showthread.php/103454-Utilizing-a-3.3v-LDO-and-a-3.7v-Lipo
  • shimniokshimniok Posts: 177
    edited 2013-02-01 15:18
    Sparkfun has a charge/regulator board that works with single LiPos: https://www.sparkfun.com/products/11231?
  • Bill HenningBill Henning Posts: 6,445
    edited 2013-02-01 16:11
    Use a Schotty diode, it will drop .3v or so.
  • Mark_TMark_T Posts: 1,981
    edited 2013-02-01 16:24
    For future reference you might want to consider LiFePO4 (lithium iron phosphate) batteries, both because of their inherent safety
    compared to lithium polymer, and the convenient 3.2V they generate (3.6V is a good constant voltage charge limit).

    For instanc: http://www.ebay.co.uk/itm/4x-3-2V-CR123A-LiFePO4-Lithium-Rechargeable-Battery-/360450520197?pt=UK_ConsumerElectronics_Batteries_SM&hash=item53ec867485
  • RaymanRayman Posts: 14,665
    edited 2013-02-01 17:49
    I think I would try an LDO regulator and see what happens...
  • JasonDorieJasonDorie Posts: 1,930
    edited 2013-02-01 18:13
    I've used these for a variety of applications and they work really well. Nice stable power from a variety of sources.

    http://www.pololu.com/catalog/product/2119
  • CountMurphyCountMurphy Posts: 19
    edited 2013-02-03 14:35
    Thank you all for your advice. Mike Green, I'll have to check out the regulators you mentioned.

    shimniok    , I didn't know those even exisited. I just ordered 2 (as they will also make charging my project a heck of a lot easier)

    MarkT, what makes those batteries safer?

    Rayman, I tried an LDO regulator before I posted the question. however do to my noobishness I misread the data sheet an got some that needed more power than I was giving them. Frustrated in not finding the regulator I needed, I posted this question to see if I could get away with out one.

    JasonDorie, the one you linked to only does 5v out perhaps you meant this one? http://www.pololu.com/catalog/product/2120. Either way they promissing. Side note, I'm not to far from petaluma. beautiful city.

    Bill Henning, I've never heard of a Schotty diode but they look to be just what I need. If the sparkfun boards dont do what I need, I will look into these.

    Again, thank you all.
  • jmgjmg Posts: 15,173
    edited 2013-02-03 15:03
    CountMurphy wrote: »
    Rayman, I tried an LDO regulator before I posted the question. however do to my noobishness I misread the data sheet an got some that needed more power than I was giving them.

    An LDO will be the best solution, but another fish-hook is many LDOs draw more power in dropout.
    You need to check the Ic vs Vin, and if they 'forget' to include dropout region, avoid that model.

    The Prop is quite tolerant of supply droop, so you really want a protection-regulator that allows charge voltage tolerance, ideally reverse battery protection too, and one that can nicely go into pass-mode below regulation.
    You could choose 3.0V instead of 3.3V, if you want less battery intrusion as it goes flat.

    Such a device can be elusive...
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