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5v regulator -vs- 5v LDO regulator... — Parallax Forums

5v regulator -vs- 5v LDO regulator...

JedJed Posts: 107
edited 2014-01-04 13:58 in BASIC Stamp
What's the difference? I'm assuming that means the regulator wont output any voltage until a low threshold is reached? What would be the benefits of this and when would it matter/

Comments

  • ZootZoot Posts: 2,227
    edited 2008-03-20 21:42
    Other way around -- low drop out refers to a kind of regulator that will not let it's stable output voltage drop until the input voltage drops very close to the desired output voltage. Non LDO regulators generally require that the input voltage be no less than 1-2 volts above the output voltage. I.E.:

    - 5v regulator - needs about 7v or higher to get 5v out
    - 5v LDO regulator -- needs about 5.5v or higher to get 5v out

    So why ever use non-LDO? Remember that the difference between input and output voltage is expressed in HEAT. If you need to drop 9v to 5v, an LDO will not handle the heat so well.

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  • kjennejohnkjennejohn Posts: 171
    edited 2008-03-20 21:46
    Hi.

    LDO: Low Drop Out means that the regulator drops less voltage internally on its own. A useful comparison is the garden variety 7805 positive 5 Volt regulator versus its LDO counterpart the LM2940. The 7805 needs at least 2.2V more than its rated output, so you need 7.2V to get 5V out. The LM part though needs only 5.7 Volts. If you put this 5.7V into the 7805 you'd get 5.7 - 2.2, or 3.5V out.

    LDO is preferable.

    kenjj
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2008-03-20 23:35
    Many LDOs are fussier about what kind of filter caps they require than non-LDO types. It always pays to read the datasheet. Also, there's no reason that an "LDO will not handle the heat so well" as a non-LDO with the same input/ouptut voltage differential. The power dissipation will be the same, i.e. (Vin - Vout) x Current.

    LDOs are selected because, when run near their dropout differential, they waste less power through heat. 5V logic powered from a 6V battery is a frequent application. This is how the BOE-Bot is powered. It uses an LM2940 5V regulator, which is an LDO.

    -Phil
  • paralaxuserparalaxuser Posts: 3
    edited 2014-01-03 15:45
    Can someone please recomment an LDO that is similar to this one http://www.flytron.com/camera-transmitter-shutter/93-tiny-5volt-regulator.html from eBay? Size doesn't matter as much. Thank you.
  • ercoerco Posts: 20,256
    edited 2014-01-03 19:00
    What's your input voltage and load current ? Linear regulators (such as the one you posted) are power wasters, very inefficient since they dissipate energy as heat. The higher the voltage drop, and the higher current, the more power is wasted. You're much better off with an efficient, dollar switching buck regulator such as http://www.ebay.com/itm/1-DC-DC-Buck-Converter-Step-Down-Module-LM2596-Power-Supply-Output-1-23V-30V-T7-/121208203049

    Stock up, $1.01 is a great price. I just bought two while replying! :)
  • paralaxuserparalaxuser Posts: 3
    edited 2014-01-03 21:01
    Two is how many I needed.

    I read up on the tiny regulator and everyone was posting that it overheats.

    I'm going to use it to drive a laser. Would this switching regulator be enough?
  • ercoerco Posts: 20,256
    edited 2014-01-03 21:16
    A real LM2596 is supposedly good for 3 amps output. Using a cheap Chinese clone like this, it's probably safe to go to 1 or 1.5 amps of light intermittent duty. If you're going to pull more current, you may need a different part.
  • paralaxuserparalaxuser Posts: 3
    edited 2014-01-04 13:58
    This should be enough. Lets see how they do once they get in.
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