Connect with us

Change LM2575 minimum input voltage to 8 volt

Discussion in 'General Electronics Discussion' started by chihwah li, Jul 31, 2015.

Scroll to continue with content
  1. chihwah li

    chihwah li

    5
    0
    Nov 8, 2014
    Dear all,

    The LM2575 has a minimum input voltage of 7V, but that is a little bit too low. I like to put 8 pieces of Nimh AA batteries in series to Get the required input voltage. But 7V would drain my batteries perhaps too low and that is not good. I read somewhere that you should not drain a Nimh battery lower than 900mV. 8 times 0.9V = 7.2V

    How can I increase the LM2575 input voltage to 8 volt?

    A working schematic for 7Volt input is in the pdf:
    http://www.ti.com/lit/ds/symlink/lm1575.pdfhttp://www.ti.com/lit/ds/symlink/lm1575.pdf
     
  2. Alec_t

    Alec_t

    2,788
    742
    Jul 7, 2015
    Which version of the LM2575 do you have?
    The TI datasheet for the LM2575-5.0 gives specs for supply voltages in the range 8V-40V, but that doesn't mean the chip will suddenly stop drawing current when the input voltage drops below 8V (or 7V). Even in the 'Off' state the chip draws ~200uA. You will need to monitor the battery voltage and disconnect the regulator if the voltage drops too low.
     
  3. Colin Mitchell

    Colin Mitchell

    1,418
    314
    Aug 31, 2014
    There is no LM2575-7.

    Use any -3.3 -5 or adjustable version and use the adjustable circuit to jack up the voltage to 8v.
    Or use a commonly available 7805 or LM 317 regulator in "jack-up" circuit.
     
  4. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

    4,960
    648
    May 8, 2012
    Odd. My TI data sheet specs 4.75V to 40V input.

    Disclaimer: It's Sunday afternoon, raining heavily and I'm working diligently at sampling my alcoholic stores. I'm an expert at this sadly diminishing science. :D

    Chris
     
    Martaine2005 likes this.
  5. Alec_t

    Alec_t

    2,788
    742
    Jul 7, 2015
    That range is certainly mentioned. The point is (so far as I understand it) that the OP doesn't want to over-discharge his battery, so he'd really like the IC to shut off completely when the input drops to 8V.
     
  6. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

    4,960
    648
    May 8, 2012
    Oh, I evidently didn't understand his question. Thanks for the clarification Alec.

    Chris
     
  7. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

    4,960
    648
    May 8, 2012
    I have a folder that has quite a few Voltage Monitor chips but they're designed for use with uCs. These chips draw only a few uA. I would think that there must be Voltage Monitor chips available for voltages >5V.

    Did you Google it?

    Chris
     
  8. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

    4,960
    648
    May 8, 2012
  9. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

    4,960
    648
    May 8, 2012
    I just happened to notice that there's Another Topic that intersects this one. Your LM2575 also has an ON/OFF pin discussed in that topic. ;)

    Chris
     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-