VOLTAGE REGULATOR IC OVER HEATING

Discussion in 'General Electronics Chat' started by AJIN NADH, Mar 10, 2015.

  1. AJIN NADH

    Thread Starter Member

    Dec 18, 2014
    79
    4
    Dear Team,
    Am using Mq-03 Alcohol sensor ,And i used lm 7805 to give supply to the sensor, But i found that the regulator ic is Over heating, Can anybody suggest a solution.

    Regards,
    Ajin nadh.v.a
    R&D Executive
    Keltron Itac.
     
  2. DickCappels

    Moderator

    Aug 21, 2008
    2,656
    632
    First, post a schematic.

    How do you know it is over-heating? The finger test is not a reliable indicator since the case of an un-heatsinked 7805 (with metal case) can feel very hot but be within the regulator's allowable thermal range. The 7805 has an internal over-temperature shutdown, and if the output voltage is low (much less than 4.75V) then either you are drawing too much current or it is too hot.

    Make sure everything is connected correctly.

    Check that the power dissipation (volts in - 5V) x current is not too high. -How much current should/does your sensor require, what is the input voltage to the 7805 and what kind of heatsink do you have on it (in degrees C per watt if you know)?

    There may be other factors that can become apparent upon examination of the schematic.
     
    AJIN NADH likes this.
  3. pwdixon

    Member

    Oct 11, 2012
    488
    56
    That sensor has a 33 Ohm heater in it so you are taking at least 150mA.
     
  4. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,998
    745
    The datasheet says power consumption is 750mW@ 150mA, so an heatsink is required.
     
  5. AJIN NADH

    Thread Starter Member

    Dec 18, 2014
    79
    4
    Dear Sir,
    Dear Sir,
    I already used the heat sink, But its become too hot.. Actually there is an internal shortcircuit na...?
     
  6. pwdixon

    Member

    Oct 11, 2012
    488
    56
    Really depends on the input voltage and the type of 7805 being used.
     
  7. AJIN NADH

    Thread Starter Member

    Dec 18, 2014
    79
    4
    Pls find the circuit...i tried this
     
  8. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,998
    745
    Ok, have you measured the current its using?
     
  9. AJIN NADH

    Thread Starter Member

    Dec 18, 2014
    79
    4
    no sir
     
  10. pwdixon

    Member

    Oct 11, 2012
    488
    56
    Lovely drawing but that doesn't tell anyone anything about the power supply or the regulator.
     
  11. pwdixon

    Member

    Oct 11, 2012
    488
    56
    Are you using an Arduino and it's on-board regulator by any chance?
     
  12. DickCappels

    Moderator

    Aug 21, 2008
    2,656
    632
    I still wonder whether it is over heating.

    Please measure the input current into the 7805, input voltage to the 7805, and output voltage from the 7805, and tell us.
    Also, please describe your heatsink (shape, rough dimensions).
     
  13. AJIN NADH

    Thread Starter Member

    Dec 18, 2014
    79
    4
    Dear Sir,
    Am also using op amp to amplify the sensor out, is it may be the problem...?
    The Other details will post soon...

    Regards ,
    Ajin
     
  14. DickCappels

    Moderator

    Aug 21, 2008
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    Yes, it might be. Eagerly looking forward to the other details.
     
    ErnieM likes this.
  15. Arx&Sparx

    New Member

    Feb 19, 2015
    11
    3
    I agree with DickCappels. Measure the current. If it is within range, it is fine, but if added measures are required (or wanted), add a little thermal paste and a decent heat sink and you should be fine.
     
  16. AJIN NADH

    Thread Starter Member

    Dec 18, 2014
    79
    4
    Dear Sirs,
    The overall current for the system is 5.33ma and the voltage is 13.05v
     
  17. DickCappels

    Moderator

    Aug 21, 2008
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    That doesn't add up. 5.33 ma and 13.05 volts is only 70 milliwatts, which is within the capabilites of all of the 7805 regulators I've see and not enough to get any of them very warm to the touch.

    What makes you think it is overheating? Is the output 5V and within tolerance (typically ±0.25V)?

    If possible, post the circuit that includes you 7805.
     
  18. Arx&Sparx

    New Member

    Feb 19, 2015
    11
    3
    I'm confused by that. If you are saying that the output after the LM7805 is 5.33mA and 13.05V, then i would say the input is too high and you fried the regulator. Otherwise, that is not enough to short or damage the regulator if that is the input side, let alone generate a substantial amount of heat.
     
  19. AJIN NADH

    Thread Starter Member

    Dec 18, 2014
    79
    4
    Dear sir,
    This is the overall current( input of 7805) and voltage..........
     
  20. Arx&Sparx

    New Member

    Feb 19, 2015
    11
    3
    Do you have a full schematic already drawn up or are you able to draw one up for us to look at?
     
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