5 Volt Regulator Getting Hot?

Discussion in 'The Projects Forum' started by BlackCow, Mar 29, 2010.

  1. BlackCow

    Thread Starter Active Member

    May 11, 2009
    In my circuit I am stepping down a 12 volt DC input to 5 volts using a standard 5v regulator.

    Part and data-sheet here.

    I wired it in like this,

    Vin - tied to ground with a 0.33 μF capacitor
    Vout- tied to ground with a 0.1 μ
    F capacitor.

    I noticed it was heating up to a point where it was uncomfortable to touch, so I threw a heat sink in. It still gets uncomfortably hot with the heat sink on.

    Is it possible that the voltage regulator will be damaged if I leave it running hot for long periods of time?
  2. rjenkins

    AAC Fanatic!

    Nov 6, 2005
    They are supposed to turn of to protect themselves if they get too hot, but a bigger heatsink plus thermal grease would be a good idea.
  3. BlackCow

    Thread Starter Active Member

    May 11, 2009
    I think I got some arctic silver somewhere around here. That's comforting to know that the will shut off if they get to hot, I was worried it would turn into a melting fiery mess if left to long! :eek:

  4. Audioguru

    AAC Fanatic!

    Dec 20, 2007
    If it overheats then it shuts off, cools then turns on again. If it happens over and over then the chip will be broken by thermal and metal fatigue.
  5. russ_hensel

    Distinguished Member

    Jan 11, 2009
    Calculate the energy dissapated in the regulator. Compare to data sheet.
  6. turboeclipse

    New Member

    Mar 30, 2010
    I suggest adding a couple of diodes in series with the 12V to the regulator to drop the voltage down a bit.
  7. SgtWookie


    Jul 17, 2007
    You can reduce the power dissipation in the regulator by using (a) power resistor(s) as current limiters between the 12v supply and the IN terminal of the regulator.

    7805 regulators have a minimum 2v dropout between the IN and OUT terminals.

    The maximum current that the 7805 is rated for is 1A.

    So, Rlimit = (12v - (5v+2v))/1A = (12-7)/1 = 5 Ohms. Power dissipation in the resistor will be 5 Watts if the 7805 has 1A current, so double that to 10W for your resistor power requirement.

    You could use a couple of 10 Ohm 5W resistors in parallel. Make sure that they have good air flow around them.
  8. MMcLaren

    Well-Known Member

    Feb 14, 2010
    I use a bunch of surplus laptop power supplies with output voltages ranging from 13 to 18 volts so I'm very familiar with this problem.

    I finally ended up building a couple 5 volt 1 amp SMPS Buck regulators using a Micrel MIC4575 which runs at 200-KHz. I sampled the MIC4575 and the 68-uh 1 amp inductor and then purchased the diode and low ESR caps for a few dollars from Mouser. The regulator is cool to the touch without a heatsink even under full load.

    You can see most of the prototype SMPS regulator in the top portion of the picture below.

    Regards, Mike

    Last edited: Mar 30, 2010