How hot can a voltage regulator get before it's dangerous?

Discussion in 'Power Electronics' started by Matt Zhang, Jul 24, 2016.

  1. Matt Zhang

    Thread Starter New Member

    Jul 24, 2016
    Hi everyone,

    I'm an amateur at electronics, so this question may be a bit stupid. I have a linear drop-off regulator which is reaching temperatures of about 60 C. This seems dangerous to me, so I'm going to try attaching a heat sink. However, on other forums online I've read about things like sizzle tests (seeing if licking your finger, then touching the component, causes sizzling), which seems to indicate that temperatures around 60 C are not that uncommon or dangerous. What kind of temperatures are safe for electronic components? This particular project is a decorative piece that's meant to be kept plugged in on an endtable.

  2. OBW0549

    Distinguished Member

    Mar 2, 2015
    The manufacturer's data sheet for the regulator will tell you what operating temperature range is acceptable; but if the case temperature of your regulator is actually reaching 60 °C then I'd seriously consider using a heatsink anyway. Better safe than sorry.
  3. dannyf

    Well-Known Member

    Sep 13, 2015
    120c (die temperature) is fairly common and some are rated 150c.

    typically, if the case is too hot for your fingers to hold onto it, it is too hot.
  4. crutschow


    Mar 14, 2008
    It sounds like the temperature is acceptable, but a small heatsink should improve reliability.
  5. #12


    Nov 30, 2010
    All this can be done with the proper math, but one needs to know which chip number, how big the case is, what the datasheet says, how much current and how much voltage. With you having provided none of these, all we can do is guess: If it's too hot to touch, give it a heatsink.
  6. Marley


    Apr 4, 2016
    Although 60deg C is OK, the device will be more reliable if you add a heatsink so that it runs cooler. Although you should do the maths, the actual thermal resistance to ambient is hard to calculate. It will be affected by things like airflow, ambient temperature, altitude, etc. It will change a lot if you enclose your circuit in a case.

    My "rule of thumb" (literally in this case) is if you can hold your finger on it for a minute without pain, then its not too hot! If not, use a heatsink.
  7. DickCappels


    Aug 21, 2008
    Most modern monolithic voltage regulators (LM340, LM317, LM78XX, etc plus the negative voltage versions) that do not have an over-temperature shut-down function. That means that if you are getting the expected voltage out, the regulator thinks it is just fine.

    Check the datasheet for your regulator to confirm it has over-temperature (or thermal) shut-down.

    On the other hand, if the regulator is exposed such that skin contact is a significant risk, take steps keep the temperature below 60° C to avoid 1st degree burns or worse.
  8. crutschow


    Mar 14, 2008
    Your rule of thumb is too conservative. ;)
    If you can hold you thumb on the device for a minute without getting burned then the temperature is likely no more than about 45°C(113°F)
    Most silicon semiconductors will run at 70°C junction temperature or more with good reliability.