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LM117: LM117 Heating Problem

Part Number: LM117
Other Parts Discussed in Thread: LM137QML,

Hi, I'm electronic design engineer at Tubitak Space. We bought LM117 and LM137QML components for satellite project but this components gets too hot. Could it be due to the structure of the materials? LM137QML component ( TO package ) don't touch printed circuit board and this component's heat doesn't decrease. The LM117 doesn't exceeding 150 deg C and the LM137QML doesn't exceeding 125 deg C. but these components are heating fastly in normal watt levels. We concern about this heating problem because these components will use in space. Do you have a suggestion? Thank you.

  • Hello,

    What are the operating conditions for the devices, i.e. VIN, VOUT, IOUT?

    LDOs typically need some form of heat sink - could be an external mounted heat sink or just the copper of the PCB - so for the TO package that does not touch the PCB, the ambient air is kind of like the heat sink. Were your tests that showed it getting too hot performed in a vacuum chamber or at atmospheric pressure? 

    Is there a way you can switch to a TO-220 package? I know it is larger but if you have the board space you can lay it over and solder the thermal pad to the board and that will dramatically improve thermal performance. 

    Best regards,


  • Hello,

    Another point that I should have mentioned is that in this case with the TO package, the leads of the package will be the main heat sink. Is there sufficient copper around the device? I'm wondering if there is not a lot of copper nearby and there is no ambient air to help remove heat then it may be a combination of effects adding up to make the device get hotter than normal.

    Best regards,


  • Hello again,

    Our LDO's convert from -15V to -12V , -15V to -10V, -10V to -5V. We bought space models of this LDO 3 months ago so we don't use T0-220 package. However, TO package LDO don't touch copper or another material, this component don't touch the PCB.  How can I make contact with copper while not contacting the PCB? Can I apply chemicals under the material and make it contact with copper on the PCB? or Can we press on the material with a mechanical piece to release the heat?  Thank you.

    See you soon.

  • Hi Ozge, 

    We don't normally provide a recommendation on the heatsink, but if you search "t0-220 heatsink", there are plenty of solutions out there. I would recommend checking them out. 

    Jason Song