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If I have a three terminal TO-220 voltage regulator where the center terminal and heat sink are connected ground terminals, is there any reason not to mount the heat sink directly to an aluminum chassis (with a bit of thermal grease)? I have a device that has an L78S12CV 12 volt regulator mounted to a finned heatsink, which itself is mounted to the chassis. Between the device and the heatsink there is a mica insulator, but the bolt holding the regulator to the heatsink/chassis is not insulated with a nylon washer. Is there any benefit to using the insulator in this situation?

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    \$\begingroup\$ Is the bolt made from metal? \$\endgroup\$
    – Andy aka
    Mar 27, 2021 at 10:56

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If the bolt isn't insulated then it will (electrically) connect the TO220 pad to the heatsink, so the mica insulator serves no purpose. You'll get better heat transfer to the heatsink if you remove the insulator.

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    \$\begingroup\$ And still better heat transfer if you apply some thermal grease or a phase-change pad. \$\endgroup\$
    – Hearth
    Mar 27, 2021 at 15:38

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