NEWB Heat sink question

lboucher

Hi All

ME by college, so here is a stupid electrical question for ya.
So i have a row of 4, 8 amp triacs.
I want to add a heat sink.

Are the tabs of metal on the back of the triacs (heat sink with the hole in it) electronical seperated from the ciruit?

I ask because i intend to use 1 heat sink for all the triacs together.
Basicly mark up 1 peice of metal and use small screws thru all 4 holes to hold the metal to all 4 heat sinks.

Will this be ok?

Lucas

Philldapill

do you have a spec sheet for the triac?

Sometimes they are, sometimes they aren't. Get a multimeter and check if there is a HUGE resistance between each lead of the triac, and the tab. If there is infinite(or close to it), then the tab is probably isolated.

Mike Green

Usually the metal tab is connected to part of the triac. Some triacs have an insulated tab. You have to refer to the datasheet. There are insulator kits made for this sort of use. Often it's a sheet of mica with a hole for the screw and an insulating washer so the screw doesn't contact the triac tab. You have to use heatsink compound, smearing a thin layer on both sides of the mica sheet to reduce the thermal resistance. It's important that the holes in the heatsink have smooth edges so there's not a short between the triac and heatsink. If the triacs are switching AC, you have to insulate the heatsink from touch in case one of the insulators fails and the heatsink becomes connected to one side of the AC line ... another important reason for fuses although that won't help the shock hazard.

Forrest

If the tab is electrically connected to ground, then you can still attach a common heatsink if you install thermally conductive, electrically insulating material between the Triacs and the heatsink. Bergquist's Sil-Pad is commonly used for this application - see here for more info and a picture of a typical application www.bergquistcompany.com/tm_sil_pad_list.cfm

lboucher

Thanks for the info everyone.