Somewhat depending on what creepage and clearance you are trying to acheive I'd have thought it difficult to maintain good thermal conductivity and meet c&c requirements. Better to have an isolated heatsink for the high voltage parts.
> -----Original Message----- > From: [email protected] > [SMTP:[email protected]] > Sent: Monday, June 08, 1998 9:37 AM > To: [email protected] > Subject: isolation of TO-220 package > > > Hello everyone, > > The following problem has probably several solutions, some of which > I've seen > implemented in power supplies. > > PROBLEM: > In many applications the metal part of the TO220 package (that's the > square with > metal backing and 3 legs in a row) is (or should be considered) under > "live" > voltage. At the same time, for thermal reasons, it is required that > this metal > be coupled to the best heat sink around = chassis. This obviously > creates a > problem of isolation, which seems to be solved by using a thermally > conductive > isolator sheet between the transistor and the chassis heatsink. > However, if a screw, which passes through the hole in the TO 220 > package is used > (even if it is a plastic screw) then creepage requirements cannot be > maintained > (because the insulator is very thin). > Solutions I saw to this problem are based on not using the hole and > pressing the > transistor to the heat sink by other means. > > I would be grateful for any suggestion on how to solve the problem: > cool the TO > 220 through the chassis while maintaining at least 1.5 mm (possibly > more for > reinforced insulation) creepage between TO 220 and chassis. > > Thanks > Moshe Valdman >
