Re: Switcher question: heatsink causing problems?


tomg@xxxxxxxxxxx wrote:
hondgm@xxxxxxxxx wrote:
I have a TO-220 buck regulator IC (LM2678) and a Schottky in a TO-220.
...

If you do need a heatsink for the TO-220 Schottky, then you should
electrically insulate the heatsink from the TO-220 package.

Yes, insulate the heatsink.

You should
probably buy a "heatsink mounting kit" that includes, in addition to a
mica insulator, an insulating "lipped washer" (can't remember the
proper name, right now) that fits into the hole in the TO-220 package.
Alternatively, maybe you could use a plastic bolt and nut, and a mica
insulator. Remember to use heatsink compound, too.

No for the plastic screw. Even if you insulate the heat sink, you want
to conduct the tab to a copper pad on the pcb, through a metal screw.


How many amps is the Schottky conducting? Maybe it shouldn't be
getting as hot as it is. Have you looked at its waveforms? Maybe a
snubber-type network would help to keep it cooler. (Or maybe something
else in the circuit also needs tweaking.) In a 56W boost-mode switcher
that I made, the TO-220 Schottky barely gets warm to the touch, without
any heatsink. Depends on the average current, of course. But any
high-frequency ringing, etc, could heat it much more than necessary.
Just a thought.

For our 12V 3A smps, only the mosfet (external, so-8) get warm. It
does not need a heatsink either.

.

Relevant Pages

  • Re: Switcher question: heatsink causing problems?
    ... If you do need a heatsink for the TO-220 Schottky, ... Yes, insulate the heatsink. ... right now) that fits into the hole in the TO-220 package. ... How many amps is the Schottky conducting? ...
    (sci.electronics.design)
  • Re: Switcher question: heatsink causing problems?
    ... If you do need a heatsink for the TO-220 Schottky, ... Yes, insulate the heatsink. ... How many amps is the Schottky conducting? ... he's not going to connect the heatsink bolt to a PCB ...
    (sci.electronics.design)
  • Re: TO220 LEDs?
    ... >TO 220 package. ... >and look like a small rectangle with a heatsink tab on one end and two ... >screw isolators to ensure isolation from the heatsink. ... or use e-mail address listed at the Web site. ...
    (sci.engr.lighting)
  • TO220 LEDs?
    ... For the uninitiated these are the same package used for many high power transistors, triacs, voltage regulators and other stuff, and look like a small rectangle with a heatsink tab on one end and two or three legs sticking out the other. ... I suppose this makes sense since it facilitates easy fixing to a standard heatsink with a wide range of standard insulating shims and screw isolators to ensure isolation from the heatsink. ...
    (sci.engr.lighting)
  • Re: A pair of LM2940CT-s getting hot - is this normal?
    ... Alexander Avtanski wrote: ... Add a heatsink. ... One barely larger than the package will provide ~25°C/W, ... which is enough to stop it cooking itself. ...
    (sci.electronics.design)
Quantcast