FreeLists / si-list / [SI-LIST] Re: Heatsink electrical isolation

["Hill, John" <John.Hill@xxxxxxxxxx>]

Carlos,

I would suggest you connect all the ground pins of your TO-220. I don't
know about you, but sometimes I run a new board with a large paper clip
as a heat sink. This is done before the product is assembled and is
still on the bench being tested in a nice temperature controlled office.

If you depend on the heat sink for ground, it has to be in place and is
sometimes inconvenient to work on. BTW, do you want to wait on the
mechanical engineers to get the Heatsink done before you power up the
board?

A simple test of the paper clip Heatsink is to touch it. If it hurts,
get a bigger heat sink or a fan. :-)

Best regards,

John

John Hill
Design Engineer
TK  HOLDINGS INC  =20
Electronics=20
27200 Haggerty Road  Suite B-12 =20
Farmington Hills, MI 48331
Office Phone: 248 699 2915
Mobile Phone 248 765 3599


=20

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-----Original Message-----

From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of Carlos Toro
Sent: Monday, October 30, 2006 9:22 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Heatsink electrical isolation

Hi all. What considerations should be used when electrically attaching
heatsinks to a net in a PCB?. We have a TO-220 packaged IC and its back
is
grounded thus it will make the heatsink be grounded too. The Heatsink
has
pins for ensuring mechanical attachment to the PCB. Do these pins also
need
to be grounded?.
For now the board is a prototype and one of our concerns is that this
heatsink is about 2 inches high and might get in contact with a probe or
a
wire and create a short circuit with it. Should the board be enclosed in
a
plastic case in spite of being a prototype?. Is there other alternative
for
electrically isolating the heatsink without compromising its heat
transfer
benefits?.

Thanks in advance.

--=20
Carlos Toro B
Design Engineer
JAVERIANA STEREO
Calle 18 No. 118-250
Cali, Colombia
South America

Office Phone: +57 2 2725032
Mobile Phone: +57 315 474 5872


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