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JojoD818 12th March 2003 02:42 PM

TO-3 or TO-247?

Which is better i terms of heatsinking?

I will use it for output of power amp.


OddOne 12th March 2003 05:32 PM

TO-3 cases can dissipate more power, but are more complex to mount since the pins have to go through the heatsink. The corresponding need to use a thin enough heatsink flange area to allow this often offsets the extra dissipation capability of the case, and thus you're at a zero-sum situation.

TO-247s are easier to mount and dissipate enough heat to get the job done, so they're becoming the TO-3's replacement for many applications. If you can get a transistor in either form, the 247 will be easier to work with especially if you're using large flat heatsinks that don't include a mounting flange or dedicated mounting area for a TO-3 device - in these cases you'd have to MAKE the flange and thermally connect it to the heatsink, and this is hardly the optimal way of doing things.


Jay 12th March 2003 06:36 PM

In terms of heatsinking, TO-3 is better (for the same amount of dissipated power/heat). But in all cases I found, the equivalent TO-247 package produces better sound.

Jay 12th March 2003 06:44 PM

But I don't think that heatsinking capability should be something to consider for this purpose. Unless you want to drive the transistor close to its limit (in case of a bipolar, a second breakdown voltage?), e.g. a class-A with limited heasink?

jackinnj 12th March 2003 09:15 PM

don't confuse TO-3 with TO-3p
just a "by the way".

TO3's take 2 screws, TO-247 only one so they are a bit less expensive to mount.

JBL 12th March 2003 09:27 PM

And you can easily use clamp or just a bar of aluminium to mount them on the heatsink. This is more convenient than using screws.

(and they look better...)

barts 12th March 2003 10:15 PM

Is the TO-247 the same size package as the plastic variant TO-3P, which is what Hitachi calls their plastic package for the 2SK1058?

I'm just wondering because I'm presently working in Protel on my pcb and will have to draw the footprint unless I can find a similar size one.


jackinnj 12th March 2003 10:50 PM

looks the same to me, but Hitachi has a dimensional picture in their pdf.

barts 12th March 2003 10:54 PM

Thanks jackinnj, I was just comparing them actually. I think they are virtually the same, bar some minor differences around the corners.

jackinnj 12th March 2003 11:11 PM

i'll put a comparison between an IRFP240 and a 2sk1058 when I get back later tonight.

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