TO-3 or TO-247?

JojoD818 · 12th March 2003, 02:42 PM

Hi!

Which is better i terms of heatsinking?

I will use it for output of power amp.

/Jojo

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.

oO

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

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.

Thanks,
Bart.

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.

12th March 2003, 02:42 PM	#1
JojoD818 diyAudio Moderator Join Date: Mar 2003 Location: searching...	TO-3 or TO-247? Hi! Which is better i terms of heatsinking? I will use it for output of power amp. /Jojo

12th March 2003, 09:15 PM	#5
jackinnj diyAudio Member Join Date: Apr 2002 Location: Llanddewi Brefi, NJ	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.

12th March 2003, 09:27 PM	#6
JBL diyAudio Member Join Date: Aug 2001 Location: Canada, N.-B.	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...) __________________ Jonathan Blanchard (J.Bl.) ---Nothing is impossible---

12th March 2003, 10:15 PM	#7
barts diyAudio Member Join Date: Feb 2003 Location: Brisbane	TO-3P? 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. Thanks, Bart.

12th March 2003, 10:54 PM	#9
barts diyAudio Member Join Date: Feb 2003 Location: Brisbane	TO-3P Thanks jackinnj, I was just comparing them actually. I think they are virtually the same, bar some minor differences around the corners.


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12th March 2003, 05:32 PM	#2
OddOne diyAudio Member Join Date: Nov 2002 Location: Earth	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. oO

12th March 2003, 06:36 PM	#3
Jay diyAudio Member Join Date: Feb 2003 Location: Jakarta	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.

12th March 2003, 06:44 PM	#4
Jay diyAudio Member Join Date: Feb 2003 Location: Jakarta	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?

12th March 2003, 10:50 PM	#8
jackinnj diyAudio Member Join Date: Apr 2002 Location: Llanddewi Brefi, NJ	looks the same to me, but Hitachi has a dimensional picture in their pdf.

12th March 2003, 11:11 PM	#10
jackinnj diyAudio Member Join Date: Apr 2002 Location: Llanddewi Brefi, NJ	i'll put a comparison between an IRFP240 and a 2sk1058 when I get back later tonight.

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