I was wondering what kind of heatsink to use for a BUF634. I calculated this for the heatsink:
Junction-to-case: 6 °C/W
Heatsink thermal resistance (just to be safe): 0.5 °C/W
Max power: 24V (+- 12V) * 0.25A = 6 W
Max junction temperature: 125 °C
Ambient temperature: 25 °C
Therefore: (R + 6 + 0.5) * 6 = 125 - 25
<=> R = 61/6 °C/W
<=> R ~= 10.2 °C/W
Could this be correct? I'd use a heatsink like this in that case: http://www.farnell.com/datasheets/14647.pdf (637 series, the smallest one, which is still 6 °C/W)
Can I let the junction temperature rise to 116 without frying the chip? Then I could use this smaller heatsink: http://www.farnell.com/datasheets/19328.pdf (12.9 °C/W)
Do I even need a heatsink? The intention is to use it with a 50 ohm terminated cable, not to abuse the thing to see if the heatsink's sufficient
.
Any help is appreciated.
Junction-to-case: 6 °C/W
Heatsink thermal resistance (just to be safe): 0.5 °C/W
Max power: 24V (+- 12V) * 0.25A = 6 W
Max junction temperature: 125 °C
Ambient temperature: 25 °C
Therefore: (R + 6 + 0.5) * 6 = 125 - 25
<=> R = 61/6 °C/W
<=> R ~= 10.2 °C/W
Could this be correct? I'd use a heatsink like this in that case: http://www.farnell.com/datasheets/14647.pdf (637 series, the smallest one, which is still 6 °C/W)
Can I let the junction temperature rise to 116 without frying the chip? Then I could use this smaller heatsink: http://www.farnell.com/datasheets/19328.pdf (12.9 °C/W)
Do I even need a heatsink? The intention is to use it with a 50 ohm terminated cable, not to abuse the thing to see if the heatsink's sufficient
.Any help is appreciated.
Well, I was going to use the T version (TO-220 5 legs). So, any heatsink is fine?
I found some really small ones in the Fischer catalog, they are only 11.8 mm wide and 8 mm long. Minimum height is 25 mm and then they're 20 °C/W (model SK 470). There are even small ones available, but they are only 36 °C/W (model SK 95). Would 36 °C/W be enough or should I go for the 20 °C/W one?
I can also get model SK 104 (it's in the Eagle library), but that's a bit big. The rating is pretty good though, 14 °C/W minimum, 8 °C/W max.
So, what do you think? Would the smallest one be enough or is it better to pick a bit better heatsink?
I found some really small ones in the Fischer catalog, they are only 11.8 mm wide and 8 mm long. Minimum height is 25 mm and then they're 20 °C/W (model SK 470). There are even small ones available, but they are only 36 °C/W (model SK 95). Would 36 °C/W be enough or should I go for the 20 °C/W one?
I can also get model SK 104 (it's in the Eagle library), but that's a bit big. The rating is pretty good though, 14 °C/W minimum, 8 °C/W max.
So, what do you think? Would the smallest one be enough or is it better to pick a bit better heatsink?
I agree with MWP if something is too hot to touch then it needs a sink.
On another thought though, (obviously if the chip leaves a burn there after a seconds touch then thats different) but it doesnt take much for something to be too hot to touch. Somewhere in the region of about 45-65 degrees centigrade is all it takes depending on the person. Now lots of devices are stable working at a temp of greater than 100 oC fets can work higher. So even if its too hot to touch it most probably will be fine. However heatsinking will probably increase the things life.
On another thought though, (obviously if the chip leaves a burn there after a seconds touch then thats different) but it doesnt take much for something to be too hot to touch. Somewhere in the region of about 45-65 degrees centigrade is all it takes depending on the person. Now lots of devices are stable working at a temp of greater than 100 oC fets can work higher. So even if its too hot to touch it most probably will be fine. However heatsinking will probably increase the things life.
Devil_H@ck said:
i am using some smallish heatsinks for my buf634T.
you can take a look at them here images of heatsink .
i used those heat transfer film thingy between the buf634t and the heatsink. as the heatsink does not have a thru-hole. i just applied glue on the edges of the heatsink and buffer.
temperature is warm to touch at the heatsink after running for more than 8 hours.
Re: hmmmm....
No, not at all, I know that I'll never be able to draw that much current via the BUF634 (well, not in normal use), it will draw 0.02A at 2V Rms in my pre normally, but that was just to be sure.
@ Garbage: Could I please see your layout for the buffer + opamp circuit? I'll attach mine, it's the smallest layout I could come up with after 2-3 hours work. (Yup, a lot of parts, and I can't leave out any of them.) I don't know if the layout is any good, tell me if you see mistakes please.
Doovieman said:
No, not at all, I know that I'll never be able to draw that much current via the BUF634 (well, not in normal use), it will draw 0.02A at 2V Rms in my pre normally, but that was just to be sure
.@ Garbage: Could I please see your layout for the buffer + opamp circuit? I'll attach mine, it's the smallest layout I could come up with after 2-3 hours work. (Yup, a lot of parts, and I can't leave out any of them.) I don't know if the layout is any good, tell me if you see mistakes please.
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