Cicero
Active Member
So I'm looking into heatsinks, and I think I'm a little rusty.
I'm thinking of using a 2N3055 (TO-3 package) to sink some decent current (0-1A) over a decent voltage range (0-60V). Or thats the idea anyway.
https://www.onsemi.com/pub/Collateral/2N3055-D.PDF
From the datasheet:
I dont want the junction temp to reach 80% of the max, so I set Tj = 160degC
Ambient will be around 40deg (and I plan to use a small fan to try keep it there or there abouts), Ta = 40degC
If I want to run it at 60W, which is 60V @ 1A, then I worked out I'd need a sink with a thermal resistance of 0.48degC/W!!!!! Which is ridiculous, or is it understandable? (this is with negligible case to sink resistance, which we know isn't negligible).
I can find a pretty small but decent looking sink with a 6degC/W rating, but that allows the transistor to only run at around 15-16W if I'm not mistaken.
Now am I doing this stuff correctly? To come up with their 115W they state, what do they do...cool the thing in liquid nitrogen or something?
I'm thinking of using a 2N3055 (TO-3 package) to sink some decent current (0-1A) over a decent voltage range (0-60V). Or thats the idea anyway.
https://www.onsemi.com/pub/Collateral/2N3055-D.PDF
From the datasheet:
- Total max power dissipation is 115W with a derating of 0.657W/degC from 25deg onwards
- Max junction operating temp is 200degC
- Thermal resistance (junc to case) = 1.52degC/W
I dont want the junction temp to reach 80% of the max, so I set Tj = 160degC
Ambient will be around 40deg (and I plan to use a small fan to try keep it there or there abouts), Ta = 40degC
If I want to run it at 60W, which is 60V @ 1A, then I worked out I'd need a sink with a thermal resistance of 0.48degC/W!!!!! Which is ridiculous, or is it understandable? (this is with negligible case to sink resistance, which we know isn't negligible).
I can find a pretty small but decent looking sink with a 6degC/W rating, but that allows the transistor to only run at around 15-16W if I'm not mistaken.
Now am I doing this stuff correctly? To come up with their 115W they state, what do they do...cool the thing in liquid nitrogen or something?
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