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Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ. |
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Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ. |
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In Reply to: Re: UPC 78M05 HF?(DATA?)168 degrees! I think I do need a higher current voltage regulator. posted by cfraser on February 23, 2001 at 21:17:57:
Interesting, the 7805 will not necessarily be able to handle much more power than the 78M05. The higher current rating has more to do with the ability of the internal pass transistor to handle the current without saturating with input voltages close to the output voltage (drop out voltage). The thermal resistance rating of both the 7805 and 78M05 is 5 °C/W from junction to case for a TO-220 package. This means that the transistor junction, where the heat is generated, will be 5° hotter than the case for each watt of power that the IC is dissipating. 168°F is 75°C, and if the regulator is delivering 500mA with 10V input, the regulator is dissipating 2.5W, and the junction temperature will be 12.5°C hotter than the case, or 75° + 12.5° =87.5°C. This is hotter than I would normally run things for best reliability, but probably OK. By the way, the projected lifetime of a semiconductor device running at 150°C is much, much less than when running at 70°C. Most of this information is available on the data sheets at manufacturers web sites.
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Follow Ups
- Re: UPC 78M05 HF?(DATA?)168 degrees! I think I do need a higher current voltage regulator. - myeung 23:43:42 02/27/01 (0)
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