Author Topic: 78L05 / 7805........Any difference?  (Read 13277 times)

stratprince

78L05 / 7805........Any difference?
« on: December 12, 2012, 08:14:28 AM »
are those two different?

greaser_au

Re: 78L05 / 7805........Any difference?
« Reply #1 on: December 12, 2012, 08:59:23 AM »
Yes...

Jdansti

Re: 78L05 / 7805........Any difference?
« Reply #2 on: December 12, 2012, 09:04:29 AM »
900mA difference :)

Google and data sheets are your friends.

78L05: TO-92, 100mA current: http://www.fairchildsemi.com/ds/LM/LM78L05A.pdf
7805: TO-220, 1A current: http://www.fairchildsemi.com/ds/LM/LM7805.pdf
R.G. Keene: EXPECT there to be errors, and defeat them...

greaser_au

Re: 78L05 / 7805........Any difference?
« Reply #3 on: December 12, 2012, 09:04:51 AM »
...the 'L'...

which means a 900mA difference in  current capacity, and 200degC/W vs 50degC/W (chip to ambient) thermal resistance. 

greaser_au

Re: 78L05 / 7805........Any difference?
« Reply #4 on: December 12, 2012, 09:05:58 AM »
78L05: TO-92, 100mA current: http://www.fairchildsemi.com/ds/LM/LM78L05A.pdf
7805: TO-220, 1A current: http://www.fairchildsemi.com/ds/LM/LM7805.pdf

hello, my friend. I think we have met here before...  :icon_biggrin:

Jdansti

Re: 78L05 / 7805........Any difference?
« Reply #5 on: December 12, 2012, 09:11:07 AM »
LOL- I think we were posting simultaneously.  ;D
R.G. Keene: EXPECT there to be errors, and defeat them...

greaser_au

Re: 78L05 / 7805........Any difference?
« Reply #6 on: December 12, 2012, 09:17:05 AM »
just wondering, did your dual pt2399 build settle down after changing the reg from the 'L05 to the '05?

david

Jdansti

Re: 78L05 / 7805........Any difference?
« Reply #7 on: December 12, 2012, 09:18:57 AM »
Actually it did!  Thanks for asking!  :)
R.G. Keene: EXPECT there to be errors, and defeat them...

greaser_au

Re: 78L05 / 7805........Any difference?
« Reply #8 on: December 12, 2012, 09:35:25 AM »
stratprince,

basically these linear regulators work by throttling the current from the supply to the load.  if you have 10V across the regulator (say a 15V supply to a 5V load) and are drawing 100mA ( the full rated load of a  'L05) you will be dissipating  10V * 0.1A = 1W in the regulator. The chip inside the TO-220 7805 will experience a 50 degrees C temperature rise over ambient temperature-   and say it's 68 deg F = 20dec C where the regulator is - it will hit 70 deg C. all good! Do this with a 78L05 in it's plastic TO-92,  the same conditions will push the regulator chip to something like 220 degrees, and it will have hit it's internal protective shutdown long before you get to this point.

As a live example: with an 'L05, and say, one pt2399 with a regulated 9V pedal supply, no problems (40mA * (9-5V)= 160mW = 32deg over ambient). Make it two PT2399s and 12V unregulated or so input (80mA * (12-5V = 560mW = 112 deg over ambient), and you're  headed for shutdown territory.

david

greaser_au

Re: 78L05 / 7805........Any difference?
« Reply #9 on: December 12, 2012, 09:39:11 AM »
Actually it did!  Thanks for asking!  :)

Excellent news! (and apropos of stratprince's query!)

david