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|23rd April 2003, 20:48||#1|
HOW-TO: changing voltage
It might occur you need a specific voltage, but you can't draw it (e.g. 9volt from a regular PSU ). Anthro found a solution for me: the 78XX chips
they can create any output that's 2V or more under the input voltage. E.g.: if you've got +12V input, the max Vout you can get is +10V. Everything under that and above 0 is possible ( If I'm not mistaking)
These chippies can alter maximum 1A, if that isn't sufficient place two or more of 'em parallel to feed that 120mm delta.
Let's say you want to let a fan, drawing 0.5A, spin @ 9volts & you'll draw the voltage from your PSU (12v and 0v). You'll need a 7809 for that.
Calculating some stuff
Take care, chips produce quite some heat.
a. (Vin - Vout)*I: (12-9)*0.5=1.5Watts of heat
b. these chips create 45 K/W.
ambient + produced wattage*45 --> 25 +(1.5*45)= 92.5°
That's quite hot, but as long as you don't exceed 100° a heatsink isn't necessairy. Please note that the metal bottom of the chips are wired to the ground, so I wouldn't all of them on the same heatsink.
I you would try this with a 2A fan, the poor chip would get 295°... hmmmmm
a frame says more then a thousand words
copypasting from www.rato.be their database:
SPANNINGSSTAB 7805 0.5
SPANNINGSSTAB 7806 0,62
SPANNINGSSTAB 7808 0,45
SPANNINGSSTAB 7809 0,5
SPANNINGSSTAB 7810 0,6
SPANNINGSSTAB 7812 0,45
SPANNINGSSTAB 7815 0,5
SPANNINGSSTAB 7818 0,5
SPANNINGSSTAB 7820 0,37
SPANNINGSSTAB 7824 0,5
they're about half a euro/piece, so they're worth the money
and thx to Anthro
|27th April 2003, 21:50||#4|
posting something in the name of Herr Anthro
It is best to mount a lil' heatsink because when your chip is near 100°c for a long period of time, it is not very good for durability. The chips will be the happiest when running under 70°. If you need higher currents you can place them in paralell, or buy the 2Amp version : 78Sxx series.
he doesn't know what the CV means tho'
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