| facundonu |
hi, i'm trying to make a standalone CD-ROM to play audio.
first of all, i need a power supply (later a controller, a display, a DAC, etc).
i own a 12v switching PS from a TFT monitor. it will drive a 3,3A load without problems.
now i need 5v...
would it be ok to connect a 7805 on the switching PS output with a couple of capacitors?? or will it explode and burn my house down? :hot:
the drive's label says "12v-1300mA/5v-900mA", so it wont be any trouble for the 7805 if correctly cooled (power dissipation should be (12v-5v)*1A=7w, and 900mA<1A).
the question arouses because i don't know much about sitching power supplys and the ways they can interact with linear ones.
the schematic should be something like this (paint rules).
thanks in advance! |
|
|
| Eva |
| That should work fine as long as you don't make any stupid mistake :) |
|
|
| facundonu |
why are we speaking english? :)
jeje, thanks a lot! muchas gracias! |
|
|
| facundonu |
thanks a lot, PS is now working.
and i can cook an egg on the 7805 heatsink! |
|
|
| davesaudio |
| quote: | Originally posted by facundonu
thanks a lot, PS is now working.
and i can cook an egg on the 7805 heatsink! |
Indeed,
one amp X ( dropping 12-5= ) 7 volts is 7 watts to dissipate
in a linear regulator |
|
|
| CBS240 |
| Perhaps you can take some stress off of the 7805 by spreading out the heat...puting a 4.3Ohm 5W resistor in series with the input to 7805 would take up 3.5W off of the 7805 so it would have only half the power and not get so hot in one spot.:) |
|
|
| sss |
what type of switching supply are u using?
is it a regular pc power supply?
if so u got a 5v output in it also .
if not :
-use a bigger heat sink
-do what CBS240 said |
|
|
| facundonu |
i'm using a PS from a TFT monitor, it has only a 12VDC/3,33A output.
i've cooled the 7805 by placing 4 big diodes in series with it's input, but i'll try the resistor option. thanks a lot! |
|
|
|
