hi, i want to make up a 13.8 volt power supply.
i have some 7812 and 7815 voltage regulators.
would it be best to increase the voltage out of the 7812 or decrease the voltage from the 7815 ?
how can i do this ? thanks, mark k
Check out the data sheet Mark, you can add a diode or three in the common leg to ground to "jackup" the regulator. Diode cathode points to ground, Each diode will add ~0.6V. Try it & see.
If its low current a quick and dirty for the 7815 could be to do the same only with the diodes in the output, each will drop ~0.6 depending on the load drawn.
These approached may not be ideal from the regulation point of view but for a GP supply they should be fine. How much current are you wanting to draw?
**Use an LM317.
-- Trevor Wilson www.rageaudio.com.au
Download the datasheet for the 7812 from National Semiconductor, there's an example on the first page.
hi, this is unbeleviable, i have a specific question relating to specific parts , and someone says use XXXX instead , next time they got a question relating to a SPECIFIC part , i think i might tell them to use something differant...
thankyou !!
**Use the correct part for the job required. An LM317 costs less than a Dollar.
-- Trevor Wilson www.rageaudio.com.au
Might be an idea to feed the diode(s) with some bias current via a resistor to ensure they develop their full Vf - from the output terminal gives the best stability.
'Different'.
You take exception to somebody helping you out by pointing out the exact right part to be using to do the job, instead of a way to bodge it up using other parts ? Bizarre.
geoff
It makes no difference, the parts are fundamentally the same.
Two resistors, it's in many datasheets like here:
Make sure you decouple the input and output. Have you done your power dissipation calculations?, it's important. (13.8V supplies usually power higher current stuff)
Dave.
Fcked up again twevy , answer the question and not try to hide behind bullshite
specific
question
something
Have to side with TW here, whilst both will work, there doesn't seem to be a lot of point in using the wrong part if you can't even read a data sheet and have to ask for help.
MrT.
read the headers , he appears to be a long way from most shopping malls so in the Ozzie tradition making do for now... as for you siding with the knucklehead you should hang your head in shame
That's a good reason of course, but he could have just said so rather than abuse anyone offering advice. I'm still not clear why he didn't just download the data sheet though.
MrT.
**Because he, like atec77, is an ignorant prick. I no longer waste my time with ignorant pricks. I have better things to do with my time.
-- Trevor Wilson www.rageaudio.com.au
He might take the time to elucidate , but I doubt it
or
?------------------- While it might not matter for your application, I would not suggest putting diodes in series with the output line the reason is that the voltage dropped across the diodes will change with the current drawn through them. (and likely the temperature as well).
Putting diodes in the ADJ or GND terminal to ground is fine, the current through them is so small that it isnt going to affect their voltage. I have never had any problems doing this even with larger
3-5 A regulators.I do like the idea from Ian Field about running a bias resistor though.
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