7812 and 7815 voltage regulators

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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



Re: 7812 and 7815 voltage regulators

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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?



Re: 7812 and 7815 voltage regulators

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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.



Re: 7812 and 7815 voltage regulators
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-------------------
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.

Re: 7812 and 7815 voltage regulators


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**Use an LM317.


--
Trevor Wilson
www.rageaudio.com.au



Re: 7812 and 7815 voltage regulators
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...


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Re: 7812 and 7815 voltage regulators



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**Use the correct part for the job required. An LM317 costs less than a
Dollar.


--
Trevor Wilson
www.rageaudio.com.au



Re: 7812 and 7815 voltage regulators
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Fcked up again twevy , answer the question and not try to hide behind
bullshite

Re: 7812 and 7815 voltage regulators

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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.



Re: 7812 and 7815 voltage regulators
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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

Re: 7812 and 7815 voltage regulators

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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.



Re: 7812 and 7815 voltage regulators



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**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



Re: 7812 and 7815 voltage regulators
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He might take the time to elucidate , but I doubt it

Re: 7812 and 7815 voltage regulators
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'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



Re: 7812 and 7815 voltage regulators
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Download the datasheet for the 7812 from National Semiconductor, there's an
example on the first page.

Re: 7812 and 7815 voltage regulators
thankyou !!


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Re: 7812 and 7815 voltage regulators
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It makes no difference, the parts are fundamentally the same.

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Two resistors, it's in many datasheets like here:
http://www.opencircuits.com/images/6/6c/LM7805.pdf

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.

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