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Electronics Forum / Electronics / November 20087812 and 7815 voltage regulators
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 > hi, i want to make up a 13.8 volt power supply. > [quoted text clipped - 7 lines] > 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? >> hi, i want to make up a 13.8 volt power supply. >> [quoted text clipped - 11 lines] > leg to ground to "jackup" the regulator. Diode cathode points to ground, > Each diode will add ~0.6V. Try it & see. 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. >>> hi, i want to make up a 13.8 volt power supply. >>> [quoted text clipped - 15 lines] > resistor to ensure they develop their full Vf - from the output terminal > gives the best stability. Good idea Ian, I've bodged them up before with just the diodes without probs but a bias resistor would probably make it better. > > hi, i want to make up a 13.8 volt power supply. > [quoted text clipped - 18 lines] > 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? ------------------- 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. > hi, i want to make up a 13.8 volt power supply. > [quoted text clipped - 5 lines] > > how can i do this ? **Use an LM317.  SignatureTrevor Wilson www.rageaudio.com.au 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... >> hi, i want to make up a 13.8 volt power supply. >> [quoted text clipped - 7 lines] > > **Use an LM317. > 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... **Use the correct part for the job required. An LM317 costs less than a Dollar. SignatureTrevor Wilson www.rageaudio.com.au >> 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 [quoted text clipped - 3 lines] > **Use the correct part for the job required. An LM317 costs less than a > Dollar. Fcked up again twevy , answer the question and not try to hide behind bullshite > >> 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 [quoted text clipped - 6 lines] > Fcked up again twevy , answer the question and not try to hide behind > bullshite. 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. >>>> hi, this is unbeleviable, i have a specific question relating to > specific [quoted text clipped - 14 lines] > > 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 > he appears to be a long way from most shopping malls > so in the Ozzie tradition making do for now... 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. >> he appears to be a long way from most shopping malls >> so in the Ozzie tradition making do for now... > > 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. **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. SignatureTrevor Wilson www.rageaudio.com.au >>> he appears to be a long way from most shopping malls >>> so in the Ozzie tradition making do for now... [quoted text clipped - 4 lines] > **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. Which in truth means "Having been outed as a self serving w.nking spammer twevy got the shites and hoped by abusing members of the fraternity denying him entry might divert the stares and accusation about his perverted ways elsewhere , but it didn't all and sundry saw twevy for the arsewipe he is . It is no surprise twevy that you failed so miserably in business and your personal life." I wish you nothing but discomfort for Christmas and hope the future to be bleak and foreboding for the few remaining years you have. >>> he appears to be a long way from most shopping malls >>> so in the Ozzie tradition making do for now... [quoted text clipped - 4 lines] > **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. Which in truth means "Having been outed as a self serving w.nking spammer twevy got the shites and hoped by abusing members of the fraternity denying him entry might divert the stares and accusation about his perverted ways elsewhere , but it didn't all and sundry saw twevy for the arsewipe he is . It is no surprise twevy that you failed so miserably in business and your personal life." I wish you nothing but discomfort for Christmas and hope the future to be bleak and foreboding for the few remaining years you have. >> he appears to be a long way from most shopping malls >> so in the Ozzie tradition making do for now... [quoted text clipped - 4 lines] > > MrT. He might take the time to elucidate , but I doubt it > 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... '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 now , just think about it for a minute you twat , now why would i want to send away a order for about $15 to get a 1.50 part , ... most places have a minimum order of 10 dollars , then at LEAST 5$ for postage..... ummmm i did point out the exact RIGHT PART , a 7812 or a 7815 I DID NOT POINT OUT A LM317 !!!! PRAYTELL,. HOW IS USING 2 EXTRA PARTS A BODGE ?? I`LL CALL IT INGENUITY...... >> hi, this is unbeleviable, i have a specific question relating to >> specific parts , and someone says use XXXX instead , next time they [quoted text clipped - 8 lines] > > geoff > now , just think about it for a minute you twat , now why would i want > to send away a order for about $15 to get a 1.50 part , ... most places [quoted text clipped - 6 lines] > PRAYTELL,. HOW IS USING 2 EXTRA PARTS A BODGE ?? I`LL CALL IT > INGENUITY...... What 2 extra parts? - the 317 needs 2 resistors to set the voltage. u a spaz ???? cant you get it thru ya head,,, i dont want to spend 15$ to get a $1.50 .... and maybe also i want to make do with what i got.. >> now , just think about it for a minute you twat , now why would i want >> to send away a order for about $15 to get a 1.50 part , ... most places [quoted text clipped - 8 lines] > > What 2 extra parts? - the 317 needs 2 resistors to set the voltage. >u a spaz ???? cant you get it thru ya head,,, i dont want to spend 15$ >to get a $1.50 .... > > and maybe also i want to make do with what i got.. You're obviously an ignorant fuckwit who can't read - I pointed out that a 317 needs 2 resistors so a couple of diodes on a 78xx aren't additional. hey toss pot , you cant read u pedafile , DID I EVER MENTION A 317 IN MY ORIGINAL POST ... NO YOU POOF.. >>u a spaz ???? cant you get it thru ya head,,, i dont want to spend >>15$ to get a $1.50 .... [quoted text clipped - 3 lines] > You're obviously an ignorant fuckwit who can't read - I pointed out that a > 317 needs 2 resistors so a couple of diodes on a 78xx aren't additional. > hey toss pot , you cant read u pedafile , DID I EVER MENTION A 317 IN MY > ORIGINAL POST ... NO YOU POOF.. You're thick as sh.t.............and then some!!! is that all u can say you faggot.... you cant answer taht can you ?? i didnt even mention 317 in my post.. mark k >> hey toss pot , you cant read u pedafile , DID I EVER MENTION A 317 IN >> MY ORIGINAL POST ... NO YOU POOF.. > > You're thick as sh.t.............and then some!!! > is that all u can say you faggot.... you cant answer taht can you ?? i didnt > even mention 317 in my post.. > mark k Age = 14, IQ = ~60. Let this angry little man go. > is that all u can say you faggot.... you cant answer taht can you ?? i didnt > even mention 317 in my post.. > mark k Goodness sake!!! Get over yourself. You ask a question, you were advised of a more appropriate alternative, and you have done nothing but bitch since. MAN UP! >> is that all u can say you faggot.... you cant answer taht can you ?? i >> didnt even mention 317 in my post.. [quoted text clipped - 5 lines] > > MAN UP! I can't understand what he got so hysterical about - all I did was correct someone who said a 78xx with a couple of offset diodes had a higher component count, it doesn't because the 317 needs a couple of resistors to set the voltage. > hi, i want to make up a 13.8 volt power supply. > [quoted text clipped - 5 lines] > > how can i do this ? Download the datasheet for the 7812 from National Semiconductor, there's an example on the first page. thankyou !! >> hi, i want to make up a 13.8 volt power supply. >> [quoted text clipped - 9 lines] > an > example on the first page. > hi, i want to make up a 13.8 volt power supply. > [quoted text clipped - 3 lines] > or > decrease the voltage from the 7815 ? It makes no difference, the parts are fundamentally the same. > how can i do this ? 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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