12V(fixed) with 3 Amp current

badboy6120 · 13th August 2011, 04:52 PM

Hi
I have a circuit that run with 12V(fixed) and need about 3 amp current
can anybody help me how can I invert 18V DC to 12V DC(fixed) with around 3 amp current
tank you

Minion · 13th August 2011, 05:01 PM

Just use a 12v Regulator with a Pass transistor to get the 3A of current .... Your 18v DC is going to have to be capable of 3A .....

The LM317 has schematics in its Datasheets that show how to do this ....

http://www.national.com/ds/LM/LM117.pdf

Cheers

badboy6120 · 13th August 2011, 05:10 PM

Thank you so much Minion
did you do it yourself?( using any of these circuits or have the same need)

Michael Bean · 13th August 2011, 05:12 PM

Here-http://www.national.com/profile/snip.cgi/openDS=LM350

Minion · 13th August 2011, 05:17 PM

I used a very simular curcuit to build a 5a 24vDC PSU for a small Class A amp and it worked fine , just remember to heatsink the Pass Transistor and regulator ......

badboy6120 · 13th August 2011, 05:31 PM

thank you "Michael bean" and "Minion" for your advices

! · 13th August 2011, 05:54 PM

I don't know what your skill level is, but I would find another way, 18W of heat for a mere 12V application is a lot in added size, weight, heatsink cost as well as chassis cooling considerations.

You seem to have left out the most important part, what the PSU is powering. Voltage and current is only a means towards an end, everything else really matters more including budget, skill level, space, weight, efficiency, powered device, permissible noise, etc.

badboy6120 · 13th August 2011, 06:54 PM

Hi !
I'm neither beginner nor pro
could you tell me what idea do you have for my goal???

! · 07:18 PM

^ Buy a ready made step down switching power supply module. I have no idea where you should look since I'm in the US and you are listed as being in England but bear the flag of Malaysia. Such a module with roughly 18V input to 12V output should be popular for DIY solar (panel) projects as a regulator between the solar panel(s) and batteries to charge them, if you can't find something with those spec at an electronics surplus website.

Of course you could try building your own, go to your perferred electronics supply house or electronic chip manufacturer's website (for example National Semiconductor) and browse to the appropriate chip product that meets the functional goals then the respective datasheet will give an example to follow.

badboy6120 · 13th August 2011, 07:12 PM

thanks a lot "!"

13th August 2011, 04:52 PM	#1
badboy6120 diyAudio Member Join Date: Feb 2011 Location: Malaysia	12V(fixed) with 3 Amp current Hi I have a circuit that run with 12V(fixed) and need about 3 amp current can anybody help me how can I invert 18V DC to 12V DC(fixed) with around 3 amp current tank you

13th August 2011, 07:08 PM	#9
! diyAudio Member Join Date: Jun 2005 Location: Midwest	^ Buy a ready made step down switching power supply module. I have no idea where you should look since I'm in the US and you are listed as being in England but bear the flag of Malaysia. Such a module with roughly 18V input to 12V output should be popular for DIY solar (panel) projects as a regulator between the solar panel(s) and batteries to charge them, if you can't find something with those spec at an electronics surplus website. Of course you could try building your own, go to your perferred electronics supply house or electronic chip manufacturer's website (for example National Semiconductor) and browse to the appropriate chip product that meets the functional goals then the respective datasheet will give an example to follow. Last edited by !; 13th August 2011 at 07:18 PM.

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13th August 2011, 05:01 PM	#2
Minion diyAudio Member Join Date: May 2006	Just use a 12v Regulator with a Pass transistor to get the 3A of current .... Your 18v DC is going to have to be capable of 3A ..... The LM317 has schematics in its Datasheets that show how to do this .... http://www.national.com/ds/LM/LM117.pdf Cheers

13th August 2011, 05:10 PM	#3
badboy6120 diyAudio Member Join Date: Feb 2011 Location: Malaysia	Thank you so much Minion did you do it yourself?( using any of these circuits or have the same need)

13th August 2011, 05:12 PM	#4
Michael Bean diyAudio Member Join Date: Sep 2004 Location: Minneapolis, Minnesota, USA	Here-http://www.national.com/profile/snip.cgi/openDS=LM350

13th August 2011, 05:17 PM	#5
Minion diyAudio Member Join Date: May 2006	I used a very simular curcuit to build a 5a 24vDC PSU for a small Class A amp and it worked fine , just remember to heatsink the Pass Transistor and regulator ......

13th August 2011, 05:31 PM	#6
badboy6120 diyAudio Member Join Date: Feb 2011 Location: Malaysia	thank you "Michael bean" and "Minion" for your advices

13th August 2011, 05:54 PM	#7
! diyAudio Member Join Date: Jun 2005 Location: Midwest	I don't know what your skill level is, but I would find another way, 18W of heat for a mere 12V application is a lot in added size, weight, heatsink cost as well as chassis cooling considerations. You seem to have left out the most important part, what the PSU is powering. Voltage and current is only a means towards an end, everything else really matters more including budget, skill level, space, weight, efficiency, powered device, permissible noise, etc.

13th August 2011, 06:54 PM	#8
badboy6120 diyAudio Member Join Date: Feb 2011 Location: Malaysia	Hi ! I'm neither beginner nor pro could you tell me what idea do you have for my goal???

13th August 2011, 07:12 PM	#10
badboy6120 diyAudio Member Join Date: Feb 2011 Location: Malaysia	thanks a lot "!"

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