48vdc to 12vdc

Originally posted by anybisi@Mar 7 2006, 06:47 PM
pls, i need to convert 48 volts DC to 12 or 24 DC,
[post=14759]Quoted post[/post]​

Hey and How are you, what you need to do to convert 48 volts to 12 volts is to get a 12 volt regulater (LM7812), once you get the regulator test it out on a breadboard

Instuctions:

Stick the regulator in the breadboard this way.


Then connect the positve Lead from your 48 volts power supply to the input put (The outer left pin) then connect the Ground or negative lead from the power supply to your The common pin of the regulator ( middle pin), and the outpin will produce 12 volts and 1 amp. it will be constant.



 

hgmjr

Joined Jan 28, 2005
9,029
If you decide to use a 3-terminal regulator to regulate your 48V power source down to 12V, keep in mind that for every watt consumed by your 12V load 3 watts will need to be dissipated by the regulator. That is because there is 36 volts dropped across the regulator and it has the same current flowing through it that the load is drawing. You will need a heatsink to keep the TO-220 package from overheating for load currents greater than 100 milliamps.

hgmjr
 

Gadget

Joined Jan 10, 2006
614
Some major problems using an LM7812.
The 1st is that the Maximum specified input voltage is 35 volts for a LM7812, and 40volts for the 7824 (24 volt version) so you would need a Pre-regulator, or some method to drop the input voltage down to a safe value for the regulator to operate at.
The next is (as hgmjr said) power dissapation. Just getting a modest current flow is gonna turn the regulator and pre-regulator into heaters.
Related to the above is efficiency. Going from 48 to 12 with a linear regulator means that 75% of your power is being wasted.. (as heat...see above).
You don't mention what current is required, or what the application is so it is hard to recommend what to use.
My choice, for most higher current applications (with the exception of powering a sensitive radio reciever) would be Switch Mode regulation, which involves generating a square wave with a mark space ratio of 1 to 3 and lots of filtering (with perhaps some feedback to adjust the mark space ratio for voltage regulation). This would give good efficiency and low heat dissipation and potential for good current ratings (depending on design). The main dissadvantage is the potential for noise on the output.
 

windoze killa

Joined Feb 23, 2006
605
Originally posted by Gadget@Mar 8 2006, 09:02 PM
Some major problems using an LM7812.
The 1st is that the Maximum specified input voltage is 35 volts for a LM7812, and 40volts for the 7824 (24 volt version) so you would need a Pre-regulator, or some method to drop the input voltage down to a safe value for the regulator to operate at.
The next is (as hgmjr said) power dissapation. Just getting a modest current flow is gonna turn the regulator and pre-regulator into heaters.
Related to the above is efficiency. Going from 48 to 12 with a linear regulator means that 75% of your power is being wasted.. (as heat...see above).
You don't mention what current is required, or what the application is so it is hard to recommend what to use.
My choice, for most higher current applications (with the exception of powering a sensitive radio reciever) would be Switch Mode regulation, which involves generating a square wave with a mark space ratio of 1 to 3 and lots of filtering (with perhaps some feedback to adjust the mark space ratio for voltage regulation). This would give good efficiency and low heat dissipation and potential for good current ratings (depending on design). The main dissadvantage is the potential for noise on the output.
[post=14770]Quoted post[/post]​
You could try one of National Semiconductor SMPS chips. The cct will be a little more complex but power dissipation is a lot less for the same current output. The NSC site has a great workbench function where you can design it on the web and actually tells you the parts you need to go with it.
 

Papabravo

Joined Feb 24, 2006
14,688
Originally posted by anybisi@Mar 7 2006, 07:47 PM
pls, i need to convert 48 volts DC to 12 or 24 DC,
[post=14759]Quoted post[/post]​
Linear Technology has LTSpice/SwitcherCADIII.
For free you get a general purpose spice simulator.
That simulator will simulate Switch Mode Power supplies with their chips
That simulator will give you a cookbook circuit from your specifications, and SIMULATE it to boot.

Just Google "LTSpice"
 

thingmaker3

Joined May 16, 2005
5,084
Demonkid, I apologise for my ambiguity. I was asking what Anybisi's budget was. The link I provided has boost converters which may or may not be within budget for Anybisi.

Note - if they work well for you, then you are welcome.
 
Top