Dividing Voltage in Series

[Brad Rubinstein]

Hey guys, 1st post. Im building a mic pre kit and i want to add a couple extras like led vu meters and possibly some tone control. The preamp circuit runs on 48v and the meters are 12v each and tone control is 24v. Im kind of a newbie. Can I just power all the extras in a series since 12v +12v + 24v = 48v? Or will it just divide the voltage equally across? In that case could anyone recommend a way to do this? Thanks so much!

 

[ecc83]

Hey guys, 1st post. Im building a mic pre kit and i want to add a couple extras like led vu meters and possibly some tone control. The preamp circuit runs on 48v and the meters are 12v each and tone control is 24v. Im kind of a newbie. Can I just power all the extras in a series since 12v +12v + 24v = 48v? Or will it just divide the voltage equally across? In that case could anyone recommend a way to do this? Thanks so much!

No, just putting things in series won't work the voltages will share as the current drawn.

The first task is to find out how much current the additional 12V devices draw (rig on a car battery FIT 100mA fuse!) Once you have that information you can use a 12V regulator to drop the 48V to 12. But, most regulators are not rated for 48V in iirc so you will need a series resitor to drop the incoming supply to the reg' The value of that R can be calculated from the current draw and the voltage needed at the input of the regulator, say about 18V you also need to calculate the power rating of the R and be generous!
You can buy pre built regulator boards very cheaply. You want a "7812" fixed 1 amp regulator. I doubt the 12V extras will draw anything like 1 amp!

I AM assuming you only need a single +12 rail. not + and -12?

Dave.

 

[skywaveTDR]

As Dave said this is an over simplification of the requirements. I could see the need first to determine if the 48V supply has enough current capability as it might be limited to only supply small current needed for FET amps in mics.
After that a suitable sub regulator system could be done using a transistor, zener diode, resistors and electrolytic for each voltage you need. This because of the question might really be too far over your head in that a seasoned Technician would know how to do this. These guys usually have spent years on a bench as well as 2 to 6 years of college depending on the degrees they got. There are HV regulators but it might be cheaper to use a transistor and Zener diode and resistor and caps to get the job done. It is really not a hard thing to do if you understand DC regulator circuits as they call them.