Joined Jul 31, 2012
8
Hey guys,
I am new here and hopefully someone can help me out with my problem.

I have a system in place that powers a LED board that runs off an adjustable 12.5-24vdc power supply.

I have to incorporate a new LED board that operates at 6-12vdc and uses about 300mA@ 12vdc.

How can I bump the voltage down from the current 24v max to the 12v max in order to use the new LED board?

My first thought was using a transistor, but wouldn't that would require additional wires from the source. And that is not an option.

My second thought was using a 12v zener diode in series with the led board to 'block' 12v from passing though. Please let me know if this will actually work or if there is another/better solution for my issue.

Thank you all ahead of time for your help. And if any additional information is required, let me know and I can supply the info.

#### t06afre

Joined May 11, 2009
5,934
Some questions. Will the input voltage be stable at 24 volt or will it be in range 12.5 to 24 volt (the output range from your power supply). Also is space critical for this application. I can see many ways to solve this problem. Just need more info on what we have to work on.

#### Dodgydave

Joined Jun 22, 2012
10,088
use a lm7812 volt regulator

#### t06afre

Joined May 11, 2009
5,934
use a lm7812 volt regulator
With some kind of cooling fin. Or the LM7812 will get to hot

Joined Jul 31, 2012
8
Space is critical. The smaller the better.
The input voltage will be adjustable from 12.5v to 24vdc in ~1-1.5v steps. That adjustable input controlled the original LED board. I need the max 24v input to output 12v. And the 1.5v steps down from the 24v input to do the same to the output.
Input: Output:
24v 12v
22v 10v
20v 8v
... and so forth (i used 2v intervals to make it simpler to understand)

A lm7812 will not work as it has a set output. Need output to mimic the adjustable input.

#### chrissyp

Joined Aug 25, 2008
82
how about controlling the gate of a power mosfet with a PWM set at 50%, then the output should be 50% of the input through the range.

#### bertus

Joined Apr 5, 2008
21,674
Hello,

How about a voltage divider with a power opamp as buffer?
A LM1875 could do the trick.
Here is the datasheet of the opamp: LM1875.pdf
Of course the power opamp needs to be cooled.

Bertus

Last edited:

#### t06afre

Joined May 11, 2009
5,934
Space is critical. The smaller the better.
The input voltage will be adjustable from 12.5v to 24vdc in ~1-1.5v steps. That adjustable input controlled the original LED board. I need the max 24v input to output 12v. And the 1.5v steps down from the 24v input to do the same to the output.
Input: Output:
24v 12v
22v 10v
20v 8v
... and so forth (i used 2v intervals to make it simpler to understand)

A lm7812 will not work as it has a set output. Need output to mimic the adjustable input.
Putting a 5 Watt 12 volt zener in series with the LED circuit might do the job.