DC power supply build

[aqibi2000]

Hi all, this is my first actual post here.
Been reading for quite a while, great information here

I'm looking to build an adjustable power supply with some DC power supplies, I have 2x 12v 32amp supplies of which I primarily require 20v with 5amp output. I've seen designs for voltage boost (12v to 24v) but to only around 2/300ma which isn't very useful.

In consideration I though placing the two supplies in series to create 24v 32amp. However I need some way to have adjustable voltage, the greater the range of the adjustability the better for the bench supply. Plus current limiting is very important, there is 32amp available, and would like to make the use of as much of that as possible, however 0-5amp adjustability is vital with precision. Each supply also has a 5v 0.6amp output to maybe drive control circuitry. Each supply does have short circuit protection, however I would like to implement this into the design also similar to the LM723 designs.

I would appreciate any input, I have an Arduino for means of programming a PIC, although would prefer not to have to go through that procedure Linear maybe?

Thanks for reading.

[mariushm]

Re: DC power supply build

It really depends on what power supplies you have and if you can connect them in series to get 24v.
I'm not sure you'd be able to.

If you want really smooth, minimal ripple on output, you have to go the big heavy transformer router and do voltage and current limit with opams and all that. Such designs are relatively simple and reliable but the transformer for 5A would be expensive.

If the ripple is not that critical (you can tolerate 10-30mV ripple or something like that), then probably your best bet would be to go to one of those ready made 24v switching power supplies.
From that point, you can use use a linear regulator to smooth out the output a lot and vary the voltage.

If needed you can switch between feeding the regulator directly or use some buck switching regulator to get 12v or something lower, because the linear regulator would dissipate the difference in voltage as heat.

You can measure the current with a pic or something (opamp etc) by using a resistor in series and measuring the voltage drop on it, and you can do current limit from there by dropping the voltage when current exceeds your preset current limit.

[aqibi2000]

Re: DC power supply build

The PSU's can be placed in series providing the earth cables are not all connected. Similar to the PC PSU hack to combine all the 12v rails (utilising only 1 connected to Earth).

They are very stable 12v, I don't want to go under the route of SMPS nor the need for a transformer as the 2 supplies I have I believe are adequate for this job.

I need help with the current limiting ultimately as 32A is far to great.
Thanks very much for the reply.