# Multiple voltages power suply, high current

high-currentpower supply

I'm trying to design a battery back-up power supply for my home network devices. I need these:

• 48 V / 40 A
• 24 V / 10 A
• 12 V / 2.5 A
• 5 V / 5 A

I got a 48 V / 60 A industrial power supply with battery backup (four 12 V car batteries in series) and need to divide the voltages.

After digging through Google and Electrical Engineering Stack Exchange, I want to use a bunch of diodes (like 1N4007, but of a type able to withstand the current) and simply take out needed voltages somewhere between these like this:

The second option is high current transistors like BC547B driven by zener diodes, but I'm not really sure if that would be better than the first option. Is my idea OK, or I should do it another way?

This is a no-go. The power which you have to dissipate in the diodes will be enormous.

``````diodes between 12V and 5V dissipate 7V @5A = 35W
diodes between 24V and 12V dissipate 12V @7.5A = 90W
diodes between 48V and 24V dissipate 24V @17.5A = 420W
Total amount of dissipated power (in diodes) = 545W
``````

The diodes able to withstand such power need to be extremely big, the absorbed power will all be transfered into heat so you would need giant cooling fans or a very big airflow.

This kinds of power really need to be converted by a switch mode conversion which will give you an efficiency in the order of 85%+.
Instead of dissipating 545W in the electronics you now only have to dissipate 15% of the output power, so 295Wx0.15=44.25W
Still a lot but way more feasible.

So you better go looking for three switched mode PSU for 48V>24V, 48V>12V and 48V>5V