Need help designing a buck device for 48v to 5v USB

Thread Starter


Joined Mar 1, 2017
I'm wanting to design and build a circuit for the purpose of using a 48v LiFePO4 battery to charge USB devices.

This device will have an input side where I connect the 48-55v battery and an output side consisting of 3, 5v USB A ports and 1, 5v USB C port
The output amperage should never exceed 1A per port.

I do not have to worry about a battery cut off provision since the battery has it's own BMS which will stop the flow of current below a per-determined voltage. It would be "fun" to incorporate a means of visually displaying the total current being consumed by all 4 ports combined, but that is a luxury and not a requirement.

I'm considering the use of an LM2575 as it seems to have some of the basic required functions built in.

One problem is that the LM2575 is rated for a maximum of 40v and my battery can reach 55v at full charge so I will need to do some pre-processing to ensure the voltage reaches the LM2575 at or below 40v, preferably around 35v

If you can give me some pointers, tips or suggestions towards this goal it would be appreciated.

Best Regards


Joined Nov 6, 2012
You can also use a single "Push-Pull" Chip to drive a single Toroidal Transformer,
then use however many Secondary-Windings and Linear-Regulators You need.
(plus one additional Winding for Voltage-Regulation-Feedback)

It will generally be more stable and generate less Electrical-Noise.

The Output is pretty close to a Square-Wave,
so it's easy to Filter after Full-Wave-Rectification.

The Secondary-Windings can be added by hand,
as you'll probably need less than ~10-Turns per Secondary for
feeding a Linear-Regulator providing ~5-Volts-Output.

This also provides complete Isolation between the Outputs
if that's deemed to be of any advantage in your design.

A single higher-Current-Secondary-Winding can feed as
many Linear-Regulators in parallel as You want.

Thread Starter


Joined Mar 1, 2017
Is there are shortage of semiconductor components right now?
each time I try to build a board I find that I cannot get the components.

For example the TI LM5117 is not available