How do I convert a PWM signal (with a specific duty cycle) to its respective analog value, for an application in a low voltage, high current circuit?

Question

I wanted a 16V,50A regulated power supply but could not find it in the market. I also searched for a buck converter for the same current output and could not find anything. So I thought of making it with a high current (60A) motor driver and a 45V, 20A SMPS. However, upon checking the output signal of the motor driver, I found out that it is actually a PWM signal (amplitude: 45V, frequency: 16KHz) and here lies my problem. Since I have a load which can take a maximum of 17V DC at input, connecting my motor driver directly to it is not a good idea. Now I am looking for ways to convert (or filter) this PWM output into an constant DC voltage (depending upon the duty cycle of PWM obviously!) so as to feed it into my load.

Could anyone please help me with the filter/converter design? I read about low-pass RC filters but given the amount of current that I am drawing, I will need an insanely small value of resistance with a high power dissipation capacity (about 800W) and also a very large value of capacitance (which makes it impractical.)

A rough schematic of my arrangement looks something like this:

^{simulate this circuit – Schematic created using CircuitLab}

On a side note, my load is expected to draw 40A current at 16V and I understand that I will need feedback to regulate my output voltage.

Answer 1

I found out that it is actually a PWM signal (Amplitude : 45V, freq: 16KHz) and here lies my problem.

You need an LC low pass filter with a cut-off frequency of a few kHz and moderate Q value: -

The cut-off frequency is defined by the equation: -

$$F_c = \dfrac{1}{2\pi\sqrt{LC}}$$

Use this filer calculator to experiment with suitable values: -

I've made a head start for you with values for L of 1 mH and C of 10 uF but be aware that the filter can produce large resonant peaks if the load is removed (R) and this is the reason for making the cut-off frequency significantly below 16 kHz.

I would also recommend an output monitoring circuit that can switch off the controller should the DC output rise above some top-limit.

Answer 2

This seems like a case of the XY problem. I think you would be better served asking for what you really want, a 16V 50A supply for a tethered drone, rather than asking for how to adapt an entirely unsuited PWM motor controller to the task of supplying a constant voltage.

An LC filter will only work when the PWM driving it is symmetrical. IE, it must source and sink equal current. If it only sources current, the output from an LC filter will be highly nonlinear, in fact it will look like an exponential charge curve. And a fixed PWM through an LC filter will yield a voltage that changes with load.

16V @ 50A is 800W. So give the power supply some headroom, and relax the restriction on voltage because LiIon cells drop during use anyway...

Mean Well sells a 15Vdc 1kW 66.7A output switch mode power supply, the SE-1000-15. Mouser Electronics sells it for about $170 USD. Short circuit and overload protection.

Here is the datasheet: Mean Well SE-1000-15