I will control a load to dissipate about ~600W using 30.3khz using 16-bit PWM. max 43A @ 14V
In order to measure the current with as little ripple as possible, I wish to smooth out the effect of a powerFET.got some inductors, with 1.25mm diameter wire, 26 windings around a ferrite ring, the inductor is 1cm wide and 3.5ch high - measured to 60uH - Which I think is realistic. - the inductors are labelled 210050A7072B - But I've not found any way to understand the marking.
So - I plan to switch the power using a FET, then power resistors (0.33ohm) - and the inductor - would help a lot, or not ?
by my quick calculations, connecting a 500nF capacitor across the resistor , but how good can the result really be ?
If you are using PWM the current is either 0% or 100% with varying duty (on/off) cycle - that's how PWM works
If you wish to measure the mean current you'll need to fit a load monitoring resistor in the line and measure the duty cycle voltage. Apply an RC filter to this to get a "fair" representation of the duty cycle voltage, hence current. It will only be "fair" since the RC filtering is non-linear but you can correct for this in a measurement algorithm.
because you're using relatively low voltages why not simply monitor the duty cycle and assess Load Current = Duty cycle x 43
jremington - what I tried to do, is to have as ripple-free load as possible, so the curect measurement could be very precise (not just smoothed by a capacitor or sampled/averaged at higher rate.)
jackrae: I know,very well, how PWM works not using a resistor, but a hall effect current sensor for high precision over wide current range.
Anyway - I'll stick the linear (darligton transistor based, clusters of MJ11015) solution I am using today, as the only high power FET's I had in stock were IRFP064 , N-FET's , while the design would be easier if I had P-FET's.
I remember you wanted to discharge ~20volt LiPo batteries for drones, to calculate flying time.
You might want to look at high-power buck converters. Like these ones.
A buck converter, with a fixed resistive load and set to a fixed voltage, draws a constant POWER from a battery.
e.g. a 1ohm resistor (10x 10ohm/10watt), and set to ~9volts will draw 100watt from the battery.
Multiple modules could be used in parallel, to reach final the power you want.
A relay module could switch them on/off.
Something like this could measure voltage and current.
Leo..
not using a resistor, but a hall effect current sensor for high precision over wide current range.