Constant power pulses

[charliecoutas]

I have been struggling for over a year now to generate clean, fast rise and fall, pulses of between 2mW and 10W. Voltage between 0.1V and 10V in resistances of 0.1 to 20 ohms. Shortest pulse length 25uS.

The question is: how fast could a dspic33 running a max speed, read two 12 bit ADC's (volts and amps), do a simple calculation then write to a 12 bit DAC? Thus providing a constant POWER in the load, not CC or CV.

I would guess that some folks on the forum will be able to advise, thanks in advance.

Charlie

[top204]

That is where the dsPIC33xxCK devices come in.

They are inexpensive.
They operate up to 100 MIPS (200MHz oscillator).
They have very fast 12-bit ADCs (up to 3.5 MSP), that, I think, can be sampled simultaneously, and which also have built in filtering.
Most have built in 12-bit DAC peripherals, and if they are not fast enough, they have high resolution PWM peripherals to operate as a DAC. These can be paired to give higher resolutions at higher frequencies with a couple of resistors and a small piece of clever coding.
They have hardware divide and multiply so the calculations are very fast, and my floating point routines work very fast indeed on them, but integer will always be crazy fast.
They have DSP peripherals built in, so extra filtering can be done if required.

They also have a host of other benefits that would make the list too long. :-)

25uS (40KHz) is not actually that fast, so a dsPIC33xCK will fly through it, with lots of time left for other things. :-) Just make sure your MOSFET can handle those speeds.

[charliecoutas]

That's very encouraging Les, thanks. I'll have a look through the available devices.
(The 25uS pulse, and the others, are one-offs. Not repeating immediately.)

Charlie