Electronics > Projects, Designs, and Technical Stuff
DC load using a CPU cooler
microbug:
@timb, I can't find a part by the name of 'REF2040'! I have already got a DAC8411 and a 16 bit ADC (I forget the part number - will add it later), both of which have built in references. I can replace them if I have to, but I'd prefer not.
Typical zero-code error @ room temperature (according to the datasheet) for the DAC8411 is 200uV - I won't need that much trimming, if any.
mrflibble:
Maybe he meant the 2041?
http://www.ti.com/product/ref2041
microbug:
@mrflibble (I like your username!) Yes, that's likely.
EDIT: Of course, it's unlikely that I'll be using the load below 10mA, however; it would be nice to have accuracy right down to 1mA.
FYI, I'm using two INA194s with .01 ohm resistors for current sensing; the output feeds into the op-amp (one IC and resistor per driver). I can put both current sense voltages through their own resistor (to get the average current sense voltage), and feed it into the ADC - I'll double it in software. A voltage divider will set the full scale current sense range.
I'm going to include a constant-voltage setting in hardware, as I can get the PSoC to act as an analog mux so all that is required is a few resistors (my plan is to divide the input voltage down and compare it to the set voltage using the op-amps). I did look into constant resistance / power modes in hardware briefly, but I don't know whether it would be worth the effort. I won't be limited for op-amps, though; the PSoC has two so I might be able to make use of them.
I put two MOVs which go at 200V or so (haven't chosen the parts yet) across the input for protection. I don't know what to do for protection against voltage above 100V but below 200V though... suggestions?
EDIT 2: For hardware constant-power, an AD633 multiplying load voltage and current would be fine. Constant resistance, which would require comparing either using a digipot (not much resolution) or doing V/I in hardware (difficult - I can't see how it could be done), is harder. I think constant-power would be more useful, anyway.
timb:
Measure the current with your INAs and the input voltage with a resistor divider using the PSoC's ADC. Now use your MCU to control the current via the DAC. This way you can do CC, CV, CR and CP through software.
BTW, doesn't the PSoC have like a 16-bit DAC and ADC? Why use external parts?
Sent from my Smartphone
microbug:
Won't the transient response be much worse? I through that was what C2000s (DSPs) were for.
The PSoC 4200 has a 12 bit ADC and a 12 bit IDAC (current DAC), which is not very useful. I chose 16 bit resolution with external parts because they aren't inhibitingly expensive so I might as well; it will let me get closer to my 1mA resolution ideal.
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