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Topic: Computer controlled PS/function gen/multimeter (Read 229429 times) previous topic - next topic

Re: Computer controlled PS/function gen/multimeter

Reply #255
It has been a while, but some progress has been made on my small mobile power supply. I have received the PCB and build both versions of the apparatus, one with the LM20323 and the other with the lm2596. Both versions function as expected actually.

The version with the LM20323 did not work, as it goes berserk when the current feedback kicks in, because it tries to compensate for what the chip thinks is an overvoltage problem. When it comes to voltage limiting capabilities it works very good, because it is much more efficient than the version with the LM2596, which above 2-2.5 amps gets quite hot.

The version with the LM2596 works quite well, although in current limiting mode there is some oscillation for the moment (I did not try to compensate for this yet). Furthermore it tends too make a high pitched noise in some load conditions. The voltage ripple is about  50mV and the current ripple 50mA. Which I think is still quite a lot, hopefully I will find some way to improve it.
So you can charge batteries with it, but it is not a laboratory supply (yet).

There were some minor errors, like the opamp apparently having two different versions, one with VDD and VSS reversed, of course I chose the most exotic of the two parts... Furthermore the Vusb detection pin was connected to a non 5V tolerant pin and started to supply 5V to the 3.3v rail via the PICs internal diodes, my bad.

So, now I need to start thinking about getting rid of the oscillations and order one of these babies, which will make it look way more badass. Let me know what you guys think of the design up till now.

On the computer control side of things. I first need to switch back to the C18 compiler instead of the XC8, too bad the USB stack does not work on the new compiler yet.

EDIT: Ok, I also found the solution to the oscillations and noise. The second coil added too much phase delay, thereby making the thing unstable. I removed the coil and now I only get 30mV of ripple while regulating a voltage and 50mV of ripple while current regulating :D


Re: Computer controlled PS/function gen/multimeter

Reply #256
This looks sweet--nice work! 

[My first DP post]

Re: Computer controlled PS/function gen/multimeter

Reply #257
Wow its great to see someone took this idea and ran with it. I had long forgotten about this project idea. Looks great, keep up the good work.

Chris "Garak" McDonald

Re: Computer controlled PS/function gen/multimeter

Reply #258
Nice work! I'll keep looking for updates. Thanks for sharing.


Re: Computer controlled PS/function gen/multimeter

Reply #259
Are you thinking to share the schematics?

Re: Computer controlled PS/function gen/multimeter

Reply #261
Are there any news? I'm quite interested on this.

I found Sigrok, it's an interesting program that needs more attention. It could be used for this pice of hardware if finally gets developed.

There's DSLogic , but it isn't Open Hardware and lacks DMM features.

Re: Computer controlled PS/function gen/multimeter

Reply #262
One thing to keep in mind as a possibility is an AC adaptor instead of DC.  They're rare, but I have seen some products which come with a wall-wart adaptor that outputs AC instead of the typical DC.  Something around 20 V AC or less.