ibdami21 wrote:I was able to get it: I had the 64 bit SDK installed. Once I also installed the 32 bit SDK everything seems to be working.
ibdami21 wrote:I have a switching power supply I'd like to do a stability test on and will use a small isolation transformer from the picoscope to the feedback loop and see if this can enable the device to be a sort of network analyser. Kind of like the setup TI shows here: http://www.ti.com/lit/an/snva364a/snva364a.pdf . But with your program this should now be very easy to make a proper bode plot without manually collecting data points.
ibdami21 wrote:I know you're working on it and I'll provide one wishlist feature:
-Upon a new run, update the display as data is acquired. I know this will have averse effects to auto-ranging. Perhaps have this option for manual window setup only? For all the work I do I'd be fine without autoranging since I know what to expect from the system at the frequencies being swept, plus if there is any data out of range I won't care about it with the window selected.
ibdami21 wrote:Thanks again for making this. Too bad I am just a HW engineer with basic programming skills else I would see about helping this project .
ibdami21 wrote:Hi Aaron,
Thanks for the remote debug. It looks like since I am new on the forums my earlier post was delayed (topic14311-90.html?hilit=hexamer#p74511)
I have it working now and am checking to see what transformers I have for some SMPS stability tests.
I've attached an image of the plot from a transformer I have which seems suitable for my needs (PFC converter with a very low Fc).
ibdami21 wrote:Hey Aaron,
The transformer I showed that data on was a regular 50VA toroidal core power transformer I happened to have lying around. For my application I know the fc of my converter needs to be quite low (around 50Hz to 70Hz), and I know these cores are decent up to a few hundred Hz. It's surprising to me it's got decent bandwidth up to 10kHz. This is an Avel Y236202 wired with both primary and secondary in series (as if being used for a 240V application with 24V out). I have a 20 ohm load on the secondary as I would have for stability tests. I've got a big W material core which would make a good wideband transformer if needed.
Probably a silly question... How do I get between low and high noise modes? Is that embedded in the "Input signal Vpp" box?
I'll check this out Monday on my switching supply and let you know the results and any issues I come across.
ibdami21 wrote:For pretty much all SMPSs, fc needs to be quite a bit lower than the switching frequency. It depends on the converter topology and what its design parameters are. Some very fast converters (CPU cores with multi-phase bucks) will be really quick, but for a buck I understand this is limited to about fsw/3 or thereabouts. For a flyback AC adapter you may be switching at 70kHz and have your crossover around 7kHz. So it really depends on the converter's design how far you want to sweep. On top of that, the crossover point will change based on the load condition. I'm actually trying to tame one now which looks a tad off at full load.
ibdami21 wrote:There needs to be good attenuation to the switching harmonics in the compensation network, else weird things happen. I had one buck a while ago show spurious instability with fc set too high, although my simulated model showed plenty of phase margin. That was an attempt at ~200kHz fc for a ~275kHz converter. Slowing the control loop's fc to 50kHz made all the issues go away.
ibdami21 wrote:Let me know if you've got any SW which I could help look at as changes are made. I know this converter is a bit weird from normal converters (single stage active PFC flyback) and requires a very low fc.
ibdami21 wrote:Not to veer this too far into SMPS control loops... but hey may as well add to the chain.
A converter shouldn't have multiple crossovers but it could happen. That would be something interesting where there typically is not correct pole/zero placement and the gain of the closed loop bounces around zero. But, the fc does move about with load variation and with input voltage variation. Measuring up to fsw does show the entire converter's bandwidth, so as to ensure you don't have anything weird happening near that point. In well behaved converters the gain just keeps dropping by the time you get near fsw that we won't see much.
Boost converters, unlike the buck, are not a linear transfer function. The 1/(1-D) is exponential as duty cycle is increased. This along with the converter naturally having a RHP zero make the control loop more difficult to stabilise than a simple buck. Not impossible by any means, just not as easy as a buck. This stems from how the boost converter operates (i.e. indefinitely closing the switch would mean we short the input to ground and no power arrives at the output in a boost, where a buck would effectively pass the input to the output). That is one of the reasons boost converters are usually current mode controlled. Then there are interesting issues which current mode presents in itself...
That TI converter you mention is a current mode device. Note the built in current sensor and the summing component in the block diagram. Current mode controllers need an artificial ramp added to not go unstable, but this does cause a little jitter in duty cycle.
I wasn't able to look at the converter today but hopefully this week I can see what the FRA application can do.
I am unable to connect my Picoscope 3406D. I have SDK 32bit installed. Below is the error message I get:
Error: Unable to initialize device with serial number CW698/004
Any help would be appreciated. Would really like to use your software.
firstname.lastname@example.org wrote:PS: Boiler Up!!
email@example.com wrote:I think it is the latest :
I'm running Windows 7 64bit and installed the SDK 32bit (did not work) and also tried the 64bit.
Really appreciate the help.
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