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| PSU Constant Current response timing comparison |
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| alm:
Selecting a power supply for minimum output capacitance to increase the output impedance in constant current mode (faster respond to change in load impedance) is valid for some applications. The 6114A actually has a connection on the barrier strap that allows you to disconnect most of the output capacitance. It might be interesting to see how it performs with the cap disconnected. Based on the calculation I wouldn't expect it to matter much for that particular supply. I would expect the mobile communication / battery simulator power supplies to perform the best here. Since they are made to measure fast current transients. A dedicated constant current source, like the HP 6177/6181/6186, should be even better. --- Quote from: switchabl on July 30, 2022, 08:32:22 pm ---Actually... guesstimating from the datasheet (80ms full-load down-prog response time), the downprogrammer in the Genesys must be able to sink something like 5A already. It just has massive output capacitors. Of course it has, it does 50A. Don't connect an expensive low-current board to a huge power supply and expect the current limit to save you. :-BROKE --- End quote --- Very true. If your circuit is sensitive, it's best to match the power supply to the load. Also don't use a high voltage power supply to power the 3.3V rail for your expensive FPGA board. In addition, switching power supplies (like the Genesys) generally require more output capacitance than linear power supplies, and have a slower transient response. So I'd expect the performance to be significantly worse even if it was designed for the same current. |
| Peter_O:
Thx to all of you for the input and discussion! So there is no programmed delay in place, but the down response is perfectly in spec. Reg. the capacitance here's a picture I found in my archive. Two of the cans of each channel seem to be 330mF. And I have a measurement with the same load, but with the TDK in fold back mode: Interesting to see, that it first adjusts the voltage to reach the CC target current, and only then folds back the output. |
| tautech:
Peter_O A little tip for better screen shots is to lift graticule brightness to 60+% for the grid to be more visible. ;) |
| Peter_O:
--- Quote from: tautech on July 31, 2022, 08:37:51 am ---Peter_O A little tip for better screen shots is to lift graticule brightness to 60+% for the grid to be more visible. ;) --- End quote --- Sounds reasonable. thx Rob! |
| jjoonathan:
I (ab)use my SMU when I need fast transient response / low output capacitance. Here are some measurements I took last night. Milliseconds: PSU: output capacitor RC, loop responds SMU: ideal Microseconds: PSU: lead inductance L/R, (internal inductance L/R?) SMU: lead inductance L/R, loop responds Nanoseconds: PSU: transmission line sloshing (not pictured), FM radio, wifi packets SMU: transmission line sloshing (not pictured), FM radio, wifi packets I went ham with the bandwidth to see transmission line effects in the leads, but those are still a work in progress. At first, I was using a 100 ohm load resistor on the reasoning "hey, ladder lines are 100 ohms, I bet mini-grabber leads are some small multiple of that." This reasoning seems to have been correct and judging from where the plateaus are the actual characteristic impedance seems to be 500-1000ohms -- but bouncing is such an unholy mess on this timescale that just repeating the experiment didn't suffice to generate clean results. Also, loose clipper leads aren't exactly going to have uniform characteristic impedance, so there is probably a map of the cable convolved on top of the bouncing mess for extra fun. I tried making the load resistor 1 ohm on the idea that it would short out transmission line effects (pictured), and I am gratified to see that it worked, but of course it means transmission line effects are no longer visible. The next step is to make a fast-acting load and a driver for it, but that's a project for another day. Of course, since the leads are unshielded they pick up 2.4G packets too -- but with 1 ohm termination those are pretty minimal. Less minimal is the terrible 2MHz switching noise from my new modem every time it passes a packet. The cable tumors I have on stock don't appear to be up to the task, so that's the next priority. In any case, I've attached the 1 ohm termination results. Using less bandwidth and ignoring the transmission line timescale is the path of sanity -- but where's the fun in that? ;D |
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