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| Power supply for home lab - do I really need a R&S? |
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| KungFuJosh:
I did blackdog's test with my SPD3303X v6.2 hw. For values set below 30mA, there's a spike to nearly 30mA before dropping to the set current. For currents 30mA and up, there's no overshoot. Inserting the probe into the scope was seen as nearly 15mA. |
| Martin72:
--- Quote ---However, the power supply has no knowledge of the attached load impedance before it's turned on and current starts flowing. --- End quote --- This is the point that should be internalized. If you set the current limit of a power supply to 30mA, for example, this is no different than setting a controller setpoint. If you then enable the output and allow current to flow, it takes a certain amount of time for the actual value to match the setpoint. This is the nature of the controller. You cannot expect the current to be limited “instantaneously”. |
| thm_w:
--- Quote from: Martin72 on October 04, 2024, 10:53:21 pm --- --- Quote ---However, the power supply has no knowledge of the attached load impedance before it's turned on and current starts flowing. --- End quote --- This is the point that should be internalized. If you set the current limit of a power supply to 30mA, for example, this is no different than setting a controller setpoint. If you then enable the output and allow current to flow, it takes a certain amount of time for the actual value to match the setpoint. This is the nature of the controller. You cannot expect the current to be limited “instantaneously”. --- End quote --- Seems beside the point when we already have demonstrated supplies that do not overshoot, and that is the desired behavior. |
| 2N3055:
--- Quote from: pdenisowski on October 04, 2024, 10:37:07 pm --- --- End quote --- I wanted to stay out of this discussion but am getting an itch.. Paul, this is not moment for clever lawyer talk that "technically" specifications are not violated because someone in R&S used clever wording in datasheet... Current limit is exactly that: a limiter that limits that current does not exceed set current limit. You can accomplish it with some kind of electronic fuse that will disconnect load, you can enable foldback limiting (that will reduce current to minimal until you reconnect load) or you can enable constant current mode that will keep constant current. In any case, current should not exceed the set limit. It is a limit, not some general recommendation. If one wants to be able to deal with difficult loads that have large startup current, than that has to be separate, configurable option. Those are, generally speaking, expectations form average user. And when they pay 3x the money (or 10x) they expect it behave better that some cheap PSU. Which here is not the case, because I have Rigol DP831 that behaves very well in this overshoot test, and to add insult to injury, I have two noname analog PSU that are even better in that regard, behaving like decent current source when starting. They also switch between voltage and current control loops without much saturation in error amplifiers, making transition quite smooth. I refuse to believe R&S cannot make it better than some noname small manufacture in China copying 50 year old HP design. But maybe design dept and product leaders should pay more attention to analog design that to "visual identity of the brand". R&S is brand that is famous for their outstanding devices with state of the art performance. It is not Versace. Or Apple. Or some luxury brand that sells and designs something that is fancy and status symbol but not mean to be really pushed to the limit. R&S is not supposed to be Vertu encrusted in diamonds but basically just an ordinary phone. R&S is supposed to be state of the art military communication device with state of the art performance. More like LeMans Porsche LMP race car than Porsche SUV with leather seats. |
| Martin72:
--- Quote from: thm_w on October 04, 2024, 11:41:51 pm ---Seems beside the point when we already have demonstrated supplies that do not overshoot, and that is the desired behavior. --- End quote --- Then they have a very, very fast controller. You have to reach the point where you have to cut back, in any case, time passes for that. |
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