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| Voltage "divider" after PSU to highten the resolution? |
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| hli:
Just as a thought: you want your PSU to supply up to 1A. Assuming that you are not using separate sense wires (I think none of the Rigol / Siglent ones have them), an accuracy of 1mV means that your wires from the PSU to your powered device must have less than 1mOhm (including all connectors). So even when then readout / voltage setting on the PSU has this accuracy, it does not mean that this what your device gets in reality. In addition to the ripple problem that why PSU with such specs are so expensive - sooner or later physics gets in your way. Maybe you should first define _why_ you want to have such a accuracy? Whats the problem you are trying to solve? |
| ebastler:
@FriedMule -- I don't think you ever mentioned why you believe you need a power supply with that high resolution?! If you actually want to supply power to some circuit (i.e. a supply current of several mA and up), the voltage should be far less critical than requiring mV resolution. If it is, I would argue that your circuit is not designed properly. If, on the other hand, you need a precise reference voltage, e.g. to set a comparator threshold or such, you will not need a significant current. Such reference voltages are usually not provided via a big adjustable power supply, but a separate "voltage reference" circuit. You can find many integrated voltage references, with fixed or adjustable output voltages, with nice built-in temperature compensation etc.. Simple 2 or 3-terminal devices which are connected to a not-so-precise supply voltage and provide the required precise and stable reference voltage at their output. |
| Doctorandus_P:
I'm a bit surprised "SMU" has not been mentioned here yet: But it probably also does not matter much because of budget constraints ;D https://www.ebay.com/sch/i.html?_nkw=keithley%20smu --- Quote from: FriedMule on February 16, 2019, 10:07:18 pm ---Would this be hard to buy / build? From: 0-10V - 0-1A Step: 100uV / 10uA --- End quote --- Have you thought about how realistic those values are? What sort of cables do you want to need if you want to keep a 5V supply within 100uV over a 0 to 1A current differential? That's a voltage resolution of 1:100000 Have you thought about how you want to adjust such a thing? That is definately not going to work with a 10 turn potentiometer. Things like these are very expensive, but most of the price does (probably) not go into the components, but in the engineering such things for a small market. But also because they are only made by companies who do not care about price, but only about qualtity and robustness. As a hobbyist it is fairly doable to slap a few DAC's onto a microcontroller, add a display, some rotary encoders and some opamps for the output section. Opamps don't deliver much current. One easy option is to add a buffer such as LME49600 (can these be parralelled?) Or on a low budget maybe even some integrated audio amplifier. For a DAC you could for example take an MCP4922. It's only 12 bit, but in the datasheet the've shown a simple trick to increase it's resolution. You can get more (absolute) accuracy by carefull calibration, or by using a good adc and fine adjustment in a software loop. Fairly good ADC's have become pretty affordable. For example take a look at ADS1220, or other DAC's in that series. Do you only want to measure current, or do you also want a current limit to work reliably at your resolution? It might be a better idea to build and adjustable current source. For measuring current, you can buy expensive high accuracy & stability resistors, But you can also use a cheap power resistor and callibrate it yourself. You can also for example glue a thermometer to it and after characterisation of the resistance deviation, you can partly compensate for it in software. How good you can build something like that and what accuracy / resolution / reliability you get will mostly be dependant on the experience you have with electronics and the amount of time you put into it. But with a reasonable amount of effort you will probably: 1). Get much better accuracy / resolution than your KORAD. 2). Have built designed something to be proud of, and have lots of fun in the process. 3). Learned a lot about electronics. 4). Have a usefull device for doing experiments. |
| alex-sh:
--- Quote from: FriedMule on February 16, 2019, 10:07:18 pm ---Would this be hard to buy / build? From: 0-10V - 0-1A Step: 100uV / 10uA --- End quote --- Try it for yourself and see why it is bloody hard to build it or why Keithley is charging so much for their voltage/current source. I wonder why or where you would need such resolution? |
| FriedMule:
First sorry for my late answer, I hade some family business to attend to. I'll try to answer all your questions. Calvin Siglent has a model without the X that goes down to 1ms on the interface with remote sense, I am glad you say that they are fine, cheaper for me, I am thinking of either buy or build but buy use to be a fare better quallety:-) I think it's a combination on wich and Ehm sort of need, I have my Korad 10mS so one more cero does not do much difference. I am hoping on learning about components at wary low power, like Dave did with his nanometer and LED's, I want to play with BJT, Mosfet, LED and other components, to se how they behave, also to build circuit that can run with as low a power as possible. And on top of that, it would be a fantastic tool to have on the bench! :-) beanflying my demands are not high in output voltage but would like to cover different types of standard batteries like 9V and 1A would be really nice. I have the Korad for just supplying power when I need it, think of it like my replacement for a car battery. Doctorandus_P about if I have thought about the realistic in my project, yes and no. You can buy a 0-60V 0-10A 1mV/0.1mA for an okay price and other with less power almost every ware, and you can buy SMU with insane specifications and price, and Dave have some "normal" power units down to 1nV, so I tought one more Zero would not be wild to go fore. I really like your advices about components and will read a lot more about them. :-) alex-sh I know that a zero more does thing harder, but as I wrote abowe, did not think we was talking about a Mars mission. Yes you can get a source meter, but I thought that the price was due to the insane specs, the 6.5 digit DMM, brand name and so on. I do not need a DMM 6.5 or these great features on top of my PSU. "All" I wanted, was a PSU, one digit better then the cheap Hong Low unit to 377$:-) |
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