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| LM358 in Consant Current Circuit Problem |
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| Benta:
Before trying to compensate the circuit with caps all over the place, I have a question: Where is the supply bypass cap(s) at the opamp? I mean, this kind of current source sink is normally a nobrainer, especially with an amp that's so well-behaved as the LM358. |
| Yansi:
--- Quote from: TheInfernoMan on December 31, 2016, 04:01:58 pm ---But if I slowly rise the Voltage at the non-inverting input the Current Rises instantly to 3A --- End quote --- The load current is proportional to the voltage on the noninverting input. Iload = U / R1 = U / 0.2 That means 1V input yields 5 amps! Benta: Sure, that is also a good question to start with! |
| orolo:
--- Quote from: Yansi on December 31, 2016, 07:14:45 pm --- --- Quote from: orolo on December 31, 2016, 07:03:57 pm ---Bypass the 12K in the noninverting amplifier with, say, 10nF. I have simulated the circuit and it oscillates like crazy, because of the noninverting stage. --- End quote --- No. The 12K resistor shall be split for two separate gate resistors (to prevent HF mosfet oscillations) and shall NOT AT ALL be EVER shunted by any cap. see my previous post. Edit: a pic of the simulation I uploaded before. --- End quote --- No, no. Look at his complete schematic. He is feeding the mosfet-driving part of the 358 with the other half acting as a non-inverting amplifier, with 3k/12k. There is the problem (or at least, a big problem). |
| Yansi:
Oh, sorry, I was thinking only about the first schematic, that is at least partially OK. The second one (Schaltplan.png) is very wrong of course. |
| TheInfernoMan:
First I have to say, that I am really sorry for my mistakes in my schematic. But I did not know it better. I think I have to redesign my schematic. How can I make that better, if I not know all these things about oscillations etc. ? I have only seen some "basics" videos. Did somebody got a tip, how it is easier for me to Look for mistakes Like Them ? Can someone make a short schematic, of the Basic Part of the CC Load, what I should make so. I would be really thankful. I am really thankful for your help. |
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