BTW - how little sense does it make that the forums will host the pictures as attachments, but not as pictures?
The answer is simple. After you post the attachments , click SAVE then put the mouse cursor over the attachment and right click "Copy Link Address", then click Modify, select the image toolbutton (computer monitor icon) and paste the link address into that, then click save.done.
Well, simple would be the img button having an option to enter a URL or a local file.
I also attached a complete circuit diagram of the current controlled battery simulator. Yes, the battery is floating. But since the OP Amp gives me only the differential voltage between the battery poles it should be ok.
The link address of the attachment would be a "local file" but if I'm not mistaken , I think what you were asking was why isn't the forum software smart enough to know an image file extension of an attachment means it should be displayed as an image instead of us having to copy the link address URL and paste it into the image toolbutton prompt window ?
If you are referring to the schematic posted in Reply#14, it is not complete. The comparator "+" input does not have any input voltage associated with it.There is no part number for the fet.There is no component type or value or label for the cylindrical object , (is that the battery ?)There is also no circuit description for what appears to be a fet switched by a comparator and nothing more. Is that a modification or addition to the original op amp subtractor ?
He doesn't show the input to the current control op-amp. I assume it's a steady reference, but if it's not then possibly that's the cause of his problems.
There's no current control. That's a simple comparator. What is the cylinder under the comparator ? Is that a battery ?
he current through the battery forms a voltage through that resistor. The voltage is then fed back into that op amp.
Yes, thats not feedback though, the comparator operates in open loop mode.Thats the input voltage and the Vref for the comparator is the +V pin.If +V > -V, Vout = +Vcc +V < -V, Vout = 0VVref = 8.2 V (in above example)The "feedback " line , as you call it is connected to the wrong pin on the comparator.The operation should be :If Icharging < 0.300 AVout = +Vcc (fet ON)If Icharging > 0.300 A,Vout = 0 V (fet OFF)
That is not a current limiting resistor. It is a shunt to get a current signal
It's a very common circuit, actually. I have one in my hand right now that uses an ATmega32U's DAC to control the positive input to the op-amp so that the current level is variable. I verified its operation from 1uA to 2A with an 8.5 digit HP3458A.
Ok. I thought you said it was a resistor.
A shunt is a resistor.
Can you post the Reply# of the post where the OP describes the current shunt you were talking about . I couldn't find it.I know what a shunt is. We use them here at work all the time but they are not ordinary resistors. The are made out laminated copper with a plastic mounting base. (and expensive)We never call them resistors. We call them shunts because if you know what that is you know it is a special form of resistor.
How did you deduce so much about the OP's circuit when none of that is mentioned ?(no mention of shunts, operating in the linear region etc etc etc) There's certainly no code posted and the schematic is not what you describe (whether you are right or not, that is not what the schematic shows). I'm interested in building a circuit like that. Can you post a link to an example project that includes a "REAL" schematic and code ? (I also use ATtiny85s which I would think would be ideal for that application) I built my own ATmega328/ATtiny85 Programmer board.
Incidently, the schematic on page 9-2 of the tutorial on LDO's shows a circuit similar to the comparator circuit the OP posted, with the exception that it has a voltage divider for -V input, and also the comparator drives a Gate drive device for the fet. I don't see a shunt there but the circuit is very similar. I haven't read it yet because I'm at work. I'll check it out tonight.