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# 100mA current sensing circuit limiter

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Please i need your help. I am to design this circuit to be able to produce an 100mA at the output as i reduce the load resistor from 1k to 0Ohm. I am having problem on how to go about it for my current circuit keep given me a 1A or more at the output even as the load resistor is at 0Ohm.

i vary the load resistor from 1k to 0hm but the maximum current i am getting is 1.9A through 0.1 Ohm. I only required 100mA current when the load resistor is at 0 Ohm.operational-amplifiercircuit-analysisanalogcurrent-limitingShareCiteEditFollowFlagedited 2 hours agoasked 3 hours agoikenna1111 bronze badge New contributor

• 21) You need to show the complete circuit, this is only part of it. 2) be more clear about the function of this circuit, is it a constant current source or something else? 3) how is it supposed to work, I do not mean “it needs to limit the current” but how would that happen? Like: a voltage develops across a sense resistor, that voltage is amplified by … and then, when larger than … pulls a current from … which means the transistor … gets a smaller Vgs and that limits the output curent. – Bimpelrekkie 3 hours ago
• 3Could you please turn off the grid and post a higher resolution image? The current image is very hard to read. – ScienceGeyser 3 hours ago
• 1Your schematic looks like it has measles and is anemic. i.stack.imgur.com/PEfj0.png If you do not define the design specs , what do you expect? – Tony Stewart Sunnyskyguy EE75 2 hours ago
• 1Draw a block diagram .. Input levels, Differential gain Amp, FET (which one is output?) Current sense amplifier and overall gain constant Amps/Volt – Tony Stewart Sunnyskyguy EE75 2 hours ago
• I read your schematic and guess what you are doing is the following: (1) MOSFET is the driving transistor, (2) 0.1R is the current sensing resistor, (3) The two opAmps form a current mirror and negative feedback to make the MOSFET driver current constant, thus making a constant current source or current limiter. The CCS circuit is OK is general. But you need to understand the basic principles before you can troubleshoot. I would recommend the a couple of CCS articles for you to refer to, so we can have a command ground and terms to explore how to debug you circuit, / to continue, … – tlfong01 1 min ago   Edit
• (1) LED Constant Current P. MARIAN electroschematics.com/led-constant-current (2) The Basic MOSFET Constant-Current Source June 06, 2016 by Robert Keim allaboutcircuits.com/technical-articles/… (3) Current Mirror BJTs Chapter 4 – Bipolar Junction Transistors allaboutcircuits.com/textbook/semiconductors/chpt-4/… (4) LM134/LM234/LM334 3-Terminal Adjustable Current Sources ti.com/lit/ds/symlink/…. Cheers. – tlfong01 1 min ago   Edit

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