Programmable from 1µA to 10mA. □ ±3% initial accuracy. Description. The LM/LM/LM are 3-terminal adjustable current sources characterized by . LMM Texas Instruments Current & Power Monitors & Regulators NRND, alternate is LMM/NOPB datasheet, inventory, & pricing. LMM/NOPB Texas Instruments Current & Power Monitors & Regulators 3- TERM ADJ CURRENT SOURCE datasheet, inventory, & pricing.
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When it’s passing less than 1 mA of current, I would expect it to be acting like a very low-value resistor, meaning that the voltage drop across it should be low. When the 1 mA of current is reached, it should begin to increase its resistance, thus increasing the voltage drop across it. I’d like to measure the voltage drop and light an LED really an optoisolator when it exceeds a threshold.
At least, that’s my thinking at the present. If anyone else has an idea of how to light an LED when an LM is actually limiting the current through it, that would work too. In the schematic, I1 represents the LM I don’t see a way in circuitlab to represent an actual LM, so the simulation likely won’t operate correctly. R1 represents the ground impedance – the goal is to detect when it’s value exceeds 10k. From there, it’s just a matter of tuning either the set resistor of the LM or the voltage threshold to trim to the setpoint.
Note as well that the actual circuit ground is on the top side of R1 – Vout is the ground potential for the purpose of this circuit. The actual earth is on the far side of R1.
Any real current source will have a voltage limit beyond which it will not deliver a constant current. In the case of the LM, it is rated with a voltage drop of 2. The typical performance is shown in the datasheet in this graph:. So for low currents, it might be delivering more-or-less constant current at 0.
3-Terminal Adjustable Current Source
This will vary over temperature and from unit to unit, that’s what they mean by ‘typical’. So if you monitor the voltage across the LM perhaps with a comparator you can have a good idea of whether it is working or not.
If the voltage datasheeh more than 2. If it’s less than that it may or may not be working there is no minimum voltage below which is it is guaranteed to not work.
So if the LM is connected low side and sinking 1mA, and you want to know when the forward voltage drops below 1V you can use a comparator with a 1V reference. The reference could be derived from pm334m regulated supply voltage such as 5V with a voltage divider. The comparator could be something like half an LM At 25C, the LM has a minimal drop-out voltage of about 0.
Othewise, the load is getting the maximum voltage that the source can provide, and is not running at full current. l,334m
National Semiconductor – datasheet pdf
Home Questions Datasbeet Users Unanswered. How to tell when an LM is limiting the current? I have an LM based constant current source configured to supply a max of 1 mA. Usually when a current supplied less than the current required, there is a voltage drop.
LM from Texas Instruments
Nov 13 ’15 at I’d expect it to be minimal, however, since the should be trying to pass as much current as it possibly can.
If it is a “constant” dstasheet source, why is the dwtasheet “variable”? Tyler Think of it rather as a current limiter. If the load impedance is high, then the current will be much lower than the limit.
If the load impedance is low, then the current will hit the limit. The LM in this case does not have an infinite voltage with which to overcome the load impedance. The typical performance is shown in the datasheet in this graph: Spehro Pefhany k 4 All of that is true.
The question at hand is how best to detect when the voltage across the LM datashheet a threshold. It depends on GREATLY on how the LM is connected high side or low side, for example and how much your current is and how much error you can tolerate any monitor circuit will lower the output impedance.
One option would be a TL or LMV, but that’s just one of an almost infinite number of possibilities. It’s not possible to give a good answer without much more information such as a complete schematic and accuracy requirements. The detection lm3334m would be something like 1V. The circuit in this case is a Ground Continuity Monitor.
A small current from an AC supply is intentionally “leaked” to ground. If that current doesn’t flow, then that’s an error. In the old circuit, the output drives an optoisolator’s LED, but that circuit isn’t accurate or sensitive enough. The trip point is intended to be no higher than ohms per volt – 10k. The intent now is to connect the output to ground and measure the voltage drop across it instead. Please edit your question and delete the comment. It belongs in the question.
Kuba Ober 1, 10 Can R3 be replaced with an opto-isolator diode and series resistor?
I need to use an opto between this circuit and the logic systems for safety. Nope, it won’t work.
datasheef You need a different design, and I question the need for a current datasehet. A couple of resistors and a comparator with built-in reference would do the job in a much simpler fashion. The current limiter is intended to limit the amount of ground leakage. It’s also intended to at least attempt to desensitize the circuit to the tolerance variation of the k resistor and the supply voltage. Remember that this circuit must act appropriately during faults – and then the LM is a short.
So what you do is connect R2 directly between L and PE terminals. R2 completely determines the behavior of the system, when looked at from lm334, and sets the leakage current. Furthermore, I think it’s rather crazy that you allow such high ground impedance 10k. Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password.