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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National Semiconductor

The current limiter is intended to limit the amount of ground leakage. Note as well that the actual circuit ground is on the top side of R1 – Vout is the ground datashee for the purpose of this circuit. The trip point is intended to be no higher than ohms per volt – 10k. So for low currents, it might be delivering more-or-less constant current at 0.

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. A couple of resistors and a comparator with built-in reference would do the job in a much simpler fashion. R1 represents the ground impedance – the goal is to detect when it’s value exceeds 10k. Spehro Pefhany k 4 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.

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. 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. 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.


I’d like to measure the voltage drop and light an LED really an optoisolator when it exceeds a threshold. If the load impedance is low, then the current will hit the limit. 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.

Datasheet «LM334»

Furthermore, I think it’s rather crazy that you allow such high ground impedance 10k. At least, that’s my thinking at the present. Post Your Answer Discard By clicking “Post Your Answer”, you acknowledge that you have read our updated terms of serviceprivacy policy and cookie policyand that your continued use of the website is subject to these policies. Please edit your question and delete the comment.

In the schematic, I1 represents the LM The LM in this case does not have an infinite voltage with which to overcome the load impedance. Sign up or log in Sign up using Google. I have an LM based constant current source configured to supply a max of 1 mA.

All of that is true. Any real current source will have a voltage limit beyond which it will not deliver a constant current. The comparator could be something like half an LM Tyler Think of it rather as a current limiter. Can R3 be replaced with an opto-isolator diode and series resistor? One option would be a TL or LMV, but that’s just one of an almost infinite number of possibilities. If the load impedance is high, then the current will be much lower than the limit.

Nov 13 ’15 at 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.

How to tell when an LM is limiting the current? If that current doesn’t flow, then that’s an error. Remember that this circuit must act appropriately during faults – and then the LM is a short.


LMM Datasheet(PDF) – National Semiconductor (TI)

Sign up using Email and Password. The actual earth is on the far side of R1.

I need to use an opto between this circuit and the logic systems for safety. The divider produces about 0.

The load has a variable impedance. Kuba Ober 1, 10 The intent now is to connect the output to ground and measure the voltage drop across it instead. By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service.

If it is a “constant” current source, why is the current “variable”? The simplest way to detect that would be by biasing a PNP transistor with a scaled-down version of the drop out voltage. Othewise, the load is datqsheet the maximum voltage that the source can provide, and is not running at full current.

The typical performance is shown in the datasheet in this graph: The typical performance is shown in the datasheet in this graph:.

I don’t see a way in circuitlab to represent an actual LM, so the simulation likely won’t operate correctly. You can increase the resistance of the divider if you can use a larger load resistor Lj334m or a higher-gain transistor.

The reference could be derived datahseet a regulated supply voltage such as 5V with a voltage divider. A small current from an AC supply is intentionally “leaked” to ground. It’s also intended to at least attempt to desensitize the circuit to the tolerance variation of the k resistor and the supply voltage. The detection threshold would be something like 1V.