LM317 voltage drop problem in constant current configuration
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ajay.chakkaravarthy 2 months ago
Hello peeps, I have been working on a 10mA constant cource that supplies atleast 5V at output. I have been using the LM317 regulator for creating the constant current source of 10mA but the voltage drop is too high. I read in the datasheet of LM317 that it has a 1.25V drop. I have been using a 9V DC input. I have attached the datasheet for LM317, the spice models I have created as well for your reference. It would be great if anyone could help me sort out the problem. I need to arrive at a circuit that outputs 5V at 10mA. Any help and comments are appreciated much. Thank you![Capture.png](//image.easyeda.com/pullimage/dxGWDwGZvG8qRRFYWA4CTFNNn9aCy6pPvvH4TC1e.png)![wrgwreg.png](//image.easyeda.com/pullimage/BnOKyvbs33M5pgG00BN2PzDWAP1fHpUAvu0U5ZIc.png)[LM317 Datasheet](https://www.ti.com/lit/ds/symlink/lm317.pdf?ts=1627362262969&ref_url=https%253A%252F%252Fwww.google.com%252F)
andyfierman 2 months ago
You have posted no links to your spice model, only two screenshots and a link to a datasheet. Your schematic has no net labels so it is not clear what voltage you are probing in the lot screenshot. You appear to be working in LTspice and not in EasyEDA. I can answer questions about LTspice but depending on the complexity of the enquiry there may be a fee for advice given as this is outside the scope of the EasyEDA free support. EasyEDA has dedicated, in-house models for a range of voltage regulators including the LM317: ![image.png](//image.easyeda.com/pullimage/DzDluCVIqwb71UQP6JNFOOZX680UZP5w5NrsPvha.png) "I read in the datasheet of LM317 that it has a 1.25V drop." No. You misunderstand the data sheet. The device requires a voltage between the OUT and ADJ pins of 1.25V and a minimum voltage of 3.0V across the IN and OUT pins. Please study the datasheet carefully and pay particular attention to sections 8.4.1, 8.4.2, 9.2.1 and 9.3.7.
andyfierman 2 months ago
Please refer to this project to see a demonstration of the EasyEDA in-house model of the LM317 in a constant current and a constant current circuit: [https://oshwlab.com/andyfierman/easyeda-lm317ee-spice-model](https://oshwlab.com/andyfierman/easyeda-lm317ee-spice-model)<br> <br> To get up to speed with using simulation in EasyEDA please read the [Simulation Tutorial](https://docs.easyeda.com/en/Simulation/Headings/index.html).
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