I got a L317T voltage regulator. I connected it to a 12V input, but the output which i get is only ~0,32Volts instead of ~5Volts. Why is that happening. Its not a problematic regulator. Every one of them did the same thing. With or without the capacitors, the regulator gave me a very low voltage
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1\$\begingroup\$ Sounds like bad design or fake parts. Either way, you'd need to post a schematic of what you did showing your load and all components. \$\endgroup\$– Andy akaNov 22, 2020 at 17:49
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\$\begingroup\$ That cannot be answered until you post which external resistors and capacitors you used, and how you connected them. \$\endgroup\$– JustmeNov 22, 2020 at 17:51
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2\$\begingroup\$ There's the error. You need external resistors, otherwise the LM317 will not know what its output voltage is. \$\endgroup\$– StarCatNov 22, 2020 at 17:53
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2\$\begingroup\$ Your schematic is from a 7805. This is completely different to a LM317. Read the LM317 datasheet (chapter 9) to see how to set the output voltage. \$\endgroup\$– StarCatNov 22, 2020 at 17:55
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1\$\begingroup\$ OK, bad design then. Not all biscuits are chocolate although I wish they were. \$\endgroup\$– Andy akaNov 22, 2020 at 18:05
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3 Answers
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The circuit is for 7805 regulator. An 317 won't work in a circuit meant for 7805.
In addition, regulators need input and output capacitors, they won't work stably if you leave them out on purpose.
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The three terminals of the LM317 are \$V_{in}\$, \$V_{out}\$, and \$Adjust\$. The terminals of the 7805 are \$V_{in}\$, \$V_{out}\$, and \$Gnd\$. The \$Adjust\$ pin of the LM317 should be biased. But the ground pin of the 7805 should be grounded. (Also, as mentioned in comment below, the pinouts of the two devices are not compatible.)
answered Nov 22, 2020 at 19:11
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1\$\begingroup\$ Good to mention the pin difference, but also the pinout is not compatible in any way. So on contrary to what you said, adjust is not grounded. 7805 has in/gnd/out, while 317 has adj/out/in so in that circuit 12V has been applied to adjust pin while out is connected to ground. \$\endgroup\$– JustmeNov 22, 2020 at 21:02
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\$\begingroup\$ D'oh. You are right. Edited my answer. \$\endgroup\$ Nov 22, 2020 at 22:32
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LM317 is adjustable regulator. Voltage divider,two resistor is must. It keeps 1.25 volts between VOUT and ADJ pin.
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2\$\begingroup\$ It does not keep 1.25V on adj pin. It keeps 1.25V between Vout and adj pins. There is a big difference. \$\endgroup\$– JustmeNov 22, 2020 at 21:04
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