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20 votes

This LM317 diagram doesn't make any sense to me

The datasheet has a pretty thorough description of the use of the ADJ pin with \$R_1\$ and \$R_2\$: Since both \$R_1\$ and \$R_2\$ appear in the equation for the output voltage $$V_{\text{out}} = 1....
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17 votes

This LM317 diagram doesn't make any sense to me

Overview I'll avoid depending upon algebra as an explanation. (Because algebra, while providing quantitative answers, doesn't often help people understand something unless they are very fluent with ...
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15 votes
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Smartest way to use current limit using LM317?

See LM317 based power supply with current limiting on SE and alexan_e's answer. Read through all the answers and comments as there were some good suggestions. The circuit avoids high-current pots by ...
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  • 161k
12 votes

LM317 µA Constant Current source possibility?

Yes, that is clever, I think it would 'work', however the problem is that Iadj is 50-100uA so that you will not be able to get an accurate load current. First, it is large, so your 200uA current might ...
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11 votes
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LM317T with weird pinout?

Neither of your circuits is correct. The correct circuit looks like this: simulate this circuit – Schematic created using CircuitLab If you connect it incorrectly (as in the first circuit) it ...
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11 votes
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12 V lead acid charger with LM317 not charging

Read the datasheet of the LM317, on page 9 it states: So when you feed the LM317 14 V it can regulate to 11 V and lower, not 13.5 V. Also there will be 1.25 V across R1 so for 13.5 V you will need ...
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10 votes
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LM317s in parallel connection

Yes, it is possible. Do not connect the outputs directly together but rather put a small resistor (0.5 Ohm or so) between each output and the summing node. Check: http://www.ti.com/lit/ds/symlink/...
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10 votes
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Does the LM317 take ANY voltage and convert it into the adjusted one?

The 317's valid input voltage range is from a minimum of 3 V above its programmed output, to a maximum of 40 V (32 V for some types). Within that range, it will provide approximately the programmed ...
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9 votes
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LM317 intermittent current source

To drive 50 mA through 330 ohms, you need 16.5 V. For 50 mA through 1330 ohms you need 66.5 V. In the constant current mode, the maximum output voltage of the LM317 circuit is \$V_{in} - 3\ {\rm V} ...
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8 votes

Making LM317 output voltage adjustable down to 0 V

To get the LM317 down to zero volts you need to bring the control pin down to -1.25 V. Figure 1. This dual LM317 circuit consists of a current limiter based around LM317(1) and a voltage regulator ...
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7 votes
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Purpose and explanation of resistor near output of LM317, high-current, adjustable-regulator circuit

Note A says the minimum load current for this circuit is 30 mA. If the circuit will not always have a load of 30 mA or more, you need a resistor there to draw 30 mA and satisfy the minimum load ...
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7 votes

LM317 voltage regulator with high current boost by 3 npn transistors

Although I've not specifically attempted a \$15\:\text{A}\$ boosted LM317 before, this is along the lines of what I'd try out first. This is roughly taken from the Figure 23 you mentioned: simulate ...
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7 votes
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Solar charger in commercial application based on an LM317 IC

Since you say this is for a comnercial product, I'll be up front about this: Given the choice between buying your product with an LM317 regulator or a product from your competition using the LTC3652, ...
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  • 59.8k
7 votes

Why is this LM317 giving an unexpected output?

LM317 is transparent to AC currents produced by switching power converters. The spikes produced by the charger go straight through the LM317 into the clock circuit, and easily overpower the crystal ...
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6 votes

Making LM317 output voltage adjustable down to 0 V

A somewhat nasty solution is to place two silicon diodes of suitable current rating in series with the LM317 output (after the voltage-setting resistor divider). This would reduce the output voltage ...
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6 votes
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Why does LM317 burnout when output is shorted in this case?

When you short the output, Q1 heavily conducts and basically connects pin 1 (ADJ) directly to 0V. Between Vout and ADJ internally is a 6V zener diode and a 50 ohm resistor: - It's very likely that ...
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6 votes
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LM317 Sealed lead acid charger

You don't need U1. Both U1 and U2 have the same nominal current limit. Just readjust R1. You don't need D1, with its variable voltage drop, but in its place, you would need a diode from U2 out to U2 ...
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6 votes
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LM317 power regulator ajust is affected by MAX485 chip

According to MAX485 datasheet, for DIP/SOP packages the ground goes to Pin5, and +5Vcc goes to Pin8. You seem to have the chip powered upside-down.
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6 votes

This LM317 diagram doesn't make any sense to me

Figure 1. As suggested by the datasheet. The LM317 works by adjusting its output to be 1.25 V above the voltage at the ADJ pin. With R1 = 240 Ω there is a current of \$ \frac {1.25}{240} = 5.2 \...
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  • 161k
5 votes
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LM317T not working properly?

It's a linear regulator. It can only decrease voltage, cap it, as you've said. It is working appropriately as you've described it. If you want to be able to go up or down from the input voltage you ...
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  • 11.6k
5 votes
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Linear Power Supply Advice

No, this won't work to give you +/- supplies, because of the common negative rail. You can, however, use the transformer you have to give you +/- adjustable supplies by using two half-wave ...
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5 votes
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Cheap switch-mode regulator "comparable" to LM317

Here is a quite short list of TI's Buck/Boost converters which have PDIP packaging. There are only 2 of 33 DC-DC converters which are available with though-hole package , and the only difference of ...
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5 votes

Cheap switch-mode regulator "comparable" to LM317

I would take a close look at the National Semiconductor (now TI) LM2575 family. Very, Very easy to use. LM2575: 1 Amp buck converter LM2576: 3 Amp buck converter I would suggest a couple of ...
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  • 22.7k
5 votes
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lm317 current source

True, but irrelevant in your case. An LED does not change forward voltage quickly- there is a slow (thermal) change, but nothing on the order of microseconds where the caps have some effect. The caps ...
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5 votes

Puzzled with the result of LM317 constant current

If your LED lamp assembly is 10W at 900mA it needs about 11.1V to operate. The LM317 current source needs 1.25V in the resistor and a further 3V headroom to operate, put it all together and your ...
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  • 27.2k
5 votes

High Side Constant Current Source

You can use this idea: - The voltage across R1 sets the voltage that is forced across R2 by the op-amp's negative feedback. Let's say that voltage is 0.1 volts and let's say R2 is 1 ohm. This means ...
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  • 389k
5 votes
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multi-tap transformer relay for LM317 tips

simulate this circuit – Schematic created using CircuitLab Figure 1. Transformer tap selector. This isn't a complete answer but will give you some ideas to work on. Whatever electronic ...
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  • 161k
5 votes
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LTspice model for LM317 and the calculators gives different output voltages for the same resistors values

The correct nominal voltage according to datasheet calculations is 9.138V (min 8.775, maximum 9.50 resulting from the reference voltage tolerance, ignoring resistor tolerances and adjust current ...
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5 votes

Voltage drop with 2 LM317 in parallel/different output voltages

Since the outputs are independent 5.1 V and 4 V supplies then the LM317s know nothing about each other. Each device needs a supply that is 2.5 V higher than the output so one needs ≥ 7.6 V and the ...
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  • 161k
5 votes
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Is it safe to charge Lithium Ion battery directly with a 4.2 volt supply?

Not a good idea - Li-Ion batteries really need a proper CC/CV charger. Switching for a fixed voltage supply is not a suitable approach. The charging circuit shouldn't be dying after a month, unless ...
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