# Questions tagged [lm317]

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### This LM317 diagram doesn't make any sense to me

So this is the basic wiring for an LM317 as a voltage regulator, and very little of it makes sense to me. First off, if one pin is for my adjustment, why do I need $R_1$? $R_2$ will give me just ...
5k views

### Problems controlling an LM317 with an op-amp

I have the following circuit, part of my LM317 digitally adjustable power supply. The problem that I have is correctly controlling the LM317 at U2: if I pull it's adjust pin to the ground, the ...
18k views

### LM317 Heat sink, how big?

Thanks to the help of a few of the other guys I have my AC to DC rectifier working, and the rest of the power supply working. Now while testing the power supply, my 18V AC transformer gets rectified ...
20k views

### Resistors values to use with LM317

I know that ratio R1 to R2 determine the output voltage of LM317. E.g. R1 = 200, R2=330 ohms will produce about 3.3V. My question is, what if I use 2K and 3.3K for R1 and R2? What is the impact of ...
4k views

### LM317 getting hot

Should an LM317 (specifically a TI LM317MQDCYR) rated for 500ma output current really be getting hot to touch when only pulling 170ma at 5V? Package is SOT-223, input is 9V. Is this normal?
25k views

### Smartest way to use current limit using LM317?

As i understand, using this circuit: Will cause the current to go right through the POT and resistor, which will generate a lot of heat. Is there a better way to use current limiting with LM317 ...
5k views

### LM317-based adj power supply output takes a while to stablize

I recently built-up a quick little LM317-based adjustable power supply schematic: However I've noticed the output can take several seconds (on the order of 10 or so) to "settle down" after turning ...
9k views

### LM317 µA Constant Current source possibility?

I want to create an adjustable µA Constant Current source using a LM317. It is typically stated to have a 5mA to 10mA minimum current for proper regulation. The On-Semi version linked above shows a ...
2k views

### How should I select the resistors for this constant-current application for a 317?

Over at OnSemi, they have a little doc about using a 317 voltage-reg as a current source: http://www.onsemi.com/pub_link/Collateral/AND8109-D.PDF Their final example, providing constant current to an ...
3k views

### Is it normal for LM317 to give a higher voltage without a load?

I just built a small 5.1V regulator with LM317, using 220 and 680 ohm resistors. However, I measure 8.6V at the output without a load connected. Is this normal, i.e. under a load (about 120 ohm) it ...
20k views

### Building a Battery Charger with an LM317

I was told that i could make a simple battery charger from a LM317 and a resistor to charge some Ni-MH Batteries. Can someone just expand on this a little such as how it works as I don't really ...
3k views

### How do I build the current regulator circuit referred to on the LM337 datasheet?

What I would like to accomplish: I am trying to add current regulators into a home built dual rail linear regulated power supply. I previously asked this question about transformer fusing and ...
2k views

### LM317 Train Power Supply

I am attempting to build a circuit to run my HO trains with a common rail. When I use this circuit LM317 works for a period of time then gets stuck at the input voltage (At that point the LM317 fails ...
3k views

### LM317 Resistor Values Performance

What is the performance tradeoff of using different resistors with the LM317. For example using a 300 Ohm and 400 Ohm resistor vs. using a 3k and a 4k resistor. Specifically I am interested in knowing ...
3k views

### LM317 running digital pulses. Results are Noisy

The set up of my experiment so far: A. I use a simple LM317 linear voltage regulator to supply constant voltage of +5V to Vdd of my Laser driver circuit. B. Also I use another LM317 linear voltage ...
13k views

### Making LM317 output voltage adjustable down to 0 V

I want to design a variable voltage regulator that will get from it`s maximum output (lets say 10V) down to 0V (or very close) considering the input as regulated 12V (from a PC power supply). All the ...
7k views

### Purpose and explanation of resistor near output of LM317, high-current, adjustable-regulator circuit

I'm trying to make a high-current, adjustable-voltage regulator using LM317 data sheets. Specifically, I am using the schematic below. So, what is the point of the resistor related to Note A? Is it ...
3k views

### Power Supply Diode Keeps Burning Out

I am trying to replicate the circuit I found here: (source: cogeco.ca) This is a photograph of what I have built: In my photo I have labeled one diode in the bridge rectifier which has burn out ...
6k views

### Cheap switch-mode regulator “comparable” to LM317 [closed]

I've always appreciated the LM317 linear power supply regulator for being a sturdy workhorse. In particular, it's easy to build a simple regulator circuit which "just works" using an handful of ...
13k views

### Potentiometer with LM317

I am trying to make an adjustable power supply with an LM317 and a potentiometer. The only problem was that there were some conflicting schematics online about how to connect everything. Can some ...
17k views

### LM317 to create constant current of 2mA?

I have a circuit where I want to have a constant current of 2mA through a variable resistor. I've been told that I could probably use a LM317 as a current regulator, with one resistor on the ouput. ...
36k views

### Add on/off indicator LED to circuit

I'm working on my first small electronics project; building a small LM317 based power supply. I've built the circuit as shown in the data sheet (black part of the circuit diagram below) on a perfboard....
2k views

### LM317 Sealed lead acid charger

I have a couple of Yuasa NPW36-12 12V 7.2Ah batteries from a phased out UPS unit. The batteries are barely one year old and have less than 100 charge cycles on them. I don't have a lead acid battery ...
1k views

### Controlling MOSFET's resistance using negative feedback

I wanted to use LM317 in a power supply project but wanted to control voltage digitally or with voltage. One possible way was to change one of the voltage divider resistors on the schematic below, ...
9k views

### Is this 7805-based design correct?

I found this design on internet: It is said to be a regulated power supply with variable DC output 5-15 V, 400 mA. My first question: Is this design around 7805 correct? I am asking because it doesn'...
3k views

### What's causing this high frequency ripple on the output of my LM317?

I'm using an LM317T to regulate 5 V to 3.38 V for a microcontroller. R1 is 330 ohms and R2 is 560 ohms. There isn't any input capacitor and the output capacitor is 470 µF 25V, because I ...
3k views

### LM317s in parallel connection

Is it possible to connect 3 LM317s in parallel to get upto 4A of current output ? I need 4A but I'm not able to figure out any other possibility. Is there any other possibility to achieve this ?
8k views

### LTspice model for LM317 and the calculators gives different output voltages for the same resistors values

I found LTspice model for LM317 in a very trustable recommended source, downloaded and simulated the following circuit: As you see above in LTspice for R1=240 and R2=1.5k the output voltage is around ...
17k views

### LM317 based power supply with current limiting

I'm trying to build my own Bench Power Supply but I'm having a hard time to find a good design (circuit/project) for it. Here are my requirements: Input: main using a 18V 2A transformer Output: 0-...
10k views

### How to protect LM317 from output short?

In the below circuit, the diodes protect the LM317 against both of the caps discharging into the IC when input or output is shorted. LM317 is itself capable of having it's output shorted without ...
11k views

### LM317 voltage regulator short circuit

I made this standard LM317 voltage regulator circuit: It worked as expected, but then I tried connecting a TDA2005 audio amplifier. I connected the LM317 to my audio amplifier as a power supply and ...
7k views

### What use are the transistors in this (LM317 based) power supply circuit?

I am looking to do a small bench power supply project and am studying various designs based around a LM317. Basic I know but I still seem to manage to have have some questions. Fig 22 on page 8 of ...
5k views

### How can I get more amps from a voltage regulator?

I'm a noob that is just getting started. I'm using an LM317T to generate 6V but I need a little more amperage. Can I just double my LM317T and resistors configuration and put them in parallel? ...
1k views

### List of LM Integrated Circuits?

Does anyone have / know of a list of all the LM integrated circuit packages available? The EE stockroom at my university recently reorganized and they cataloged several pages of part numbers without ...
22k views

### Simple LM317 variable voltage supply, does it limit current too?

I had wanted to build a power supply for so long, and had never really understood the calculations involving the LM317. I had found a kit (pcb+parts) online and it had renewed my interests in using it ...
3k views

### Why a diode to GND in 0-30V LM317 circuit?

I'm looking at reference design 9.3.1 from http://www.ti.com/lit/ds/symlink/lm317.pdf where a LM317 is used between 35V and -10V to obtain a 0-30V regulation. What is the purpose of the diode? would ...
9k views

### LM317 - bringing down to 0 volts (with a uC)

I am wanting to build a custom power supply for myself, and am having trouble understanding how to drive the adjust pin with a microcontroller. The datasheet for it is here: http://www.ti.com/lit/ds/...
1k views

### 12V lead acid charger with LM317 not charging

I have this circuit built and tested. I think this should work and charge the battery with 0.4A to about 13.5V. The Problem: it doesn't charge and between U1 and U3 (Battery) is a current of about 0....
301 views

### LM317 intermittent current source

I need a 50 mA current source despite the load value (resistor LOAD), and I need the current flowing just when the microcontroller says so. It works fine with LOAD = 0 ohm and IL = 50 mA, but when I ...
468 views

### LM317 potentiometer

I'm designing a voltage regulator using the LM317, and I've seen people using 2 different configurations when it comes to the potentiometer. I tested both on a simulator and on a breadboard, and both ...
13k views

### Two LM317 Based Voltage and Constant Current Regulator Circuit

I have read some articles on on the following circuit. I was wondering if I can create such a Voltage and Constant Current Regulator for my Power Supply or not. My Question is - is this circuit ...
3k views

### Practicality of this LM317T PWM Voltage and Current control circuit

Ive been trying to design a LM317T power supply with a PWM (Arduino MCU etc) adjustable voltage and current limit. After various circuits, videos and tutorials i have designed the following circuit in ...
327 views

### How to measure positive, negative and inbetween currents

I am making a variable +12V / -12V bench power supply, where I will have 3 output pins: 0- -12VDC | GND | 0- +12VDC, where I want to measure all possible voltages and currents. I will use voltmeters ...
1k views

### LM317, supply connected to output

I am designing a prototype 5VDC fan speed control unit. I am using an LM317 as a voltage regulator. This will step the voltage from a LiPo battery or arbitrary wall adapter down to 5V. Pulse width ...
1k views

### LM317 TO-220 heat sinking: Junction to case or junction to pad?

I have some LM317 ICs (TO-220) that I'm using on a power supply. I'm trying to figure out the heat sink values necessary to keep the IC under safe operation. All of my requirements are with 700 mA ...
98 views

### LM317 regulator with PNP pass transistor voltage drops when adding load

I'm trying to make a ~4V 2A regulator with the LM317. It works with minimal load but when I increase the load the voltage drops instantly to 3.4V. I'm not sure what's happening. I'm trying to build ...
2k views

### Eliminating negative output voltage in a LM317-based power supply adjustable down to 0V

I've been looking to build a linear power supply with current limiting and output adjustable down to 0V and I found this circuit in a LM317 datasheet.: So I've built it on a breadboard with minor ...
3k views

### How to improve load transient response of an LM317 voltage-regulator powering an audio amplifier?

I am building a voltage regulator circuit for powering a pair of mini-speakers (about 3-5W) with built in amplifier and an old mp3-player/FM radio. The power source is an old mobile phone charger (...