|
Terrazureus


Registered: 06/06/14
Posts: 88
Last seen: 7 years, 8 months
|
HELP, electronics question - LM317 voltage regulator circuit not working. why?
#20954792 - 12/09/14 08:21 PM (9 years, 1 month ago) |
|
|
hey guys i'm new to electronic circuits, but i thought i'd have a crack at making an adjustable voltage regulator. I have run into a problem that i don't know what it is, i was hoping someone here could help out. This is to control the speed of a 12v computer fan for a magnetic stirrer project.

possible problems that i can think of- -I think i have too high of a value for my resistors? i don't know how to do those calculations. R1 =560ohm R2=10k pot
-the C2 capacitor is 450v, i don't know if this is too high or doesn't make a difference? its all they had in the shop and the guy there said it shouldn't matter?
here's a pic of the circuit I've made, the horizontal lines are the conductive strips of the prototyping board. the input is 12v
--------------------
Edited by Terrazureus (12/09/14 08:27 PM)
|
Nodal
E=IR



Registered: 01/07/14
Posts: 42
Loc: Trapped in the 4th Dimens...
Last seen: 8 years, 10 months
|
Re: HELP, electronics question - LM317 voltage regulator circuit not working. why? [Re: Terrazureus]
#20955045 - 12/09/14 09:25 PM (9 years, 1 month ago) |
|
|
First, what is the problem? Is it not doing anything at all or just not what you want it to? Make sure the board is oriented the way you think it is and that the conductive strips don't run the other way. The output voltage for the LM317 is Vo = 1.25V*(1+(R2/R1))+Iadj(R2) where R1 is the 560 ohm and R2 is the pot. According the data sheet you should be within the 1.2 to 25 volt range. So other than double checking your wiring I would need the fan specs to find out for sure. Also, what is powering this? This is supposed to be DC right?
-------------------- My Magic Garden
Edited by Nodal (12/09/14 10:33 PM)
|
Terrazureus


Registered: 06/06/14
Posts: 88
Last seen: 7 years, 8 months
|
Re: HELP, electronics question - LM317 voltage regulator circuit not working. why? [Re: Nodal]
#20955368 - 12/09/14 10:57 PM (9 years, 1 month ago) |
|
|
thanks nodal. its just not doing anything at all. the board is oriented with strips going from left to right as in the pictures. the diagram is drawn to match the layout on the board
when calculating, what value is Iadj? and I'm not sure whether I calculate 560ohms as 0.56 and 10k as 10. would this be correct? vout= 1.25 (1+(10/0.56)) + Iadj x 10
I'm powering it with a 12v DC 300mA adapter. the fan specs are 12v 0.14A (is that what you mean?)
Edited by Terrazureus (12/09/14 11:01 PM)
|
Nodal
E=IR



Registered: 01/07/14
Posts: 42
Loc: Trapped in the 4th Dimens...
Last seen: 8 years, 10 months
|
Re: HELP, electronics question - LM317 voltage regulator circuit not working. why? [Re: Terrazureus]
#20955512 - 12/09/14 11:53 PM (9 years, 1 month ago) |
|
|
You will use the 560 and 10k and Iadj is the current coming from the adj pin (which is pretty much negligible). So my initial thought is maybe the fan isn't getting enough current so increasing the amp size of the adapter might be the answer, but I will try and figure this out and get back to you.
-------------------- My Magic Garden
|
koraks
Registered: 06/02/03
Posts: 26,670
|
Re: HELP, electronics question - LM317 voltage regulator circuit not working. why? [Re: Nodal]
#20955837 - 12/10/14 02:26 AM (9 years, 1 month ago) |
|
|
12V input is too little to allow the LM to regulate to voltages bove about 10v; it requires a voltage drop of at least something like 1.5v in order to regulate at all. Secondly, a fan like this won't start if the voltage is below 8v or 9v. Voltage variation is not a very useful way to vary fan speed; what you want is a pwm controller.
|
koraks
Registered: 06/02/03
Posts: 26,670
|
Re: HELP, electronics question - LM317 voltage regulator circuit not working. why? [Re: koraks]
#20955887 - 12/10/14 02:55 AM (9 years, 1 month ago) |
|
|
In addition: to get the circuit to work, it's important to know what the voltages on different places of the circuit are so you can figure out where the problem is. Start at the end, with the voltage across the fan pins to see if you get the output from the LM317 circuit that you'd expect. If not, start working your way backwards towards the power supply to see where the unexpected stuff begins; this greatly helps you to locate any problem.
But like I said above; varying the voltage isn't a very appropriate way to regulate the speed of a fan like this. A pulse width modulator (PWM) circuit is what you need. There are ready-made IC's for this. You generally need a PWM controller and a driver transistor to handle the power that the fan needs.This can be a very simple, low-power one like a trusty old BC107 if the power requirements aren't too high; otherwise you may need a 2N2222 or a 2N3081 or even a big transistor in a TO220 or TO3 package depending on power requirements, but then you'll probably need a driver for the driver as well (or a Darlington pair). For very low power applications, you may not need the driver, but a computer fan can easily draw 100~200mA and many of the smaller PWM controllers cannot deliver this kind of power, so look for a transistor that can handle at least 300mA and the total dissipation that your circuit demands of it.
|
Terrazureus


Registered: 06/06/14
Posts: 88
Last seen: 7 years, 8 months
|
Re: HELP, electronics question - LM317 voltage regulator circuit not working. why? [Re: koraks]
#20956040 - 12/10/14 05:07 AM (9 years, 1 month ago) |
|
|
thanks koraks, so I've measured the voltages across the circuit and found the following. I'm using an analog voltmeter that maxes out past 15v on the input.
--------------------
|
koraks
Registered: 06/02/03
Posts: 26,670
|
Re: HELP, electronics question - LM317 voltage regulator circuit not working. why? [Re: Terrazureus]
#20959857 - 12/10/14 10:12 PM (9 years, 1 month ago) |
|
|
Aren't you supposed to buffer r2 with a small cap in this circuit? Check the lm317 datasheeeet for the reference circuit, I'm pretty sure it requires a small cap there.
|
Terrazureus


Registered: 06/06/14
Posts: 88
Last seen: 7 years, 8 months
|
Re: HELP, electronics question - LM317 voltage regulator circuit not working. why? [Re: koraks]
#20959969 - 12/10/14 10:54 PM (9 years, 1 month ago) |
|
|
what do you mean by cap? this is literally the first and only electronic circuit I've attempted to make, so i don't know the lingo.
--------------------
|
koraks
Registered: 06/02/03
Posts: 26,670
|
Re: HELP, electronics question - LM317 voltage regulator circuit not working. why? [Re: Terrazureus]
#20960135 - 12/10/14 11:41 PM (9 years, 1 month ago) |
|
|
A capacitor. I don't think the value is critical; something like 1uF of 2.2uF would be fine. Anything between 300nF and 10uF would work I'd say. But like I said, have a look at the data sheet as it features circuits like the one you're making.
|
Seuss
Error: divide byzero



Registered: 04/27/01
Posts: 23,480
Loc: Caribbean
Last seen: 2 months, 20 days
|
Re: HELP, electronics question - LM317 voltage regulator circuit not working. why? [Re: Terrazureus]
#20991147 - 12/17/14 07:01 PM (9 years, 1 month ago) |
|
|
You don't show where you have the wiper on the 10K pot connected. It should be tied to the adj pin on the regulator (along with one of the other two pins on the 10K pot). The third pin on the 10K pot should be tied to ground (as shown).
> Aren't you supposed to buffer r2 with a small cap in this circuit? Check the lm317 datasheeeet for the reference circuit, I'm pretty sure it requires a small cap there.
The LM317 usually only requires two caps (these should be electrolytic caps and properly oriented in the circuit), one on the input side (0.1uF) and one on the output side (10uF) for stability. However, it is always best to check the datasheet of the specific regulator vendor being used.
-------------------- Just another spore in the wind.
|
Jean-Luc Picard
I only wish i was this good!



Registered: 12/30/07
Posts: 4,177
Loc: New Mexico, USA
|
Re: HELP, electronics question - LM317 voltage regulator circuit not working. why? [Re: Seuss]
#20994352 - 12/18/14 02:14 PM (9 years, 1 month ago) |
|
|
It looks to me like you have something going on with the 10k pot. If the ADJ pin is clamped to GND, you'll see ~1.2V b/w OUT and GND. From your drawing that shows the voltages, the 0V across the 10k pot and the 1.4V b/w ADJ and GND seem to suggest that this is the case. I would guess that the way you wired your 10k pot is reversed from what you would expect from it. Normally, turning the pot clockwise would result in an increase in output, as where you're circuit seems to be wired the opposite direction, where turning the pot completely clockwise results in minimum resistance at R2, driving OUT to a minimum voltage (1.4V).
Have you tried measuring voltages while turning the 10k pot?
Additionally, here is the typical application circuit from the datasheet

peace, agmotes165
-------------------- The universe is under no obligation to make sense to you - NDT
|
|