Experimenting with Voltage Regulators

Thread Starter

q12x

Joined Sep 25, 2015
1,694
- In the next few days, I will concentrate on building a couple of circuits using Voltage Regulators. I have only 2 models, LM317 and AMS1117. Also a few scrapped as well and they may be fixed voltage ones. But mostly I will use these 2.
I already compile a list with all the ccts they show in the datasheets from different brands. VoltageRegulatorHandbook I didnt look inside All of them yet. Only in 1 and all the ccts were copied from datasheets, maybe 1 was different. I have the rest to check as well.
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- So, in my little quest here, I want some more consecrated circuits, your ideas, your experience and knowledge to hint me with more interesting tweaks or even circuits that they dont show in the datasheets themselves.
- I will start with a few to make, and on the way, I will post each of them and everyone is free to intervene to tweak them, or repurpose or test some things we all never thought of. This will be an Experimental thread. Also, be free to add anytime, your cct that you build it in the past and worked for years or at least awhile, ideally different from the ones that are already posted.
Thank you and stand by.
 

crutschow

Joined Mar 14, 2008
34,465
Here's an interesting dual tracking regulator (LTspice sim below) that has an output adjustable to 0V, and uses an LM317 and LM337s so that both outputs have desirable over-current and over-temperature protection.

U3 LM337 (which can be an LM337L type in a small TO-92 case) provides a -1.25V reference for U1's pot, which allows both outputs to be adjusted to near 0V.
If that is not needed, then U3 can be eliminated and pot U5 connected to ground.
In that case the minimum output magnitudes will be 1.25V.

Edit: If a different voltage is desired at each output, then a pot could replace R3 and R6 with the wiper to U6, to adjust for the desired difference.
You could also add switch to select between balanced and unbalanced output.


1705183330985.png
 
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MisterBill2

Joined Jan 23, 2018
18,589
While experimenting with regulators you may happen to demonstrate what goes wrong when those close-connected bypass capacitors are left out. The oscillation can be quite impressive.
 

LowQCab

Joined Nov 6, 2012
4,075
I'm well aware of that, that's why it'a big-fat FET.
Anything else is a SMPS.
I didn't thing that's what this Tread was about.
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Thread Starter

q12x

Joined Sep 25, 2015
1,694
Sorry guys... like in my previous post, I had elementary problems with my LM317's !
I start to believe my LM317 are some reboots-damaged or out of specs, partially operational, but only for very low loads, like IC's or very light current circuits.
If Im loading them with a coil -motor or relay- they dont regulate anything ! What a disaster for me...... and I didnt know this thing at all, I had to hit a hard wall with them to get to this conclusion !
I wish I could had a GOOD one as yours to actually compare it side by side.
In a certain percentage, I am thinking maybe Im still doing something wrong !
I really am very uncertain if they are good or bad. They seem to work fine, but under a certain load current. I didnt determine what that value is yet. But is definitely under 1A.
Thank you for testing yours !
 

dl324

Joined Mar 30, 2015
16,943
I really am very uncertain if they are good or bad.
Where did you acquire them? If they reputable distributer/reseller, it is quite possible that they're rejects/trash.
They seem to work fine, but under a certain load current. I didnt determine what that value is yet. But is definitely under 1A.
If you have at least a 10mA load on them, they should regulate. Whether they can provide 1A depends on the power being dissipated by the regulator. Thermal protection will be activated if junction temperature is too high.
 

Thread Starter

q12x

Joined Sep 25, 2015
1,694
To determine at which current load they are actually working, I need a Current Load Circuit but Im not that good or experienced with these kind of devices. I saw some interesting toys for this very purpose, but... I would prefer to make it myself. I dont need the greatest precision, just to be in the ballpark and is good enough.
See if you can find some affordable (doesnt matter how complicated it is) Current Load Circuit for me, please. Ideally with some precision dial or display of some sorts. Probably dial or jumper will be the most affordable to make.
Thanks.
 

dl324

Joined Mar 30, 2015
16,943
See if you can find some affordable (doesnt matter how complicated it is) Current Load Circuit for me, please. Ideally with some precision dial or display of some sorts. Probably dial or jumper will be the most affordable to make.
Here's something I've been thinking about breadboarding. No precision dial or display. You measure the voltage drop across R6 to determine current:
1705361574509.png
As drawn, it will let you set a current up to 2A 4A. Can load test sources down to 1V or so, but the opamp needs its own 9V supply.

EDIT: corrected arithmetic error
 
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MisterBill2

Joined Jan 23, 2018
18,589
In any power supply there are other things that will affect the operation, and that includes connections and clip leads. A while back somebody had a terrible voltage drop problem and it was caused by a very poor quality clip lead. So before you blame the parts verify that every connection is adequate. Connections often do matter a lot.
 

Thread Starter

q12x

Joined Sep 25, 2015
1,694
Here's something I've been thinking about breadboarding. No precision dial or display. You measure the voltage drop across R6 to determine current:
View attachment 312796
As drawn, it will let you set a current up to 2A. Can load test sources down to 1V or so, but the opamp needs its own 9V supply.
Excellent ! and thank you very much ! I will make it.
In any power supply there are other things that will affect the operation, and that includes connections and clip leads. A while back somebody had a terrible voltage drop problem and it was caused by a very poor quality clip lead. So before you blame the parts verify that every connection is adequate. Connections often do matter a lot.
Yes, like I mentioned already in my other post, the wires on the breadboard got warm (to hot in some late tests, where the plastic started to melt) and also the clips were warm as well !
In all my other tests I did over the years, I never encounter such a problem like with these LM317. I believe is the chip itself that is misbehaving, influencing perhaps everything around it.
 
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Because of post 7.......
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yeah, understood, but that huge voltage drop really shouldn't be done with a linear regulator. A common strategy is use a switcher to drop most of the voltage, and then, if you need low noise power, cascade a linear regulator (LDO or emitter follower structure)
 

LowQCab

Joined Nov 6, 2012
4,075
Sometimes there are convenient methods of getting rid of Heat,
that are much less expensive, and time consuming, than designing and building a SMPS.
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Thread Starter

q12x

Joined Sep 25, 2015
1,694
Instead of burning all that energy in the power transistor, why don't you use an off-line switcher or a buck converter for the big voltage drop?
Interesting ideas. I may add a wire transformer as well to drop down to 1.5V directly.
- The thing is, for all of them, I dont have them, for the task specific of 1.5V drop. And the drop is not that high, is from 5V DC and in my head it should have worked with my LM317. On another hand, I dont have the knowledge to build buck converters specifically to 1.5V. And if you tell me to buy them, well, I will a few in the future, since I have none in my hands, but it will be very cool to be able to build them as well, from a lot of scrapped components I have.
- I never heard of off-line switcher ! This is my first encounter with them. Or [off line regulator] in wikipedia pages where I read a very short description and by "off the mains voltage line" part of their explanation I believe they refer to the off as "from" or "directly" mains voltage line. Very interesting and is a chip. It will be interesting to be able to build circuits with them.
 
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