Wiring Up Lm1084 Regulators

Question

Hey everyone. Just making sure I'm correct on this, would this diagram be correct?  Thanks, Tech

Jeremie · Answer

Hey Tech, I can verify that it looks good!

Luis Vazquez · Answer

I have not used the 1084 but this is the wiring i use for 7805 I'm wondering why you are not using capacitors with the regulator between.  the blue bar at top will be ground and the red bar is regulated 5v.

Jeremie · Answer

Good call with the missing Caps @Luis The LM1084 does have a different pinout than the classic 7805, it's more like a LM317 pinout

Dunning-Kruger · Answer

I have soldered dozens of LM7805s into servo extension cables... all without caps... They seem to work flawlessly with pings and other 5v sensors I have been using. I have even used them with micro servos... Why do we need the caps?

Jeremie · Answer

Caps are used for input line filtering and keeping the output voltage stable (less voltage sag) when in high current demand situations.

Luis Vazquez · Answer

wow you guys are fast

Dunning-Kruger · Answer

I understand what a cap does... but with a device like a ping that uses such a low amount of current, would that still be an issue?

DJ Sures · Answer

You won't need a cap As an electrical engineer, jeremie is trained to make everything super stable. However, the device you are connecting to the LM1084 most likely has a filter cap of it's own - otherwise i'm certain it isn't a microprocessor that you're running so it'll be fine

Luis Vazquez · Answer

no that would be find to run the ping sensor with out the caps. but if you did use the caps then you could make a 5 v. break out because most of the other sensors will be looking for 5v. so you may can use it to power other such devices.

CardboardHacker · Answer

Hey guys... I use this setup, but there's hardly and light coming from lights I wired up. (Yes they do light up on 5V from another battery pack) Direct to the battery the lights are bright as day. Going from my science homework, do I need a resistor or something before the power enters the regulator? Any ideas?

Robot Doc · Answer

Use a voltmeter and measure the input and output voltages.

CardboardHacker · Answer

1V! I'm not sure why they there not regulating 5V! Amperage is 0.05 on output. Here's a link to where I was told to use LM1084's. DJ in second post. YAY or NAY for these regulators

Robot Doc · Answer

Here's what I just got on ebay. They're small so they don't take up much room, input 4.75 to 20 vdc, output 1 to 17 vdc @ 1.8 amps.

CardboardHacker · Answer

Thanks, but I want to figure out why these don't work. I found that the regulator has an ADJ mark on it, though the regulator on the ez-b v3 has a 5.0 mark instead. Could this be I got the wrong one?

thetechguru · Answer

Sounds like maybe you got something like a NTE1929 by mistake. They look about the same. I ordered an LM1084 from an ebay seller and wound up getting a TIP310C transistor instead. It was only like $1 so I didn't bother trying to return it. Alan

CardboardHacker · Answer

These definitely look like lm1084s...

CardboardHacker · Answer

Any ideas? Does everyone think I got duds? Or is there something related to the ADJ marking on them.

thetechguru · Answer

There is an adjustable version of the LM1084, and that is what you have.

https://www.ti.com/product/lm1084

"The LM1084 is available in an adjustable version, which can set the output voltage with only two external resistors. It is also available in three fixed voltages: 3.3V, 5.0V and 12.0V. The fixed versions intergrate the adjust resistors. "

My ability to read schematics is too out of practice to follow the diagram on that page, but apparently you use resisters to set the adjustable output.

Alan

Dunning-Kruger · Answer

@Tech... How Many do you need? I have some LM1084 (5V versions)... Just need your mailing address so I can mail them out to you....

CardboardHacker · Answer

Thanks Richard, but I'm not comfortable with giving out my mailing address. Thanks for the offer though. I guess I have to buy the right version this time.

Dunning-Kruger · Answer

No worries... I was going to give you them for free... If you want them email me at ryersonroofing(at)yahoo dot com

CardboardHacker · Answer

These look like the right ones, don't they? JK_Part ebay

Robot Doc · Answer

Yes, according to the ebay title, they would appear to be the ones you seek.

Jeremie · Answer

Hi @Technopro,

You could still use the adjustable version of the LM1084 if you have a few common resistor values and follow the pictured diagram:

Use a R2 value of 1kohm and an R1 value of 330ohms and it should give you a value of 5V. Equation is 1.25V(1 + R2/R1) = 1.25V(1+1000/330) = 5.04V

CardboardHacker · Answer

Thanks Jeremie, but I don't have any resistors or anything like that. I still have to order the diodes for those relays! I sure hope they are Robot-doc!

CardboardHacker

Wiring Up Lm1084 Regulators

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