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JMS

:) Voltage Regulator Help :)

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I just fabricated a very primitive voltage regulator over the weekend and it works (many thanks for THIS forum!)but it's not 100% of my work. :(

It consist of a Dimension Engineering DE-SWADJ and a LM7805 v-reg.

As we know those LM78XX v-regs are not always the greatest because of heat issues which causes inefficiency, but I had a few kicking around. ;) Anyhow so now I was thinking of using a 12 volt LDO http://www.st.com/stonline/books/pdf/docs/9035.pdf with a pot at the end to have the option to change the voltage to a lower/higher setting. This way if I decide to change cameras, I can adjust the voltage accordingly to the camera volt specs. Is this possible? If so do I use a surface mount pot like a Vishay TSM43 http://www.vishay.com/docs/51045/tsm43.pdf?

Oh BTW... on the DE-SWAD, what type of capacitors are those? Also do you know what the other component is? It has a marking of 470. Is it a micro voltage regulator as well? :huh:

Thanks in advance!!! :D

post-6-1176422083_thumb.jpg

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How do you intend to connect the pot ? can you explane/diagram.

Terry

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Mark:

Thanks for the info! You don't know how hard I tried to find that info on my own, with no success of coarse. :( So which is why I came to you guys for help. Takes me days and you a second!!!! :)

Hmmm now that you mentioned the unshielded part from your observation, I have heard complains about signal interference and servo glitching possibly from these DE V-regs. For what it's worth, how do you shield it?

Terry: Well I was thinking of the placing the pot on the output of the LDO. If I guess correctly on the (+)output I would have it connect to the pot. A common pot has 3 pins right? One (+) in, then one to (-) and the third one to (+) out which is variable?

Just a quick word.....I realize this kind of stuff is preschool to you HIGH CALIBER guys, but for me it's a new learning curve. Learning this stuff from fabricating PCB, understanding v-regs and how to apply it... etc. I'm loving every second of it and this beats my day to day routine stuff! Thanks to you awesome people at RC-CAM forum! I wish to tackle chip programing and how to apply it after I graduate from this v-reg project. :D

John Lee

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Remember that the pot can only carry very low current and the voltage output will change as the load varies. You need to use the pot to adjust a variable voltage regulator and not use a fixed one. A circuit diagram would be good to make sure we are on the same track.

Terry

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To shield it.. buy a shielded one :P

If you check the spec document for the vreg (i'm assuming that its an adjustable one.. not a set voltage) you will find that you can vary teh resistance on the centre pin to change the output voltage. The spec has diagrams which should be pretty easy to follow :)

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Ok guys, I will make sure that I choose only a variable volt reg and make sure that the pot can handle the current. I will follow the diagram as recommended by the manufacture of the v-reg on how to apply it, thank again guys!!!!!!!!!!!!!!

Mark: Ohhh mannnn you mean there's a shielded inductor :blink: ? Hey I was expecting something more complicated! :lol: You definitely gave me a chuckle when I read your reply!!!! :lol::lol::lol:

Thanks again for the help!!!

John Lee

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JMS,

Here's a nice website with info on variable resistors on the bottom half. It should make it clearer what the pins are and which you should use.

http://www.st-andrews.ac.uk/~jcgl/Scots_Gu...art2/Page2.html

It's also worth noting that there are two types, liner and logarithmic, which define how the resistance increases as you move the move the wiper across the pot. For your application you would probably want a linear one to make it easier to set.

Don't forget that the vibrations inside your plane could slowly change the setting over time. You used to be able to get some trim pots that you could drip wax onto once they had been calibrated to prevent this, but I've just had a quick look and couldn't find anything like it. The wax stops it moving over time, but you can break the seal if you need to change it later.

Si

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Mark: OUCH! That hurts looking at your picture! :o:o:o

Si: Thanks for the valuable link and your experience regarding the wax trick! I like the wax idea over Lock Tite since wax will not do damage to anything sensitive! Very cool! :D:D;)

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sure you were looking for voltage regulators?!

:lol::lol::lol::lol: LOL

HEY BELIEVE ME MARK!!! I was looking for volt regs! :lol::lol::lol:

Ohhh I stepped in doggy doo doo and opened myself for that one! :lol:

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I'm attempting to power the Airwave 633 TXs at 3.3V and RFI on switchers bugs me too. So I'm thinking of using a LDO linear regulator on a low input voltage instead.

As a test, I dropped a 640mA load across a NTE1904 3.3V Linear LDO Regulator and powered it with a single cell LiPoly (4.2V fully charged). The NTE1904 was mounted vertically (stuck in a breadboard) without a heatsink. I took temperature measurements at 5-minute intervals with a Fluke 61 IR Thermometer at 2". Room temperature was 70F and the air was static. After 10 minutes the chip leveled off at 81.5F (11.5F over ambient) and stayed there for the 20-minute duration of the test.

Given the informal testing I did at input voltages of 8.4V and 5.5V, I believe that a linear regulator may run too hot unless in constantly moving air. It may be an option worth considering at an input voltage of 4.2V if one, like me, doesn’t like introducing the potential for RF interference with a (albeit more efficient) switching power supply.

Before I finalize my AWM633 PCB design, I’d like to know if anybody here is powering their AWM633TX with a linear regulator?

Jeff

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I've actually just re-done my power in the plane.. had two 5v vregs for the 631 and OSD. Going 3S -> 5v -> 3.3v doesnt get them to the point where they burn you instantly if you touch them. Put heatsinks on them and its not too bad at all.

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Yeh, no problem with the 631... but the 633 is a whole other story!

Or did you mistype that one? I guess so, the 631 is 5V :unsure:

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the 631 is 5v.. i have 5v going to it. For the 633 i use the 5v which would have gone to the 631 and give it to the 3.3v vreg instead ;) It seems to split the load out a little bit better.

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Just to put some numbers to it... at 5.5V the NTE1904 rose to 108.5F (42.5C) in three minutes. I didn't push it past that. That should be OK with a heatsink and perhaps outside of the fuselage.

I was hoping to design a PCB without a heatsink and keep it exposed to air (relying on the AWM633 to self cool). :rolleyes: If I mount the VReg upside-down, it can be folded over and attached to a piece of brass or aluminum that is laid across the top of the AWM633. Sort of like a heatsink sandwich (heatsink, component space, PCB).

The heatsink only adds the option to use 5.5V rather than a single LiPoly cell. So perhaps IT should be an option. Just thinking...

Jeff

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