TL750M08 - regulated power circuit...HELP

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bob332
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TL750M08 - regulated power circuit...HELP

Post by bob332 » Sat Feb 05, 2011 3:02 pm

i have some TL750M08 that a buddy gave me and i need to take ~12V in from i am pretty sure is going to be a wall-wart to power and arduino. i am dropping the V to 8V because of the heat that this project will be exposed to and i didin't want the arduino 5V regulator to overheat.

can the TL750M08 be used just like a LM7808, w/ a capacitor before and after it? also, what type of capacitor should be used - alumnium polymer, ceramic, electrolytic, tantulum ?? i have seen a circuit in the book i have 'practical arduino' and they call for a 780X, 100μF before and after the 780X, then a 100nF after the 100μF on the output side, and finally a 1n4004 in between the 2 100μF surrounding the 780X. is this overkill? is it a good design? it seems every data sheet and circuit w/ a 780X i see has different capacitor ratings. for anybody w/ the book it is on pg 383, if necessary i can get a pic of it up.

i do not know how clean the 12V will be as it will be powering other things in seperate circuits w/ different relays. i am tapping off of it to do what i would like it to do because it is there.

at the moment this is just for a test circuit, but after confirming it works i will get some boards made and use smd components to reduce the size so it is all more manageable. fwiw, it could see temps in the 140F ranges and if a heatsink is necessary, then it is necessary, no problem.

thanks in advance for your expertise,
bob

Robert Reed
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Re: TL750M08 - regulated power circuit...HELP

Post by Robert Reed » Sat Feb 05, 2011 5:32 pm

In general -10MF tantalum electrolytic parrelled with 0.1 MF ceramic on the out put to ground should be sufficient. On the input-nothing is needed except- If the regulator input to wall wart wires start approaching 1 foot in length, add a 0.33 ceramic right at the input terminals and also, if the wall wart ripple is too high under load, then a 'lytic of proper size will be needed there for more smoothing. Since you did not mention specs on the wall wart, this is impossible to tell at this time.The ripple can be quite large as long as the valleys are about 2 1/2 volts higher than the 8 volt regulators output.

bob332
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Re: TL750M08 - regulated power circuit...HELP

Post by bob332 » Sat Feb 05, 2011 6:31 pm

thank you for your reply. appreciate it greatly. as far as distance from the wall wart i think it may be quite a distance. i have just been told that there will be 12V-13V present but i don't know where the source of the electricity is coming from. since the input does seem to make a large difference, is there way to make a regulator that may be overkill to compensate for the things i do not know? i don't have any problems adding additional components if it will rectify many issues.

also, what is "MF"? i thought the large "M" meant "mega", a small "m" meant milli and the backwards u w/ the 'tail' meant "micro" then an "n" was for nano.

i use to be into electronics but things have changed so i am relearning and it seems some naming convetions have been modified like 3V3 instead of 3.3V or 1K8 ohm instead of 1.8K ohm. but the "MF" i just don't know.

also, does it matter if i use the TL750M08 vs a LM7808 for this? either way the output is more than adequate for the load that the arduino will have.

thanks you very much for your assistance,
bob

dyarker
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Re: TL750M08 - regulated power circuit...HELP

Post by dyarker » Sat Feb 05, 2011 8:56 pm

also, what is "MF"? i thought the large "M" meant "mega", a small "m" meant milli and the backwards u w/ the 'tail' meant "micro" then an "n" was for nano.
Right! Back when vacuum tubes were popular, MF was used for micro farad. Us old guys use context not to get confused, as it certainly would someone who hasn;t seen it before.
1K8 ohm instead of 1.8K ohm
I don't really "like" this convention myself. I think it came about because the omega character is not in most computer character sets.
also, does it matter if i use the TL750M08 vs a LM7808 for this? either way the output is more than adequate for the load that the arduino will have.
Doesn't matter. But if TL750M08 would need a heatsink, then LM7805 might do it without a heatsink, saving board space and price of heatsink.

Another way is to get 8V or 9V switchmode regulated wall wart and skip the intermediate regulation. {edit} Reread original post. 12V also used for relays. A switching 12V wall wart would save energy, better power factor load on mains, and no worries about size of ripple. You will still need intermediate regulator to keep 5V regulator cooler


Cheers,
Dale Y

Robert Reed
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Re: TL750M08 - regulated power circuit...HELP

Post by Robert Reed » Sat Feb 05, 2011 9:08 pm

You are correct with capital/small case. Its just that I don't give it much thought any more when referring to a particular function such as capacitance value where the letter m stands for micro. I suppose one could misread my post and take that for a very large value, but in the circuit I described its almost certain to take it for micro. Sometimes when describing circuits I have designed and built dozens of times I don't always cross my Ts and dot my Is. :smile:
The 1K8 crap started in either the UK or Europe and seems to be slowly spreading our way.
You don't need any more circuitry than described to accomplish your goals as the wizards of Silicone Valley have already done that for you. All you need is for the proper wall wart to handle the current load required. 12-13 volts dc output is perfect and the ripple content could conceivably be 4 v p-p riding on that and you are still in good shape. Since I don't know your current requirements the regulator may need a heat sink. Fire it up and put your finger on the back side. Warm is OK, Hot will need a heat sink. Any of the 78xx series of regulators will work almost the same. You could add "what if circuitry" until you are blue in the face, but for your app, I think what you have is enough, maybe fuse the dc output from the wall wart.

HOLD EVERYTHING! I just noticed from your first post a discrepancy confusing me- Is this a 5 volt regulator or a 8 volt regulator? Your chip numbers conflict.I was under the impression that we were talking 8 volts. This could change things. Clear this up with me and give me a load current spec and I can tell you better what will work.

bob332
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Re: TL750M08 - regulated power circuit...HELP

Post by bob332 » Sat Feb 05, 2011 11:28 pm

i just re-read my first post and see i noted 7805, it should be 7808, so yes, 8V. as far as current, i need to verify that 100% but i am thinking less than 500mA, but the one thing i do know that will be present is the the high heat, that is a guarantee.

is my thought process correct in using this middle voltage regulator so the arduino regulator doesn't have to drop down the V so much? again, i am doing this because of the high heat the device will be subject too and also not sure how clean the 12V will be so am trying to give the arduino a good clean 8V and not a dirty 12V to deal w/.

would the TL750M08 put off less heat than a LM7808? or does it really matter since they are both working w/ 12V in and outputting 8V? is the TL750M08 used only when you have a smaller Vin to work w/? i have no issue picking up some LM7808s if they will work better.

again, thanks for these noob questions,
bob

bob332
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Re: TL750M08 - regulated power circuit...HELP

Post by bob332 » Sun Feb 06, 2011 12:42 am

the board says in the lower right i can edit posts....but...i can't...any help?

dyarker
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Re: TL750M08 - regulated power circuit...HELP

Post by dyarker » Sun Feb 06, 2011 11:42 am

Edit button should be in upper right of your own posts.

For a given current and voltage drop. Either part will disipate the same heat. The one in the smaller physical package will have a higher temperature.
Dale Y

bob332
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Re: TL750M08 - regulated power circuit...HELP

Post by bob332 » Sun Feb 06, 2011 2:26 pm

dyarker wrote:Edit button should be in upper right of your own posts.

For a given current and voltage drop. Either part will disipate the same heat. The one in the smaller physical package will have a higher temperature.
thanks for the heat displacement explanation.

as far as the edit button, i don't see any buttons but if i drag my mouse around under the time i do get a link to edit, quote and report the post which has allowed me to quote this. weird...maybe i will try a different skin/theme if one is available.

Dimbulb
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Re: TL750M08 - regulated power circuit...HELP

Post by Dimbulb » Sun Feb 06, 2011 7:25 pm

The TL750Mxx TI ldo regulators automotive family 8V is page 4 can be found here:
http://focus.ti.com/lit/ds/sgls312i/sgls312i.pdf

dyarker
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Re: TL750M08 - regulated power circuit...HELP

Post by dyarker » Sun Feb 06, 2011 7:54 pm

Invisible edit and quote buttons is a problem of which "skin" you've chosen for the forum.
Dale Y

Robert Reed
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Re: TL750M08 - regulated power circuit...HELP

Post by Robert Reed » Sun Feb 06, 2011 8:52 pm

OK Bob, that clears things up a bit. With 12vdc feeding your chip and a 500 ma load current , the chip will dissipate 2 watts of power as heat - thats hot. So you will need a heat sink and you can probably use any of the TO-220 regulators with the same results. If your wall wart is rated for 500+ma, it probably has sufficient capacity so that you will not have to add any more for smoothing and as I mentioned, you can withstand up to a 4 volt ripple content without any problems.
If your Arduino has its own 5 volt regulator it would have to dissipate 3.5 watts which would probably overload it, so some pre- regulation wouldn't hurt. But here is some food for thought - in the case of using a pre-regulator (7808), a dropping resistor in series with that regulators input could be used to dissipate a portion of the heat thus reducing the size of the heat sink required ( maybe 4 ohm @2watts). Or maybe only a dropping resistor between the wall wart and arduino, but then why not just use a wall wart of 7 or 8 volts output. I am guessing that you already have a 12 volt one in hand and desire to use what you've got?

dyarker
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Re: TL750M08 - regulated power circuit...HELP

Post by dyarker » Mon Feb 07, 2011 12:12 am

... but then why not just use a wall wart of 7 or 8 volts output. I am guessing that you already have a 12 volt one in hand and desire to use what you've got?
I missed this first time around too. 12V relay coils.

Cheers,
Dale Y

bob332
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Re: TL750M08 - regulated power circuit...HELP

Post by bob332 » Mon Feb 07, 2011 1:33 am

the 12V is what will be where the arduino is going as i am tapping off the 12V that is there for a different project. i really need to figure out exactly how much A i will be needing, the more research i am doing i may have overshot the A i initially stated and may only need 250mA. the wall-wart will not be close where these items are going - is that going to be an issue? i have been told though that at the site 12V will be there through cable.

sorry for the changing details, i am getting changes as this is going on and i am trying to stay at the same speed as what is going on at the project site...

i have no issue using heatsinks as i am not really size constrained if that matters, at least not constrained to not being able to use a heatsink.

one other question, slightly off topic, if a schematic says to use a 16V capacitor, does it matter if i use a 50V unit of the same type and capacitance value?

thanks again all for the assistance.

another interesting anomaly about the forum is that i don't get updates that this post got any more responses even though i have it set that way, but as soon i check it, i get an email stating replies were made...anybody else have this happen?

again, thanks for not flogging the noob :).

Dimbulb
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Re: TL750M08 - regulated power circuit...HELP

Post by Dimbulb » Mon Feb 07, 2011 8:04 pm

a higher voltage rating should not effect the performance.
Your power supply starts at the wall and ends at the input of the components fed.
If I understand you correctly.

The last capacitor needs the correct farads to match the milliamp draw if it is not enough
you could get weak dampened wave. The ldo reg will sense this and mess up your performance.

put your power supply together and measure the voltage then throw a load on it and feel the regulator.
the load can be a light bulb and a resister that will draw your milliamps.
If it gets hot pull the input off right away.

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