Is LM317T suitable for powering propeller at 3.3v
HollyMinkowski
Posts: 1,398
The cheapest 3.3 regulator I can find is the 800ma rated LM1117T at .57ea
But I can get a 1500ma LM317T for .27ea and the 2 extra resistors that are needed
to set its V to 3.3 cost .02 each.
These are the prices including shipping..so
.57 for the LM1117T vs a total of .31 for the LM317T.
So, is the 317T just as good used with the prop as a standard low drop out 3.3 regulator?
I was thinking that not only do you save more than a quarter for each board using the 317T
but it would allow you to easily tweak the voltage up a bit for running above 80mhz...if you needed to.
But I can get a 1500ma LM317T for .27ea and the 2 extra resistors that are needed
to set its V to 3.3 cost .02 each.
These are the prices including shipping..so
.57 for the LM1117T vs a total of .31 for the LM317T.
So, is the 317T just as good used with the prop as a standard low drop out 3.3 regulator?
I was thinking that not only do you save more than a quarter for each board using the 317T
but it would allow you to easily tweak the voltage up a bit for running above 80mhz...if you needed to.
Comments
so, you will need a minimum input voltage of 3.3 +about 2.0 = 5.5 volts.
SO, you cant run it from 5 volts.
p.s., dont tweak the voltage from 3.3
Mike
au.mouser.com/ProductDetail/ON-Semiconductor/NCP1117ST33T3G/?qs=sGAEpiMZZMtqO%252bWUGLBzeP6Utf3GmNVB
BTW, tweaking adjustable regulators can be a pain as you really want to use stable 1% resistors and you might need to use a few of them to get the exact value.
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*Peter*
the dissipation will be the limiting factor, which of course depends on the input voltage range.
they may be good for 200milliAmps
the sot223 has a rating of 160 C/watt in air (ie no copper heatsinking), so
max die temp is 150C, assuming 30C case,
so worst case dissipation will be 150C-30C case ambient =120C gives 120C/160=0.75Watts
so assuming best case of 5V-3.3 = 1.7V, max current is 0.8/1.7= 470mAmps.
being realistic, say 9 volts input gives 140mAmps.
since we can assume some heatsinking from the pcb, then we can deliver more current.
12 volt input only allows 92mAmps.
, so sot223 is a bit on the small size.
better of with a 863-NCP1117DT33RKG, but then we are back to cost.
Holly, if you are only making 1 or 2 off, then try to get a To-220 package, and then whats a 1$ or 2
if you are designing for volume, i dont think you have the experience
not being critical, just realistic
Mike
Anyway, as for experience, how else do you think anybody gains it? The one who ventures out into deeper waters will gain experience, one way or another they will gain experience, you can never really sink. Experience teaches us not to jump to conclusions too much by hitting the = key until we have the figures.
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*Peter*
if someone says " my car speedo handles up to 200mph", the implicit statement is that the car will do 200MPH.
If I say "this regulator handles 1 Amp", then the implication is that i can use it up to 1amp.
If parallax say "the outputs of a prop are rated for 40mAmps", then many people ( check the forum), believe they can source 40mAmps from a pin, even hough it probably 10mAmps.
as for your last paragraph. "Anyway, as for experience, how else do you think anybody gains it?"
lets hope Neil armstrong didnt go to the moon saying " well, this is how we gain experience".
also your statement "The one who ventures out into deeper waters will gain experience, one way or another they will gain experience"
is open to challenge. sharks eat people who venture beyond their capabilities and judgment.
Knowledge and education is tempered by experience, not replaced by it.
that's why I stepped through the process of decision making in my post.
I am an old engineer(61), so cautioned the misuse of spec sheets, that's all.
p.s. Leon rocks !!
Mike
As I said about experience (and keeping it in context), we are not actually going to the moon or swimming with sharks, here on the electronics bench and the forum you can never really sink.
Remember you were the one who said "not being critical, just realistic"
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*Peter*
I totally accept you are correct.
I wont post anymor
Mike
Cheers mate
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*Peter*
Thanks for pointing me to the low cost NCP1117.
I ordered 10 of them and will give them a try...I think they might work just fine
I bought a lot of small surplus 5v switching cell phone chargers rated at 800ma.
They have a small usb plug at the end of a cable. I will be removing that
and replacing with a more standard power plug. The 317 data sheet said it needed
1.5v more than the v you want the 317t to output....so with 5v in it should work
but it's very close. I tested the little 5v switchers and at full load they dropped to
about 4.9v I think the circuit will need about 350ma max at 3.3v ....the NCP1117
has a lower v requirement to regulate at 3.3v so it seems a much better fit.
@mikestefoy
You are absolutely right. I really don't have enough experience with hardware...the
fact that I am asking such basic questions like this one proves that.
I'm basically a software person but I really want to get my feet wet trying
to design some simple hardware....I gotta start somewhere.
Now I need to find the cheapest board house...probably in China, to make a few
prototype boards for me.
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Links to other interesting threads:
· Home of the MultiBladeProps: TriBlade,·RamBlade,·SixBlade, website
· Single Board Computer:·3 Propeller ICs·and a·TriBladeProp board (ZiCog Z80 Emulator)
· Prop Tools under Development or Completed (Index)
· Emulators: CPUs Z80 etc; Micros Altair etc;· Terminals·VT100 etc; (Index) ZiCog (Z80) , MoCog (6809)·
· Prop OS: SphinxOS·, PropDos , PropCmd··· Search the Propeller forums·(uses advanced Google search)
My cruising website is: ·www.bluemagic.biz·· MultiBlade Props: www.cluso.bluemagic.biz
3 prototypes for 54.00 looks really good
My boards will be 2layer and about 3.5" by 2.5"
I'm hoping to get them made for less than
10.00 ea... I hope that is realistic