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<nicksydney>
just want to check if what i'm thinking is current....if datasheet says the backlight max current is 40mA and voltage is 20 which means it is 0.81W than I can supply 24v but 25mA which is 0.6W ... am I correct ?
<nicksydney>
just want to check if what i'm thinking is correct....if datasheet says the backlight max current is 40mA and voltage is 20 which means it is 0.81W than I can supply 24v but 25mA which is 0.6W ... am I correct ?
<wpwrak>
designed for windoze, but apparently somewhat runnable on linux as well
<nicksydney>
"somewhat runnable" is not comforting :)
<wpwrak>
it seems that people are working on improving runnability issues :)
<wpwrak>
if your display says 20 V, 24 V could be dangerous. check the "absolute maximum ratings". they tell you where the transition between comfort zone and black smoke happens
<wpwrak>
and what happens if your power supply can't provide the current the display wants depends on the display :) maybe it'll just get a little darker
<wpwrak>
you can imagine the display as a resistor: for 40 mA at 20 V, it would be 500 Ohm. if you can only supply 25 mA, you'll get 12.5 V. so that's quite low.
<wpwrak>
it may be that it still works, though. since it's a bit more complicated than a resistor :) you can test such things with a lab power supply. just set the voltage to 20 V, current to 25 mA, and see what happens
<wpwrak>
if you intend to operate outside the specification, you also have to make sure you know under what circumstances you'll exceed the limits. e.g., if the display has highly variable consumption depending on content, then you need to make your tests with the "worst-case" content
<wpwrak>
in the case of an OLED, that would be with all the pixels on
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<nicksydney>
wpwrak: the datasheet mention this http://postimg.org/image/50km94spd/ so the Forward Voltage is what I was looking at is 20.4v max correct ?
<nicksydney>
the schematic has a jumper 25mA and 100mA so assuming 25mA is selected that means it supply 24v with 25mA ... that's very high right ?
<wpwrak>
okay, current-controlled. then you're fine if you set it to 25 mA. the circuit will figure out the rest.
<wpwrak>
i assume that the converter is part of your display circuit ? i.e., it's known to work ?
<wpwrak>
because it doesn't look quite right. but that may be a labeling problem
<nicksydney>
it's from another project not mine but trying to get idea from different projects...and this project uses that kind of schematics and yes it does work
<wpwrak>
ah, if you're mixing designs you have to be careful
<wpwrak>
why not use fairchild's application circuit ?
<nicksydney>
no not mixing design just trying to learn how other similar project are powering the backlight driver....if i mix i become a rapper than ... hehehee
<nicksydney>
i was surprised when i saw this design why it supply 24V whereas the datasheet of the TFT being used is 20V
<wpwrak>
maybe it's for a different display ?
<nicksydney>
yes it is for different display...the datasheet i posted is the display that the project is using
<nicksydney>
the display that i'm goingt o use has different parameters...max is 19v for my display....
<nicksydney>
so trying to understand how it was used :)
<wpwrak>
in any case, that circuit doesn't control the current through the LEDs. that's why it may be a bit dangerous for your case
<wpwrak>
just do what fairchild suggest ? :)
<nicksydney>
i'm using TPS61040 not this chip
<nicksydney>
let me paste the datasheet for the TFT i'm going to use
<wpwrak>
then do what TI say ... it's not that hard ;-)
<nicksydney>
it doesn't say MAX but it has the TYP which is 19.2v so i assume that will be the voltage i need to generate via TPS61040
<nicksydney>
what you mean by "okay, current-controlled. then you're fine if you set it to 25 mA. the circuit will figure out the rest." ... are you saying that the IC even it outputs 24V and the current via jumper is specified 25mA it knows how much current to pass ?
<wpwrak>
if the IC's output is defined by the current, the voltage varies depending on the current
<wpwrak>
24 V would then be the maximum voltage, but what's really controlled is the current. and yes, current is what matters most with LEDs, not the voltage
<nicksydney>
so logically for that schematic if the voltage was not 24V but say 35V but the current is 25mA the backlight for the corresponding TFT will be ok or it will smoke ?
<wpwrak>
just design your power supply circuit for 40 mA. if the chip also has a settable maximum voltage, set it to 20 V.
<wpwrak>
and design everything else (inductor, etc.) for at least 40 mA and 20 V.
<nicksydney>
ahhhh this "if the IC's output is defined by the current, the voltage varies depending on the current" ... click in my head now :)
<nicksydney>
ok thanks it make sense to me now :)
<wpwrak>
hehe :)
<nicksydney>
somtimes the concept and relationship between voltage and current is not sticking in my head so need an easier explanation :)
<nicksydney>
upgraded to the latest kicad and now the module in PcbNew is not showing up :(
<nicksydney>
wpwrak: which branch did you use for your kicad ? the latest code is not stable getting lots of crash
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<wpwrak>
bzr 4150. almost a year old :)
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<sb0>
roh, do you think it's possible to engrave text on a powder-coated aluminum surface by burning the powder coating using a laser cutter, and obtaining a visually good result?
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<roh>
sb0: maybe.
<roh>
dunno about powder coating. black anodizing can be made lighter
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<sb0>
roh, ok, can I try it at rfa sometime?
<roh>
yeah.. but i do not know if and when i find time
<roh>
i hurt my hand some week ago and work is piling up as we speak ;)
<roh>
if its powder coat and not anodized we need to check what kind of plastic it is/was. one cannot laser anything with cloride in it
<roh>
eh chlorine
<wpwrak>
i;m sure the chlorine won't mind its liberation. "Free Chlorine !" :)
<wpwrak>
btw, just had an idea regarding biometric authentication. with the advances in the field of induced pluripotency, i wonder if it could become feasible to use cloning to get at someone's biometric markers.
<roh>
true. but our lungs and machines mind.
<roh>
chlorine destroys machines. -> anything which contains it => no go.
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<wpwrak>
DocScrutinizer51: question: am i right assuming that making a test fixture that produces a variable field roughly resembling a human finger making controlled movements would be fairly simple ? e.g., without moving parts or other fancy components ?
<wpwrak>
(for production testing of the capacitive sensor)
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<nicksydney>
so good to be able to use the old version of kicad .. all the footprints works again :)
<wpwrak>
what happened with the current version ? random crashes ? or something more specific ?
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<nicksydney>
random crashes and also the footprint menu changed a lot ... now the way it works you need to specify the footprint .mod file as each parameter
<nicksydney>
with the old version you can just select all .mod files and automatically it is added
<nicksydney>
too much work with the new version
<wpwrak>
ah, i just add them to the .pro, with vi
<nicksydney>
too lazy to do all that better focus on the design for now :)