hey everyone
i am working with a project that involves lightning of multiple "sentences" in a fading matter, for that i am using multiple LED's ( the number of led's is different from "sentence" to "sentence" according to the lenght of it ) i am using 2 tlc5940's for drinving the LED array.
the longest array has : 93 led's
the shortest array has : 23 led's
the led's are connected in a parallel way
My issue, is how / where to connect resistans ? should i use, a resistant for every array according to its lenght + ekstra led for the tlc5940 ?
or should i only use resitans for tlc5940 ? any suggestion for the power supply.
i am a new beginner in electronics, so please anyhelp will be appreciated
TLC5940s do not require resistors in the LEDs because they limit the current through the LED.
However you can't wire LEDs in parallel with this chip, there is nothing to make them share the current. You could wire them in series and up the LED supply voltage up to a value of 17V.
ohh i should have asked for help, before soldering 1000 led .. hehe .. but thanks for the answer. what about the resistans i have to use, should i calculate it according to the array that has the most led's ? ( i dont that some of them dim )
what about the resistans i have to use
What part of:-
TLC5940s do not require resistors in the LEDs because they limit the current through the LED.
Do you not understand?
However:-
The number of LEDs and the number of TLC5940s do not appear to add up. How are you trying to wire them?
i guess, i understood that we do not need resistors for the Led's .. but dont i need a resistor for the at the IREF ? ( channel 20 ). so my question is what should i consider when calculating the value of that resistor.
i do have 2 TLC5940, and 30 "sentences" ... every sentence is lightend with a number of led's ( from 23 to 94 led's depending on the length of that sentence ), and every sentence ( led array ) is hooked up to an out channel in the Tlc5940
Sorry but I don't know what a 'sentences' is. You need to show a circuit of how you have wired it up.
I suspect that you are massively misunderstanding something but before I can tell what it is I have to know what you are doing.
so my question is what should i consider when calculating the value of that resistor.
You should consider the current you want the TLC5940 to supply to each channel.
i understand .. here is my diagram, nothing really fansy i guess 
OK that simply will not work.
You need about 2V for each series LED. Therefore for 17V you get a maximum of 8 LEDs in series, no more.
For those 8 you set the current the same as if it were one LED, that is if it is 20mA you set the resistor for that.
wow .. it means that i need 48 v to power 93 led's in series ?
should i just hook the 48 v power supply as if it was 17 v or should i use some kind of ULN for limitting the power, i am sorry for the banal questions, but i am trying to learn somthing.
any suggestion on how i can do it the best way
should i just hook the 48 v power supply as if it was 17 v
Yes if you want to blow up the TLC5940.
Otherwise no.
There is a TI application note slva280 that shows you how to use higher voltages with this chip.
focus.ti.com.cn/cn/lit/an/slva280/slva280.pdf