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31  Using Arduino / LEDs and Multiplexing / Re: TLC5940 + high current + keep the constant current sink (looking for part) on: December 11, 2011, 09:38:46 am
Ok! Fine!
I hooked it up again (attachment). Could it be that there is a mistake in my first try from yesterday with the upper right transistor? Its emitter is facing to Vcc - this is wrong, isn't it?
Also interesting for all german speaking people: http://www.hobby-bastelecke.de/grundschaltungen/konstantstromquelle2.htm
Very "humanreadable" explanation of the constant current source with 2 transistors - just to share this here...

Parallel i was looking for a part that provides many transistors in one package to make manifacturing easier, and i found this transistor array:( http://www.fairchildsemi.com/ds/FF/FFB2907A.pdf <- not available in germany...my bad. Alternative: http://www.nxp.com/documents/data_sheet/PBSS4041SP.pdf )

For the LM317 thing: i planned it in eagle and in comparison with the 2 transistor circuit the soldering effort will be the same (i was assuming that i need fewer parts when using the LM317)

32  Using Arduino / LEDs and Multiplexing / Re: TLC5940 + high current + keep the constant current sink (looking for part) on: December 11, 2011, 07:45:07 am
EVP:
Best toy store ever smiley-grin Quite cheap if i compare them to the planned Seoul P5! Do you know how good colors are mixing for example with this one? http://www.satisled.com/10w-9w-rgb-led-emitter-3w-for-each-color_p236.html Or do you know which diffusers are matching them? I already wrote a question to the shops tech support. I have a 10w white high power led ordered from ebay http://www.ebay.de/itm/120563047449 which looks similar. Very bright and a lot of fun to play around (try strobe effects! smiley-wink )! As mentioned i expect a not very homogenous lighting when using this in rgb without diffuser.

dc42:
I will give it another try! I'm searching for a explanation why this works and where the regulation in current happens (i hate working with black boxes smiley ).
Did i calc the resistor the right way? It was like: "Oh, let's take 0.65V, gimme 350mA -> divide ==> 1,8 Ohm Resistor"
The Common Cathode/Anode is all fine - i just need leds which are freely configurable (which all are i mentioned)

I still 'd like to know why the LM317 will not work smiley-wink

Thank you guys! You are great!
33  Using Arduino / LEDs and Multiplexing / Re: TLC5940 + high current + keep the constant current sink (looking for part) on: December 10, 2011, 08:27:35 pm
This is what i planned (attachment) - i have to say that i didn't understand what i was drawing. How do you figuered out the 0.65v? You also said:
Quote
...the 4K7 resistor would also need...
but:
Quote
...You don't need the 4k7 resistor...
In my diagram it misses...

I guess this will f*** me up when it comes to soldering. I need this 48 times. I will also need Common Cathode RGB Leds, right?
34  Using Arduino / LEDs and Multiplexing / Re: TLC5940 + high current + keep the constant current sink (looking for part) on: December 10, 2011, 07:00:27 pm
Hmm...ok! That is very helpful about the first circuit. At the moment i am creating a eagle file for this  - i hope things become more clear then.
I don't get the second one...why can't i do like him? http://arduino.cc/forum/index.php/topic,80353.0.html
My approach would be similar:
Create an ccs with the lm317 and interrupt it with a FET before the LED's GND. Then drive the Fet with the Tlc.
Thank you so much for helping me (and excuse my stupid questions smiley-wink )! I am learning a lot of new stuff right now!
35  Using Arduino / LEDs and Multiplexing / Re: TLC5940 + high current + keep the constant current sink (looking for part) on: December 10, 2011, 05:14:30 pm
Thank you for the effort!
dc42:
i think its technically the best way to build up a constant current source by my own.
I found some circuits online and it might look like this in the end:

Im quite unsure how this works - also with this nasty PNP/NPN problem (i always mix up the two). Also i will have to plan it for 350mA and additionally i need a control pin to turn this on and off(do i need special transistors due to pwm?) Isn't it strange that i cant buy this in an ic?

This will make my circuit more complex than expected!

EVP:
I'd like not to change the code (the tlc arduino lib is soooooo nice <3 ) - and also this part is quite expensive. 2,95€ when i take 16 which is 47,5€. Now i pay about 10€ for my tlc's and i guess if i do dc42's solution with 2 transistors i'll end up at about 20€ for the whole circuit.

Thank you both for your input!
I'd be glad if you could drop a few lines about the homemade constant current sink above!

----ADDED----
I just read some interesting things about Constant Current Sources! In this example a voltage regulator is "abused" as ccs. The ic is an LM317 http://www.farnell.com/datasheets/76338.pdf

Here appear some BIG questionmarks! How do i turn it on or off? Simply by transistor at the end? And there is again this PNP/NPN thing...


36  Using Arduino / LEDs and Multiplexing / Re: TLC5940 + high current + keep the constant current sink (looking for part) on: December 09, 2011, 12:37:05 pm
Hi!
Thanks for your advice!
Nice part - but definitly too expensive! I searched for similar parts and found this http://uk.farnell.com/microchip/mcp1640t-i-chy/boost-regler-synchr-500khz-6sot23/dp/1800205  - far cheaper! Are both compareable? Keep in mind that i need 16*3 of those smiley-wink So i also need to care the price....
37  Using Arduino / LEDs and Multiplexing / Re: LED Cube Troubleshooting... on: December 09, 2011, 09:29:30 am
Can you post a photo of your circuit/breadboard?
38  Using Arduino / LEDs and Multiplexing / TLC5940 + high current + keep the constant current sink (looking for part) on: December 09, 2011, 09:22:12 am
Hi Community!
I'm experimenting with TLC5940 and some LED's. Works great so far (3 chained TLC on 16 RGB-Leds)!
Now the tricky part:
The TLC provides 120mA. Now I'd like to drive a power consuming LED (a Seoul P5 to be exactly http://www.farnell.com/datasheets/615004.pdf).
This hungry piece consumes 350mA per color.
I read about solutions driving the Led via a MOSFET/Transistor/Darlington Arrays http://www.ti.com/lit/an/slva280/slva280.pdf. In my understanding i'm losing the constant current sink with this solution, so my LED is driven via resistor, which i'd like to avoid.
My solution in dreams is a constant current sink providing my led with 350mA/color - and this constant current sink takes its information about dimming (pwm) from the TLC.
I crawled farnell a lot -  but i didn't find any proper part (i also did'n know what i was searching for  smiley-lol) Can you help me out?
This problem was discussed on many places here and in some other tinkerforums (GrumpyMike provided a lot of helpful information - thanks a lot) so i feel a little bit awkward asking this again. As said it's important to have a constant current sink when driving such hungry leds...and i think all given solutions break up with this.
Thank you for helping me!

39  Using Arduino / General Electronics / Re: Me vs. P-Channel MOSFET & LED | Led never turns off completely on: August 17, 2011, 05:13:59 am
Hey you all!
This was the solution!!!  smiley-red    - and a fairly embarassing mistake of me smiley-wink
I also figured out that my MOSFET ist not working on logic level - so i will have to put a transistor before...

Thanks a lot to all the people giving a helping hand!
40  Using Arduino / General Electronics / Re: Me vs. P-Channel MOSFET & LED | Led never turns off completely on: August 11, 2011, 08:28:09 am
Sry grumpy_mike for my highly unprecise answer!
I took 2 pictures of my circuit to make things easier! - Take a look at the attachment...
These show the wireing of the FET and the Led. The pictures were taken at 12V.

Interesting about this: It doesn't matter if the Gate (leftmost pin i suppose -> datasheet) is positive or gnd!

Datasheet and FET are the same! I checked this again...

I hope the pictures will help! I suppose it's exactly as you say...
Quote
often the problem is not actually where you are looking

41  Using Arduino / General Electronics / Re: Me vs. P-Channel MOSFET & LED | Led never turns off completely on: August 11, 2011, 06:14:45 am
Ok - i feel cheated by a little piece of silicon  smiley-eek
I tried grumpy_mikes "direct way" and NOTHING HAPPENS?! I tried it with 5 different MOSFETs of the same type....so blown up is nearly impossible. I checked the datasheet twice - it's quite hard to misunderstand the Gate-Drain-Source diagram...
http://www.fairchildsemi.com/ds/FQ/FQP27P06.pdf - perhaps sby can lift the secret of my weird MOSFET.

And the strangest thing at last - it DID some kind of triggering with the arduino! But none when it's connected directly?! I'm so confused...gnah - why it's always depressing when it starts to be interesting....

thanks for your effort!!!
42  Using Arduino / General Electronics / Re: Me vs. P-Channel MOSFET & LED | Led never turns off completely on: August 10, 2011, 08:53:10 am
I build it (with a transistor - as you described) as given in Circuit11 but it's still the same - the led just dims a little bit when it should be turned off. Im quite new to all this as you probably see smiley-wink - perhaps i'm just doing the same mistake over and over...  smiley-cry
The alternating connection between GND/V++ and the Gate can be measured by a circuitanalyser - but the MOSFET does "anything??"...
I also understand why there is an transistor for triggering the MOSFET but i don't get it why the Led isn't turned off completely...

Thank you all for helping me!
43  Using Arduino / General Electronics / Re: Me vs. P-Channel MOSFET & LED | Led never turns off completely on: August 10, 2011, 05:36:44 am
Hi again!
Thanks for your ideas!
I tried Circuit16 (the first one) but the result is the same - in fact it doesn't matter weather i pull the gate low or high  smiley-confuse

Quote
...and what making mosfet to conduct is difference between Vgate and Vsource.
Is it possible that my Led power consumption is to low to get the MOSFET triggering off again? Could you explain this difference-thing again? I read Wikipedia twice and watched some nice Video-Tuts - but i didn't get the point yet, i guess.

Quote
How much current your led's consume?
The Led needs about 3.3V and 20mA. The further plan is to set up an Led matrix, controlled by MOSFETS on each row and column to get each Led adressable.

44  Using Arduino / General Electronics / Me vs. P-Channel MOSFET & LED | Led never turns off completely on: August 09, 2011, 08:16:36 am
Hi!
I'm struggeling with a simple p-Channel Mosfet - controlling an LED.
It's basically this circuit:
http://ruggedcircuits.com/html/circuit__28.html
The MOSFET im using is this:
http://www.fairchildsemi.com/ds/FQ/FQP27P06.pdf

!!!The MOSFET in the given circuit is N-Channel - i changed mine accordingly (put the LED on the source-side of the MOSFET).

The Arduino is powered by USB - but has a common ground with the circuit.
The circuits V+ is 3.3V.

The code to drive the MOSFET is the Blink-Demo from the Arduino examples.

And here is the Problem:
When the Arduino triggers the MOSFET the Led changes their intensity (alternating to the debug Led on the Arduino -> p-channel has switched logic) correctly, but it never turns off completely!
As i can see the circuit does the job - but the Led still lights a tiny bit when in should be turned off. If i change the voltage, the brightness in the Led-off-State changes, too.
I found this problem in one other related Post - but no solution was given...can you help me to turn off my evil Led?

Thanks!!!
OptimusPrime


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