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Help with transistors - PWM and LED prosject

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thastian

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Hey everyone

I need someones help, and i'm very thankful for all help. I have searched the net for hours without finding out the answer to my question.

I have a simple diagram. I have a LED light (6W, 320mA), a driver, and a Audrino board.
The driver gives power to the LED light, between the driver and the LED is an unknown transistorm and from the transistors base it goes to the PWM output (5V, 40mA) of the Audrino board.

What i need help for is figuring out the circut between these 3 compenents. The driver, LED and audrino. I dont know what transistor i shuld use and what kind of resistor.

The idea is that the Audrino board is dimming the LED light with PWM thro the transistor.

Can anyone help me with this prosject?

And sorry about my bad english =P
 
Is your 'driver' specifically for the LED you have? Does it have current limiting? Can you post a link to its specification?
 
The driver is made specifically for the LED yeah. It's part of a package. All the specification i got on the driver is what i have provided.
The driver and the led comes preassambled from the vendor, but the driver is exsternal. I can open the driver and the LED amature to look for more infomation on what components there is.
 
The LED spec implies that its drive voltage is 6W/320mA = about 18V. In the circuit you posted the transistor is connected as a high-side switch and would need at least 18.6V on its base to turn on. The Arduino can't provide that directly, so it would be better IMO to use a low-side switch instead. To avoid loading the Arduino significantly I think a MOSFET would be the transistor of choice. Something as per the attached perhaps?
 
Thank you for your help and schematics. Will try this.

If i change the LED load to 4W (making the drive voltage about 12.5) can i still use the same MOSFET?
And is there a similar MOSFET with pins?

Thank you very much for the help =)
 
Sorry for the late reply.
The same MOSFET should be ok, but almost any N-MOSFET specified as 'logic-level input' and with a low Rdson (say <0.1Ω) will do. However, if your LED driver is made specifically for a 6W/320mA load then it may fry your new LED unless a current-limiting resistor or other limiter is used.
 
Thanks for the reply.

Can i use this MOSFET? **broken link removed**

The 4W LED lights have the lower wattage driver =)

Thanks again
 
No, that's not a 'logic level' FET so the Arduino can't fully turn it on.
 
ah, i see. Trying to find a better MOSFET as the one you requmended was a bit small and i can't solder the wires to it, so im looking for a MOSFET i can use that have long pins.
 
That looks fine. Good luck with the build.
 
Have tested this setup now, and it works nice. Some flickering when turning on (on low dim(PWM)) and off the light with Audrino, but it might be something else, or no problem at all.

Anyways. The question i got on my mind is how faar can the distance between the MOSFET and Audrinoboard be? can the wire be as long as 25 meters?

Thanks
 
can the wire be as long as 25 meters?
Click to expand...
I don't know what the Arduino's output current/impedance are, or the PWM frequency, but a wire that long will have appreciable inductance/capacitance and unless well screened could pick up RF interference; so it may cause problems. Can you just try it and see?
 
Thanks for the reply. Will try it one day. can allways buy screened cable.

I have another question tho. I have a problem with the dimming/fading of the LED's. When i go from off to very low dudy cycle the LED's is turning on very bright, very fast, and then going down to the set dim light. Its like a lightburst. Have discussed this on Ardurino's forum, and some of them said i maybe had to move the current cutting (the mosfet) to the other side of the driver, becouse its a bad idea to cut the constant current power to the LED's. What do you think? I'm a bit "affraid" to cut the live 230v power
 
The initial bright pulse is possibly due to a large capacitance charging. You could try connecting a ~2k2 resistor from the + side of the LED to ground to allow the cap to charge with a trickle current before theLED is switched on.
I don't see any way can you apply PWM control to the 230V power input to get dimming.
 
The same resistor would be ok......providing it does the trick with your present setup. Keep us posted on the result.
 
Still waiting for the resistor to try the trick you suggested. will keep you posted on the result.

But another question arrises. since i have maybe to have a resistor between the + side of the LED to ground, can i maybe have the driver, MOSFET and the audrino board togheter, and then have a up to 15 meters wireing to the LED? Will that work better? considering that i have to have that distance somewhere as all lightpoints are connected to the same aurdinoboard in the appartment,
 
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