I'm trying to use MOSFET led driver with 10W 12V COB LED as a transmitter for my Visible Light Communication Project. I'm using IRFZ44N MOSFET with a Vgs(min)=2V and Vgs(max)=4V.
I'll be using my Nano to send the data. When the circuit is used for normal switching the LED glows completely but when I transmit my data the LED turns on partially. It works fine for a one second ON and one second OFF code but as soon as I use say PWM signal of 1kHz it doesnt work. I have atached the driver image. I want the LED to be turned ON with highest intensity and still be able to turn ON and OFF.
When the Vgs is measured it reads 1.9V on DMM with Vin of Nano coming from 7805. But when USB cable is used for Nano Vgs measure 2.5V and this effectively switches on the LED.
Edit: I'm no longer usiing the 10k resistor from arduino to Vgs as it was essentially a voltage divider circuit.
DrDiettrich:
You are using a LED module that does not allow for fast switching. This is most probably due to a built-in current and temperature controller.
Also use a logic level MOSFET. A Vgs(max) of 4V is not sufficient because a much higher voltage is required for sufficiently high current.
I'm using 10W 12V COB LED.
When the Vgs is measured it reads 1.9V on DMM with Vin of Nano coming from 7805. But when USB cable is used for Nano Vgs measure 2.5V and this effectively switches on the LED.
Hence data transmission takes place and the LED does transmit data. But I'm designing this for a project and so the Vin for Nano should come from 7805.
Your main problem is that LEDs are "current driven". With regular little LEDs we use a [u]series resistor[/u] to control/limit the current but high-power LEDs normally use a switchmode constant-current (or "controlled current") driver.
Without some kind of current limiting, the LED or power supply can burn-up. Or, maybe the power supply safely shuts-down, etc.
If you choose to use a resistor make sure to calculate the power and choose a resistor with an appropriate power rating. And, you need "extra voltage" for the resistor. If the LED is really rated for 12V you need to allow for the voltage drop across the resistor.
When the Vgs is measured it reads 1.9V on DMM with Vin of Nano coming from 7805. But when USB cable is used for Nano Vgs measure 2.5V
I assume you're using the same 12V that's powering the LED. I'll bet it's dropping by a LOT when the LED turns-on and the Arduino is running at less than 5v.
Also, your two 10k resistors make a 1/2 voltage divider, cutting Vgs in half. But the whole driver circuit is wrong anyway...
Your MOSFET is wrong, should be a logic level type like IRLZ44N or equivalent, your schematic is wrong, you have a voltage divider that cuts your signal voltage in half. Do it like this, your LED replaces heater:
"with Vin of Nano coming from 7805"
"Vgs is measured it reads 1.9V"
The above lines indicate a (too) low 5volt supply on the Nano. I guess 3.8volt (the 1.9volt Vgs).
A Nano needs a minimum of 6volt on V-in for the Nano's build-in 7805 1117 to make a stable 5volt for the board.
If you have regulated 5volt, then connect it to the 5volt pin.
I assume you do have the two required capacitors on the 7805.
Leo..
look at jca34f's schematic above. It has a much, much lower resistance between arduino's pin and gate.
Also Vin supply is regulated by nano's own regulator, which has its own drop, so it needs be fed between 7 and 12V
So you can either:
feed unregulated 7 to 12V (but no more) to nano's Vin
feed regulated 5V (but no more) to nano's 5V
IRFZ44 might not be ideal but at 1A could also work with only 5V on gate Just check its temperature. Beware that having both resistors at 10kohm effectively drops arduino's digital output voltage in half. You want to feed that gate with as close to 5V as possible. 100-150ohm between digital output to gate should be ok.
Can you please post a copy of your circuit, in CAD or a picture of a hand drawn circuit in jpg, png?
Have you got the bypass capacitors recommended by the data sheet for the LM7805?
What is your input voltage to the LM7805?
Thanks for pointing this out. I thought IRFZ44N is a logic level mosfet and that it could be driven by arduino without a driver.
Yes, I initially did that blunder of having the voltage divider circuit. I later on used only the 10k resistor between the gate and source to act as a pull down resistor but the output would still remain the same.
So I'll now consider buying IRLZ44N or some logic level mosfets. Thanks a ton.
Wawa:
"with Vin of Nano coming from 7805"
"Vgs is measured it reads 1.9V"
The above lines indicate a (too) low 5volt supply on the Nano. I guess 3.8volt (the 1.9volt Vgs).
A Nano needs a minimum of 6volt on V-in for the Nano's build-in 7805 1117 to make a stable 5volt for the board.
If you have regulated 5volt, then connect it to the 5volt pin.
I assume you do have the two required capacitors on the 7805.
Leo..
The voltage to the Nano from LM7805 is a stable 4.95V. Yes, I have the capacitors connected to 7805.
And yes quite surprisingly the digital output bumps up to 2.3 volt(as read by DMM so it might be twice) when Nano is connected to the PC via a USB cable and it is now that the the LED is brighter.
Can you please post a copy of your circuit, in CAD or a picture of a hand drawn circuit in jpg, png?
Have you got the bypass capacitors recommended by the data sheet for the LM7805?
What is your input voltage to the LM7805?
Tom...
Thanks for pointing out. I think I should be buying a logic level Mosfet.
