Hello:
I am looking for advice on how to implement dimming of a 12 volt, 1.25 amp LED. I anticipate to do this by pulse-width modulating a 12 volt supply voltage. Actually the supply voltage would be a 4S LiFePO4 battery, so the actual voltage would be a bit higher (~13 to 14 volt).
Are there any low drop-out PWM modulators out there to do the job?
I appreciate the constructive criticism!
Thanks all
Don
Please reword this.
The simplest solution is to use a N-Channel MOSFET. You can compensate for a much higher voltage if you want, you control the apparent voltage by the PWM duty cycle. You use maybe a 10K resistor to pull the PWM port pin to ground and a 50 Ohm from the port pin to the gate. The reason for the pull down is that it keeps the MOSFET off until you get all your stuff setup.
So would an IRFZ-44N do the job?
Hello schmarduino
Use a COTS MOSFET module.
So I Googled “COTs Mosfet “ module and I believe I already have some on hand. My only worry is that there will be too much of a voltage drop across the PWM modulator to fully drive the LED.
Please post a link to that LED.
Most white LEDs have a Vf of about 3.3volt.
Is this a COB LED, with several (3) LEDs in series, or does the LED have built-in CL resistors.
A mosfet is a poor way of driving a LED when powered by a battery.
Led current (light) will vary too much between full and discharged battery.
A Meanwell LDD-1200 could be what you're looking for.
But that won't work if your LED has CL resistors built-in.
Leo..
Thank you Leo! I got the LEDs from Ali Express and I don’t have any data on them. Actually all I know about the LEDs is that they ARE cobs, and they are advertised as “12 volt, 15 watt” LEDs.
Do you think the Meanwell that you mentioned have a low enough drop-out voltage to fully drive the LEDs?
The one that I have is the 15 watt flavor.
They are advertised as “dimmable” so I assumed that that meant they could be easily PW-modulated….
Your guess is as good as mine.
Connect one to a variable lab supply, and monitor current while changing the voltage (10-15volt).
If the light has switching electronics inside, the current will go down when voltage increases.
If current stays constant, it has linear regulation.
And if current increases with voltage, it simply has a resistor for current limiting.
Can't advise you what do do without first knowing what's inside.
Leo..
You need a 12V CONSTANT VOLTAGE dimmable LED driver.
Meanwell has a few.
It would be marginal at best. You need one that will accept a logic level and turn on with about 2.5 to 3V. This one starts turning at about 4V and will not be fully on. You might try it, If it gets hot do not use it. It is important you turn it on and off fast so no caps in the gate circuit.
Well I can make the LiFePO4 battery into a 5S I suppose without too much trouble and that would give me enough voltage for a modulator to feed the 12V LED?
A 4S LiFePo4 battery is very close to 13.2volt for most of it's discharge.
I would try that first.
I highly doubt that that MR16 is 15watt.
That kind of LED power would need a heatsink and a fan.
As said, use a lab supply and test it.
Leo..
That will not help, it is the output of the Arduino, that is limited to 5V because of its regulator. Much higher and the processor would fry, that is its operating voltage. If you connect something to power it via Vin it goes into the 5V regulator then to the processor so adding more battery voltage will not help the gate drive. Try your MOSFET it probably will work but it will be marginal. When you can get a logic level one that has an avalanche rating. You could find a lot of usage for that.
Hi so with the lack of documentation of these I will try the Meanwell Driver idea. According to Mouser and Digikey, the LDD-1200h is no longer available, but the NLDD-1200h seems to be its replacement.
It's CONSTANT CURRENT.
You need CONSTANT VOLTAGE
How can you be so sure that a constant voltage supply is needed? I really don’t know anything about what is inside of the case of these….I would assume they would need a current regulator of some kind…..?
