Use some nice big NMOS transistors, and the slowest PWM you can bear. Might need to drive the gates higher than 5V to avoid heating.
As those LEDs have only 4 connections, they are either common anode or common cathode. You need to determine which. The connection on the left is probably the common one. To determine the polarity, connect your power supply between that connection and one of the others through a 10K series resistor and see if there is a faint glow from it. If necessary, do it is a dim light and reduce the resistor to 1K.I suggest you drive them through a mosfet+BJT constant current circuit, because your power supply gives very little spare voltage so a series resistor won't give good current regulation. The details of the mosfet+BJT circuit depend on whether the led is common anode or common cathode.
I'm going to illuminate a room using these LEDs, (very cheap so not very reliable).The total theoretic power will be 250w but I don't want to put all the LEDs working at full power
Quote from: Hinjeniero on Jan 20, 2013, 12:11 amI'm going to illuminate a room using these LEDs, (very cheap so not very reliable).The total theoretic power will be 250w but I don't want to put all the LEDs working at full powerI wouldn't run eBay LEDs at anything like their full power. The numbers they give are for perfect laboratory conditions using huge, active heatsinks. Under any real conditions they're going to get HOT if you try and run them at the quoted power.Aim for 50-60% of those numbers and you'll be a lot happier/safer. 150W of LED is still an awful lot of light.
I know and that's why I need to know if enabling PWM will be as easy as BJTransistor + MOSFET,
also there is not too much space inside of a ceiling spot light and I will have problems to dissipate 50w per led. Hope that running the LEDs at <55% plus a bunch of these fans the temperature won't raise too much.
Hope that running the LEDs at <55% plus a bunch of these fans the temperature won't raise too much.Anyway before installing them, I will run some tests to see what could I expect in every single situation so I'll be sure that I won't blow up something or set my house on fire.
It should be that simple, yes...The amperage of those LEDs isn't too bad (300mA), that should make the PWM switching easier on the PSU than low-voltage/high-current LEDs. If you want to be extra sure you could add some extra capacitors on the power lines near the LED. Get come big ceramics.Fans will make a big difference, yes(if the noise doesn't bother you...)
At first glance that heatsink/fan looks small for 50W... think they're for 5-10W LEDs. THere are some nice big, round LED heatsinks on ebay that should work without a fan. Is there good airflow in those ceiling fixtures?http://www.ebay.com/itm/20W-30W-High-Power-Led-Heatsink-Aluminium-Cooling-For-20-Watt-30-Watt-Led-Light-/190774600422?pt=LH_DefaultDomain_0&hash=item2c6b0d62e6If you want 15 separate PWM channels then you'll need some sort of multiplexer since Arduino only has 6 PWM channels... or you can run all the reds together, greens together, and blues together so only need 3 PWM channels.Does the suggestion for "NMOS transistors" really mean NMOS FETs (N-channel MOSFETS)? Look for devices with low drain-to-source resistance (Rds) otherwise you'll waste power in the FETs and may need to heatsink them too. If driving the gate with a transistor (recommended since they'll drive the MOSFET gates with sharper-edged signals that minimize heating) you won't need "logic compatible" devices.
You should also plan for the Arduino crashing and leaving all the LEDs at 100%, eg. Add a fuse that can't handle that much power.Fuses are cheap and might save you from killing some expensive LEDs due to a software glitch.PS: Be sure to test it to see if it blows!
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Manufacturer: IRManufacturer Part No: IRFZ44NPackage / Case: TO-220RoHS: YesDatasheet: Click HereSpecificationsTransistor Type: MOSFETTransistor Polarity: N ChannelDrain Source Voltage, Vds: 55VContinuous Drain Current, Id: 49AOn Resistance, Rds(on): 17.5mohmRds(on) Test Voltage, Vgs: 10V