I am building a led mood light with a high power RGB LED (30W) using 3 constant power supplies for each color.

These are the items I had in mind (but open to suggestions):

30W Integrated RGB LED Light Bulb (10 Series and 3 in Parallel) JR-30W 30W Waterproof LED Power Driver (AC 85~265V)

Each color will be controlled with PWM by arduino. So far so good, the problem is that the bc337 transistors I have can only go up to 800ma so I need something significantly beefier. What is my best and simplest option here? I'm not very knowledgeable in electronics so simplest solution would be best.


Well, the specifications of the device you linked are grossly inadequate.... but given you have 10 LEDs in series, I expect you'll operate at something like 40VDC...

Arduino analogWrite function generates PWM at about 490Hz.

I would suggest setting up a high side switch with a P-channel MOSFET (e.g. IRF9Z24) conrolled by an NPN BJT (e.g. 2N3904). Say 100ohm resistor into the base of the BJT and a 4.7kohm pullup on the gate of the MOSFET. Connect LED between MOSFET drain and GND. Connect PWM input to the aforementioned 100 ohm resistor.

enter image description here

  • \$\begingroup\$ Great answer! Will keep it open for a bit until I know I have it all figured out :) \$\endgroup\$ – DominicM Dec 5 '12 at 17:43
  • \$\begingroup\$ actually 32~36v for LED's which is what he spec'd as his chosen power supply 24~36V except these are 3 strings. YOu can choose $0.20 HEXFETs in SMT with 150 mOhm Ron or use the Thru-hole parts, without heatsink. Use a series 4K7 between collector and Gate 4K7 to reduce Vgs 50% , no zener needed. You might want to consider the 50W version, but your bigger problem is a good LED heatsink...& fixture A CPU heatsink can be retrofit with a low speed fan. I recently posted a PWM circuit with 3 pots, but you can use Music to drive each color using Bass, mid, treble filters and rectifiers. \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Dec 5 '12 at 19:24

This should perhaps be a comment, but I couldn't see how to do that.

Most FETs like the IRF9Z24 have a 20V maximum gate to source. So,
you should add a 10V zener across R2, and another 4.7K resistor in
series between T1 collector and Q1 gate R2 node.

  • \$\begingroup\$ Unless I am reading the wrong thing the only voltage value I see is 60V. Take a look at the spec and let me know if it's 60v or 20v: Spec: vishay.com/docs/91090/91090.pdf \$\endgroup\$ – DominicM Dec 5 '12 at 18:35
  • \$\begingroup\$ Look in the absolute maximum table on sheet 1, second row ... Gate-Source Voltage ... +/-20V limit. It appears that the circuit as drawn would put 40V gate to source when T1 is on. \$\endgroup\$ – gsills Dec 5 '12 at 18:45

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.