I am trying to figure out some electrical values for a circuit I am designing. I am wiring 66 RGB CA LEDs in parallel. Each color channel takes 20mA (2.2v for Red and 3.2v for Green and Blue). How do I figure out the total ammout of current I'll need to drive each channel?
1
-
\$\begingroup\$ Take a wild guess! \$\endgroup\$– Marcus MüllerCommented Jul 15, 2018 at 20:36
Add a comment
|
2 Answers
\$\begingroup\$
\$\endgroup\$
3
If you run all colours at the maximum rated current of 20 mA, that will be 60 mA per RGB LED. for 66 RGB LEDs, you will need 3.96 amp.
If you run at a lower current, for less brightness, or know that all three colours won't be on at the same time, you will require less current.
answered Jul 15, 2018 at 20:37
-
\$\begingroup\$ So I am guessing that I'll need to use a 2A rated transistor on each channel to isolate my LED driver IC from that much current. The base needs to be negative and I can compensate for the voltage drop. Is there a transistor you'd recommend for this application? I would prefer an SMD one. \$\endgroup\$ Commented Jul 16, 2018 at 12:08
-
\$\begingroup\$ @MuscleNerd there are plenty of LED driver ICs with integrated FETs that are rated at 1.5-2.0 Amp \$\endgroup\$ Commented Jul 18, 2018 at 1:24
-
\$\begingroup\$ The closest driver IC's I have found are intended to be used for camera LED flashes. Sadly it's not suited to my needs. \$\endgroup\$ Commented Jul 21, 2018 at 0:44
\$\begingroup\$
\$\endgroup\$
7
Nch FET will drive 66*20mA =1.32A per colour, so for 100mV drop or less RdsOn=<0.1/1.32 Ohms and Vgs(th)<=1/3 Gate voltage with each LED having a current limiting R.
Red =(5-2.0-0.1)/20mA=145 Ohms per Red and BG R’s = (5-3.1-0.1)/20mA= 90 Ohms
PSU needs to be 5V 5A 2% or better.
-
\$\begingroup\$ @Misunderstood can’t string in series for LEDs given as CA. .. kma. 1.32A per FET \$\endgroup\$– D.A.S.Commented Jul 17, 2018 at 21:59
-
\$\begingroup\$ Nonsense you can’t wire CA’s in series \$\endgroup\$– D.A.S.Commented Jul 17, 2018 at 23:41
-
\$\begingroup\$ You are confused my answer is clear \$\endgroup\$– D.A.S.Commented Jul 18, 2018 at 0:37
-
\$\begingroup\$ Since 3 drivers are needed my answer defined what was needed for parts and R’s and suggested 5V 5A for headroom on power. But the OP does not understand what is actually needed. So it matters not to me if they yet don’t understand the details but it is necessary to complete the design. \$\endgroup\$– D.A.S.Commented Jul 18, 2018 at 1:07
-
\$\begingroup\$ You only need a transsitor switch and resistor for each colour, . An IC is not necessary for 5V \$\endgroup\$– D.A.S.Commented Jul 18, 2018 at 1:55