Practical PIC Projects

   

Power MOSFET RGB
 LED PWM Driver

for PIC12F6xx

 

Available now from the Picprojects on-line shop page- PCB,pre-programmed PIC and self-assembly kit for this project


Description

Since I published the original RGB LED driver (photo right) I've had many enquiries from people asking how they could make the original board work with more LEDs.  I'd already made a couple of custom boards up for myself, so I finally decided it was time to put together one for the website.

The RGB LED driver described on this page uses logic level 'N' channel MOSFETs which allow it to control LED arrays or lamps at up to 5 amps per channel without heatsinks.

The driver uses exactly the same firmware as the small RGB LED driver  so you can use the same code and sequences with this board to control big arrays of LEDs.


original RGB driver

Piranha LED colour bar

Here's a one off light bar I built using 20 Piranha RGB LEDs and the (prototype) MOSFET driver board.  Assembled into a 25mm x 50mm x 1000mm aluminium 'U' section.  This was fitted under a wall shelf to illuminate the floor.  It's very bright and gives a nice even illumination without any additional diffuser. 

 

I used 0805 SMD resistors, 68R for the Red and 47R for the Green and Blue LEDs. Running from a 5 volt supply it draws about 1.7 amps max.



Schematic

Download schematic in PDF

Circuit Description

This circuit is essentially the same as the smaller RGB driver using the 5mm LEDs elsewhere on this website except that this version uses high power MOSFETs capable of sinking 5 amps on each channel without heatsinks (at 5amps the MOSFETs will run hot)

The input power to the board must be regulated DC and be capable of suppling the power requirements of the output load.

The circuit will operate from a supply voltage in the range 9 to 24 volts.  This voltage range is dictated by the input requirements of the 78L05 voltage regulator and capacitors C3/4.

Switch S2 is not used with the firmware on this website and you do not need to fit it.  I've incorporated it the PCB design because I've written some customized versions of the code that did require two switches.

How much power can it handle?

During testing I connected the controller to some 50W / 12Volt halogen downlight bulbs, one on each channel then ran them at 100% PWM duty cycle.

Ambient temperature during test 22oC  
MOSFET temperature after 5mins (measured on metal tab) 52oC  
Current (sink per channel) 4.4A  
Voltage drop across MOSFET Source-Drain terminal (measured) 20mV  

Based on these measurements and the specification of the MOSFETs and PCB connectors, the controller should comfortably handle 5 amps per channel.  While the individual MOSFETs could handle more current, the PCB screw terminal connectors are rated at 16 amps and since there is only a single Ground connection to the board, total load for the three RGB channels should not exceed this.


PCB

PCB only option is available to buy
from the on-line shop page

Component List

Buy the complete kit for this project from the Picprojects on-line shop page

You can buy all the parts needed to build this project from most component suppliers world wide. In the UK you can get everything from Rapid Online and I've included a parts list with their part numbers below.

 

All Rapid parts/descriptions correct at 16-November-2008.  You should check part# and descriptions are correct when ordering in case I've made a mistake transferring them onto this page.

Component Description Part #
R1,2,3 (order 1 pack) PACK 100 120R 0.25W CF RESISTOR (RC) 62-0348
R4,5,6 (order 1 pack) PK 100 10K 0.25W CF RESISTOR (RC) 62-0394
R7 (order 1 pack) PACK 100 1K 0.25W CF RESISTOR (RC) 62-0370
R8 (order 1 pack) PK 100 270R 0.25W CF RESISTOR (RC) 62-0356
C1 100N 2.5MM X7R DIELEC.CERAMIC (RC) 08-0235
C2 220N 5MM Y5V DIELECT.CERAMIC (RC) 08-1015
C3, C4 100UF 25V LOW IMPEDANCE ELECTROLY CAP RC 11-2922
D1 1N4148 SIGNAL DIODE 75V 150MA (TRU) RC 47-3416
Q1,2,3 (alternative) STP36NF06L MOSFET LOGIC N 60V 30A (RC) 47-0552
IC2 DA78L05 V REG +5V 100MA TO-92 TRU (RC) 47-3612
LED1 L-34GD MIN 3MM ROUND GREEN LED (RC) 56-0745
socket for IC1 8 PIN 0.3IN TURNED PIN SOCKET(RC) 22-1720
IC1* PIC12F683-I/P MICROCONTROLLER (RC) 73-3374
CN1, CN2 (order 3) 2 WAY 16A 5MM END STACKABLE TERM-BLOC RC 21-1810
S1 3.85MM RIGHT ANGLE TACT SWITCH (RC) 78-1152
     

Parts List Notes

* IC1 will need programming with the firmware code before use

PIC Programmer
If you need a PIC programmer you can also buy the PICkit2 starter kit from Rapid, part # 97-0101

Alternate MOSFETS

The STP36NF06L MOSFETs specified are logic level devices and are specified to operate with a low gate voltage.  You can use standard N Channel MOSFETs with a suitable Ids current rating if you can't obtain this part and they should work fine with load currents of 2-3 amps. 


Construction photos:

Identifying components
Component id visual guide

Assembly reference image

We've also put together step-by-step construction details for this project on the Instructables website.  
Refer to the schematic diagram for component values used in this project.

Fig.1

Fig .2

Fig. 3


Fig 1. Before you start make sure you observe ESD procedures when handling and installing the MOSFETs Q1-3 to avoid destroying them through electrostatic discharge.

Fig 3. Start assembly with the small components first and work through to the large parts.


Fig.4

Fig .5

Fig. 6

Fig. 4 When fitting D1 make sure the black band is in the same direction as shown on the overlay.

Fig. 5 The LED has its legs bent through 90o before installation.

Capacitors C2/3 should be installed with the negative terminal towards the middle of the PCB.
One lead of each capacitor is shorter than the other.  The short lead is the negative terminal.

Fig. 6 Fit LED with cathode toward top edge of the PCB, anode toward S1.
         The short lead on the LED is the cathode.


Fig.7

Fig .8

Fig. 9

Fig. 7/8 General assembly views

Fig. 9 The PCB screw connectors are end stackable.  Slot the connectors together before installing.


Fig.10

Fig .11

Fig. 12

Fig. 10/11  General assembly views

Fig.12  The PCB is laid out to take a second switch.  It is not used by the firmware and isn't required so unless you're planning to use the hardware with your own code, do not install it. 


Fig.13

Fig .14



Fig .15

Fig.13  It is recommend to heavily tin with solder the PCB tracks between the connectors and MOSFET to increase the current carrying capacity of these tracks. This is shown in the photo.

Fig.14  Don't bridge solder across the gap indicated in the photo.  Due to an oversight with the solder mask the exposed PCB track looks as though it should be connected - it should not.  If you accidentally bridge this point it will short-circuit the input power supply to the board.

Fig.15   Testing the basic circuit function using 5mm LEDs


Connecting to the PCB

DC in should be in the range 9 to 24 volts.  It should also be able to supply the current requirements of all three output channels.

Maximum output per channel is 5 amps for a total of 15 amps.  Connecting cables should also be able rated for the current they will be carrying.

LED arrays, modules etc should have their negative or cathode terminals connected to the MOSFET outputs and the positive or anode connection to the common terminal as shown below.

A very good 'free' web based tool that will design arrays of LEDs for you, check out this site.  http://led.linear1.org/led.wiz

If you're looking for high power LEDs and arrays to use with this driver you might want to check out Sure Electronics.  I have no affiliation with them but I've bought LEDs from them.


Firmware

This driver board uses the same firmware as the RGB LED Driver elsewhere on this website.

Please download the code from here



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