RGB LED driver, Any comments?
Hi there,
I'm thinking of building a RGB LED driver for 8 LEDs. I want to use a PIC16F777 for this task as it has a very convenient 3 hardware PWM channels.
I've made a little schematic, but have some questions.
http://users.telenet.be/maxpowa/sche...leds_small.jpg
larger image:
http://users.telenet.be/maxpowa/schema_RGBleds.jpg
I wonder, are the transistors I've choosen OK for the task at hand? Should I use MOSFETs instead, if so, which mosfets are my best choice?
I would power the circuit with an MC33269T-3.3 LOW drop 3.3Volt regulator. Is this OK or are there better options to power the circuit?
Anything missing or other comments?
Thanks in advance,
Steve.
I am a new user.Where is the asm or hex code for this cicuit
I am a new user.Where is the asm or hex code for this cicuit.
Thank you very much.
Metal-Oxide-Semiconductor-Field-Effect-Transistors
MOSFETS are a voltage controlled current source as apposed to BJT's which are a current controlled voltage source. FETs in general have a relatively higher impedance than their BJT counterparts.
I think there's a lot of personal preference between the two. I will make a bold statement and say that "BJTs make better audio amplifiers" In many cases, either of the two can be made to work.
3 Attachment(s)
ZXLD1350 constant current high power LED driver
This is a pretty old thread. But thought I would add a link to a constant current driver circuit for 1 watt LED's. There are a couple other products around, but this is pretty low part count, and allows from 1 to multiple LED's, so its pretty versatile. It also accepts 7 to 30 volts. They also happen to use a PIC.
Project site: http://picprojects.org.uk/projects/hbld/index.htm
Calculator tool for ZXLD1350 chip: http://www.diodes.com/_files/calculators/zxld1350calcv2.xls
Attachment 5794
Attachment 5793
Re: RGB LED driver, Any comments?
No, however they will require more heat sinking than a Mosfet of equivalent current capacity. Since it is a switch (PWM) the LOW RDSon of most all power mosfets < .1 Ohm Vs a VCEsat of > 1Volt makes it a kinda No Brainer unless all you have are some tip121's? I don't remember which... But @5V gate voltage an IRF 540 is hard to beat for a GP Power Mosfet.
Doc