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4 X 3watt RGB LEDS

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pixman

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Hi TO ALL

I HAVE GOT A PIC16F767 THAT HAS 3 HARDWARE PWM. I HAVE GOT THIS DRIVING 1 X 3 WATT RGB. WHAT I WOULD LIKE TO DO IS DRIVE 4 OR MORE 3WATT RGB LEDs.
I HAVE A FEW TIP41 TRANSISTORS LAYING AROUND COULD I US 3 OF THEM, 1 PER COLOR.EACH LED HAS ITS OWN CURRENT REGULATOR CIRCUIT.

THE TIP41 IS REATED AS FOLLOWS:
COLLECTOR BASE 40V
COLLECTOR EMITTER 40V
EMMITTER BASE 5V
COLLECTOR CURRENT 6A
BASE CURRENT 2A

A PIC CAN DELIVER 20mA AT THE PIN, BUT THE TIP41 REQUIRES 2A.
I HAVE LOOKED AT CIRCUITS FOR TRANSISTORS AS A SWITCH BUT CAN'T FIGURE OUT
WHAT RESISTOR TO USE ON THE BASE.

DAVID
 
The MAXIMUM allowed base current is 2A.

When using it as a switch, the actual required base current to get the rated Vce is ~Ic/10 as depicted on Fig 2 of the Fairchild data sheet.

Since all you have is 20mA, you will likely need a logic-level NFET (which draws no current from the PIC pin), or a Darlington NPN (which can be turned on with ~1 to 2mA). You can make your own Darlington by combining a 2n3904 with your TIP41.
 

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I just found a circuit at pic projects that makes use of mosfet. I have never used them before
and they are not to expensive. It is a stp36nf06l.

Is that what you ment by alogic level nfet.
 
It really wants 10Vgs to be fully turned on with the rated Ron, however if your Id is less than 3A, and you power your PIC with 5V, it will work ok.
 
THE MAX CURRENT WILL BE 2.8A THAT IS 8 RGB LEDS AT 350mA EACH. THE GATE WILL HAVE A 120R TO PIC AND A 10K RESISTOR TO GROUND.
 
I just found a circuit at pic projects that makes use of mosfet. I have never used them before
and they are not to expensive. It is a stp36nf06l.

Is that what you ment by alogic level nfet.

That is a logic level MOSFET, check that you are buying the STP36NF06L and not a STP36NF06 - the L part has a maximum Vgs threshold at 2.5 volts, the non-L part maximum is 4 volts. The L part is characterized for an Rds(on) of 0.05 ohms at Vgs= 5 V, Id=15A.

https://www.electro-tech-online.com/custompdfs/2011/02/CD00003405.pdf





 
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