Multiple IR LEDs from 1 port using transistor

[belpe123]

Hey guys,

Ive got a PIC16F819 here, which has 2 PWM ports, each is capable of sinking and sourcing 25mA. I need to connect multiple IR LEDs to both of these ports, as many as is possible, however each LED will draw atleast 15mA which means I can really only use one per port.

Is there a way, using a BJT transistor, that I can run multiple IR LEDs off the same port. Also, the PWM frequency is 38KHz so the transistor would have to be able to cope with this.

Thanks

Michael Belperio.

[Luciano]

See URLs below.

http://www.rentron.com/Infrared_Communication.htm
http://www.rentron.com/Files/2n4403.pdf

Luciano

[ardhuru]

Hi Michael,

Assuming you have a 12 volts raw DC available, you should be able to drive at least 4 LEDs in series, thru' a transistor connected to the PIC pin.

If you need even more, you could have multiple of these LED strings in parallel, depending on how much current your transistor can take. The 38 khz carrier would not be a problem to any of the general purpose transistors.

Regards,

Anand Dhuru

[Bruce]

I have used the ULN2803A to drive large banks of IRLED's for video
cameras.

Wire all of the ULN2803A inputs together. Use a single I/O-pin to drive
the 2803A inputs. You have 8 NPN darlington high-current drivers in a
single package that can control a whole herd of IRLEDs.

FET's are also a good option, but pretty much any GP transistors will
work ok at this low a frequency.