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multiplexing LEDS with ULN2803

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georgz

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Hi i want to use a pic microcontroller to control an array of 50 leds. I'm using two ULN2803 ICs to control the anode and cathode of the leds but
i'm having problems with my schematic because ULN2803 is a NPN transistor array and i can only sink the voltage and not supply it. Is there any PNP array
IC?

pic.png

This is the schematic for one led but it doesn't work. The IC1 can't sink the voltage when i apply voltage to the input.
 

There is no need to control both sides of LED.
Just use only one IC.


+++
 

Hi i want to use a pic microcontroller to control an array of 50 leds. I'm using two ULN2803 ICs to control the anode and cathode of the leds but
i'm having problems with my schematic because ULN2803 is a NPN transistor array and i can only sink the voltage and not supply it. Is there any PNP array
IC?

View attachment 66524

This is the schematic for one led but it doesn't work. The IC1 can't sink the voltage when i apply voltage to the input.

Hi!

In your design the open collector goes straight to +5V and the emitters are grounded. So in reality you will have a burned 2804 gate. Above all you need a pull up to 5V on O1 and not 5V straight. Actually as andre_teprom pointed out, you could leave IC2 unconnected, put a led in series with the pull up and you are ready.
Alexandros
 

There is no need to control both sides of LED.
Just use only one IC.


+++

I need to control each one of the 50 leds the way i want. I found some PNP driver ICs such as UDN2981A and TD62783 but i need more equivalent in case it's hard to find these.
 

Why don´t you use ULN2003, wich is easiest to find ?


+++
 

I already have the ULN2803 which is the same as the ULN2003, it's a NPN array. I need a PNP array.
 

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