WS2811 with Darlington Array IC

Thread Starter

adeleee

Joined Dec 16, 2012
11
Dear All ;

I am trying t make LED project with 6 LEDs and WS2811 LED driving IC and Darlington npn transistors as shown in the first image , but now i need to convert this npn transistors into 1 IC ULN2001D Darlington Array IC , All info attached

please notice that , WS2811 is current sink output 18.5 mA

32446632828-imgpb639407613613407639799.jpg

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Thread Starter

adeleee

Joined Dec 16, 2012
11
Yes it worked fine , but when i removed the 2 trandistors bare , but my question is , how to replace this transistor bare with Darlington array IC ?
 

eetech00

Joined Jun 8, 2013
1,706
Dear All ;

I am trying t make LED project with 6 LEDs and WS2811 LED driving IC and Darlington npn transistors as shown in the first image , but now i need to convert this npn transistors into 1 IC ULN2001D Darlington Array IC , All info attached

please notice that , WS2811 is current sink output 18.5 mA
Hi

What is the part number for the LED's?

eT
 

TeeKay6

Joined Apr 20, 2019
435
Yes it worked fine , but when i removed the 2 trandistors bare , but my question is , how to replace this transistor bare with Darlington array IC ?
@adeleee
First, note the logical operation of your old vs new circuits. In the old circuit, an LED lighted when the WS2811 output went low (ground), thus driving the output of your cascaded discrete transistors low. In the new circuit, using the ULN2001, the logic will be reversed: When the WS2811 output goes low, the ULN2001 Darlington transistor will turn off, not on. This means that whatever is providing your data into the WS2811 will need to change the requested duty-cycles (i.e. 100% becomes 0%, 0% becomes 100%). Alternatively, you could keep an external inverter transistor for each channel, but much of the advantage of the ULN2001 is then lost (extra parts needed for the inverter).

As for connection, the ULN2001 Darlington simply replaces your cascaded transistors. For each color channel connect the WS2811 output to a Darlington input; from that same input connect a 470Ω or 1K resistor to +5V. That resistor will pull the base of the Darlington toward +5V, raising it at least to 2.8V--the min spec to turn on a ULN2001 Darlington. Connect the ULN2001 COM terminal to +24V.
 

eetech00

Joined Jun 8, 2013
1,706
Hello,

If you use the ULN200x you will loose constant current drive capability of the WS2811.
Better to use a separate constant current driver.

eT
 

Thread Starter

adeleee

Joined Dec 16, 2012
11
@adeleee
First, note the logical operation of your old vs new circuits. In the old circuit, an LED lighted when the WS2811 output went low (ground), thus driving the output of your cascaded discrete transistors low. In the new circuit, using the ULN2001, the logic will be reversed: When the WS2811 output goes low, the ULN2001 Darlington transistor will turn off, not on. This means that whatever is providing your data into the WS2811 will need to change the requested duty-cycles (i.e. 100% becomes 0%, 0% becomes 100%). Alternatively, you could keep an external inverter transistor for each channel, but much of the advantage of the ULN2001 is then lost (extra parts needed for the inverter).

As for connection, the ULN2001 Darlington simply replaces your cascaded transistors. For each color channel connect the WS2811 output to a Darlington input; from that same input connect a 470Ω or 1K resistor to +5V. That resistor will pull the base of the Darlington toward +5V, raising it at least to 2.8V--the min spec to turn on a ULN2001 Darlington. Connect the ULN2001 COM terminal to +24V.
Dear TeeKay6 , thanks a lot for your replay , i appreciate your help , please take a look at the diagram attached , i made as your instructions and then i will modify the programming to reverse the code output . and answering why i am using cascaded transistor driver is that i need to drive 12 LEDs with only one WS2811 , and the output of WS2811 can not be used as its equal only to 18.5 mA .
 

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TeeKay6

Joined Apr 20, 2019
435
Dear TeeKay6 , thanks a lot for your replay , i appreciate your help , please take a look at the diagram attached , i made as your instructions and then i will modify the programming to reverse the code output . and answering why i am using cascaded transistor driver is that i need to drive 12 LEDs with only one WS2811 , and the output of WS2811 can not be used as its equal only to 18.5 mA .
The LED diodes need to be reversed in your latest drawing: anode to +24V, cathode to ULN2001. (Current is to flow from +24V, thru LEDs, to ULN2001, to ground.)
In your post#1, you show two 4-pin connectors with "12V" on a pin; yet in the remainder of the drawing I see no reference to 12V. ???
 
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Thread Starter

adeleee

Joined Dec 16, 2012
11
The LED diodes need to be reversed in your latest drawing: anode to +24V, cathode to ULN2001. (Current is to flow from +24V, thru LEDs, to ULN2001, to ground.)
In your post#1, you show two 4-pin connectors with "12V" on a pin; yet in the remainder of the drawing I see no reference to 12V. ???
Dear TeeKay6 , as you can see in the attached picture , i reversed the LEDs with +24 V on Anode . And for 12V o the two 4-pin connectors in my post#1 , its a typing mistake , its 24V not 12V

thanks a lot for help , i am going to test the circuit soon and i will inform you about result . if you have any other instructions , please let me know

Regards
 

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TeeKay6

Joined Apr 20, 2019
435
Dear TeeKay6 , as you can see in the attached picture , i reversed the LEDs with +24 V on Anode . And for 12V o the two 4-pin connectors in my post#1 , its a typing mistake , its 24V not 12V

thanks a lot for help , i am going to test the circuit soon and i will inform you about result . if you have any other instructions , please let me know

Regards
See reply by @bertus. He is correct that the current limiting resistor in each string of LEDs must be retained.
 
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