Can open drain output be used as led driver,without requiring extra pullup resistor

[nicky.r]

Hello,

Can open drain output be used as led driver,without requiring extra pullup resistor other than the led current limiting resistor.

lets say the led power voltage is 5v and its cathode is connected to the open drain o/p and there is a current limiting resistor.Now when the ouput goes to high impedance state,will the output get pulled up to 5v.

Thx

 

[Jack// ani]

Yes, it will work.

Open collector will drain current when output is high, remember it, however, can not source current.

Hope this helps

 

[nicky.r]

Thank you for your clarification.
when the ouptut goes into high impedance,how does the pin get pulled up to 5v through the led and series resistor? , because from what I understand the led should be off.

 

[alexan_e]

Think of the open drain/collector as a switch to ground, it either provides ground (on) or leaves the output floating (off).
When the output is off (floating) then there is no current flowing through the led resistor and led so you have no voltage drop on that resistor.

Alex