Lm339 output

[Tha fios agaibh]

I repaired a board yesterday where I had a bad optocoupler driven by a LM339N.

I was expecting the output to be 0V (ground) when triggered. (When Neg > Vth)
Instead it was about 0.5v.
From pin 3 Vcc with respect to pin 12 gnd I got 15v.
From pin 3 Vcc with respect to output pin 2 I only got 14.5v

Everything now works fine on the board but I'm wondering about the extra voltage?
Is this normal?

 

[Nanren888]

The data says that the ouput will sink typically 16mA with test conditions being that the device Vo not exceed 1.5 volts.
The Saturation voltage spec says typically 130mV, max 400mV at a test current of 4mA.
.
This does not sound too far off what you got if you consider the 15mA output current.
The plot of Output current versus Output saturation voltage, shows a few temperatures, and stops at 6mA, but looks as if it might get to 500mV or more by 15mA.

 

[Tha fios agaibh]

Thanks Nanren888,
I didn't realize 15ma was enough of a load to sink 500mv.
BTW, the opto switches on at ~ 1.7v. So a little better than the data.

 

[Nanren888]