Troubleshooting LM311P Output Issue - Tips and Suggestions

[Stonestreecty]

TL;DR Summary

I'm using a LM311P. It is has a collector/emitter output. Because my circuit didn't function the way it should, I started debugging. But not following the input signal.

Hello, all
For this little project, I'm using a LM311P. It is has a collector/emitter output. Because my circuit didn't function the way it should, I started debugging.
With the collector unconnected the emitter (pin 1) still sinks (11 mA) and sources (20 mA) current, when applying a square wave input. I measured mean dc amperage to either rail, so the max is higher. I cannot explain this behavior.
Doing the current measurement on the collector (pin 7) with an unconnected emitter I get 14 mA when sinking, and none when sourcing. But not following the input signal.

Any suggestions what could cause this?

 

[Baluncore]

Summary:: I'm using a LM311P. It is has a collector/emitter output. Because my circuit didn't function the way it should, I started debugging. But not following the input signal.

With the collector unconnected the emitter (pin 1) still sinks (11 mA) and sources (20 mA) current, when applying a square wave input. I measured mean dc amperage to either rail, so the max is higher. I cannot explain this behavior.

The output is designed to be used as a voltage output that drives a load.
If you measure the output current you are testing the output current limiting.
Ground the emitter output, pullup the collector without the LED using a resistor to +5V, measure the output voltage on the collector.
Check the voltage needed by the LED. I cannot read the circuit text.
Check the input voltages and verify they are both in the common mode range. Some input structures invert when one input goes out of CM range.