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 of this?
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 of this?
Lm311 is a comparator. It is unlikely to be stable in any normal amplifier configuration. What you are seeing might be the result of an oscillation caused by this
Comparators are not opamps, opamps are not comparators(*), choose the right device for the purpose!
(*) people often do this, but any cheap comparator is a far better comparator than any opamp, and many opamps will be fried if you use them as comparators.
(*) people often do this, but any cheap comparator is a far better comparator than any opamp, and many opamps will be fried if you use them as comparators.
The 311 also has a rather specialized output stage designed to be digital compatible with several modes of operation. The uncommitted emitter is *designed* to move the ground reference so that steering diodes are not needed when operating off a split supply, and could be used as an inverting output. In normal operating mode you need a pull up resistor. Using it in typical op-amp ways can cause misbehavior. There are better choices of comparator if you want something that behaves more like an op amp, and a lot of op amps that are perfectly happy being used as comparators, if the slew rate limits don’t bother you.