Author Topic: Off voltage of LM311 with pin 1 grounded  (Read 669 times)

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Offline aneevuserTopic starter

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Off voltage of LM311 with pin 1 grounded
« on: February 07, 2020, 04:11:12 pm »
I have an LM311 where I've grounded pin 1, the pin that goes to the emitter of the o/p transistor. (Grounded here means connected to 0V with a +10V, 0V, -10V power setup.)

Am I right in thinking that the lowest voltage that I'm going to see on the o/p is \$V_{CE(sat)}\$ of said transistor, say, about 0.3V - or am I confused?
 

Offline fcb

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Re: Off voltage of LM311 with pin 1 grounded
« Reply #1 on: February 07, 2020, 04:16:46 pm »
Yes, in your present configuartion, you'll see VCEsat on the collector/pin7 (assuming you've got some sort of pull-up thing going on).  You can take pin1 to -ve BTW
https://electron.plus Power Analysers, VI Signature Testers, Voltage References, Picoammeters, Curve Tracers.
 
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Offline aneevuserTopic starter

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Re: Off voltage of LM311 with pin 1 grounded
« Reply #2 on: February 07, 2020, 07:10:38 pm »
Thanks.

I'm guessing that there's a fair bit of flexibility in setting the high/low o/p voltages, given that both the emitter and collector are brought to the outside of the device - these voltages seem pretty independent (within reason) of the power rail voltages to the device itself?
 

Offline fcb

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Re: Off voltage of LM311 with pin 1 grounded
« Reply #3 on: February 07, 2020, 08:03:35 pm »
Don't take it below the substrate voltage (-v).
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Offline David Hess

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Re: Off voltage of LM311 with pin 1 grounded
« Reply #4 on: February 09, 2020, 12:25:05 am »
Neither ground nor the output should be pulled below the negative supply for the reason fcb identified.

Ground may be up to 30 volts above the negative supply (according to the datasheet) and the output may be up to 40 volts (or more with some parts) above the negative supply.  This would allow open collector operation with an output voltage higher than the supply voltage.

I am not sure why someone would raise ground above the positive supply but it is allowed.  The output will not work then though.
 


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