What minimum V input has a LM741

Thread Starter

stefanvr

Joined Aug 23, 2017
13
Hi, i'm relative new on circuits. Now i'm learning the OP Amp LM741. I putted a voltage divider on both input pins (2 and 3). If the voltage on pin 2 drops below pin 3 the output goes high. When it goes up again the output gets low. So it works fine. But if the voltage on pin 2 drops below 2V the output stays high!. Whatever the other voltage is. Is there a minimum input voltage on the input pins?
Thanks
Stefan
 

ericgibbs

Joined Jan 29, 2010
10,018
hi stef,
It is always a good idea to get the datasheet for the device you are working on.

It says +/-5V, but be aware that the Vout swing is much less than the Vsupply rails.

E.
 

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Thread Starter

stefanvr

Joined Aug 23, 2017
13
Thanks, i watched a datasheet but there was only a maximum. I used 10 opamps with a voltage divider to make my first (elementary) voltagemeter :)
But the first 4 leds kept on. I can raise the first divider to 2V so i can measure it from 2V to above.
 

Thread Starter

stefanvr

Joined Aug 23, 2017
13
No. do you know some good new OpAmps? not to expencive. So i can buy them. In the 80's electronics was a hobby. A month ago i decided to start again.
 

Thread Starter

stefanvr

Joined Aug 23, 2017
13
i know but a voltmeter was an example. to learn and experiment with opamps. A VU-meter is also one of my experiments. But as the 741 has a minimum of 2V input i have to amplify the signal first.
Alec or Bordodynov, do you know any todays time opamps (dip-8 ic) the 741 is an old one.
 

ericgibbs

Joined Jan 29, 2010
10,018
hi,
I use the MCP6002, dual rail to rail output OPA, the CA3140 and CA3240 where advertised as replacements for the 741
LM234 .

E
 

dl324

Joined Mar 30, 2015
10,718
i'm relative new on circuits.
When discussing circuits, it's best to include a schematic.
Now i'm learning the OP Amp LM741. I putted a voltage divider on both input pins (2 and 3). If the voltage on pin 2 drops below pin 3 the output goes high. When it goes up again the output gets low. So it works fine. But if the voltage on pin 2 drops below 2V the output stays high!. Whatever the other voltage is. Is there a minimum input voltage on the input pins?
upload_2017-8-23_7-29-52.png
upload_2017-8-23_7-30-13.png
upload_2017-8-23_7-30-43.png
The LM741 was designed over 40 years ago. It's claim to fame is that it was the first internally compensated opamp; which made it easier to use.

You don't specify the supply voltages you're using, but it seems that you're operating it with a single supply. The input voltage range is only guaranteed to be about 3 volts from the rails. That makes it inappropriate for use with a single 5V power source.

You should study the difference between opamps and comparators. What you want is a comparator. An opamp can be used as a slow comparator, but since you're learning it would be best for you to learn to use the more appropriate component.

The LM339 is a quad comparator that has an input voltage range of 0 to VCC-1.5V. You could make it work for your volt meter application by using a voltage divider on the voltage being measured to keep it in the comparator's input voltage range.

For example:
upload_2017-8-23_11-39-28.png
 
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