I am attempting to create a high voltage signal when the voltage from a sensor I am using drops below a certain threshold, which will be between .05 and .1 Volts. I was trying to use an LM741 op amp to do this, but I could not get it to work as a comparator for these small voltages. Can anyone recommend a component or suggest a way to get an LM741 to work for comparing such small voltages?
Comparator: What is appropriate for comparing ranges of about 50-100 mVs? Can I use an LM741 op amp
comparatoroperational-amplifier
Related Solutions
The wiring was correct and the code was mostly correct. It came down to incorrect #define statements. To fix the problem all I had to do was change them to
#define GREEN BIT6
#define RED BIT0
Take something like below and add in current limit or protection circuit as necessary. Variations of this circuit are commonly found in isolated SMPS. The current limit box in the schematic can be a simple resistor if appropriate (when input range is not too great).
U1 can be replaced with a simple NPN transistor using the Vbe as the threshold. The accuracy would be lower, but from what you said it should be good enough.
simulate this circuit – Schematic created using CircuitLab
Best Answer
The allowable input voltage range for a 741 is 2 volts inside the power rails. This means that on a +/-15V supply, the inputs will still adequately function from -13V to +13V.
If you are trying to tempt performance from a 741 with a grounded negative rail then don't expect the inputs to function lower than 2V above ground and worst case 3V.
Let's look at a few other things too.
My advice is this - don't use it - pick a better device - even the LM324's inputs encompass the neg rail. My general purpose work-horse op-amp is the AD8605 because it's not at all like the 741 and comes in single, dual and quad packages.