I have just observed how hard it is to come with a design of "absolute" value.
The pristine problem is to get a "simple" (less than 4 opamps ! ) solution which will light on a green LED if the difference between two rails is less than, say, 2 V. Evenbetter if the "2' is "adjustable" by design. I first thought that is was a piece of cake, but even with four standard op-amp (which unfortunately most behave as they do with negative voltage even if their low supplied voltage is the "ground", while some Analog Devices OpAmps claim to do otherwise, these failed to be ... "simple" and commonly available in simulators) I have a hard time to come with a solution. Humble me! Here are the specs: with two rails which can be at +12V or -12V or absent (battery polarity inversed, or one is at an open circuit), light on a standard green LED (can use a reliable available source at an unspecified voltage, independently of the rails source... else, how can you light on a LED with no power at all? ) if the difference of voltage ( what is a voltage if not a difference ? ) between the two rails is less then 2.5 to 2 volt (absolute value, that is). I have spent too much time trying to solve that apparent simple riddle that I resolved ... to post the question here. Once again, humble me with a "simple" solution. TINA (Texas Instruments) or LTspice (Analog Devices) circuit simulation really appreciated, with triangular rails variations for -12V to +12V (different non congruent frequency) appreciated, but any insight thought of "old timer" not deprecated either (and doubly appreciated, in truth). With respect dues, after all, that sounds so simple that I have a strong feeling that I miss something so elementary... Thanks in advance.
The pristine problem is to get a "simple" (less than 4 opamps ! ) solution which will light on a green LED if the difference between two rails is less than, say, 2 V. Evenbetter if the "2' is "adjustable" by design. I first thought that is was a piece of cake, but even with four standard op-amp (which unfortunately most behave as they do with negative voltage even if their low supplied voltage is the "ground", while some Analog Devices OpAmps claim to do otherwise, these failed to be ... "simple" and commonly available in simulators) I have a hard time to come with a solution. Humble me! Here are the specs: with two rails which can be at +12V or -12V or absent (battery polarity inversed, or one is at an open circuit), light on a standard green LED (can use a reliable available source at an unspecified voltage, independently of the rails source... else, how can you light on a LED with no power at all? ) if the difference of voltage ( what is a voltage if not a difference ? ) between the two rails is less then 2.5 to 2 volt (absolute value, that is). I have spent too much time trying to solve that apparent simple riddle that I resolved ... to post the question here. Once again, humble me with a "simple" solution. TINA (Texas Instruments) or LTspice (Analog Devices) circuit simulation really appreciated, with triangular rails variations for -12V to +12V (different non congruent frequency) appreciated, but any insight thought of "old timer" not deprecated either (and doubly appreciated, in truth). With respect dues, after all, that sounds so simple that I have a strong feeling that I miss something so elementary... Thanks in advance.