This is a Voltage Comparator circuit can be uses indicates the input voltage differs from two defined limits, V1 and V2.
One application here is to monitor a 12V car battery. V1 can be set to 14V and V2 to 11V thus giving an indication of more than the cost or weak batteries. Op-amp used here is the CA3140 MOSFET. They are used to advantage because they have less output offset voltage and can switch to 0volts close. If any other use op-amps like the LF351 or CA741 will need to have an offset null control. This is just a 10k preset reached between pins 1 and 5, the wiper connected to the negative supply op-amps or 4 pins. The following is a schematic drawing:
With this circuit the op-amp will turn on the LED if the input voltage out of limits, the two 1N4148 diodes to form an “AND”-gate at the output. Input voltage to be monitored are fed through a series of 10k resistors on the input of both op-amps. If the input voltage is greater than the limit set by V1 it will CA3140 output swing to almost full supply voltage and LED lights. Similarly, if the input voltage is less than the limit set by V2 the op-amp will swing to the Vcc and the LED light.
IC CA3140 Description
The CA3140 is integrated circuit operational amplifiers that combine the advantages of high voltage PMOS transistors with high voltage bipolar transistors on a single monolithic chip.
Absolute Maximum Ratings
DC Supply Voltage (Between V+ and V- Terminals) . . . . . . . . . 36V
Differential Mode Input Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . 8V
DC Input Voltage . . . . . . . . . . . . . . . . . . . . . (V+ +8V) To (V- -0.5V)
Input Terminal Current. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1mA
Output Short Circuit Duration∞ (Note 2) . . . . . . . . . . . . . . Indefinite
Temperature Range. . . . . . . . . . . . . . . . . . . . . . . . . -55oC to 125oC
Maximum Junction Temperature (Plastic Package) . . . . . . . 150oC
Maximum Storage Temperature Range . . . . . . . . . -65oC to 150oC
Maximum Lead Temperature (Soldering 10s) . . . . . . . . . . . . 300oC