Dear TI expert,
Pls check the output voltage(CH1) of a comparator LM258(Pin1), the voltage pulse width is small and small with time.
Background information: I use LM258 as a comparator with signle voltage power supply, +12.6V (V-=0, V+=12.6V). IN- connected to 8V source.
IN+ connected to a signal varying from -4V to +5.6V(Not CH2 below but similar as it, the negative side is only -4V ), there is a 10MΩ resistor between IN+ and input signal.
The IN+ input is around -0.45V and clamped at negative half-cycle.
Analysis: In the datasheet, either input more than 0.3 V below V– then input current should be limited to 1 mA and the output phase is undefined.
I don't know if the negative input voltage casues this output abnormal or other reason. Pls help me to check.
If like this, why the abnormal happened in the positive half-cycle? I assume the output voltage should be Zero in the positive half-cycle coz 5.6V< 8V.
BTW: I already used IN4148 in the front of 10M resistor, so the negative voltage is not happened again. But I am not sure the abnormal is due to the -0.45V voltage.
Thanks!