Hi,
Good day.
Customer is encountering disturbed output in their valve using LM258. Below is the details.
"
I used LM258 op amp to design the following circuit.
And on the outside of this circuit there is a motor controlled valve. The valve is powered to 220VAC. The output of this circuit will be greatly disturbed when the valve is found to be on and off during use. The actual measured input and output are shown in the figure below:
The yellow is the 7-pin output of the op amp. Green is 5-pin input. Blue is 6 pin input. In this case, we can see that Pin 5 is not disturbed. There is no similar interference on the power supply 15V. But both pin 6 and pin 7 showed a downward pulse. The strange thing is that pin 6 is the reverse input terminal, if there is a downward pulse output should be up, but the result is the opposite. What could be the cause?
There is another opposite situation as follows: that is, pin 6 and pin 7 simultaneously appear upward pulse, but pin 5 is not affected. These two conditions occur during valve opening and closing respectively.
It is tested that the power supply is stable during valve operation. The C1 capacitor was later removed. Same result. I would like to ask what is the reason for this effect on the operational amplifier?
"
Thank you in advance.
Regards,
Maynard
