TL082: ask the usage of capacitor between the output PIN and input PIN5

?? ?

Prodigy 40 points

Part Number: TL082
Other Parts Discussed in Thread: TLC2574

Tool/software:

I am confused with the C192 capacitor, the C192 capacitor will lead the positive feedback of the input signal of TL082.

Normally, we design the circuit will avoid the positive feedback, it will lead to the circuit instability.

So I wan to look the support from you Why this circuit will use the C192(100nf) in the output PIN and input PIN5？

Any concern from the TL082 or TLC2574 component？

this circuit is used so many years and no problem.

2 months ago

0 Raymond Zhang1 2 months ago

TI__Guru* 77221 points

Hello,

?? ? said:
So I wan to look the support from you Why this circuit will use the C192(100nf) in the output PIN and input PIN5？

The circuit is configured as Sallen-Key 2nd order active LPF with cutoff frequency at approx. 101Hz. The C192, 100nF capacitor is to shape the 2nd-order frequency response and control the Q factor of the filter.

The 2nd order LPF looks ok, but you could add another RC filter after the filter to further attenuate the AC frequency to eliminate the hump or peaking in higher frequency of the magnitude response. But since the application is working for years, I would leave it as is.