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LM324：What is the role of the diode

jacky wang1
Intellectual 340 points
Part Number: LM324

Hi，

input signal is pwm ，high level is 3.3V,output is Analog adjust voltage （0--10V）

   1. I do not understand why need diode，What is the role of the diode?

2. I have found add a capacitor (1nF)in parallel between pin6 and pin7 in other application ，What is the role of the capacitor ? how to calc capacitance？

3. In as above picture application，if need add a capacitor in parallel between pin6 and pin7 or not？

  • 0
    TI__Genius 15410 points

    Hi Jacky,

    1. I am not 100% sure why the diodes are added but my guess is that they provide protection for the op amp should a negative voltage get connected to the 0 - 10V node.

    2. A 1nF capacitor between the pins 6 and 7 will reduce the gain of the op amp at higher frequencies. It essentially provides filtering. If the customer does not require any high frequency signals then adding a capacitor in parallel to R110 will only filter out noise. The value of the capacitor should be low enough such that you do not filter out any of your input signals. The cut off frequency can be calculated by 1/(2*pi*R110*C).

    3. See #2. The customer can only determine if a capacitor should be added in parallel to R110.

    Thank you,

    Tim Claycomb