The reason for the variability of capacity is in the pn transition. If the diode operates in lock direction, growing space charge zone with rising tension. This reduces the capacity.


  with



However, the above formula only up to a value of





Above this area CS can no longer be shown concretely. Therefore, the further course with CS approximated by the tangent below. This approach, however, is sufficiently accurate.



 



Through use to obtain:

  with