Zener diode- to protect- BJT

Discussion in 'Homework Help' started by Daniel_p, Apr 26, 2010.

  1. Daniel_p

    Thread Starter New Member

    Mar 31, 2010
    Could any body please help me with the following problem:
    As shown in the attached picture I have 2 networks, network-1 and network-2. Network-1 charges the capacitor to positive voltage levels and network-2 charges it to negative voltage levels.
    the network-1 must be seprated from the capacitor for the time in which the network-2 is working. I have selected a BJT as a switch to break the path when network-2 is working.
    (Transistor must be off during the negative charge period)

    1-since the capacitor is charged to positive voltages is a protecting zener diode necessary?when yes how should it be connected?
    2- Or a zener diode is required because of negative voltages on the capacitor?when yes how should it be connected?

    Note: care must be taken that the zener diode doesn't provide an unwanted current path while charging to negative voltages(no current path through this BJT).

    How can I solve this problem? or any other idea?

    thanks a lot in advance
    Last edited: Apr 27, 2010