Zener diode-to protect_BJT

Daniel-p Guest #1689387
Rate this post
• ▲ useful
▼ not useful 
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-2 should takes current out from the capacitor(charge 
it to negative voltage levels).
Transistor must be off during the charge period.


Problem:The zener diode I used to protect the transistor provides a 
current path while the voltage level in the capacitor becomes smaller 
than zero, therefore I can't charge the capacitor!!

How can I solve this problem?

thanks a lot in advance
Attached files:
Reply Quote Edit Move Thread sperren Anmeldepflicht aktivieren Anpinnen Delete topic Thread mit anderem zusammenführen Report post
Daniel-p Guest #1690726
Rate this post
• ▲ useful
▼ not useful 
Sorry I think I should modify the question:

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)

Question:
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
Attached files:
Reply Quote Edit Delete Report post
Watch this topic

Reply

Note: the original post is older than 6 months. Please don't ask any new questions in this thread, but start a new one.

Formatting
  • [c]C-Code[/c]
  • [code]code in other languages, ASCII drawings[/code]
  • [math]formula (LaTeX syntax)[/math]
  • [[Title]] – link to an article
  • Link to another post: right-click its post ID (#8078628), copy the address, paste it into the text

More about formatting

Post long source code as an attachment, not in the text.

Your name and e-mail address

Already registered? Log in

Not shown to anyone. We send you a link; your post appears once you confirm it there.

By submitting you create a free account and accept the terms of use.