cascode switching

 

I tried firing a car ignition coil by connecting
a 400 volt transistor in cascode, like this:

   +12 v
      |
      |
   +--+-------+
   |          |
   |          |
  10R          )
   |   ignition)
   |      coil )
   |           )
   |    _______)
   |  c/
   +--| MJE13009
      e\
        |
        |
      points
        |
        |
       gnd

but it blew out the transistor after a few cycles.
I have fired ignition coils using igbt's and mosfets
(although not in cascode)
with similar voltage ratings to the MJE13009 and nothing
ever went wrong.
Recently I also tried the MJE5852,
which is a 400 volt pnp transistor, in the following configuration,
and didn't have any problem

          +12 v
             |
             |
              )
      ignition)
         coil )
              )
              )
             |
             |
           e/
      +----|  MJE5852
      |    c\
      |      |
   points    |
      |      |
      |      |
      +---+--+
          |
          |
         gnd

Did I get a bad MJE13009 or is there something wrong with
the arrangement in the top diagram?

 


kell wrote:

Yes, the top diagram is completely wrong.

 


cbarn24050@aol.com wrote:

Let me show you and example of cascode switching.  Look at figure two
in the datasheet in this link.
http://www.st.com/stonline/products/literature/ds/10854.pdf
"high voltage bipolar low voltage mosfet" -- I'm using the same
switching topology, with mechanical points where they have a mosfet in
the pictured circuit.

 



kell wrote:


No you're not ! Look at what the base is connected to.

Graham

 


cbarn24050@aol.com wrote:

Let me show you and example of cascode switching.  Look at figure two
in the datasheet in this link.
http://www.st.com/stonline/products/literature/ds/10854.pdf
"high voltage bipolar low voltage mosfet" -- I'm using the same
switching topology, with mechanical points where they have a mosfet in
the pictured circuit.