boost converter question

Hi,
i'm designing a boost-boost in order to obtain a negative 24 voltage from 12Volt input.



i'd like to avoid that with a bad mos pilot of the first stage boost or with a fault that put the first mos always opened, the second stage could generate a -12V negative voltage from a 12V out of the first stage.

Is it possible? What kind of measures could i take to put my converter in safe state in case of fault?
Thanks.

p.s in safe state i mean a 0 voltage out of the second stage.

What current?
Here is a page from the datasheet of the MC33063 and MC34063.
This will input 6V and output -12V.
To change the input to 12V change L to 220uH.
To change the output to -24V change R1 or R2.
To increase current change Rsc.
Note: Pin 4 is normally "ground" but in this circuit it is -Vout.

Is it possible? What kind of measures could i take to put my converter in safe state in case of fault?

Click to expand...

Resistor Rsc measures the current. If the current is too big the IC will stop working.