boost converter question

[franticET]

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.

 

[ronsimpson]

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?

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