Joe said

>> http://www.intusoft.com/onsemipdfs/an920-d.pdf

Very droll.

Fig 22 does what you want.
Use PNP of choice.
If saturation voltage too high (which it ought not be) use MOSFET



>>
>>
>> Very handy when the input DC can be wide-ranging. For example
>> an SLA that could go from 11V+ to 14V and you need 12V out
>> or being able to grab just about any wallwart (particularly if a bridge
>> is added to the input to fix wrong polarity or AC)
>
> Hmmm... after checking out that MC34063 app note, I think the PIC + PWM
> design is the way to go.  Only one high current component (cheap MOSFET)
> and I can also implement low voltage shut-down and other function very
> easily in firmware.
>
> I think the PIC method is also the safest bet for something I have to
> build a prototype of and ship overseas in the next couple of days.  Once
> we get client feedback (overall project needs to be approved by someone
> else), we can go from there.
> David...
>
> --
> ___________________________________________
> David Duffy        Audio Visual Devices P/L
> Unit 8, 10 Hook St, Capalaba 4157 Australia
> Ph: +61 7 38235717      Fax: +61 7 38234717
> Our Web Site: www.audiovisualdevices.com.au
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