Thanks Russell, that is what I needed. 

John.

--- Russell McMahon <apptech@paradise.net.nz> wrote:

> There are many ICs that will do this.
> 
> > Do you know what ic was used to increase the
> voltage?
> 
> The MC34063 is old, less efficient than many,
> cheaper than almost any, 
> available, small (DIP8, SO8) and very very very
> flexible in what it 
> can do. (eg the high side current sense is rare,
> 1.25v ref allows low 
> minimum supply, access to both ends of power switch
> allows about all 
> conceivable topologies,
> A semi typical application diagram is attached
> (drawn Joe Colquitt aka 
> Jinx, my circuit).
> 
> This is more complex and makes far far more power
> than you need (20+ 
> watts) but gives a good idea of the IC's
> functionality. Most low power 
> applications use the internal switch transistors and
> no external 
> switch.
> 
> Onsemi 42 page app note AN920 available here and
> elsewhere
> 
>        
> http://www.onsemi.com/pub/Collateral/AN920-D.PDF
> 
> Gives many examples and much description. An
> excellent basis for 
> building small switching power supplies.
> 
> Note that the circuit attached drives an external
> FET - FETs had not 
> really been considered as power elements in this
> application when the 
> app note was originally written :-) - so you won't
> find any in the app 
> note - but the FET driver works OK.
> 
> 
> 
>         RM 
> > -- 
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