> My tip: throw away this 1000 boards.
> Create a new one with an LM2574 or better MC33063.
>
> You have too much heat !

Resistor.
Series resistor.
Add a 10 watt 56 ohm series resistor.
Do it now. You'll like it :-).

And, as he says, for the next batch look at the MC34063 / MC33063.
Olde.
Cheap. Far cheaper than any equivalent modern part.
Exceedingly flexible and capable. Can drive any topology desired. 
Unlike many modern parts.
Efficiency is OK if not right up there.
BUT even if it was 50% efficient (and it will be far better than that) 
you'd only dissipate 1.5 watt in the switcher.
At 80% efficient, which you would achieve with a MC34063, switcher 
dissipation is 0.2/0.8 * 5V * 0.3A = 375 mW.

A PCB that fits a 7805 footprint could be made.

MC34063 is 0-70 C version
MC33063 is -40 to +85C version

MC34063 / MC33063 stuff here

        http://others.servebeer.com/temp/mc34063smps

and

        http://others.servebeer.com/temp/mc34063_smps.htm

or for those with real browsers [ :-) ]

        http://others.servebeer.com/temp/mc34063_smps.mht








The fantastically useful App note AN920 here





        Russell McMahon.


        RM

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