Have you tried a resistor from pin 8 to +16V instead of connecting=20
it to pin 1?
     MC34063 output is a Darlington if pin 8 is tied to pin 1.

     Mark Jordan


On 28-Jan-17 09:37, IVP wrote:
> Hi all,
>
> I'm trying to get 5V at a few amps out of an MC34063 circuit using
> an external high side P-ch FET
>
> Schematic, scope captures and layout
>
> https://www.flickr.com/photos/97814409@N04/albums/72157675978832174
>
> With no load I get 5V
>
> Output into a 6R8 100W load is only 2.5V. Nothing is heating up
> and the inputs are a steady 9V and 16V. The transformer has two
> 8A secondaries so there's plenty of juice available. Some switching
> noise can be seen on the 2.5V at 20mV/div, not any significant
> ripple
>
> The drive seems to be OK, certainly better rise/fall than without the
> totem pole, although I do wonder about the gate not going to 0V,
> only down to just below 1V, so maybe the FET isn't fully on
>
> I've tried tinkering with a few components and values, no change
>
> Any ideas ?
>
> TIA
>
> Joe
>
>
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