On 12 Mar 2005 at 23:20, D Platt wrote:

> Forgive my ignorance, but I'm still not seeing a problem which needs to 
> be overcome. I read that page already and what I saw was their 
> description of why the LM3524 was a poor choice. The other issue they 
> addressed was the need to have the gate voltage a little greater than 
> the source. How is that a "problem"? Also, that doesn't explain why NPN 
> or PNP transistor (my original question was about transistors not FETS) 
> are used together instead of simply using all NPN's.

Hi David,

There's nothing wrong with using NPN transistors, even on the high 
side. However, you will end up using some PNP transistors somewhere 
in your circuit, or else do some heating with low-value resistors and 
suffer from not being able to turn the final stage fully on(or maybe 
multiple power supplies or bootstrap capacitors?). Also, you will 
likely do some quasi-darlington thing with a PNP driving an NPN, so 
you are really creating a PNP anyway, unless you really want to argue 
the finer points.

Cheerful regards,

Bob

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