ADC negative VREF on 18F4550 question

[rmteo]

Firstly, a FET does not have a base (or emitter for that matter) and it requires more than 0.6V (typically 3-10V relative to the source) on its gate to turn on.

Best way to do what you want is to use a SEPIC DC-DC Converter switching converter. It's output voltage can be lower or higher than its input voltage.

[Acetronics2]

Hi,

For such a simple task, I would use a simple capacitive voltage doubler, driven by the µP clock output, i.e. and then use a linear regulator ( or a voltage ref ... or TL431 ).
using some MAX 630 ( a max 232 or ICL 7660 could also do it ... ) as a step-up converter is there somewhat overkill.
Max 761 ANs are to look at too ...

a convenient one had been the MAX 879 ... but production stopped !

Alain

[comwarrior]

looked at the max660... It's expensive and does not give the required output...
I'm looking for 1Amp @ 3.4V
And cost is an issue...

For testing purposes i'm using the TIP35(C), gate to source threshold 2V but i generally find that it operates as low as 1V just not in the 'fully on' setting...

If the -Vref is tied to the voltage rails by those diodes... then what is the point of having an external -VREF?