more on level shifter

Thread Starter

tibbles

Joined Jun 27, 2008
249
i do quite a bit with automotive stuff ,so i thought the circuit http://forum.allaboutcircuits.com/attachment.php?attachmentid=13208&d=1257131549
well worth saving.
just a couple of points,the output componant will of course depend on the load,but why an fet in this case?.

when on, i'm only getting 7 volts at the output on a simulator (a pretty basic one) even if i apply 12 volts to the gate. what am i doing wrong?

im fairly new, so i hope my question isnt too crazy,although ive somehow become a senior member, (a reference to my age no doubt).
thanks in advance
dougal
 

MikeML

Joined Oct 2, 2009
5,444
Because the existing NFet is being used as a source follower. Its source will always be more than one threshold voltage below the gate. If you want a fully-on or off FET switch, you will have to put the FET in a common-source configuration. Depending on if you need the driver to be inverting or not, that will determine if you need to use an NFet or PFet.
 
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