[sdiy] Generating +5V gate signals from +3.3V logic

[Steve Lenham]

> Hmmm, maybe there's something I'm not quite clear on (wouldn't be the
> first time)... Wouldn't the output of an analog switch swing from +V
> (whatever voltage is at the input of the switch) when ON, to a high
> impedance state when OFF? If you really want that output to swing to
> 0V when off, I think you'll need a pull down resistor. Of course, the
> pull down will change the voltage at the output, but that's easy to
> compensate for and should be very repeatable. Still, the analog switch
> method seems pretty straightforward. Other than that, what about a
> non-inverting buffer? Are those capable of level translation?
>
>
> Tim (lost in level translation) Servo

Sorry, I should have been more explicit about what I was suggesting.

WRT the original query about how to get a more precise and stiff (in the 
non-varying voltage sense!) gate output, I was imagining:

- a 5.000V reference feeding the input of an analogue switch e.g. 4066, 
4053, etc.

- a non-inverting/unity gain opamp output buffer with current limiting 
resistor inside the feedback loop.

- the output of the switch connected to both the non-inverting input of 
the opamp buffer and a large value (say 1Meg) pulldown resistor to 
ground. As long as the on-resistance of the switch is << the pulldown 
value, the effect on accuracy will be minimal (e.g. 40ohms into 1Meg 
gives 4.9998V).

- the control input of the switch matched to whatever input voltage is 
expected; can be less than the gate output voltage if the right switch 
family is chosen, or higher with the addition of a potential divider.

Of course there are much simpler methods if you don't care about the 
precision of the output voltage.

Cheers,

Steve L.

Benden Sound Technology
www.bendensound.co.uk