Electronics > Beginners
Drive a 12V analog switch from logic level input
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vk6zgo:

--- Quote from: hermitengineer on November 22, 2019, 09:05:55 am ---
--- Quote from: jhpadjustable on November 22, 2019, 08:26:53 am ---Invert the control input and use just one transistor? :)

--- End quote ---
Oh, duh.  You mean something like the upper part of this?

(Attachment Link)

--- End quote ---


If it doesn't have to be very fast, the bottom part would be better.
Zero999:

--- Quote from: hermitengineer on November 23, 2019, 07:40:01 am ---
--- Quote from: Zero999 on November 22, 2019, 11:42:02 pm ---Why not simply use a logic level translator IC such as the CD4504 or CD40109? It's non-inverting and doesn't require any other components.
http://www.ti.com/lit/ds/symlink/cd4504b.pdf
http://www.ti.com/lit/ds/symlink/cd40109b.pdf

Oh and if you do want to go discrete, a BJT can be used in non-inverting configuration by connecting the input to the emitter, rather than the base.


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A 4504 may indeed be the most robust and simple solution.  I just turn up my nose at the number of unused gates  >:D  Why don't they make a single-gate version that can take 12V+?

As mentioned above, the existing circuit within the "black box" that I'm interfacing to uses a 10K pull-down, so a resistive supply would not be a good match.  So unfortunately, that level shifter circuit has the same problem as the MOSFET ones.

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I don't know why they don't make a single gate version, but they're not expensive, so not using all of the gates shouldn't matter. It will certainly use less power than a discrete solution and probably work out cheaper too.

In the discrete solutions, an additional transistor can be added to pull the output hard up to the positive rail or use the opto-coupler, as you posted before, but both options will be more expensive and power hungry than a logic level translation IC.

The pull-down resistor is also no problem for a logic level shifter IC.
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