[sdiy] non-mechanical switching solutions

ASSI Stromeko at nexgo.de
Mon Jun 27 21:21:20 CEST 2016


On Montag, 27. Juni 2016 08:43:43 CEST Ian Fritz wrote:
> My latest VCO design uses MOSFET switching.  After a bit of searching I
> settled on the VN0104. So please let me know if you find a better one!

I'm biased, but unless you really need through-hole, then have a look at the 
OptiMOS2 transistors.  Much lower on resistance at very low gate overdrive 
(logic: 4.5V, super logic: 2.5V, ultra logic: 1.8V).  If you need pMOS or want 
to make passgates, look at the complementary transistor series.

http://www.infineon.com/cms/en/product/power/power-mosfet/small-signal-mosfet/
channel.html?channel=5546d4624e765da5014e8d1528636b49

> Don't forget -- modern MOSFETS all have built-in body diodes, which
> means you have to use two back-to-back devices for bipolar signals.

Not all of them, only the DMOS variants (almost all power MOSFETS are these 
days, of course).  Even for those it would be technically possible to separate 
the bulk terminal, but since you can't swap source and drain even then anyway 
because these are inherently asymmetrical devices, nobody cares to do it (for 
discrete transistors, that is -- story is different for DMOS integrated with 
other circuitry).

Don't forget that when connecting the transistors back-to-back you will need 
more gate overdrive since the Vth will go up due to the backbias effect.


Regards,
Achim.
-- 
+<[Q+ Matrix-12 WAVE#46+305 Neuron microQkb Andromeda XTk Blofeld]>+

SD adaptation for Waldorf microQ V2.22R2:
http://Synth.Stromeko.net/Downloads.html#WaldorfSDada




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