Availability of parts (was: Compensated Exp generators)

Rick Jansen sscprick at horus.sara.nl
Thu Jun 1 09:49:55 CEST 1995

In message <2FCDE89E at MSMGATE.M30X.NBG.SCN.DE> JH writes:

About discharging a capacitor with MOSFET/JFET/HC4066 switches
and Rds(on):

> I know that there is a difference between
> '4016 and '4066, and I thought the standard CD4066 had 60 Ohms.
> Anyway, what about using all 4 switches in parallel?

Great idea! *applause*

S. Franco in his book says there are special FETs with a Rds(on) of
just a few ohms, but the not-so-extensive spec lists I have do not list
such devices. One of my biggest reasons to choose a certain part is
*availability* though. Especially with discrete transistors semiconductor 
manufacturers have bombarded the market with tenthousands of different
types and numbers. And, transistor equivalent guides often simply lie
about equivalent parts. So, especially if you're after a certain
important quality I think it's better to use a common ic. That's why
I use the 4007 instead of a single MOSFET even.

> But if You want ultra-fast discharge, why not go for the thyristor
> solution? (Thyristor made of 1 NPN + 1 PNP transistor. I haven't done
> this myself, but it seems to work fine in many Roland and Korg VCOs.)

I'll look into this. I think I've seen such a circuit in The Art of
Electronics, but hadn't given it more thought.

Rick Jansen
rick at sara.nl   http://www.sara.nl/Rick.Jansen
S&H's a module and s&h's looking good

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