Availability of parts (was: Compensated Exp generators)
The Old Crow
oldcrow at Access.Mountain.Net
Thu Jun 1 18:28:26 CEST 1995
On Thu, 1 Jun 1995, Rick Jansen wrote:
> 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.
I've found the Signetics DG308A/DG309 series of analog switches to be
the most suitable in low-impedance switching. They are quite common, and
have the advantage of working at +15/-15V.
> > 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.
For an example, the same National Semiconductor appnote (AN-299) that
demonstrates the LM3046 temperature-controlled exp converter also shows a
sawtooth VCO where the firing circuit is this PNP-NPN pair wired as a
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