[sdiy] Transistor questions

[David G Dixon]

The cap I'm using is 680pF, and it is discharging about 4V.

According to my rough calculation, it would require a collector current of
1.36A to discharge that in 2ns, but only 0.136A to discharge it in 20ns.
Hence, the 3904 could do it (with its maximum I_c of 0.2A) but the 945 could
not (with its maximum I_c of only 0.1A).

Well, I have both versions of the VCO built.  I'll calibrate them and see
which one gives better tracking. 



-----Original Message-----
From: Synth-diy [mailto:synth-diy-bounces at synth-diy.org] On Behalf Of René
Schmitz
Sent: Monday, March 03, 2025 4:43 AM
To: synth-diy at synth-diy.org
Subject: Re: [sdiy] Transistor questions

> On Mon, 3 Mar 2025, Roman Sowa via Synth-diy wrote:

To discharge a 10nF cap in 2ns you need currents in the amps range. You 
don't get that with these transistors.

And even if you managed, you spew fast transients all over the place. 
Faster is not always better.