push-push on/off switch

You've been Judged by The High Muckety-Muck, and found ***LIBERAL***.

I wonder if he's going to strike you down with a bolt of lightning? ;-)

Cheers! Rich

Nope; you need picoamp or less gate leakage. Electrons per second is good.

John

I've always been liberal. But I've never been leftist.

That would not be Good Engineering Practice.

John

Would that be in a vacuum or in a gas ?:-)

...Jim Thompson

how about; push on - sw discharges cap into gate push off - sw grounds gate.

Le Wed, 24 Oct 2007 17:34:10 -0700, John Larkin a écrit:

I guess you've missed the smiley :-) But darlingtons have no gate current, so...

Yeah, they have a base. Oops!

Silly Me! :-)

Cheers! Rich

I wonder if it'd flip if, instead of a switch, you used a touch-pad pair? (a round pad, slit down the middle, for example.)

Cheers! Rich

Gosh, I wonder why nobody suggested that before.

Best regards, Spehro Pefhany

It is interesting that nearly all electronic devices - tubes, transistors, jfets, mosfets, gaasfets - have voltage gain only in inverting mode.

There was one mode of operating a pentode that had non-inverting gain.

John

Ahem. BJTs don't have voltage gain in a common base configuration?

Best regards, Spehro Pefhany

Yes, but that's not the primary gain mode, and you can't apply positive feedback from the collector to the emitter, to any useful extent. In other words, you can't make a schmitt or an oscillator without adding some sort of impedance transformation device.

Funny that all these devices behave the same way.

The pentode could make all sorts of interesting oscillators and one-shots and frequency dividers and sweep generators, with just a few external r's and c's. Phantastrons.

John

In custom IC's (*) I've done a synchronizable sawtooth with two BJT's, with a trick that finds the bottom of the ramp by noting that base current rises when a device saturates.

(*) Ignition control chip for Chrysler circa 1966.

To do it proper (linear ramp) generally requires something like several sections of an LM339, plus accurate current mirrors.

...Jim Thompson

That's because there is no *current* gain, n'est ce pas?

Single devices that can have two stable states.. hmmm... tunnel diodes.. neon lamps.. various and sundry thyristors, but not the really common devices.

Hmmm.. a linear sawtooth generator with one active component:

I wonder if you could fiddle something similar with a MOSFET with two gates or a gate and a "back gate".

Best regards, Spehro Pefhany

One problem is if someone holds the switch down for any length of time you will have an oscillator !

Once you have two devices, a lot more becomes possible. The UJT/PUT oscillator is one.

You can make your own PUT from a pnp and an npn transistor.

John

John,

Despite all the critical comments I simply took it as a "concept" idea which does basically work, but would need "tidying up" to become fully functional.

We probably all have seen push-on/push-off or touch toggle switches which have been implemented using CMOS gates etc but the nearest I can find to your concept circuit is this practical design by Bill Bowden "High Current MOSFET Toggle Switch with Debounced Push Button" shown here

I cannot do it with one active component, but this works:

------------------------------ +12 | a | | D1 R3 R5 -- ------ +12V | k | | | | R2 e |----R6 ----- |_| sync 0V |---- b PNP | | c | | | |--- | |---------\\| UJT | | |--- | / |-> out | R1 C1 R4 /| | | /// /// ///

R1 is a potentiometer that sets the frequency, by controlling the PNP current source that charges C1. Sync lowers the UJT voltage a bit via R5 / R6 to cause early trigger (normally it runs at f < normal). You can drive the base of the PNP too, from say a phase comparator. Else you could make a current mirror I guess.

Le Thu, 25 Oct 2007 12:30:49 -0700, John Larkin a écrit:

Not quite: look at CB/CG. It's just the way we usually use them, and that probably because CE/CS is the only configuration to have both current *and* voltage gain.