Two-transistor circuits--can we get to 100?

But a bidirectional shifter still needs only one transistor.

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(see link to schematic on that page)

Your RS232 example is bidirectional but the signals are on separate lines, so it's really 2 separate level shifting circuits.

Reply to
Tom Del Rosso
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Sorry, my bad. Make that 200circuits.com.

There's a whole family of circuits with one PNP and one NPN, emitters connected.

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John Larkin         Highland Technology, Inc 

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Reply to
John Larkin

That's right. And you need them both to implement RS-232 protocol. My nomenclature seems to confuse you. Allow me to explain it.

The circuit shifts two separate unidirectional signals. Both signals must be unidirectional in order to honor the RS-232 protocol.

The first unidirectional signal passes "one way," right to left, through Q1. The second unidirectional signal passes "one way," left to right through Q2. "One way" right to left plus "one way" left to right makes it a "two way" level shifter, if that makes sense.

Thank you,

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Reply to
Don Kuenz

On 02/09/17 12:41, Tom Del Rosso wrote:

Unfortunately that circuit is slow in one direction. Being basically like an open-drain pullup, it either consumes too much power, or pulls up slowly. Here's an LTSpice simulation of the low-to-high direction.

Clifford Heath.

Version 4 SHEET 1 1004 772 WIRE 16 48 -128 48 WIRE 96 48 16 48 WIRE 256 48 96 48 WIRE 608 48 384 48 WIRE 672 48 608 48 WIRE 384 80 384 48 WIRE 256 192 256 48 WIRE -128 208 -128 48 WIRE 96 208 96 48 WIRE 672 208 672 48 WIRE 384 240 384 160 WIRE 384 240 336 240 WIRE 544 240 384 240 WIRE 96 384 96 288 WIRE 240 384 240 240 WIRE 240 384 96 384 WIRE 288 384 240 384 WIRE 240 432 240 384 WIRE 384 432 384 240 WIRE -128 560 -128 288 WIRE 240 560 240 496 WIRE 240 560 -128 560 WIRE 320 560 240 560 WIRE 384 560 384 496 WIRE 384 560 320 560 WIRE 672 560 672 288 WIRE 672 560 384 560 WIRE -128 592 -128 560 WIRE 320 608 320 560 WIRE 96 720 96 384 WIRE 320 720 320 688 WIRE 320 720 96 720 FLAG 544 240 Sig5 FLAG 288 384 Sig3 FLAG -128 592 0 FLAG 608 48 5Vcc FLAG 16 48 3Vcc SYMBOL nmos 336 192 R90 SYMATTR InstName M1 SYMATTR Value 2N7002 SYMBOL voltage -128 192 R0 SYMATTR InstName V1 SYMATTR Value 3.3v SYMBOL voltage 672 192 R0 SYMATTR InstName V2 SYMATTR Value 5v SYMBOL res 400 176 R180 WINDOW 0 36 76 Left 2 WINDOW 3 36 40 Left 2 SYMATTR InstName R1 SYMATTR Value 470r SYMBOL res 112 304 R180 WINDOW 0 36 76 Left 2 WINDOW 3 36 40 Left 2 SYMATTR InstName R2 SYMATTR Value 10k SYMBOL voltage 320 704 R180 WINDOW 0 24 96 Left 2 WINDOW 3 24 16 Left 2 SYMATTR InstName V3 SYMATTR Value PULSE(0 3v3 .01u 10n 10n 0.1u 0.2u 5) SYMATTR SpiceLine Rser=20 SYMBOL cap 368 432 R0 SYMATTR InstName C1 SYMATTR Value 5p SYMBOL cap 224 432 R0 SYMATTR InstName C2 SYMATTR Value 5p TEXT -88 -16 Left 2 !.tran 1u

Reply to
Clifford Heath

Should be "RC oscillators." Yeah I know a "tank" is not RC.

Reply to
Tom Del Rosso

Baker clamp using BE junction?

Maybe it's cheating, but could be faster than standard diode based clamp

Cheers

Klaus

Reply to
Klaus Kragelund

Good one -- it's adjustable, too:

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(Note that you want C-B because of Vcbo, leakage and speed.)

Tim

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Reply to
Tim Williams

Here are a few astables. There are at least half a dozen more...

Vcc -+- Vcc | -+- .-. | | | .-. '-' | | | '-' +-----+----+----> | Ct | | | | |/ | | +---| .-. | | |>. | | --- | | '-' --- --- Rt | | | --- '>| | | | |---+----' | /| | === | .-. | | | === '-' | ===

Vcc -+- | .-----+----------. | | | | .-. | | | | | .-. '-' | | | | | | .-. | | '-' | ===

'Wenzel' Oscillator (e.g. 'Curious C-Beeper')

+3V -+- | | 180 deg | | | | | |/ '---+-| 2n4401 |>. | === Complementary Astable Pulse Gen. 220Hz, 10uA, .05% duty output

Cheers, James Arthur

Reply to
dagmargoodboat

You could do that with a germanium transistor as the clamp, but not a silicon one, because the BE drop is too large. You could make one with a PNP and a negative supply as the clamp, though.

Cheers

Phil Hobbs

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Reply to
Phil Hobbs

I guess that's sort of a Baker clamp, but not really. Still counts for the collection, though.

Cheers

Phil Hobbs

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Reply to
Phil Hobbs

A 2-transistor audio AGC should be possible.

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John Larkin         Highland Technology, Inc 

lunatic fringe electronics
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Reply to
John Larkin

Darn, I invented a couple of things like that last night, in the general class of NPN and PNP with emitters connected. [1]

This could get addictive.

[1] while reading a Discworld book. Pratchett didn't use chapters, he just kept writing. It's hard to know where to stop.
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John Larkin         Highland Technology, Inc 

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Reply to
John Larkin

Probably. A diff pair with the emitter swing used as the level detector, RC from there to one of the bases, input to the other, output taken from one collector.

How about a two-transistor squelch? I suppose you could use a monostable for that.

Barrie _must_ have meant just circuits you could put on an IC. A guy of his ability couldn't possibly have missed this many, so his criteria must have been different.

Cheers

Phil Hobbs

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Reply to
Phil Hobbs

A no transistor audio agc is easy enough: a lightbulb.

NT

Reply to
tabbypurr

clamp

r

I've seen quite a few speakers with a lightbulb in series with the tweeter as overload protection

Reply to
Lasse Langwadt Christensen

Are diodes allowed? Are diodes not allowed? Do diodes "count" as transistors?

The performance of the single transistor inductance gyrator could probably be improved by using another transistor to bootstrap the collector:

Reply to
bitrex

Sure, that would be basically a two-stage cap multiplier run backwards. ;)

Cheers

Phil Hobbs

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Reply to
Phil Hobbs

Yep. I first saw that in one of the hobby magazines. I didn't bother with the PUT-connected relaxation oscillator--that one's fiddly (easy to stall 'ON').

Here's another complementary astable:

+3V @ 15uA -+- | .-------------+-------------. | Ct1 | R1 10k 22n | 60Hz . [1] while reading a Discworld book. Pratchett didn't use chapters, he

Cheers, James Arthur

Reply to
dagmargoodboat

Am 01.09.2017 um 22:03 schrieb snipped-for-privacy@gmail.com:

There was this negative voltage generator that Bob Pease once presented in his EDN musings. One transistor BE driven to Zener, the neighbor on the chip collects the photons, IIRC.

regards, Gerhard

Reply to
Gerhard Hoffmann

I don't think an opto should count as a transistor in this game.

Dual-opto totem poles can be useful, though.

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John Larkin         Highland Technology, Inc 

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Reply to
John Larkin

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