Voltage limits

Good, then let's make it even bigger!! :-)

Here's an old-school solution:

Output is high-impedance--it'd need buffering--and accuracy's limited by the diodes' matching & drift, but there's no problem with speed or wind-up in the clamped amp.

Clamping the input's a good idea.

Okay, enough goofing around -- here's a serious suggestion (a non- inverting version of your .PDF):

That's accurate and fast, and doesn't wind anyone up.

-- Cheers, James Arthur

If the opamp's R-to-R, the clamping's pretty accurate.

-- Cheers, James Arthur

OK my mistake. It worked (sorta), as the opamp heated, the max current went down so the limits were a bit 'fluid'.

Ah, well I might be able to make that work.

The zero volt limit on that one takes some thought... At least for me. (I'll have to build it, to really 'get it'.)

Much Thanks.

But please no more circuits anyone. (I've got enough to figure out.)

George H.

Geesh I'm so slow.... I still don't get that one.

(Maybe during the morning shower.)

George H.

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That one works better if you draw the diodes below the opamp, so the trons don't have to climb uphill.

Clamp amp, JJL, 12/2007

| .-|+/ | D1 V | |/ V D2 --- =3D=3D=3D --- | | D1,2 =3D BAV99 '------+-------' | R3 | --- -12v

There, maybe that'll make it clearer.

-- Cheers, James Arthur

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=A0 =A0 ...Jim Thompson

=A0 =A0| =A0 =A0mens =A0 =A0 |

=A0 | =A0 =A0 et =A0 =A0 =A0|

=A0|

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Thanks Jim, My brain's still spinning from three circuits back.... The latest is at least easier to understand. I hadn't thought about clamping the input!

George H.

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Ahh, OK do I have to up the gain on the input to compensate for the loss?

George H.

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No the modulation input needs to do DC too. I figure you can send in a slow square wave and measure delta (frequency)/ delta (voltage)

George H.

I biffed the high-side clamping voltage (corrected above). Other than that, this would go between the driving op amp and that 2nd stage you're trying to protect--no extra op amp req'd.

If I understand your description, you've got this:

.----R3----. | | | |\ | .----R5---. v1 >---R1----+---|-\ | | | | | \ | | |\ | v2 >---R2----' | >--+---R4---+---|-\ | | / | >--+---> Vc, CD4046 .--|+/ .---|+/ | |/ | |/ =3D=3D=3D =3D=3D=3D

Here's Jim's idea, applied to that circuit:

.----R3----. -3.1v | | | R6 | |\ | D1a V .---20K---. v1 >---R1----+---|-\ | --- | | | | \ | R4 |Va R5 | |\ | v2 >---R2----' | >--+--10K--+---10K-+---|-\ | | / | | >--+---> Vo .--|+/ D1b V .---|+/ | |/ --- | |/ =3D=3D=3D D1=3DBAV99 | =3D=3D=3D -1.1v

The diodes clamp (-2.5v < Va

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Thanks James... I finally got this one too.

And thanks again to all of SED for the fun ideas. I must admit I like a circuit with resistive voltage dividers on the output. It guarantees that the ouput will never get 'out of bounds' and blow up the 4046. (When someone forgets to solder in some other component.)

George H.

And the OpAmp version I alluded to...

Nice accurate limiting.

Caution: If you need lots of speed, and are using bipolar OpAmps, an extra diode and resistor per clamping OpAmp will be needed to prevent slow recovery from being railed. ...Jim Thompson

George Herold a écrit :

George, I've seen that you want no more circuit but this one is a pretty good one, uses only one opamp and have low Zout, so...

___ .-|___|--. | R2 | | | +--||----+ | | ___ | |\ | Vin >----|___|-+ -|-\ | R1 | >- +---> Vo .--|+/ | | |/ | | | ___ | ___ | .--|___|-+-|___|--' | R1 R3 /+\ 3V ( ) \-/ | | === GND

For R1=10K, R2=2K, R3=5K and Vd=0.67 you clamp between 1V and 5V and have a gain=-1

You can replace the 3V-R1 source by a divider with it's Thevenin equivalent set as 3V and 10K

Use a pair of diode connected 3904 for a better clamp.

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=A0 =A0 =A0 ...Jim Thompson

=A0 =A0 ...Jim Thompson

=A0 =A0| =A0 =A0mens =A0 =A0 |

=A0 | =A0 =A0 et =A0 =A0 =A0|

=A0|

=A0 =A0 =A0 |

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Thanks for the circuits Jim, I don't think I'll use the above. But I've tucked it away in my notebook for future use. :^)

George H.

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Oh, I was only (half) kidding about not wanting more circuits. I was sitting at home trying to puzzle one out... and when I got back to respond, I found three more.

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That's interesting... I'm not quite getting R1 - R3 section at the non- inverting input. Should I try following the current?

BTW I forgot to thank you for the inverting composite amp circuit on a different thread. I haven't had a chance to try it yet.

Things are a bit crazy at work at the moment. I've got half a dozen circuits laid out on copper clad, (or just air wired), all in various stages of completion.

George H.

Why are diode connected transistors sometimes better than diodes? I've got this 'silly' (educational) double balanced mixer made with audio transformers. I get the cleanest looking signals using diode conected 3904's.

Geo

IIRR Laurence G Cowles said that the diodes in a transistor were much more nearly ideal than most rectifier diodes. I can't remember why - my copy of the book (bought in 1968) fell victim to a frozen pipe in Cambridge around 1985.

-- Bill Sloman, Nijmegen