voltage limting problem

View in a fixed-width font such as Courier.

. . . . . |\\ . +1V---|+\\ . | >--|

link.http://img69.imageshack.us/my.php?image=circuitdiagrambd1.png

What sort of frequencies and recovery times do you need and how accurate do you need the 1V to be?

This sort of circuit is slow but accurate:

Hi,

I am unable to follow your drawing. It is possible for you guys to draw in paint brush and post it on imageshack.com.

Thanks alot, John

Select the drawing , copy it to clipboard, paste into word processor, select it again in word processor, change word processor font to Courier...

Hi,

I still have some problems viewing the drawing, did you guys use diodes in the circuit too and if yes then Why?

Regards, John

Fred used them on the op amp outputs and drew them like this -|>|- or -|

Hi,

I simulate your design in PSPICE but its not working as It should. The diodes are not limiting the signal to +/- 1 volts. The signal from the current source is directly appearing across the load with peak to peak voltage of +/-15 volts.

Thanks John

I did not post a design - I only answered your question: "I still have some problems viewing the drawing, did you guys use diodes in the circuit too...?"

I suggest that you address your post to whichever person created the design you simulated. And, I suggest that you quote at least part of the text they posted so the reader has a chance to figure out what you are talking about.

Ed

The original problem was with a voltage controlled current source

OP wanted a voltage compliance limit on the load.

I believe the basic concept suggested by Mr.Bloggs looked something like this:

Capacitively coupling the output of a current source is asking for trouble, but we have to assume the original circuit was functional.

If you need help with the a simulation, perhaps you could post your pspice file?

RL

Hi,

The output of the opamps are +/- 15 volts ( hitting the rails) . and the diodes inputs are tied to current source voltage drop across the load. So, the diodes are getting +/-15 v DC from the opamps on one end and the ac voltage drop across the load on the other end. I do not know how this circuit will work. The original circuit is functional.

Regards, John

Hi,

The opamps are in unity feed back configuration. They should put +/-1 volts on their outputs but they are outputing +/-15 volts.

John

John, the clamper was intended as an add-on circuit to your original Voltage Controllrd Current Source. Your VCCS circuit is represented in the clipper sketch by the current source symbol.

Without a controlled current, the op amps in the clipper will be normally 'off', with the diodes reverse-biased. They will only begin to function when your driver circuit induces an overvoltage at the clipping node.

You should be aware that it is a bare-bones concept only. Speed, overshoot and recovery of the circuit are not considered. The op amps in the clipper must be capable of absorbing full current of the VCCS.

RL

Hi,

The thing is that my application needs full VCCS current to go into the Load and the Opamps should only be monitoring the voltage across the load and the capacitor in series. The opamp usually have very impedance input. How much controlled current do you think opamp needs to operate properly? The maximum current the VCCS is producing is

John

John,

Please examine the clipper circuit.

Op amp #1 has +1V on it's non-inverting input. The output of this op amp can only reduce the voltage on the monitored point through D1. If the voltage on the monitored point is already less than one volt, its output will remain high until required to function.

Op amp #2 has -1V on it's non-inverting input. The output of this op amp can only increase the voltage on the monitored point through D2. If the voltage on the monitored point is already more positive than

-1V, its output will remain low until required to function.

This is the simplest explanation I can give you. Op amp 2 will normally have an output near the negative rail. Op amp 1 will normally have an output near the positive rail. If your VCCS forces the mode outside the range of +/- 1V, you should see the two op amps beginning to do something.

I'm not going to troubleshoot your VCCS. Just make sure its doing everything that you think it's supposed to be doing before applying the limiting circuitry.

RL