Oh, ok.

I will try to simulate it with this program. BTW, can u post the file?If it is no problem, of course. Otherwise, don't bother. :roll:

One thing to note:

In your simulation of the last circuit, do you still set IC cap = 0 ?

In my sim, I can't do that for capacitors (or maybe I don't know how?), and I was wondering what the potential problems would be when I don't set that initial condition.
I mean, voltage cap when the sim starts is zero by default, right?

Last but not least, in my sim I use an "ideal" flip flop (not the the model u mention). Is this a potential problem?
During my simulation, the cap does not discharge when the ramp exceeds the control voltage; it continues to charge up to the point the circuit can handle.So, what could i be doing wrong? ops:

Help appreciated.Really!

 

If I disable .IC v(cap)=0, the cap starts out charged to 8V, but it runs down to zero and then runs normally.
My flip-flop model is actually a behavioral model (no subcircuit with transistors, etc.) that is in the SwitcherCAD library. I changed the parameters (Vhigh=9, Td=100n, Trise=100n) to approximate the behavior of a CD4013.
Your problem with not discharging - I don't know. What op amp model are you using for U4? Do you have the neg. supply pin connected to a negative voltage, or to GND?
I'm going to attach two files, but the forum won't accept a .asc file (will it?), so I will zip them. I hope it accepts zips.

Attached Files

vco.zip (3.7 KB, 12 views)

__________________
Ron

 

Ok, I will try this and we see what comes. :shock:

Than God that with the sim I cannot be electrocuted 8)

For U4, I used a LM 741 and LTC272 and LT 272. So, common used o-pamps, I guess.
The best result came from the sim' s "ideal" opamp, though. :?

U4 is connected appropriately. All things are. Yet it seems not to work due to wrong component selection? :roll:
Even when I use all "ideal" components, the circuit does not work as expected.The cap does not discharge. ops:

So, can you suggest component selection :?:

Help greatly appreciated.

 

Can you post your schematic?

__________________
Ron

 

You mean the workbench file :?:

What schematic?

In case u mean the picture of circuit, I ll post it a few hour later that and the graph from the signals.I am not at home right now.

 

I meant the schematic of what you were simulating, i.e., the picture of the circuit (that's what a schematic is).

__________________
Ron

 

the schematic is exactly the same with the one you have in your post with the signals (in,out) graph.

The only difference is that all transistors, diodes, opamps and flip flop are "ideal".
The supply voltages are exactly as you have depicted. ops:

So, what could be the case?

Anyway, I will load your files into the program you mentioned and will shall see. :roll:

 

When you copy a schematic to another simulator, there is always the possibility for error. I do that as part of my job, and believe me, it happens, and sometimes the errors aren't obvious.

__________________
Ron

 

The obvious ones are spotted! The worst is copying from old, photocopied paper into some electronic form. Invariably, something gets a wrong value..

Have you guys figured out an application for this? I like the circuit but am confused about what it could really be used for. As I understand it, it started as some exercise for school?

 

The voltage-controlled current source is useful as a ramp generator, VCO, variable load, etc., but I have no idea why our OP wants to stop the ramp when it reaches the control voltage. I think he was having trouble with the concept that the cap voltage has no relationship to the control voltage.

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Ron