LM13700 sim in TINA-TI help!

[bobtech]

Hi all,

I'm trying to get a VCO circuit using an LM13700 up and running.

It's a bog standard spec I'm trying to simulate, which I couldn't get going in LTSpice first off, so I tried TINA TI, but still to no avail. Has anyone any ideas?

 

[Audioguru]

If The old LM13700 IC is still available then why not build and test the circuit instead or trying to simulate it?

 

[bobtech]

I've blown a few LM13700's already, so the sim route is cheaper

looking back over past threads, I came across this one, saying initial conditions may be needed, as with simulations working in the "ideal" world, the oscillator is stuck in equallibrium.
https://www.electronicspoint.com/threads/lm13700-strange-simulation-problem-on-ltspice.273077/
https://www.electronicspoint.com/threads/lm13700-strange-simulation-problem-on-ltspice.273077/
So I did and this is what I got in TINA-TI

Any ideas though as to why the square wave is offset?

 

[bobtech]

I also tried to simulate the ramp/pulse vco from the datasheet, and still getting the same issue, any ideas anyone? I've even put in initial values, but to no avail.

 

[Audioguru]

The squarewave has offset voltage because it comes from the emitter of the output darlington that has no negative feedback. The darlington has two base-emitter voltage drops.

 

[Arouse1973]

Hi all,

I'm trying to get a VCO circuit using an LM13700 up and running.

It's a bog standard spec I'm trying to simulate, which I couldn't get going in LTSpice first off, so I tried TINA TI, but still to no avail. Has anyone any ideas?

View attachment 33280

View attachment 33281


View attachment 33282

What was the problem you had in LT Spice?
Thanks
Adam

 

[bobtech]

The squarewave has offset voltage because it comes from the emitter of the output darlington that has no negative feedback. The darlington has two base-emitter voltage drops.

I see, thanks

What was the problem you had in LT Spice?
Thanks
Adam

I was getting the same flat output, as I attached in my first post.



Managed to crack the issue

So first thing I did was just go 100% as per data sheet, so all values are the same as above, except the supply voltage was changed from +/-9 to +/-15..

I took out the initial conditions and simulated.... nothing

Then I put an initial condition on the pulse o/p, and it came to life !!
As per values of the datasheet, it was oscillating at about 37 MHz so any sort of Vc above 1 volt resulted in saturation again....

I changed Rc and C and have it oscillating in the KHz range...

It also allows the supply votage to be dropped again to +/-9V

 

[CDRIVE]

Whenever simulating oscillators in Tina always select "Use Initial Conditions" or "Zero Initial Values".

BTW ... Welcome To EP!
Chris

 

[bobtech]

Thaks CD