Hello, I am struggling to identity why the simulation will not run. Replacing the PTC Thermistor with a simple resistor of the same resistance yields the expected output. I also obtained an expected output from the PTC in a simple voltage source - PTC - load circuit. This error seems to occur when the LM317 and PTC are used concurrently. I attached the sim and LM317 model. Thanks!

PTC models - http://www.vishay.com/doc?29184

 

So what does this PTC model actually do, as it's not apparent from the data you posted, and the PTC model reference gives me an error?

 

So what does this PTC model actually do, as it's not apparent from the data you posted, and the PTC model reference gives me an error?

Ah, sorry. Here are the PTC references. The PDF contains the working link to the LTspice models.
This PTC should trip at 135 mA, so according to my sim, it should really behave similarly to an ideal resistor under the conditions provided. Then if the current was increased above 135mA it should eventually trip like this:

 

Sometimes changing one of the simulation parameters can eliminate the timestep error.
Try one of these:

 

hi mike,
These sims are using Alternate.
Looking at the last image plot #3, it shows a maximum current limit of less than 135mA....
Image #2 shows a current greater than 135mA, no effect.

E

 

hi mike,
The reason that post #3, shows the reduction as expected is because you are driving from a constant voltage source a not a constant/limited current source, as in the main circuit.
E

Update:
Added a 300sec sim plot of your basic circuit, it may help you to follow the operation.

 

Hi Eric, I am very appreciative of your efforts, but I must admit that I am not following your feedback. I am a novice of this field.

I noticed you set the minimum timestep to 100us, but I tried mirroring that and still received an error and no run.
Furthermore, I set the LM317 output adjustment resistor to 9.3 Ohms to limit the current to approx. 135 mA ( IOUT = 1.25V / R), but still received an error and no run. Lastly, I added a 1uF cap with no change in the result.

The circuit and plot without the PTC does make sense; I am expecting the LM317 to provide 125mA max under normal conditions.

Regarding the 300sec sim plot in your second reply's update, I don't see any differences between your circuit and my circuit but it appears you were able to run it. How did you accomplish that?

Thanks,
Mike

 

Sometimes changing one of the simulation parameters can eliminate the timestep error.
Try one of these:
View attachment 280400View attachment 280402

Thank you, I will experiment with these settings/values this evening.

 

hi mike,
Try Alternate.
Also say Trol at 10
When you have done that Save and shut down LTS and restart.
Let me know how it goes.
E
E

 

hi mike,
This plot shows the change in PTC resistance.
E

Is the project intended to be a battery charger.?

 

hi mike,
Try Alternate.
Also say Trol at 10
When you have done that Save and shut down LTS and restart.
Let me know how it goes.
E
EView attachment 280458

Thank you I was able to recreate your result and run a sim with the LM317 and PTC so that's a big milestone. I have further questions I will direct towards your subsequent reply.

 

hi mike,
This plot shows the change in PTC resistance.
E

Is the project intended to be a battery charger.?

View attachment 280461

I had to figure out how to plot the potential difference of two nodes over current - that's a neat trick.
The only thing I'm thinking is - because its a PTC, the resistance should increase like this right?:

 

Is the project intended to be a battery charger.?

Hi Eric, This is intended to charge a 1000uF cap that is discharged into a low duty cycle solenoid. The larger circuit is below.

The solenoid can be operated at 9W continuously, 18W at 75% duty cycle, 36 at 50%, 90 at 10%, etc. So my intention is to pulse it with a micro, but I want to create a circuit that protects against over-duty power consumption.

The LM317 here works well (I have built this circuit many times and it performs well). It limits the solenoid to 9W even if the MOSFET fails closed.

My new idea is to bump the LM317 adjustment resistor to 2.5 or so, allowing more than 9W to the solenoid, but relying on a PTC to reduce the power to the solenoid after a period of use. This could theoretically allow the solenoid to be used with more power for shorter periods of time.

I don't have LTspice models for the actual PTC thermistors I purchased ( PTCCL13H321HBE, PTCCL13H281HBE, PTCCL17H401HBE) to experiment with, so I am experimenting with this Vishay model in the meantime because is has a similar trip current and resistance.

 

because its a PTC, the resistance should increase like this right?:

hi Mike,
Yes, a positive temperature coefficient resistor.
The PTC you have has a very small resistance change with temperature, also ensure it is specified for the 135mA range of currents.

BTW: if you have the Temp versus Resistance equation for the PTC of your choice, it is possible to control the resistance of a LTS standard resistor value using that equation.
E

Note: the orientation of a passive component in the circuit of an LTS sim, sets it's 'apparent' current direction.
So if you get a plot showing the polarity of the signal, which is the wrong sense, try rotating the suspect component by 180 degrees using 'R' key.