understanding inductor behavior in switching threw simulation question

[yefj]

Hello,From the theory of inductors we know that in a case ofcurrent jump it has to keep the current continues but the voltage is has to change .
However as you can see in the simulation below when source current changes then the current threw the coil changes also.
So what does it mean when they say that inductor inforces a continuety in current?
How can I see it in the simulation below?
Ltspice file is attached.

 

[FvM]

You are driving inductor with an ideal current source (infinite compliance), respectively the inductor is hindered from keeping current continuous. That's an unreal test setup because a real current source has limited voltage capability.

 

[yefj]

how you recommend to improve the sitution and simulating a change in current then?
Thanks.

 

[crutschow]

Use a voltage source.

 

[yefj]

Hello,I have used a voltage source as shown below ,So although I have a pulse on the input , the voltage on the output is almost zero,but the current is continues.
How can I see the V=L*di/dT in action here?
I have a current rise of 1mA inductance of 1uH T=1nsec but Vout=629mV however according to calculation Vout needs to be 1V.
Two questions:
1.why My vout doesnt fit the calculation?
2.Why do I get these small spike in the voltage on the inductor?
Thanks.

 

[BradtheRad]

The inductor does several complicated things. To grasp the relationship between voltage and current...
It may be easier to imagine the inductor operating in propulsive mode. That is, at a moment when the flux field has built and current is flowing.

Quickly attach an ohmic resistance across the ends but no voltage source is attached. Call the time t=0. The inductor generates voltage, sending current through the resistance around a loop.

Now the above setup serves as a tutorial to see how inductive reactance works. Time constant is LR. Convention agrees that the characteristic behavior lasts for 5 time constants. Ampere level immediately is at a peak, then declines on a familiar curve. Volt level likewise immediately starts at a peak, then declines on a familiar curve.

 

[FvM]

1.why My vout doesnt fit the calculation?
2.Why do I get these small spike in the voltage on the inductor?

1. Current waveform isn't shown. If you look at it, you'll see that V= L di/dt is still fulfilled. When voltage ramp finishes after 1 ns, current hasn't yet reached final value, current rise time is larger than 1 ns, respectively L di/dt smaller than 1V.
2. "Small spike" is L di/dt.

--- Updated Monday at 7:57 AM ---

See all-in-one:

 

[yefj]

Hello ,So how can we see from the plots the property that inductor inforces continuety in the currnt threw it?
Thanks.

 

[crutschow]

,So how can we see from the plots the property that inductor inforces continuety in the currnt threw it?

What do you mean "inforces continuety"?

 

[yefj]

Hello, from the manual below ,where can I see in simulation the the continuety of current in inductor?
Thanks.
"If you don’t have a source of infinite voltage, the current through an inductor will not change instantaneously. That is the principle of continuity for an inductor."

Continuity of capacitive voltage and inductive current

We explain two principles of continuity. One for capacitors and one for inductors.

spinningnumbers.org

 

[crutschow]

Hello ,So how can we see from the plots the property that inductor inforces continuety in the currnt threw it?

 

[D.A.(Tony)Stewart]

Post #1 is accurate with a current ramp of 100 mA in 1ns thru 1 uH yields 100 V

Just do not try a current source step pulse with Tr=0 except to test the insulation strength of your simulator (hah)
Your calc. be using old or wrong data.

It's always a good thing to calibrate your mental calculator and your handy simulator. At least once you need a correction somewhere.

Here I use an ideal VCCC with 1V in and 100 mA out with an ideal R, L and R shunt to limit voltage with a step current with 0 ns risetime.

The L/R = 1e-6/1e6 risetime is 1ps and the voltage has decayed 63% and current risen the same.

 

[BradtheRad]

Hello, from the manual below ,where can I see in simulation the the continuety of current in inductor?

"If you don’t have a source of infinite voltage
...

The words in the textbook step into a realm of fiction...
Although underlying is a nearly unbelievable characteristic of inductors. Namely as a component that crosses over from magnetism to electricity and back. We make use of them, and apply formulas, yet we little understand how they do what they do.

Attempting to convey a feeling of what we can't see in the inductor, I devised my home-brew animated simulator to portray:
* current bundles
* flux field
* voltage.

Even with that we need something more in a simulator before it gives a feel for what's happening.

<iframe width="967" height="480" src="

" title="Inductor behavior with DC (Animated)" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share" referrerpolicy="strict-origin-when-cross-origin" allowfullscreen></iframe>