@WBahn

I totally agree with what you say. I reasoned about the issue and my approach was completely wrong. As realistic parameters could I use values like Rise and Fall time around 10nS?

Your simulation spike can be coming from a few things, some of which may be real issues and some of which may not.

You are using a voltage regulator in a way that it is not intended to be used. Voltage regulators are expected to take a reasonably steady input voltage and regulate it down to a very steady output voltage. They are intended to reject high frequency noise at the input. But you are essentially trying to power it with high frequency noise. You are turning it on or off every 3 ms. In doing so, you are constantly taking it below the input voltage at which it is designed to behave well and, in that region, it's behavior may be very erratic, unpredictable, and uncharacterized. Every time you power up the regulator, it is going to take some time for all of it's internal circuitry to power up and stabilize. The behavior during that period may not be modeled well (if at all) in the simulation model.

The next issue that your simulation has is that you are driving things with ideal voltage sources, which means extremely short rise and fall times and able to drive extremely large currents during those transitions. To get better simulations when you have changing inputs, make the inputs change at reasonably realistic speeds. Whether the simulation models can respond realistically to such unrealistic signals is questionable.

 

@WBahn

I totally agree with what you say. I reasoned about the issue and my approach was completely wrong. As realistic parameters could I use values like Rise and Fall time around 10nS?

10 ns is a time, 10 nS is a very small conductance (better known as 100 MΩ).

Whether 10 ns is realistic depends on what the signal is coming from.

Also, if you are still talking about powering a regulator up and down, whether it is realistic or not is beside the point -- that basic approach is not a very good one (unless the regulator is specifically intended to be used that way -- I don't know of any that are, but there are lots of regulators out there that I have never heard of).

 

You are using a voltage regulator in a way that it is not intended to be used.

Really? That constant current circuit has been on every flavor of the datasheet for 49 years. If your application can support the headroom requirement, it is a spectacular performer. My garage goes from -10F to over +100F. and the current changes less than 1%.

ak

 

That constant current circuit has been on every flavor of the datasheet for 49 years.

Of course.
But it's designed for a steady DC output, not to provide a rapid square-wave on/off current.

 

Really? That constant current circuit has been on every flavor of the datasheet for 49 years. If your application can support the headroom requirement, it is a spectacular performer. My garage goes from -10F to over +100F. and the current changes less than 1%.

ak

Really? While you are powering it up or powering it down every three milliseconds?