then anything low power would even work.

This circuit requirement is a very common thing to build. Let's say you want to measure a voltage that has a large amount of power. (car battery, power line, audio amplifier) You have a meter or ADC that used almost zero power to make a reading. The measuring device must never see a voltage greater than (some voltage). The chances of getting to that voltage is small, but it will happen and kill the meter. You must build a circuit that limits the voltage to a safe level and limit the current to a safe level.

This homework is something that many of us have done 100s of time in the job.
I do not care of you pass this test question. I care that you pass your job.

 

This circuit requirement is a very common thing to build. Let's say you want to measure a voltage that has a large amount of power. (car battery, power line, audio amplifier) You have a meter or ADC that used almost zero power to make a reading. The measuring device must never see a voltage greater than (some voltage). The chances of getting to that voltage is small, but it will happen and kill the meter. You must build a circuit that limits the voltage to a safe level and limit the current to a safe level.

This homework is something that many of us have done 100s of time in the job.
I do not care of you pass this test question. I care that you pass your job.

Yes been there, done that, but also have seen the higher power versions come up that's why I mentioned this.
I liked a circuit that National Semi came up with some many years back using two back to back voltage regulators. One was for positive voltages and the other for negative, so an AC input would get limited on both polarities. That allowed something like 1 amp or so on the output. Not sure if I would ever need something like that but it was kind of cool.

 

This is for a class. The teacher wants a simple answer and wants the students to know how it works.

 

This is for a class. The teacher wants a simple answer and wants the students to know how it works.

Yes I understand that.