part 3

This part of the lab requires you to investigate an Op Amp controlled linear regulator circuit with current limit shown in fig 14:

Fig 14

Points to note

The Voltmeter and Ammeter symbols are used (from the Active library)

The zener used is from the device library with the voltage set to 5.1V

ISIS runs another type of simulation (called animation - animation is used here.

From the tool bar menu select Graph - animation and an animation tool will appear at the bottom of the screen (see fig 15).

Fig 16

Once you have the basic circuit operational, you can investigate its functionality.

How is the output voltage related to the zener voltage?

At what load does the current limit start to operate?

What is the short circuit output current?

Under short circuit conditions, what is the power dissipation in Q1?

What steps can you take to limit the power dissipation in Q1 to its rated level of 1W?

Modify the circuit so that with the use of a potentiometer, the output voltage moves from 0 to its max. value with the given zener.