While doing the diode characteristics experiment I was instructed to keep the voltage at zero and current at max before starting the power supply. Can I know the reason why?
Answer
I'm assuming you are talking about using a bench power supply.
Under normal experimental conditions you apply a voltage gradually while monitoring the current meter to determine if there is something off with your circuit that causes it to draw too much current. Since you really do not want to fry your circuit, you normally back off the voltage when you see this and try and figure out and fix whatever is sucking all the power. As such you want to power on with the voltage at zero.
Bench power supplies are also current limited. That is, when the current reaches the set limit, the output voltage will fold back, or stop rising as you crank the voltage knob. Initially you do not want that feature enabled, or you want it set to a tolerable high level, or you will not be able to apply much voltage without the supply reaching whatever current limit you have dialed in.
Typically, once you are satisfied that your circuit is behaving appropriately, it is normal to back off the current limiter to some point above the normal operating current so as to provide you with some protection while you work on your board or experiment.
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