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### Course: Modern Physics (Essentials) - Class 12th>Unit 5

Lesson 5: Building tiny tiny switches that make up our computers!

# Transistor as a switch

Let's see how we can exploit the cut off and saturation behaviour of a transistor and build an incredibly efficient switch.  Created by Mahesh Shenoy.

## Want to join the conversation?

• sir,why not you connected led to the emmiter?then results would be opposite
• You could put the LED in series with the transistor, yes. This would mean the LED is on when the transistor is conducting. Yes this is opposite to the behavior of his circuit.
• ISn't there a disadvantage? The power consumption is more when the transistor is ON i.e when LED doesn't glow ?
• Current doesn't exceed the saturation which is in mA, and hence it's not significant.
• mahesh sir after this topic please explain 'logic gates'_in _'semiconductors' class12.
sir because we have a lot of questions on that topic.
• What Happens if we Further Increase the input current "IB"? will there be any sort of breakdown in the transistor?
(1 vote)
• You can increase IB to the point where you destroy your transistor (after all, the base emitter junction is like a diode and can only handle so much current before melting).

No matter how much current you drive into the base, the transistor voltage from collector to emitter can only go as low as 0V. This means the collector current depends on the supply (3V) and RC (1K) and can therefore never exceed 3mA. (I=E/R=3V/1mA=3mA)
(1 vote)
• cant we replace the led with the resistor?
(1 vote)
• At , considering only the 2nd advantage, how is a transistor better than a normal switch? Both of them use (almost) no current.
Also, at , a normal switch would use no current at all.
I just feel that the 2nd advantage is not an advantage at all.