Digital Electronics - Multivibrators and 555 Timer - Discussion

Discussion :: Multivibrators and 555 Timer - General Questions (Q.No.5)

5. 

What does the discharge transistor do in the 555 timer circuit?

[A]. charge the external capacitor to stop the timing
[B]. charge the external capacitor to start the timing over again
[C]. discharge the external capacitor to stop the timing
[D]. discharge the external capacitor to start the timing over again

Answer: Option D

Explanation:

No answer description available for this question.

U R said: (Sep 12, 2015)  
Why answer D?

Uday Pratap Singh said: (Oct 20, 2016)  
555 timer discharge pin is connected to the open collector of a NPN transistor, the emitter of which goes to ground, so that when the transistor is turned "on", pin 7 is effectively shorted to ground. Usually, the timing capacitor is connected between pin 7 and ground and is discharged when the transistor turns "on". The conduction state of this transistor is identical in timing to that of the output stage. It is "on" (low resistance to ground) when the output is low and "off" (high resistance to ground) when the output is high.

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