Hi Guys,
I am trying to understand this circuit but could not understand.
Could any body explain me the how this works ?

1. How Q1 turns ON and OFF ?
2. Do we really need R1 ?
3. Why do we need R and R3 ?
4. Why do we need R4 and C1 ?

Thanks in Advance !

 

 

View attachment 326859

Hi,
Thanks, can you explain it.

 

It would help if we knew what it is supposed to do. Seeing as there is no input or output, that is a little difficult to divine.

 

1. How Q1 turns ON and OFF ?
2. Do we really need R1 ?
3. Why do we need R and R3 ?
4. Why do we need R4 and C1 ?

Why do we need the circuit?

 

Hi Guys,
I am trying to understand this circuit but could not understand.
Could any body explain me the how this works ?

1. How Q1 turns ON and OFF ?
2. Do we really need R1 ?
3. Why do we need R and R3 ?
4. Why do we need R4 and C1 ?

Thanks in Advance !


View attachment 326856

This circuit looks more like an astable generator (oscillator) with an emitter follower and bootstrapping I guess.
I've even built the circuit on a breadboard to see if this is the case.
This is what my Rigol scope has shown.


The yellow trace is the voltage across R5. The bluish trace is the voltage between C1 and R4.
As you can see this circuit indeed is a relaxation oscillator.
So can you elaborate on your question a bit more? Because it was not clear that you knew that this circuit is an oscillator.

 

The circuit is a flasher as stated in post #1 "it turns on and off." Certainly the schematic shown in post #1 was intended to be misleading and more difficult to follow.
The redrawn schematic in post #2 makes it clear how it works, as post #6 explains.

 

 

it is just an oscillator but designed to be used in series with load... the downside of such circuit is large voltage drop.
R1 and Q1 are there just to increase output current of Q3. you can remove R1 and Q1 to make studying of the circuit easier.

Q3 (and Q1 when present) are used to activate load (R5).
C1/R4 forms RC delay network that allows Q2 to work. When Q2 is on, it disables output.

 

Two cascaded inverters and an NPN Emitter Follower. It also works on 5V but changes frequency.
SIM https://tinyurl.com/29p75q5n

 

Although the NPN may not be needed.