Hey everyone !)

I am new in the area of electronic engineering and I am currently designing a circuit of a small alarm system. Although everything works well, I still need to ask the following questions for a clearer understanding:

1. Why do we need 2k2 resistor ?
2. Why is the loudspeaker jointed to the collector of a transistor ? (as by my logic it should be the collector)

Have a good day !)

 

1. To limit the current flowing through the grey transistor and the base/emitter of the black transistor otherwise the transistors would be destroyed.
2. I assume you mean you think the speaker should be in the emitter of the transistor?
The emitter and collector provide roughly equal current gain, but the collector provides voltage gain where the emitter does not so the power available to the speaker is greater.

 

1. To limit the current flowing through the grey transistor and the base/emitter of the black transistor otherwise the transistors would be destroyed.
2. I assume you mean you think the speaker should be in the emitter of the transistor?
The emitter and collector provide roughly equal current gain, but the collector provides voltage gain where the emitter does not so the power available to the speaker is greater.

Thanks so much for your reply !!

 

1. To limit the current flowing through the grey transistor and the base/emitter of the black transistor otherwise the transistors would be destroyed.
2. I assume you mean you think the speaker should be in the emitter of the transistor?
The emitter and collector provide roughly equal current gain, but the collector provides voltage gain where the emitter does not so the power available to the speaker is greater.

But in this circuit there is no resistor for the collector6 though th transistor is the same and the voltage is twice greater...

 

The relay coil has some resistance which will restrict the current. A 12V PCB relay might be about 1kΩ

 

The relay coil has some resistance which will restrict the current. A 12V PCB relay might be about 1kΩ

Now definitely thanks a lot !!!!