Hi everyone !

I am new in the sphere of electronics and have just began to construct my circuits

Have a question about the following small alarm system:
Why do we put this bipolar transistor with its collector to a loudspeaker ? How does it help us in any way ?
With my logic the transistor should be put with its emitter to amplify current

Will be happy to receive any help from you !

 

Putting the load in series with the emitter only gives current gain. When the load is in the collector circuit it provides both current and voltage gain.

Les.

 

Putting the load in series with the emitter only gives current gain. When the load is in the collector circuit it provides both current and voltage gain.

Les.

Thanks a lot ?

But does it give the amplification at th collector already ?
I thought that it only happens at the emitter

 

The collector current is almost equal to the emitter current (the emitter current is lightly greater because the emitter also passes the small base current).

 

In the circuit you've shown us, it won't make much difference.

 

In the circuit you've shown us, it won't make much difference.

why ?
Could you please explain ?

 

To try to explin it fully you would need to provide the full shematic. It is a reasonable assumption that it will be a low impedance speaker so that only current amplification was required so the signal across the speaker would be almost the same if it was connected between the emitter and ground as it is connected in the collector circuit.

Les.

 

Assuming you're using a speaker driver, it's a passive device that's voltage driven, it doesn't matter if the voltage is pulled to ground (like in the diagram you've supplied) or if it's... Actually, we can't even tell as we can't see the whole circuit. The 100r resistor, does get fed from the supply or does that connect to Gnd?

 

Assuming you're using a speaker driver, it's a passive device that's voltage driven, it doesn't matter if the voltage is pulled to ground (like in the diagram you've supplied) or if it's... Actually, we can't even tell as we can't see the whole circuit. The 100r resistor, does get fed from the supply or does that connect to Gnd?

Here is the whole circuit)

 

To try to explin it fully you would need to provide the full shematic. It is a reasonable assumption that it will be a low impedance speaker so that only current amplification was required so the signal across the speaker would be almost the same if it was connected between the emitter and ground as it is connected in the collector circuit.

Les.

See the circuit above)

 

Ahh right, there's 2! It looks like a pretty simple oscillator and 2-stage amplifier. Judging by the value of that ceramic capacitor (0.0047uF), the speaker will produce quite a high pitch sound. The first transistor is used to detect the tiny oscillation and turn it into a discernible signal, the second one will give some proper amplification.

Still, it would work the same if the speaker driver was on the emitter but those resistors would need to stay where they are as the 2k2 resistor is limiting current to the base of the second transistor and the 100r resistor is stopping the 2k2 resistor from shorting.

 

Ahh right, there's 2! It looks like a pretty simple oscillator and 2-stage amplifier. Judging by the value of that ceramic capacitor (0.0047uF), the speaker will produce quite a high pitch sound. The first transistor is used to detect the tiny oscillation and turn it into a discernible signal, the second one will give some proper amplification.

Still, it would work the same if the speaker driver was on the emitter but those resistors would need to stay where they are as the 2k2 resistor is limiting current to the base of the second transistor and the 100r resistor is stopping the 2k2 resistor from shorting.

But won't connecting speaker to the emitter give also voltage gain, while the collector will give only current gain ?

 

Read post #02

 

But won't connecting speaker to the emitter give also voltage gain, while the collector will give only current gain ?

The difference will be noticed only with an oscilloscope, not your ears