Car Alarm Circuit

[abuhafss]

Hi

I opened this 12V-20W car siren



and found this PCB



I converted it into schematic



The sound is ear-piercing. I am interested to know the amplifier section, which can be used in other gadgets, Please help me separate the amplifier.

Thanks.

 

[Colin Mitchell]

The amplifier is just Q5. However Q4 will improve the gain of the amplifier by 100 if all the other components are removed.

 

[abuhafss]

The amplifier is just Q5. However Q4 will improve the gain of the amplifier by 100 if all the other components are removed.

Thanks for your response, Uncle Colin.

The siren is rated 20W.
Do you think only a single 2A transistor can amplify to that extend?

 

[Gryd3]

Thanks for your response, Uncle Colin.

The siren is rated 20W.
Do you think only a single 2A transistor can amplify to that extend?

Don't forget that the output power is the product of voltage and current.
A 2A transistor putting out 10V will certainly be 20W. (Not completely accurate when you start dealing with signals and AC... This is typically when you need to distinguish between peak and RMS outputs.)