555 Timer & loud 4 ohm speaker

Discussion in 'The Projects Forum' started by BBrandon, Aug 3, 2011.

  1. BBrandon

    Thread Starter New Member

    Aug 3, 2011
    I have been designing a siren circuit around 2 555 timers (no I don't plan to do any thing illegal with it) and I have come to a point where I am unsure of something.
    I wish to connect a 4 ohm speaker (it's also labeled 4 W nom. 8 W max) through a capacitor (10 uf) to pin 3 on the 555 timer and the other side of the speaker to ground. I have tested it on a breadboard and it works good but I am concerned that I will burn out the 555 timer. I would like to design the circuit to run continuously for at least 10 minutes so that is why I am conscious of slow overheating. Any advice / suggestions would be greatly appreciated!
  2. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    1) Place finger on 555.

    2) Turn circuit on. Wait 10 minutes.

    If your finger is still on the 555 then everything is fine. It it got so hot you had to remove your finger then remove the power.

    A very fine engineer I once know could tell you how hot a part was to 2°C just by touching it.
  3. KJ6EAD

    Senior Member

    Apr 30, 2011
    You can use a transistor amplifier on the output but if you want to only use 555 timers, try paralleling several. The 555 has a totem pole output, so it should be possible to share the load this way. Also, the higher your supply voltage, the more current you can source to the speaker.
  4. iONic

    AAC Fanatic!

    Nov 16, 2007
    A circuit diagram would really be helpful.
  5. Wendy


    Mar 24, 2008
    Measure the power supply current, it should under 200ma. If it is over 200ma there is a good chance the 555 will eventually die (I would use 150ma as the magic number actually).

    Building a simple transistor driver is pretty easy though.


    Leave off the MOSFET and resistor and this would work...


    It's big disadvantage is it looses 1.2V of the power supply voltage, but it is extremely simple and pretty high power.
  6. BBrandon

    Thread Starter New Member

    Aug 3, 2011
    Thank you for the suggestions guys, the idea of checking the temperature seems like it would work but I think that I am going to go with checking the ma of the whole circuit.