555 overheating

[audioguru]

The 555 can have an output current of 200mA without getting too hot. Its max saturation voltage loss is 2.5V at 200mA which is a heating dissipation of 0.5W which is fine for the DIP-8 package that is rated at 1.18W at room temperature.

If the "9V" adapter is actually 10V and the load is capacitive-coupled to a 6.8 ohm resistor in series with an 8 ohm speaker then the output of the 555 swings from +5V to +7.5V and down to +2.5V. The load is (6.8 ohms + 8 ohms)= 14.8 ohms and the 2.5V peak voltage across it causes a current of only 169mA. The heating dissipation in the 555 is 2.5V x 169mA= 0.42W. It will be pretty warm but not too hot.

 

[Hero999]

I'd recommend a 64 Ohm speaker.

 

[MrDEB]

what about just adding a transistor

on the output of the 555??
or even an amplifier to the output??
an easy one is a LM386
down N dirty

 

[audioguru]

A 12V supply is wasted on an LM386 because its max output swing is limited by its max output current rating. The output swing for a 12V supply (6.5V p-p) is almost the same as for a 9V supply (6.0V p-p) and the difference just heats the LM386.

 

[MrDEB]

am lost as to heating of LM386??

I think audioguru is refering to the max current of the LM386??
the 8 ohm speaker will draw too much??
this peak to peak stuff gets me lost as to why the lm386 would get hot??

 

[at0mbxmb]

confounded: Would you mind posting a photo of the circuit you built so I could compare? I made the changes and I'm still having the same original problem. There must be something I'm not seeing.

 

[audioguru]

I think audioguru is refering to the max current of the LM386??
the 8 ohm speaker will draw too much??
this peak to peak stuff gets me lost as to why the lm386 would get hot??

When the output transistors of an amplifier cannot provide enough current into a low impedance speaker then voltage is wasted across them. The wasted voltage times the current equals heat.

The LM386 is designed to provide 0.5W into 8 ohms.
With a 9V supply the max output is 6V p-p which is 2.12V RMS and the power at clipping into 8 ohms is 0.56W. Its datasheet shows a dissipation of 0.55W of heat.
With a 12V supply the max output is 6.5V p-p which is 2.3V RMS and the power at clipping into 8 ohms is 0.65W. Then it has a dissipation of 0.82W of heat and it will be very hot.

The output power has increased only 16% buts its heat has increased 49%.

 

[MrDEB]

audioguru again amazes me

this guy gets my vote anytime where audio electronics are concerned.
Do I understand it all - not a chance.
wish I could comprehend it all

 

[the eagle]

dear all
the 555 is so much gentle
in the last i say to put tr-bc237 to amp the signal ,ok
and now i well to explain it
if you want to power it with vcc=12v in the out well be 10.5v nearly .
so if you put the speaker on the out you well to pull the curent about ( I=V/R,I=10.5/8=1.3A) SO I to suggest to him put the tr bc237 on the out
,he well get an amp to the signal too.
if that right that,s good .
or not please tell me .

 

[confounded]

Which changes did you make?
Do you follow what everyone is saying about your 555s output?

I'm quite new myself but if i was you this is what i would do..

I presume at the moment you just want sound the easiest way possible and are not worried about maximun efficiency.
You must add a small resistance in series with your 5kpot and speaker

When i built my circuit i found that the original values of capacitor and light dependant resistor produced an inaudible frequency. You may not have this, it depends upon your LDRs resistance

If you replace your light dependant resistors (LDRs) with aprox 10K resistors and if you use 0.1uf capacitors you should get an audible frequency.

If you get sound then all you must now do is try different capacitor values with your LDR in order to get audiuble frequency (you can fine tune by adding resistors in series with your LDR). Measure your LDRs resistance and compare to 10k to get an idea of what you need.
If you dont get sound then either you've wired up wrong or one of your components is faulty.

By the way i'm not sure how your breadboard works but on mine if there is a space between the sets of pins then they are not connected, ie i must place a wire to connect them, are you certain yours are connected?
As shown in your pic attached, each set of 10 pins on my breadboard would require 2 wires to be connected to the next set of 10 pins etc

(btw my supply in my pic is variable so although it says 15v im using 9v)

 

[audioguru]

i say to put tr-bc237 to amp the signal .....
if you want to power it with vcc=12v in the out well be 10.5v nearly.
so if you put the speaker on the out you well to pull the curent about ( I=V/R,I=10.5/8=1.3A).

The max allowed output current from a BC237 is only 100ma. 1.3A will kill it.
Your idea puts DC pulses in the speaker which might break it, an AC signal is required for an audio signal.

 

[the eagle]

The max allowed output current from a BC237 is only 100ma. 1.3A will kill it.
Your idea puts DC pulses in the speaker which might break it, an AC signal is required for an audio signal.

you are not understand me well.
dear
when i say the out will be 10.5v-1.3a that true if him put the speaker directly between the out of the 555 and the GND.
i just to knwo him why the 555 heater ,so i suggest put the tr-bc237 to save his circuit.
thank for clearing up .