Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Wall wart problems

Status
Not open for further replies.

aalauzier

New Member
Hello once more everyone. I bought a used 9VDC wall wart, and it puts out around 11.2V at around 300mA. This amount of power is causing my lm386n-1 IC's to become warm to the touch, and I didn't worry about it, until the sound quality began to change a little bit, so I tried to add some resistance to it but that did not change the voltage. So what is the simplest way to bring down the voltage to 9-10V besides a regulator, because I am trying to get this to be a cheap as possible yet still effective. Thank you again
 
First wall warts are not generally a regulated device. If a unit is specified at 9 VDC that 9 VDC is a function of the input line voltage. If the line voltage is high then the output is high. Additionally if a unit is rated at a given current it should see close to that current. The E peak of 9 volts is equal to 12.726 which would be the open circuit (unloaded) output of a simple 9 volt wall wart. A little above what you are seeing.

If you want to go this route I would suggest placing a resistance in series with your load. Try a few to drop some voltage depending on the load.

Additionally the LM386 should work between 4 to 12 volts. Depending on the load it drives some heat is normal. The change in sound quality could have other contributing factors.

Ron
 
Last edited:
Thanks Ron, I will try to add more resistance to the circuit and see how that works out, if it doesn't, than i will try and get a smaller wall wart
 
A power amplifier like the LM386 needs a very low resistance power supply. Adding resistance in series with its supply voltage will probably cause it to oscillate and fluctuate its output power all over the place.

A wall wart has resistance in its transformer. The peak voltage has nothing to do with it since all power supplies charge the filter capacitor to near the peak voltage (minus the rectifier voltage drop). The resistance in the transformer and poor magnetic coupling from primary to secondary windings cause the output voltage to drop when loaded. Usually a wall-wart makes its rated voltage when loaded with its rated current and has its rated input voltage.
 
Hello once more everyone. I bought a used 9VDC wall wart, and it puts out around 11.2V at around 300mA. This amount of power is causing my lm386n-1 IC's to become warm to the touch, and I didn't worry about it, until the sound quality began to change a little bit, so I tried to add some resistance to it but that did not change the voltage. So what is the simplest way to bring down the voltage to 9-10V besides a regulator, because I am trying to get this to be a cheap as possible yet still effective. Thank you again

I personally don't like lm386's, there are dip chips that put a few watts or so of power with better quality sound.:)
 
You cannot get "a few Watts" in an 8 ohm speaker when the amplifier is powered with only 9V.
The max output of the amplifier will be about 6V to 7V p-p which produces only 0.56W to 0.77W. But if the amplifier is actually two bridged amplifiers then the output will be 2.3W to 3.1W. A DIP case cannot dissipate the heat.

A TDA2822M has two bridged amplifiers in an 8-pins DIP case. With a 9V supply its output into 8 ohms is high enough to melt itself.
 
You cannot get "a few Watts" in an 8 ohm speaker when the amplifier is powered with only 9V.
The max output of the amplifier will be about 6V to 7V p-p which produces only 0.56W to 0.77W. But if the amplifier is actually two bridged amplifiers then the output will be 2.3W to 3.1W. A DIP case cannot dissipate the heat.

A TDA2822M has two bridged amplifiers in an 8-pins DIP case. With a 9V supply its output into 8 ohms is high enough to melt itself.

Really? the TDA2822M can melt itself?! I don't understand why it would be in a DIP case!

I have a TBA820M based amplifier, and it puts about 2 watts in an 8 ohm load powered at 12volts, it gets warm to the touch, but doesn't melt itself. I assume it is bridged, didn't look it up though.
 
The TDA2822M is a stereo or a bridged amplifier in an 8-pins DIP case. As a stereo amplifier with 8 ohm speakers and a 9V supply, each amplifier clips at 0.75W and the total heating is about 1.1W so the case is very close to its max allowed temperature.
When it is bridged then the output power into 8 ohms at clipping is about 2.8W and its heating is about 2.1W which is much too high for the little case without a heatsink tab. Its heating is much less when it has a 6V supply.

The TBA820M is a single amplifier similar to an LM386 but it is bootstrapped for a higher output swing. It clips at about 0.9W into 8 ohms with a 9V supply and its heating is about 0.5W. With a 12V supply it clips with an output of about 1.6W into 8 ohms and heating of 0.9W. With an output of 2W then its output is horribly clipped with 10% distortion.
 
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top