Battery operated headphone amplifier IC

[RohanDey]

Hello,

I am looking to design a simple stereo headphone amplifier circuit to be able to amplify a electric guitar signal and drive a 4 ohm and 8 ohm headphone. I want it to be battery (1.5V x 2 - AAA) operated, having a decent battery life.

I was searching through Google and found that Class 'D' amplifiers are used in portable battery operated devices, because it is power efficient.

So far I have tried with LM386 with a 9V battery, but it does not give good battery life.

Can anyone tell me about some ICs which can be used for this application? Any other ideas/suggestions are also welcome.

Thanks..

 

[barry]

TI (e.g. TPA6166A2), Maxim and others make switching headphone amps. Class G, Class H. These will give you much more efficiency than an LM386.

 

[samy555]

Hi
Also:
https://www.electroschematics.com/4375/tda-2822-stereo-amplifier/

try to get datasheet of TDA2822 to see mor circuits

 

[BrunoARG]

Depending of the power you evaluate the amplifier class. A D class one has an efficiency of around 98% but is mostly used for high power since it has a 'off-state' current loss which is not good when portable supplies are being used.

Check that G and H class amplifiers or those TDA, you may also want a small circuit so those are the best options.

Physical space and power consumption are your main problems to deal with.

 

[Audioguru]

The TDA2822M and a few other low power audio amplifier ICs is obsolete and is not available anymore.

 

[RohanDey]

The TDA2822M and a few other low power audio amplifier ICs is obsolete and is not available anymore.

I think TDA2822D is available in element14, but it says this chip is a Class AB amplifier.

Can you please guide me, how should I compare TDA2822D with LM386 with respect to power consumption and performance. What are the main parameters which I should check in the datasheet to get a better idea?

Thanks..

 

[udhay_cit]

Hope it will help you...
https://www.digikey.com/product-sea...=1&stock=1&quantity=0&ptm=0&fid=0&pageSize=25

 

[Audioguru]

The TDA2822D is available. But it is surface-mount. Can you connect to a tiny surface mount IC?
It has two amplifiers for stereo but the LM386 is only a single amplifier. Use the TDA2822D for stereo.

The power from an audio power amplifier depends on its supply voltage and load impedance but we do not know the impedance of each earphone in your headphones so I will guess 32 ohms.
Headphones are very loud at 100mW per earphone.

The datasheet shows that with a 2V to 6V supply the output power is too low. A 9V battery drops to 6V during its life. At 6V the output power is 120mW into 32 ohms when the sound is horrible with 10% distortion. The power with low distortion into 32 ohms when the 9V battery has dropped to 6V is about 96mW which is plenty.
When the 9V battery is new then do not damage your hearing by turning up the volume too high.

If your headphones have an impedance of 32 ohms for each earphone and you want to hear deep bass sounds to 20Hz then the series output capacitor from each amplifier should be 330uF. 220uF might produce low frequencies good enough.

Playing loud music continuously, the average output power is about 40mW and the heating is another 40mW for a total of 80mW. The idle current is 15mA max or maybe 10mA. The average current from 9V is 80mW/9V= 9mA plus the 10mA= a total average battery current of 19mA.

A name-brand 9V alkaline battery will last for 28 hours.

 

[RohanDey]

Hi,

Thanks for your reply. The output power concept got clarified from your reply.

The TDA2822D is available. But it is surface-mount. Can you connect to a tiny surface mount IC?

Yes I will be able to solder it on a SO-8 adaptor.

The power from an audio power amplifier depends on its supply voltage and load impedance but we do not know the impedance of each earphone in your headphones so I will guess 32 ohms.
Headphones are very loud at 100mW per earphone.

The load impedance of the earphones will vary. It can be 32 ohm also and 4 ohms also. The datasheet of TDA2822D does not say the output power for a 4 ohm load when connect to a 6V supply. I believe the earphone will get damaged if I use 6V for 4 ohm load.

What is the formula to compute the output power, from the load and input voltage?

Also, is it possible to control the output power depending on the load?

Thanks

 

[Audioguru]

The load impedance of the earphones will vary. It can be 32 ohm also and 4 ohms also. The datasheet of TDA2822D does not say the output power for a 4 ohm load when connect to a 6V supply. I believe the earphone will get damaged if I use 6V for 4 ohm load.

Where will you get 6V from? A dead 9V battery?
The output power per channel into 4 ohms is shown as 330mW with 10% distortion when its supply is 4.5V. A higher supply voltage will cause a higher maximum output power and more heating. The IC and headphones will be damaged by the heat and you will be deafened.

What is the formula to compute the output power, from the load and input voltage?

You can't calculate the output power because you do not know the losses in the amplifier. The amplifier wastes about half the supply power producing heat.
The datasheet shows a graph of Total Power Dissipation (heating) vs Output Power (bridge into 8 ohms) which is the same as both channels driving 4 ohms with a 4.5V supply. When the bridge output power is
600mW (or 300mW per channel into 4 ohms) then the IC heats with about 580mW. The first page of the datasheet shows that when the heating is 500mW then the IC chip is close to its maximum allowed temperature of 150 degrees C which is extremely hot.

Also, is it possible to control the output power depending on the load?

Power is voltage times current. The amplifier tries to maintain a constant output voltage but Ohm's Law says that a low resistance draws more current than a high resistance. Then a low impedance load uses more power than a high resistance load.
Some Mickey Mouse headphones amplifiers use a power rheostat (low resistance variable resistor) to reduce the current to each earphone but then the headphones sound "boomy" because their resonances are no longer damped by the extremely low output impedance of the amplifier.