LM386: LM386 working below 4V

József Hermann

Part Number: LM386
Other Parts Discussed in Thread: TINA-TI, LM4819, LM4861, LM4902

Dear Forum Members,

I would like to use LM386 in the 2..3V supply range as replacement for TDA2822. I would like to ask remarks whether this idea is resonable or

the circuit design tolerates this operating condition?

Taking a focus onto its internal schematic (biasing, room for signal swings etc.), it seems to be OK. /However, the available output power can be smaller then specified, of course/.

Thank you for your responses!

Kind regards

Jospeh

over 8 years ago

0 José Luis over 8 years ago

TI__Mastermind 20085 points

Hello Joseph,

I don't think that LM386 can work with power supply lower than 4V because this device is designed to work with power supply from 4V to 12V.
We can't guarantee the right behavior of the device if you don't follow the given guidelines in the datasheet.

Best Regards
José Luis Figueroa
Audio Application Engineer

0 József Hermann over 8 years ago in reply to José Luis

Expert 1040 points

Hello José,

thanks for the feedback!
You may have right, because the output stage swing would be very small without saturation.
Swing @2,5V: 2,5V-3*VBE=0,7V (output lower "PNP" transistor is a composit pair)
Peak=0,7/2=0,35V->RMS=0,25V. Po=(0,25)2/8=8mW.

Best regards,
József

0 József Hermann over 8 years ago in reply to József Hermann

Expert 1040 points

Hello,

I made a mistake in the calculation: LM386 output stage "lower" PNP comosite pair needs only 1*VBE room..so, at 4V the swing: 4-2*VBE (NPN+PNP VBE)=2,8V. ->Vp=1,4V->Vrms=1V->P=V()2/8Ohm=0,125W.

Anyway, I tried: '386 cannot work in the 2..3V supply region despite the output stage topology may suggest it.

Instead of, I designed and made a simple amp using SMD components and it works from 2V supply.

It was also simulated in TINA-TI. The R6 resistor might be fine tuned to a proper Iq current value. At the output, series R-C (10Ohm-47nF) may also be needed.

0 José Luis over 8 years ago in reply to József Hermann

TI__Mastermind 20085 points

Hi Joseph,

Your application circuit could work fine. Another alternative could be to use an LDO regulator since these devices are designed for this kind of application.

Best Regards
José Luis Figueroa
Audio Applications Engineer

0 József Hermann over 8 years ago in reply to José Luis

Expert 1040 points

Hi José Luis,

thanks for the response! Sorry but I do not understand enterely what you meant referring to LDO audio application.

Can you please explain? It sounds interesting.

Best regards,

Joseph

0 José Luis over 8 years ago in reply to József Hermann

TI__Mastermind 20085 points

Joseph,

LDO regulator is just a DC linear voltage regulator, I recommend it to you instead of your circuit because the regulator will be more exact in the provided power supply.

Best Regards
José Luis Figueroa
Audio Applications Engineer

0 József Hermann over 8 years ago in reply to José Luis

Expert 1040 points

Hi José Luis,

the presented circuit is the amplifier instead of the LM386 driving a speaker in the 2..3V supply range (I could not operate the '386 in this range).

Another alternative would be to use a tiny step-up converter to produce 5V supply from 3V for the LM386.

Best regards,

Joseph

0 José Luis over 8 years ago in reply to József Hermann

TI__Mastermind 20085 points

Joseph,

All right, I understand now. As I mentioned, you can use an LDO regulator in order to regulate the LM386's power supply.
Another alternative would be to use another device, you could have a look to the following devices: LM4902, LM4861 and LM4819, they can be fed since 2V.

Best Regards
José Luis Figueroa
Audio Applications Engineer

0 József Hermann over 8 years ago in reply to José Luis

Expert 1040 points

Hi José Luis,

Thanks vm for the recommended devices! The '4861 would perfectly fit into my application. It has excellent parameters.

Best regards,

József

Audio

Audio forum

LM386: LM386 working below 4V