5W amplification at low voltage

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
Dear DiYAudio,

I'm completely new in here and in audio circuits as well. Thus, I thought this community might be helpful.

I'm designing a circuit running on battery from (3 to 9 volts) which must have a 5W audio amplification stage. I've been browsing the internet quite a lot for such amps but no one was running under 12volts.

Do you have any ideas ?

I wish you a nice day and thank you for all the knowledge available on that website.
 
AX tech editor
Joined 2002
Paid Member
Albert what is your load, an 8 ohms speaker?

For 5W into 8 ohms you need about 6.3V RMS signal voltage, which means a peak-to-peak value of about 18.5V.
So you would need at least a total supply voltage of 20V or more.

You can't do that with a 3-6V battery, unless you use specialty amps with output transformers.

jan didden
 
Thank you janneman for your answer !

My speaker is 6Ohm impedance and I want to amplify inputs in the order of 1.5Volts in a range [1.35;1.65]Volts. So maybe 5W is not needed.

The idea is that I have different customized sensors i should amplify the outputs to apply some treatments. I need low voltage because i want all my devices to be portable and run on small batteries.

Thanks a lot.
 
The Texas Instruments TPA3111 will get you fairly close. It's a class-D mono amp spec'd for 7-W into an 4-Ω Load at 10% THD+N from a 8-V supply. As Jan suggested, you'll need to wring every millivolt possible from the supply and amp, so a bridged load is virtually a must. There's other chips with similar specs to the TI chip, but I can't recall them offhand.
 
Albert,
a single supply voltage of 9V limits the output voltage from a "normal" amplifier to ~3Vac.
3Vac into a 6ohm speaker is roughly 1.5W. One cannot get more than that from a 9V battery and a normal amplifier. The distortion at that maximum power is likely to be unacceptable and a more reasonable maximum with tolerable distortion is probably around 700mW to 1000mW of output power.

Now you can use bridged amplifiers to get more power output from a fixed 9V supply.

Take a pair of those "normal" amplifiers and design each of them to drive a 3ohms speaker load. 3Vac into 3r0 is ~3W.
If you bridge these two 3ohm capable amplifiers, you can get ~6W into your 6ohm speaker. The same limitations on tolerable distortion apply as before. Expect a usable/tolerable maximum output of around 3W to 4W into your 4W amplifier.

A 386, and the others, designed for low voltage supplies are excellent, but they are severely limited in maximum output power. That is the consequence of designing for high efficiency to suit battery use.
You must use a high efficiency speaker to get higher SPLs, That's why we see headphones used on portable equipment that has limited battery power.
 
Last edited:
Thank you Andrew for your answer !
I'll try to bridge the amplifiers i already have tonight ( only one lm386 at 9v wasn't indeed sufficient last time).

Thanks to your remarks and my readings, i'm seeing clearer but some points are still not clear at all.

I'm considering the fact that i may not need a 5W amplification (I choosed 5W, because in a research paper dealing with such kind of speakers, they said they used that value with no justifications)
Considering my speaker specifications:
Bandwidth: 50-500Hz
Impedance: 6 Ohm
Maximum Input Voltage: 3V
Maximum Input current: 0.5A

Power = voltage^2/impedance, thus 3*3/6 =1.5W, should be sufficient ? I'm right ?

I was able to perfectly use those speaker on my cellphone (3.7V) headphone output without any amplification. Do think they use those texas instrument amplifier you suggested ?

Thanks to all of you, this hep me a lot! i only have this forum and google to ask questions on that topic !
 
The cellphone no doubt uses a lower power amplifier than the TI chip I linked to. Just guessing, the phone probably can't output even 1.5W. It sounds like you could get by without a bridged amplifier, and if so that would allow a greater choice of chip amps and simplify getting the circuit put together. It appears that you don't need much voltage gain.
 
Disabled Account
Joined 2009
Dear DiYAudio,

I'm completely new in here and in audio circuits as well. Thus, I thought this community might be helpful.

I'm designing a circuit running on battery from (3 to 9 volts) which must have a 5W audio amplification stage. I've been browsing the internet quite a lot for such amps but no one was running under 12volts.

Do you have any ideas ?

I wish you a nice day and thank you for all the knowledge available on that website.

Use a voltage booster - dc-dc converter from low to high. Plenty of them and pretty cheap on eBait and you can use any high quality amp behind it (e.g. LM1875 - cheap as well on oBoy)

Mini DC to DC Converter Boost Step Up Module Wide Voltage Input 2.5-25V to 5-25V | eBay
 
Last edited:
Yesterday i was looking through my parts bin looking for something to build a low power stereo amp for my MP3 player to run in my car , like an Ipod dock type thing ....
Anyways I found a HA13001 chip in my parts bin , it is appearantly a 2 x 5w into 4 ohms amp chip that runs off of 12v DC which is perfect for my car .....

So I did up a home made PCB from the datasheet curcuit and hooked it up to my MP3 player and a set of home theater speakers and a 12v dc PSU and it sounds pretty good , way better than the LM386 amps i have built ......

I don"t think they make them anymore but you can find them on the net , if you can find one I can supply you with a simple PCB design if you want to etch a pcb at home ......
 

Attachments

  • ha13001 pcb-002.JPG
    ha13001 pcb-002.JPG
    82.2 KB · Views: 237
TI have just released TPA2025D1 : 1.9W into 8r0 @ 1% THD from +3.6Vdc
Nice to know.
So nice, that I rushed to download and *read* its datasheet :eek:
Cool chipamp ... but not to be even mentioned here ... except as a curiosity.
Light years away from any "DIY".
Why?
Well, for starters , its pinout is BGA (Ball Grid Array), forget hand soldering there.
Even more, the package is match head sized; 1.5mm x 2 mm :eek:
Oh well, too good to be true (for us I mean) :(
So it looks like I'll have to go back to the chicken farm, light the kerosene lamp up, and grab a couple of my obsolete TBA820, which at least are through hole, DIP8, and can provide 3.6W RMS bridged out of a 9V supply.
Oh well. ;)
 
AN7522N will do the job nicely! I see them in Stereo CRT TV's all the time. (I salvage TV's for scrap and parts)

http://www.lemona.lt/LIUSE/Pdf/AN7522N.pdf

It's a 2-channel BTL stereo amp designed for low voltage.
I built an amp with one, and on only 9V it will fill the room with sound. It's easy to mount on a heatsink, and does not get very hot. Even though the pdf specs @ 8 ohms, I can drive 4 ohms easy with a bigger than stock heatsink, and it's still a relatively small heatsink. 6 ohms should be easy and loud!
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.