LM1875 on a single supply
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Posted by Don Bowey on July 1, 2008, 3:06 pm
Please log in for more thread options >> I was reading the datasheet for the LM1875
>> http://www.national.com/ds.cgi/LM/LM1875.pdf >> >> and I noticed that they do have a schematic for a single supply (as >> opposed to a +/- supply). >> >> If running on a single supply, does the chip amplifer consume >> significant power during quiet tracks? >> >> Would this be pretty much the same as running the amplifier in Class A >> mode (vs. Class AB)? >> >> I'm trying to figure out if I really need a +/- power supply, or if I >> can just go with a single supply (easier to build). >> >> Thanks, >> >> Michael >
> The datasheet does have a "Typical Single Supply Operation" schematic. > Have another look. > > Oops! I misread your post. You shouldn't have any problem with a single supply, but be sure to follow the guidelines on heat sinking. It appears the amp operates in Class B and will idle at about 6W of heat dissipation. | |||||||||||||||||||||||||||||||||||||||||||
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Posted by Paul E. Schoen on July 2, 2008, 2:43 am
Please log in for more thread options >I was reading the datasheet for the LM1875
> http://www.national.com/ds.cgi/LM/LM1875.pdf > > and I noticed that they do have a schematic for a single supply (as > opposed to a +/- supply). > > If running on a single supply, does the chip amplifer consume > significant power during quiet tracks? > > Would this be pretty much the same as running the amplifier in Class A > mode (vs. Class AB)? > > I'm trying to figure out if I really need a +/- power supply, or if I > can just go with a single supply (easier to build). > > Thanks, > > Michael Since the LM1875 is inexpensive, you might try using two of them on a single supply, and putting the speaker between the outputs. You would have to make one amp inverting and the other non-inverting, but you will get twice the output voltage and save the capacitors. A single 24 volt supply will then give +/- 24 volts, or about 17 VRMS, to an 8 ohm speaker, or 36 watts. There are lots of 24 VDC supplies available. The downside of this approach is making sure the DC level of both amps are equal and about 1/2 the supply. If you check SemiElectric's eBay store you will find PC boards and kits for the LM3875, as well as other single and dual amplifier ICs: http://search.stores.ebay.com/semielectric_audio-amp_W0QQfciZQ2d1QQfclZ3QQfsnZsemielectricQQfsooZ2QQfsopZ3QQfsubZ0QQsaselZ650588702QQsofpZ0 His LM3875s are about $6.50 each. They are larger (56 watts vs 20 watts), but seem to be otherwise quite similar. Most of the additional IC pins are NCs, for heat sinking and mechanical mounting, I suppose. They are only $5.90 each from DigiKey, and the LM1875 is $3.28. Wow: 10 to 15 cents per watt! Paul | |||||||||||||||||||||||||||||||||||||||||||
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Posted by on July 2, 2008, 12:51 pm
Please log in for more thread options >
> > > > >I was reading the datasheet for the LM1875
> >http://www.national.com/ds.cgi/LM/LM1875.pdf >
> > and I noticed that they do have a schematic for a single supply (as
> > opposed to a +/- supply). >
> > If running on a single supply, does the chip amplifer consume
> > significant power during quiet tracks? >
> > Would this be pretty much the same as running the amplifier in Class A
> > mode (vs. Class AB)? >
> > I'm trying to figure out if I really need a +/- power supply, or if I
> > can just go with a single supply (easier to build). >
> > Thanks,
>
> > Michael
>
> Since the LM1875 is inexpensive, you might try using two of them on a > single supply, and putting the speaker between the outputs. You would have > to make one amp inverting and the other non-inverting, but you will get > twice the output voltage and save the capacitors. A single 24 volt supply > will then give +/- 24 volts, or about 17 VRMS, to an 8 ohm speaker, or 36 > watts. There are lots of 24 VDC supplies available. The downside of this > approach is making sure the DC level of both amps are equal and about 1/2 > the supply. > > If you check SemiElectric's eBay store you will find PC boards and kits for > the LM3875, as well as other single and dual amplifier ICs: > > http://search.stores.ebay.com/semielectric_audio-amp_W0QQfciZQ2d1QQfc... > > His LM3875s are about $6.50 each. They are larger (56 watts vs 20 watts), > but seem to be otherwise quite similar. Most of the additional IC pins are > NCs, for heat sinking and mechanical mounting, I suppose. They are only > $5.90 each from DigiKey, and the LM1875 is $3.28. Wow: 10 to 15 cents per > watt! > > Paul That's a good idea. Thanks. Michael | |||||||||||||||||||||||||||||||||||||||||||
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