LM1875 on a single supply
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Posted by John Fields on July 1, 2008, 6:07 pm
Please log in for more thread options >> On Tue, 1 Jul 2008 11:55:35 -0700 (PDT), mrdarr...@gmail.com wrote:
>> >> On 7/1/08 11:30 AM, in article
>> >> a1662fad-e0d7-4306-9e20-195abb1e7...@c19g2000prf.googlegroups.com, >>
>> >> > 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. >>
>> >Yes, that's what I said. There is a schematic. It's on Page 2.
>> >(amused grin) >>
>> --- >> Look at "Supply Current" on page 2 and read: "Power Dissipation and >> Heat Sinking" on page 6. >> >> JF >
> > >Ah, so apparently the chip does not use more power with a single >supply than with a +/- supply. > >Is there any reason why I should NOT use a single supply with this >chip? --- I don't think so, but try it and see if it works the way you want it to. If it does you've saved a supply, but if it doesn't it's only cost you a handful of discretes. JF | |||||||||||||||||||||||||||||||||||||||||||
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Posted by on July 1, 2008, 6:09 pm
Please log in for more thread options > On Tue, 1 Jul 2008 13:30:05 -0700 (PDT), mrdarr...@gmail.com wrote:
> >> On Tue, 1 Jul 2008 11:55:35 -0700 (PDT), mrdarr...@gmail.com wrote:
> >> >> On 7/1/08 11:30 AM, in article > >> >> a1662fad-e0d7-4306-9e20-195abb1e7...@c19g2000prf.googlegroups.com, >
> >> >> > 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. >
> >> >Yes, that's what I said. There is a schematic. It's on Page 2.
> >> >(amused grin) >
> >> ---
> >> Look at "Supply Current" on page 2 and read: "Power Dissipation and > >> Heat Sinking" on page 6. >
> >> JF
>
> >Ah, so apparently the chip does not use more power with a single
> >supply than with a +/- supply. >
> >Is there any reason why I should NOT use a single supply with this
> >chip? >
> --- > I don't think so, but try it and see if it works the way you want it > to. If it does you've saved a supply, but if it doesn't it's only > cost you a handful of discretes. > > JF Good point. Thanks. Michael | |||||||||||||||||||||||||||||||||||||||||||
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Posted by Dan Coby on July 1, 2008, 6:46 pm
Please log in for more thread options >> On Tue, 1 Jul 2008 13:30:05 -0700 (PDT), mrdarr...@gmail.com wrote:
>> >> On Tue, 1 Jul 2008 11:55:35 -0700 (PDT), mrdarr...@gmail.com wrote:
>> >> >> On 7/1/08 11:30 AM, in article >> >> >> a1662fad-e0d7-4306-9e20-195abb1e7...@c19g2000prf.googlegroups.com, >>
>> >> >> > 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. >>
>> >> >Yes, that's what I said. There is a schematic. It's on Page 2.
>> >> >(amused grin) >>
>> >> ---
>> >> Look at "Supply Current" on page 2 and read: "Power Dissipation and >> >> Heat Sinking" on page 6. >>
>> >> JF
>>
>> >Ah, so apparently the chip does not use more power with a single
>> >supply than with a +/- supply. >>
>> >Is there any reason why I should NOT use a single supply with this
>> >chip? >>
>> --- >> I don't think so, but try it and see if it works the way you want it >> to. If it does you've saved a supply, but if it doesn't it's only >> cost you a handful of discretes. >> >> JF >
> > Good point. Thanks. > > Michael I would like to point out that the single supply schematic has a 2200 uF capacitor in series with the output speaker. In theory, with an ideal capacitor, this is going to give an 18 Hz cutoff frequency into a 4 ohm speaker (36 Hz into 8 ohms). A real capacitor will have some internal resistance. This is going to give a higher cutoff frequency. | |||||||||||||||||||||||||||||||||||||||||||
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Posted by Jasen Betts on July 10, 2008, 6:47 am
Please log in for more thread options
> I would like to point out that the single supply schematic has a 2200 uF
> capacitor in series with the output speaker. In theory, with an ideal > capacitor, this is going to give an 18 Hz cutoff frequency into a 4 ohm > speaker (36 Hz into 8 ohms). A real capacitor will have some internal > resistance. This is going to give a higher cutoff frequency. Higher? I would have thunk lower. Bye. Jasen | |||||||||||||||||||||||||||||||||||||||||||
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Posted by Dan Coby on July 10, 2008, 5:39 pm
Please log in for more thread options >
>> I would like to point out that the single supply schematic has a 2200 uF
>> capacitor in series with the output speaker. In theory, with an ideal >> capacitor, this is going to give an 18 Hz cutoff frequency into a 4 ohm >> speaker (36 Hz into 8 ohms). A real capacitor will have some internal >> resistance. This is going to give a higher cutoff frequency. >
> Higher? I would have thunk lower. Yes. My mistake, the series resistance of the capacitor is going to move the break frequency lower. However the series resistance of the capacitor is going to cut the overall gain of the circuit since it will form a voltage divider with the speaker impedance. | |||||||||||||||||||||||||||||||||||||||||||
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