LM1875 on a single supply

Guest
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
 
On 7/1/08 11:30 AM, in article
a1662fad-e0d7-4306-9e20-195abb1e7311@c19g2000prf.googlegroups.com,
"mrdarrett@gmail.com" <mrdarrett@gmail.com> wrote:

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
Click to expand...
The datasheet does have a "Typical Single Supply Operation" schematic.
Have another look.
 
On 7/1/08 11:48 AM, in article C48FCA1C.BCF88%dbowey@comcast.net, "Don
Bowey" <dbowey@comcast.net> wrote:

On 7/1/08 11:30 AM, in article
a1662fad-e0d7-4306-9e20-195abb1e7311@c19g2000prf.googlegroups.com,
"mrdarrett@gmail.com" <mrdarrett@gmail.com> wrote:

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.
Click to expand...
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.
 
On Tue, 1 Jul 2008 11:55:35 -0700 (PDT), mrdarrett@gmail.com wrote:

On Jul 1, 11:48 am, Don Bowey <dbo...@comcast.net> wrote:
On 7/1/08 11:30 AM, in article
a1662fad-e0d7-4306-9e20-195abb1e7...@c19g2000prf.googlegroups.com,



"mrdarr...@gmail.com" <mrdarr...@gmail.com> wrote:
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)
Click to expand...
---
Look at "Supply Current" on page 2 and read: "Power Dissipation and
Heat Sinking" on page 6.

JF
 
On Jul 1, 11:48 am, Don Bowey <dbo...@comcast.net> wrote:
On 7/1/08 11:30 AM, in article
a1662fad-e0d7-4306-9e20-195abb1e7...@c19g2000prf.googlegroups.com,



"mrdarr...@gmail.com" <mrdarr...@gmail.com> wrote:
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.
Click to expand...

Yes, that's what I said. There is a schematic. It's on Page 2.
(amused grin)

Michael
 
On Tue, 1 Jul 2008 13:30:05 -0700 (PDT), mrdarrett@gmail.com wrote:

On Jul 1, 12:15 pm, John Fields <jfie...@austininstruments.com> wrote:
On Tue, 1 Jul 2008 11:55:35 -0700 (PDT), mrdarr...@gmail.com wrote:
On Jul 1, 11:48 am, Don Bowey <dbo...@comcast.net> wrote:
On 7/1/08 11:30 AM, in article
a1662fad-e0d7-4306-9e20-195abb1e7...@c19g2000prf.googlegroups.com,

"mrdarr...@gmail.com" <mrdarr...@gmail.com> wrote:
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?
Click to expand...
---
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
 
On Jul 1, 12:15 pm, John Fields <jfie...@austininstruments.com> wrote:
On Tue, 1 Jul 2008 11:55:35 -0700 (PDT), mrdarr...@gmail.com wrote:
On Jul 1, 11:48 am, Don Bowey <dbo...@comcast.net> wrote:
On 7/1/08 11:30 AM, in article
a1662fad-e0d7-4306-9e20-195abb1e7...@c19g2000prf.googlegroups.com,

"mrdarr...@gmail.com" <mrdarr...@gmail.com> wrote:
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
Click to expand...


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?

Thanks,

Michael
 
On Jul 1, 3:07 pm, John Fields <jfie...@austininstruments.com> wrote:
On Tue, 1 Jul 2008 13:30:05 -0700 (PDT), mrdarr...@gmail.com wrote:
On Jul 1, 12:15 pm, John Fields <jfie...@austininstruments.com> wrote:
On Tue, 1 Jul 2008 11:55:35 -0700 (PDT), mrdarr...@gmail.com wrote:
On Jul 1, 11:48 am, Don Bowey <dbo...@comcast.net> wrote:
On 7/1/08 11:30 AM, in article
a1662fad-e0d7-4306-9e20-195abb1e7...@c19g2000prf.googlegroups.com,

"mrdarr...@gmail.com" <mrdarr...@gmail.com> wrote:
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
Click to expand...

Good point. Thanks.

Michael
 
On Jul 1, 11:43 pm, "Paul E. Schoen" <pst...@smart.net> wrote:
mrdarr...@gmail.com> wrote in message

news:a1662fad-e0d7-4306-9e20-195abb1e7311@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

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
Click to expand...

That's a good idea. Thanks.

Michael
 
On 2008-07-01, Dan Coby <adcoby@earthlink.net> wrote:

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.
Click to expand...
Higher? I would have thunk lower.

Bye.
Jasen
 
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