# Power output of TBA820M (audio amplifier chip)?

Started by May 12, 2017
```Does anyone know a formula for calculating the power output of the
TBA820M audio amplifier IC?  The data sheet gives the following
examples:

supply (V)   load (&Omega;)  output (W)
12             8        2
9             4        1.6
9             8        1.2
6             4        0.75
3.5           4        0.25

but the output isn't consistently proportional to V^2/R (which was my
first guess).

Thanks.

--
Ambassador Trentino: "I am willing to do anything to prevent this
war."
President Firefly: "It's too late. I've already paid a month's
rent on the battlefield."                          _Duck Soup_
```
```On Fri, 12 May 2017 13:33:12 +0100, Adam Funk wrote:

> Does anyone know a formula for calculating the power output of the
> TBA820M audio amplifier IC?  The data sheet gives the following
> examples:
>
> supply (V)   load (&Omega;)  output (W)
> 12             8        2
>  9             4        1.6 9             8        1.2 6             4
>       0.75 3.5           4        0.25
>
> but the output isn't consistently proportional to V^2/R (which was my
> first guess).
>
> Thanks.

I tried fitting it to (Vss - V0)^2/R on the supposition that it had
something to do with not being able to hit the rails, and didn't get a

No discussion in the data sheet?  It does seem wimpy.

--
www.wescottdesign.com
```
```Adam Funk wrote:

---------------------
> Does anyone know a formula for calculating the power output of the
> TBA820M audio amplifier IC?  The data sheet gives the following
> examples:
>
> supply (V)   load (&Omega;)  output (W)
> 12             8        2
>  9             4        1.6
>  9             8        1.2
>  6             4        0.75
>  3.5           4        0.25
>
> but the output isn't consistently proportional to V^2/R (which was my
> first guess).
>

** There is no formula.

The IC's max output power with varying DC supplies is a result of its internal design.

....  Phil
```
```On 2017-05-13, Tim Wescott wrote:

> On Fri, 12 May 2017 13:33:12 +0100, Adam Funk wrote:
>
>> Does anyone know a formula for calculating the power output of the
>> TBA820M audio amplifier IC?  The data sheet gives the following
>> examples:
>>
>> supply (V)   load (&Omega;)  output (W)
>> 12             8        2
>>  9             4        1.6 9             8        1.2 6             4
>>       0.75 3.5           4        0.25
>>
>> but the output isn't consistently proportional to V^2/R (which was my
>> first guess).
>>
>> Thanks.
>
> I tried fitting it to (Vss - V0)^2/R on the supposition that it had
> something to do with not being able to hit the rails, and didn't get a
>
> No discussion in the data sheet?  It does seem wimpy.

Oops, I didn't notice this before, but there is a grainy plot of power
vs supply voltage for 3 loads in Figure 3.

<http://www.kolumbus.fi/~mirian77/d/tba820.pdf>

--
Now you're climbing to the top of the company ladder
Hope it doesn't take too long
Can't you see there'll come a day when it won't matter?
Come a day when you'll be gone               --- Boston
```
```On 2017-05-14, Phil Allison wrote:

> Adam Funk wrote:
>
> ---------------------
>> Does anyone know a formula for calculating the power output of the
>> TBA820M audio amplifier IC?  The data sheet gives the following
>> examples:
>>
>> supply (V)   load (&Omega;)  output (W)
>> 12             8        2
>>  9             4        1.6
>>  9             8        1.2
>>  6             4        0.75
>>  3.5           4        0.25
>>
>> but the output isn't consistently proportional to V^2/R (which was my
>> first guess).
>>
>
> ** There is no formula.
>
> The IC's max output power with varying DC supplies is a result of its internal design.

I guess so, but I just noticed there is a plot of this in figure 3 of
the datasheet.

--
Most Americans are too civilized to hang skulls from baskets, having
been headhunters, of course, only as recently as Vietnam.
--- Kinky Friedman
```
```On 5/15/2017 5:09 AM, Adam Funk wrote:
> On 2017-05-13, Tim Wescott wrote:
>
>> On Fri, 12 May 2017 13:33:12 +0100, Adam Funk wrote:
>>
>>> Does anyone know a formula for calculating the power output of the
>>> TBA820M audio amplifier IC?  The data sheet gives the following
>>> examples:
>>>
>>> supply (V)   load (&Omega;)  output (W)
>>> 12             8        2
>>>  9             4        1.6 9             8        1.2 6             4
>>>       0.75 3.5           4        0.25
>>>
>>> but the output isn't consistently proportional to V^2/R (which was my
>>> first guess).
>>>
>>> Thanks.
>>
>> I tried fitting it to (Vss - V0)^2/R on the supposition that it had
>> something to do with not being able to hit the rails, and didn't get a
>>
>> No discussion in the data sheet?  It does seem wimpy.
>
> Oops, I didn't notice this before, but there is a grainy plot of power
> vs supply voltage for 3 loads in Figure 3.
>
> <http://www.kolumbus.fi/~mirian77/d/tba820.pdf>

What Tim said would be my first guess.  Most devices can't supply power
at voltages close to the power rails, so some voltage would need to be
subtracted off.  The result should be close to linear.

The curves in figure 3 look fairly parabolic with a Y intercept below
zero which confirms that.  If the square root of the power is used
instead of the power I expect the curves would be mostly linear.

I wonder how figure 6 differs from figure 3?  Figure 3 shows some
measurement conditions and figure 6 doesn't.

--

Rick C
```
```On 2017-05-15, rickman wrote:

> On 5/15/2017 5:09 AM, Adam Funk wrote:

>> Oops, I didn't notice this before, but there is a grainy plot of power
>> vs supply voltage for 3 loads in Figure 3.
>>
>> <http://www.kolumbus.fi/~mirian77/d/tba820.pdf>
>
> What Tim said would be my first guess.  Most devices can't supply power
> at voltages close to the power rails, so some voltage would need to be
> subtracted off.  The result should be close to linear.
>
> The curves in figure 3 look fairly parabolic with a Y intercept below
> zero which confirms that.  If the square root of the power is used
> instead of the power I expect the curves would be mostly linear.
>
> I wonder how figure 6 differs from figure 3?  Figure 3 shows some
> measurement conditions and figure 6 doesn't.

Does Figure 6 refer to power dissipation *in the IC itself*, whereas
Figure 3 is power output (to the speaker)?

--
The three-martini lunch is the epitome of American efficiency.
Where else can you get an earful, a bellyful and a snootful at
the same time?                                 --- Gerald Ford
```
```On Tuesday, June 6, 2017 at 9:15:09 AM UTC-4, Adam Funk wrote:
> On 2017-05-15, rickman wrote:
>
> > On 5/15/2017 5:09 AM, Adam Funk wrote:
>
> >> Oops, I didn't notice this before, but there is a grainy plot of power
> >> vs supply voltage for 3 loads in Figure 3.
> >>
> >> <http://www.kolumbus.fi/~mirian77/d/tba820.pdf>
> >
> > What Tim said would be my first guess.  Most devices can't supply power
> > at voltages close to the power rails, so some voltage would need to be
> > subtracted off.  The result should be close to linear.
> >
> > The curves in figure 3 look fairly parabolic with a Y intercept below
> > zero which confirms that.  If the square root of the power is used
> > instead of the power I expect the curves would be mostly linear.
> >
> > I wonder how figure 6 differs from figure 3?  Figure 3 shows some
> > measurement conditions and figure 6 doesn't.
>
> Does Figure 6 refer to power dissipation *in the IC itself*, whereas
> Figure 3 is power output (to the speaker)?

That's how I read it.

George H.
>
>
> --
> The three-martini lunch is the epitome of American efficiency.
> Where else can you get an earful, a bellyful and a snootful at
> the same time?                                 --- Gerald Ford

```
```On 2017-06-06, George Herold wrote:

> On Tuesday, June 6, 2017 at 9:15:09 AM UTC-4, Adam Funk wrote:
>> On 2017-05-15, rickman wrote:
>>
>> > On 5/15/2017 5:09 AM, Adam Funk wrote:
>>
>> >> Oops, I didn't notice this before, but there is a grainy plot of power
>> >> vs supply voltage for 3 loads in Figure 3.
>> >>
>> >> <http://www.kolumbus.fi/~mirian77/d/tba820.pdf>
>> >
>> > What Tim said would be my first guess.  Most devices can't supply power
>> > at voltages close to the power rails, so some voltage would need to be
>> > subtracted off.  The result should be close to linear.
>> >
>> > The curves in figure 3 look fairly parabolic with a Y intercept below
>> > zero which confirms that.  If the square root of the power is used
>> > instead of the power I expect the curves would be mostly linear.
>> >
>> > I wonder how figure 6 differs from figure 3?  Figure 3 shows some
>> > measurement conditions and figure 6 doesn't.
>>
>> Does Figure 6 refer to power dissipation *in the IC itself*, whereas
>> Figure 3 is power output (to the speaker)?
>
> That's how I read it.

The charts look almost the same except for the scale of the Y-axis, so
I guess internal power dissipation is close to proportional to output
power.

--
Cats don't have friends.  They have co-conspirators.
http://www.gocomics.com/getfuzzy/2015/05/31
```