Max. supplies ) = ± (Vopeak + Vod)(1 + regulation)(1.1).

[epilot]

Hi guys,

Regarding the equation #7 in the datasheet of the LM3886 power amplifier(page #20):
Max. supplies ) = ± (Vopeak + Vod)(1 + regulation)(1.1).
Several lines below that equation there is an example called "DESIGN A 40W/4Ω AUDIO AMPLIFIER".
Sorry if it is a crazy question but I do not know how they found "supply required" ie +-21v and of course the supply voltage of ±26.6V using Equation (7)?

What is Vod really? is it the 4V drop out voltage of the IC?

thanks for any help.

[epilot]

furthermore what do they mean by "input sensitivity" just below the equaetion #7 at the datasheet? are they mean the gain of the amplifier?

Thanks

[epilot]

I guess that in the example they replaced the (Vopeak + Vod) with the supply required i.e ±21.0V.
If so why they told that dropout voltage is 4V for LM3886, while they considered it as:
(Vopeak + Vod)=(17.9+3.1)=21V?

[AndrewT]

Could Vod be something to do with the voltage drop across the rectifier diodes?

The (1.1) looks like a correction for mains supply overvoltage, i.e. nominal mains voltage + 10%

[pacificblue]

The chapter before the equation gives the answer.

Vod = LM3886's dropout voltage calculated from the Clipping vs Supply Voltage graphs on page 10. It is 4 Volt typical.

1.1 = as Andrew assumes the correction for mains overvoltage according to IEC specs.

[epilot]

Originally Posted by pacificblue

The chapter before the equation gives the answer.

Vod = LM3886's dropout voltage calculated from the Clipping vs Supply Voltage graphs on page 10. It is 4 Volt typical.

1.1 = as Andrew assumes the correction for mains overvoltage according to IEC specs.

Thanks.
Yea, I honestly do know that the dropout voltage regarding the datasheet is 4V, But plz calculte the and solve the exam in the datasheet as I stateed it in my first post and you will get a wrong respond! I want to know how they got a supply required of ±21.0V while Vopeak was 17.9V in the example of page 20??!

What do you mean by mains overvolatge really?

Thanks

[epilot]

Yea. I noticed what they mean by "1.1". It is due to 10% increasement in supply voltage.

Now the main question is that why they in the examination of page #20 used a droput voltage of 3.1V instead of 4V????

[pacificblue]

Because the dropout voltage depends on the output current. 3,1 V is the dropout voltage at the maximum output of the 40 W amp. At the bottom of page 10 there are diagrams that show the clipping = dropout voltage. For a supply voltage of 21 V, Vee is 3,1 V.