LM4702 triple darlington output

[Mark St. Denis]

Nothing Is Wrong

Hi,

Nothing is wrong with discrete Darlington triples. In fact, many

of the popular car audio amps do it that way. All I was tring

to say, is that no IC makes it a little harder to design. Triple

Darlington is a good idea, discrete or IC.

Mark

 

[jackinnj]

leach used triple darlingtons and still in use to day....no reason not to try them out for lm4702....

and the paper is on Dr. Leach's website.

 

[Carl_Huff]

I just did a quick calculation that told me that the LM4702 can sink enough current to drive 3 SAP16N/16P pairs. Is that right??

Somebody please check my math ....

 

[gmikol]

I just did a quick calculation that told me that the LM4702 can sink enough current to drive 3 SAP16N/16P pairs. Is that right??

Somebody please check my math ....

Sounds reasonable.

Min. hFE is 5000. Min. drive current is 3mA.

Minimum Ic translates into 15A. Probably need +-70VDC rails for that into 4 Ohms. That's 150W (15A*10V) dissipation per output pair. Doesn't seem like you'd want less than 3 pairs.

15A peak output current translates into 450WPC into 4 Ohms resistive. Of course, the output devices cost 10X the front end, but for ~$80 total, that's not bad.

Now if you get "Y" grade devices, min hFE of 8000...

...But hey, I'm just starting to learn about this stuff. I could be wrong, too.

--Greg

 

[Mark St. Denis]

Ask National?

Hi,

3 FAQs have been asked on LM4702 in National's Knowlege Base:

(1) How to get 300 watts?
(2) LM4702 need heat sink?
(3) Why need output stage?

http://search.national.com/iphrase/query?query=LM4702&render1&categories=1phrase

Can LM4702 current drive 3 SAP16N/16P? I think this is a good

enough question for National to answer.

Mark