P-Channel MOSFET Common Source Connection

[ayeong]

common source mosfet battery

Hi,

I have encountered a circuit whereby I could not understand how does it suppose to work.

There are 2 similar P-Channel MOSFET (Vishay Si1413) which I shall termed it as Q12 & Q15.

Both MOSFET have their gate connected to a single control point which means if a low is applied, both MOSFET will be turned on.

Drain of Q12 : DC supply from AC/DC adapter
Drain of Q15 : DC supply from the battery

Both MOSFET's gate will be LOW whenever the user depress the start button which will result in both MOSFET to turn ON.

What I do not understand how would Q12 & Q15 work together to PREVENT the adapter DC supply from charging the battery and yet allow the DC supply from battery to supply to the circuit in the absence of a adapter supply.

Anybody can help ?

Thanks

 

[atmaca]

ltc9707x

what about the source terminals of MOS transistors

 

[ayeong]

Both source of Q12 & Q15 are connected to each other as shown in the diagram.

Thanks

 

[guamak_menanak]

I'm little bit confuse here!
If you are using PMOS, the current should flow from source to drain! But in your diagram,it's differ for Q12! Current flow from drain to source! Maybe this is the technique for answering you question!

:roll:

 

[ayeong]

Guess I may have found some answers to my question

See the following links :

http://www.xicor.com/pdf_files/an164.pdf
http://www.linear.com/pdf/an53.pdf
**broken link removed**
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http://www.lovoltech.com/pdf/AN200.pdf

Thanks for those who reply.

Cheers,

 

[white_shadow]

What is the common source circuit used for?