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[SOLVED] Solar charger Mosfet Connection

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ismu

ismu

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Please check one of solar chager mosfet configration, here lower mosfet connection is ok , but upper is not propper i think (Drain < Sourse even it is a N- channel) . But it is working fine as per the schematic graph [in and out section]. Then How ? I want to explanation about upper mosfet how behave in this circuit? and what the benifit for this connection?
 

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I can't see the point on this circuit operating as a solar charger. However it may work as kind of low efficiency PWM voltage regulator depending on what load you connect at the output...
When Q2(G) signal is 12V, Q1 is OFF since Vgs = 0 and Q2 is ON. The current flows from R1 through Q1 intrinsic diode and Q2 (ON), therefore ouptut voltage is 0.
When Q2(G) signal is 0 V, Q2 is off and Q1 is off too because VGS = -12V... Therefore the output voltage is 12 V (considering you have no load).
The upper switch is useless in this application.
 
Here Solar pannel > battery then Gate ==12V
Now check is ther any use of upper MOSFET?
 

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There is no point in using Two Fets as you said, One is sufficient if the drain source voltage to the FET is within its limit
 
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    ismu

    ismu

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I think its used for to prevent battrey volt return back to solar pannel .right ?
 

No solar panels are protected by giving output from it through a Diode
 
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    ismu

    ismu

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When night what will happen ? battery will dischrge through Solar pannel ,Right?
 

The diode is placed at the solar panel output to prevent the battery discharging through the solar panel at night or during the day when light level is okay and panel output voltage is less than battery voltage.
 
ismailpp2008 said:
When night what will happen ? battery will dischrge through Solar pannel ,Right?
Click to expand...
see the diagram diode will prevent any discharge at any time
4246261600_1359356358.jpg
 
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    ismu

    ismu

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ismailpp2008 said:
Please check one of solar chager mosfet configration, here lower mosfet connection is ok , but upper is not propper i think (Drain < Sourse even it is a N- channel) . But it is working fine as per the schematic graph [in and out section]. Then How ? I want to explanation about upper mosfet how behave in this circuit? and what the benifit for this connection?
Click to expand...

The upper MOSFET is used not as a MOSFET, but actually as a diode (the MOSFET body diode is utilized) to prevent the battery discharging into the panel. Instead of a MOSFET, however, a diode should be used here, preferably a schottky diode, because the MOSFET body diode has a high forward voltage rating and so contributes to high voltage loss in the path.

Hope this helps.
Tahmid.
 
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