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Example of using Mofset driver

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abouabdelmajid

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Hi everyone.Here is a a circuit showing how a "PWM Solar Charge controler" works. the principal work of this controler is using arduino's PWM to switch on the transistor 2N3904 to let the 12V battery absorb the energy from the solar pannel when the voltage of the solar pannel is bigger than the actual battery's voltage and in an opposite situation the transistor should be switched off. so using the mosfet driver (wich is in the middle of red circle) is an important thing but i still dont know how it works ?!
after many researches i found that the driver is there to provide the current and also drives the gate with an appropriate voltage level not high to avoid the risk of damaging the mosfet but also high enough to produce a low Rdson. But my question is how it works ?!! when the transistor 2N3904 is switched on where the curent goes ? why do we need the mosfet IRF95530 ? to amplify the voltage ? but how the current get into the mosfet ? can anybody tell me how the Mofset driver work ?!!

2017-08-24_212119.jpg
 
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ronsimpson

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Most Helpful Member
to let the 12V battery absorb the energy from the solar pannel when the voltage of the solar pannel is under the actual battery's voltage
no, If the solar panel voltage is lower than the battery no current flows.
to amplify the voltage ?
No amplification. It is just a switch.
can anybody tell me
Diode D2, (don't know what kind) but it will do nothing if the solar panel is connected right. The diode will (maybe) blow the fuse if the panel is connected backwards. I think this is why the diode is there but I think it will not function the way the designer thinks. If you have a 1 amp panel it can not produce more than 1A. If you connect backwards the panel will only make 1A. So you can't pop a 2A fuse with a 1A panel. I know there is on amp rating on the fuse.

F1 is for protection but I think it does nothing.

D1 is to keep the battery voltage off the panel, when the panel is not making power. Note it is a 1A high voltage diode. I think a 1N4001 will also work. (low voltage) Three are better diodes for this place.

R1&R2 allows the computer to measure the panels voltage. (there is 0.7V loss in D1) The computer can only measure 0 to 5 volts. A 3:1 divider will allow a measurement of 0 to 15 volts.

Q1. No amplification! If there is 0 volts across R3 then Q1 is "open" and no current will charge the battery. If R3 has -3 volts across it then charging current will flow. (assuming the panel is making more voltage then 12V)

There are other reasons why I do not like the circuit.
-----------------------------
What do you want the circuit to do?
What panel do you have? Volts and current and power?
 

abouabdelmajid

New Member
thank you for answering me mr ronsimpson. Yes you are right i have just corrected the error about when the transistor should be switched on.

A zener diode (D2) is placed at the input terminal to suppress the over voltage.

As an answer to your questions : what i realy want to know is how the mosfet driver (wich is in the middle of red circle) works ?
i am using a 20 watt/17 Volt solar pannel to charge a 12 Volt 7.2 Ah lead acid battery ... do you think i should not use this circuit to charge my battery with no damages ? please tell me if i am doing something useless or wrong
 

ronsimpson

Well-Known Member
Most Helpful Member
upload_2017-8-25_6-58-54.jpeg
what i realy want to know is how the mosfet driver (wich is in the middle of red circle) works ?
Starting condition: (PWM=low)
SOLAR_IN = 17 VOLTS.
D1 right side = 16.4 volts, Q1-source, A1-gate, C1
BAT = 12 volts, Q1-drain, T1-collector
T1-base = 0 volts, PWM
No charging current! (because Q1-source to Gate is o volts Q1 is open)
------------------------------
Now with PWM high.
PWM = about 4.5V
4mA goes into T1-base. Transistor turns on. T1-base to emitter = 0.6 volts.
T1-collector = 0.2 volts. R3 voltage is about 16 volts. Q1-S to G volts is about 16 volts. Q1 is on. (Source to Drain is almost a short)
Current will flow from SOLAR_IN, FUSE, D1, Q1 into battery.
---------------------------
PWM low:
See starting condition.
 
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