Example of using Mofset driver

Thread Starter

abouabdelmajid

Joined Aug 20, 2017
13
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 under 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
 

shortbus

Joined Sep 30, 2009
8,337
The mosfet is a "P" channel type. To get that type to conduct the gate needs to be lower voltage with respect to the source. The transistor allows this to happen when it is turned on.
 

hobbyist

Joined Aug 10, 2008
889
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 ?!!
When the PWM goes to a positive output, it drives the 2n3904 on, this in turn provides a path through the collector emitter of that transistor to ground, thereby placing a negative going signal to the gate of the mosfet, turning it on, with the mosfet turned on the solar input source can feed a positive going current into the battery charging it up.

The purpose for the mosfet is to act as a switch, think of it as a normal open relay, think of the 2n3904 as a relay driver, so when the 2n3904 is turned on, it supplies current to a relay coil and the relay closes, when the 2n3904 loses base input it turns off thereby turning off the current supply to the relay coil, so the contacts open again.

In this case the mosfet is now the relay and the 2n3904 supplies gate voltage to the mosfet and the mosfet acts as a relay switch and turns on, and follows the same function for turning off.

The mosfet takes the place of the relay so as to remove mechanical switching and make all switching electronic.
 

wayneh

Joined Sep 9, 2010
16,834
In addition to the comments so far, the transistor arrangement achieves level shifting of the PWM signal. If that PWM signal went from rail-to-rail, you wouldn't need the transistor (although you might have to reverse the logic of the PWM signal). You could drive the MOSFET fully on or fully off without the transistor. But that PWM signal probably doesn't go high enough in voltage to turn off the P-type MOSFET. Using the transistor allows boosting the voltage at the gate all the way to the high voltage rail, ensuring that the MOSFET turns off.

The transistor also isolates the source of the PWM signal from the current needed to drive the MOSFET gate, which increases with frequency. If the switching speed is high enough, the load on the PWM signal could become too high.
 

ebeowulf17

Joined Aug 12, 2014
3,275
You need a few more basics before you starting working with such circuits by my opinion! The circuit is simple.
Saying the circuit is simple isn't particularly helpful.

Are you advising against working with solar battery charger systems, or against working with MOSFETs, their drivers, and pwm? If it's the former, I guess I can understand that - charging batteries improperly can get dangerous quickly. If it's the latter, I'd disagree. You've got to start learning somewhere, and if there's a circuit that interests you, even if you're in a little over your head, it's more fun to work on understanding it.
 

ArakelTheDragon

Joined Nov 18, 2016
1,350
Saying the circuit is simple isn't particularly helpful.

Are you advising against working with solar battery charger systems, or against working with MOSFETs, their drivers, and pwm? If it's the former, I guess I can understand that - charging batteries improperly can get dangerous quickly. If it's the latter, I'd disagree. You've got to start learning somewhere, and if there's a circuit that interests you, even if you're in a little over your head, it's more fun to work on understanding it.
What I mean is that he should read a lot more first and then do what so ever with electronics and electrics!
 
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