Arduino Forum

Using Arduino => Project Guidance => Topic started by: markthespark on Jul 17, 2012, 11:04 pm

Title: IRL520 schematic help for all led circuits
Post by: markthespark on Jul 17, 2012, 11:04 pm
hi all
is it safe for me to say that i should use this circuit for all power mosfets IRL520 and small transistors such as the 2N2222A
I know R1 is current limiting
but what about R2/R3
is this just for safe measure ??
cheers
marko
Title: Re: IRL520 schematic help for all led circuits
Post by: Magician on Jul 18, 2012, 12:40 am
MOSFET usually has quite high value of internal capacitance, Gate - Source and Gate - Drain. To protect arduino digital output from current spike when this cap is starting to charge ("0" to "1" transition) or discharge  ("1" to "0" transition) 130 Ohm resistor. To keep MOSFET OFF, if you disconnect arduino, 10 k resistor.
Title: Re: IRL520 schematic help for all led circuits
Post by: runaway_pancake on Jul 18, 2012, 01:32 am
Another member pointed out to me that, as you've placed them, the resistors form a voltage divider, R2 >> R3 notwithstanding.  
He suggested that I change the arrangement slightly, as attached.  I could not argue.
Guess I'd always implemented the divider reflexively.
The low-? resistor still limits the in-rush but without a voltage divider effect which diminishes VGS.  
In the context of these "logic-level" MOSFets, you want to get as much of that logic-level output applied to the gate as you can.  (This especially if a much lower value of R2, to accomodate faster switching, were used.)