question about pull down resistor

[hayowazzup]

Will the R2 still work as pull down to the mosfet if it is placed in parallel with the TTL (microcontroller)? because I think the one in the diagram below will divide the voltage..

 

[alexan_e]

Yes there is a voltage divider formed but the pull down resistor should be a high value like 5k-10K and compared to low value Rg the division factor will be very small and there will be almost no voltage drop.

 

[mehtadhaval]

Pull down is only needed when you don't know the o/p state and want to make it default low, means if you are not giving any input on TTL line (either it is disconnected or in High Impedance mode), it will PULL DOWN the pin, so R2 will act as a pull down resistor. But, keep R2 of high value compared to "Rg", otherwise when TTL line is "1", the resistor network will work as a voltage divider and you will no be able to drive the MOSFET.