How do I calcuclate the resistance for a simple transistor circuit

Hi, I have a 12V motorcycle system that I am trying to use a IRF540N to use to switch 45 watts (on or off). When I look at the datasheet: http://pdf.datasheetcatalog.com/datasheets/134/283734_DS.pdf I am having trouble figuring out what resistance I need for the gate resistor. I think I want between a 2 and 4V drop between the source and gate but I can't see in the data sheet what the gate current draw is. Can someone please help me and also show me where in the datasheet the relevant numbers are? Oh, I am a software guy, so please forgive the noob questions.

Thanks!

by staggart
February 05, 2017

Good choice of device! Should handle your four amp load without getting hot. Looking at the On State Characteristics the gate threshold is measured at 250uA, then the next line shows it passing 33A with 10V on the gate. You need to apply your full battery voltage to turn it on fully. Perhaps 10k in series and 100nF to ground would be a good idea to take out any nasty supply voltage spikes.The 10k will not drop any volts because there is no gate current. Hope this is helpful, mike.

by mikerogerswsm
February 05, 2017
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