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: 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.


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

No Answers

No answers yet. Contribute your answer below!

Your Answer

You must log in or create an account (free!) to answer a question.

Log in Create an account

Go Ad-Free. Activate your CircuitLab membership. No more ads. Save unlimited circuits. Run unlimited simulations.

Search Questions & Answers

Ask a Question

Anyone can ask a question.

Did you already search (see above) to see if a similar question has already been answered? If you can't find the answer, you may ask a question.

About This Site

CircuitLab's Q&A site is a FREE questions and answers forum for electronics and electrical engineering students, hobbyists, and professionals.

We encourage you to use our built-in schematic & simulation software to add more detail to your questions and answers.

Acceptable Questions:

  • Concept or theory questions
  • Practical engineering questions
  • “Homework” questions
  • Software/hardware intersection
  • Best practices
  • Design choices & component selection
  • Troubleshooting

Unacceptable Questions:

  • Non-English language content
  • Non-question discussion
  • Non-electronics questions
  • Vendor-specific topics
  • Pure software questions
  • CircuitLab software support

Please respect that there are both seasoned experts and total newbies here: please be nice, be constructive, and be specific!

About CircuitLab

CircuitLab is an in-browser schematic capture and circuit simulation software tool to help you rapidly design and analyze analog and digital electronics systems.