MOSFETS and Solenoids

Discussion in 'General Electronics Chat' started by Tobias, Sep 12, 2009.

  1. Tobias

    Thread Starter Active Member

    May 19, 2008
    I am using a MOSFET to power a solenoid. I was told the biggest reason for a MOSFET to fail in this case is the voltage spike when the solenoid is turned off. Below is a link of the MOSFET I am using. I don't know what to look for to tell if is has the diode circuitry to protect it from the voltage spikes.

  2. hgmjr

    Retired Moderator

    Jan 28, 2005
    Typically, the flyback protection diode is added across the relay coil. There is an intrinsic diode that is often found internally across the drain and source of a MOSFET but it is the external diode that is most often used to greatest effect.

  3. The Electrician

    AAC Fanatic!

    Oct 9, 2007
    Look at the single pulse avalanche energy rating; it's 281 mJ.

    To start, you might measure the inductance of your solenoid and calculate how much energy you must dissipate when you turn it off.

    If I is the operating current, and L is the inductance, then you must dissipate something like L*I^2/2 joules.

    This rating applies when the FET is allowed to cool down between pulses. In other words, when you only turn off the solenoid every few seconds. If you turn it on and off many times per second, then the single pulse rating doesn't apply.