IRF1405 Relay/Switch

Discussion in 'The Projects Forum' started by Discharger, Mar 30, 2012.

  1. Discharger

    Thread Starter New Member

    Mar 30, 2012
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    I'm working on a mosfet IRF1405 relay to switch power on/off from a Lipo battery 22V to a brushless model aircraft motor via it's own speed controller. max current 70A average 35A. The gate V is 7V from a separate supply. The device will be either fully on or off as selected. The initial bench test was quite promising, the heat sink barely warm at 38A. My questions please -
    (1) Is the IRF 1405 OK for this application or is there another device that would be better suited?
    (2) Would two devices in parallel be a better way to go?
    (3) Are the pins on the device heavy enough to sustain these current levels?
    Thanks for any replies.
     
  2. wayneh

    Expert

    Sep 9, 2010
    12,156
    3,063
    That's a bit low for a standard (not logic level) MOSFET. Any improvement up to say 10V would help keep your FET cooler. I'd be concerned about the 7V sagging any lower, also. At 5V, you might toast your FET. Those are big currents.
     
  3. Discharger

    Thread Starter New Member

    Mar 30, 2012
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    Thanks for your reply Wayneh, I'll keep that in mind. Is there another device that might be better suited?
     
  4. wayneh

    Expert

    Sep 9, 2010
    12,156
    3,063
    Well, usually folks would recommend a logic-level FET for a 7V gate voltage. It'd be fully on by 4V or so, versus the 10-12 needed by the regular FET.

    But you're dealing with some whopping currents and I don't have any particular device to recommend. Same specs but logic level is what I'd recommend, but I sorta doubt there is such a beast.

    I guess what you really need to pay attention to is Rds(on) at 7V, and the datasheet will usually divulge that. The Rds(on) resistance is what will cause heating. If your current choice has a lower Rds than a lesser-spec logic-level FET, it'll generate less heat even though it's less "on".
     
  5. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    You might go for something like this one:
    http://search.digikey.com/us/en/products/IPB009N03L G/IPB009N03L GDKR-ND/2231344
    It has a logic-level gate, and has an Rds(on) of ~0.95mOhm at 100A when Vgs=10v. That's less than 1/5 the resistance of the IRF1405, which means less than 1/5 the internal power dissipation.

    It has a pretty hefty gate charge, so you won't want to be turning it on and off very frequently.

    Here's another; the Rds(on) is 1.5mOhm, Vdss is higher, and so is gate charge - package is also SMT, but a bit easier to work with:
    http://search.digikey.com/us/en/products/IPB015N04N G/IPB015N04N GCT-ND/2231119

    Here's another MOSFET in a TO-220 package if you really want a thru-hole. Rds(on) is up to 1.7m Ohms @ 195A:
    http://search.digikey.com/us/en/products/IRLB3034PBF/IRLB3034PBF-ND/2096638
    If you want to look for something else, try using Digikey's parametric search.
     
  6. Discharger

    Thread Starter New Member

    Mar 30, 2012
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    Thanks again Wayneh and Sgt for your advice. I will take note of the marginal gate V and redesign the circuit for 10/12V on the gate which should ensure it is fully on.
    If I parallel two devices can I connect the two gates together or should I separate each with a resistor? Thanks again.
     
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