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Simple IRL530 Driver -- Am I Crazy (Loaded question, I know....) — Parallax Forums

Simple IRL530 Driver -- Am I Crazy (Loaded question, I know....)

JonnyMacJonnyMac Posts: 9,154
edited 2010-08-05 05:25 in Propeller 1
I want to experiment with some high-current LEDs for Christmas lighting and have whipped up the following circuit to buffer the 3.3v output of the Propeller to the gate of an IRL530; am I nuts or should I proceed to prototyping without worry of making a big cloud of smoke?

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Jon McPhalen
Hollywood, CA
IRL530_Drive.jpg
506 x 344 - 33K

Comments

  • ElectricAyeElectricAye Posts: 4,561
    edited 2010-08-04 19:57
    Have you considered the irf3708? Beyond a couple of resistors, I don't think any buffering is required.

    search.digikey.com/scripts/DkSearch/dksus.dll?vendor=0&keywords=irf3708pbf
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2010-08-04 19:59
    Jon,

    Try an IRF3708 instead. You can drive the gate directly from the Prop.

    -Phil
  • JonnyMacJonnyMac Posts: 9,154
    edited 2010-08-04 20:14
    I need to switch 36v @ 3A.

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    Jon McPhalen
    Hollywood, CA
  • AribaAriba Posts: 2,690
    edited 2010-08-04 21:42
    Then an IRLZ34 with the Gate direct at the Prop (and a Pulldown resistor).

    Andy
  • Graham StablerGraham Stabler Posts: 2,510
    edited 2010-08-04 21:52
    The circuit looks fine, if you have those parts already go for it.

    Graham
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2010-08-04 22:15
    The IRLZ34 might work, but it's not fully characterized for gate drives below 4.0V. A better choice might be the FDS4672A.

    -Phil
  • FredBlaisFredBlais Posts: 375
    edited 2010-08-04 22:36
    Phil Pilgrim (PhiPi) said...
    The IRLZ34 might work, but it's not fully characterized for gate drives below 4.0V. A better choice might be the FDS4672A.

    -Phil

    Hi Phil, what do you mean by not fully characterized?
  • william chanwilliam chan Posts: 1,326
    edited 2010-08-04 22:42
    The 5v drive to the mosfet gate is a little low but it will work for 3A load. ( not much more )
    If possible, increase the gate voltage to 9-12v to reduce the heating on the mosfet.

    The pull up resistor to V33 is unnecessary if the prop pin is set to output.
    The pull up resistor to V50 could be changed to 5k-10k to save current if the load is on for long periods.

    I use this circuit all the time.

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    www.fd.com.my
    www.mercedes.com.my
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2010-08-05 00:08
    william chan said...
    The pull up resistor to V33 is unnecessary if the prop pin is set to output.
    Don't forget that the pin is an input when the Prop powers up or is otherwise in reset.
    FredBlais said...
    Hi Phil, what do you mean by not fully characterized?
    There's no data for RDS(on) for gate voltages that low. Moreover, VGS(th) can be as high as 2.0V, which is too close to 3.3V for comfort.

    -Phil
  • JonnyMacJonnyMac Posts: 9,154
    edited 2010-08-05 00:46
    @William,

    As Phil points out, the Propeller takes quite a long time to boot up, so I have to make sure the FET doesn't come on when the pins are not configured, hence the pull-up.

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    Jon McPhalen
    Hollywood, CA
  • Beau SchwabeBeau Schwabe Posts: 6,567
    edited 2010-08-05 05:25
    Jon,

    I would at least provide 12V to what you have labeled V50 ... either through a zener diode off of the VIN supply or a voltage regulator off of the VIN supply.

    What you will need to watch out for is when you turn the IRL530 'OFF'. It will spend more time in the linear region because you are not driving the signal High and relying on a pull-up resistor to do the job. Under heavier current loads this will cause heat buildup that could otherwise be avoided or reduced if the IRL530 was driven instead of pulled-up.

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    Beau Schwabe

    IC Layout Engineer
    Parallax, Inc.
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