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    7Amp Heater and PWM using MOSFET

    Hello everyone,

    I'm working on a project that controls 12Vdc 7Amp silicon heater pad using MOSFET.
    I tried HA210N06 MOSFET with a heatsink but it doesn't work correctly, the heater doesn't get hot but the MOSFET is getting very hot, I tried another lower amper heater it's work but also not get very hot with a 100% duty cycle as I connect it directly to the power supply.

    I'm using dual output power supply 5v for microcontroller and 12v 15A for the heater.
    PWM frequency is 500hz.
    I'm using pic 18f4685 and programming with MikroC.

    The circuit is attached.

    my question is this MOSFET could work correctly but I have some connections problem or coding problem?

    Thank you.

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    Re: 7Amp Heater and PWM using MOSFET

    Hi,

    If HA210N06 is getting hot, then you didn't drive it correctly.
    It should not even need a heatsink when driven correctly.

    Sadly your schematic does not show how you drive the gate...thus we can not validate it.

    Did you read the Mosfet datasheet?

    Klaus
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    Re: 7Amp Heater and PWM using MOSFET

    If you will mix up drain and source, all current will pass throuhg the internal diode and thus it can warm up also
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    Re: 7Amp Heater and PWM using MOSFET

    Quote Originally Posted by KlausST View Post
    Hi,

    If HA210N06 is getting hot, then you didn't drive it correctly.
    It should not even need a heatsink when driven correctly.

    Sadly your schematic does not show how you drive the gate...thus we can not validate it.

    Did you read the Mosfet datasheet?

    Klaus
    Thanks Klaus,
    I think the problem is VGS in HA210N06 is 10V so it will never work with pic microcontroller. i just realized that.
    but i still need help for chossing the best one for this application.

    the gate is coneccted with RC2/CCP1 PIC 18F4685



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    Re: 7Amp Heater and PWM using MOSFET

    Quote Originally Posted by Easyrider83 View Post
    If you will mix up drain and source, all current will pass throuhg the internal diode and thus it can warm up also
    did you mean mix the ground? or what ?



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    Re: 7Amp Heater and PWM using MOSFET

    Hi,

    Two options:
    * use a Mosfet working with low V_gs, also called "logic level Mosfet"
    * or use a gate driver that is able to drive 10V gate voltage

    Klaus
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    Re: 7Amp Heater and PWM using MOSFET

    .... or add a small NPN bipolar transistor as a MOSFET driver. Emitter to ground, drive the base from the PIC through a suitable current limiting resistor (~100 Ohms) and connect it's collector to the gate of the MOSFET. Also add a pull-up resistor (~470 Ohms) to the collector/gate junction to 12V. That should let the bipolar transistor saturate when the PWM signal is high, taking the gate to near zero volts and let the gate go to 12V when the PWM signal is low. It is only two more components but it lets you keep the existing MOSFET.

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    Re: 7Amp Heater and PWM using MOSFET

    Quote Originally Posted by KlausST View Post
    Hi,

    Two options:
    * use a Mosfet working with low V_gs, also called "logic level Mosfet"
    * or use a gate driver that is able to drive 10V gate voltage

    Klaus
    I think it is easier to change the MOSFET to a Logic level MOSFET, but can you please recommend me one..
    this heater will work 24 hours with PWM and PID system so I need a good MOSFET.

    - - - Updated - - -

    Quote Originally Posted by betwixt View Post
    .... or add a small NPN bipolar transistor as a MOSFET driver. Emitter to ground, drive the base from the PIC through a suitable current limiting resistor (~100 Ohms) and connect it's collector to the gate of the MOSFET. Also add a pull-up resistor (~470 Ohms) to the collector/gate junction to 12V. That should let the bipolar transistor saturate when the PWM signal is high, taking the gate to near zero volts and let the gate go to 12V when the PWM signal is low. It is only two more components but it lets you keep the existing MOSFET.

    Brian.
    Thank you Brian.
    I'll try this and give you the feedback.



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    Re: 7Amp Heater and PWM using MOSFET

    Hi,

    I can not recommend one...
    If I wanted to find a suitable Mosfet, then I'd use online selection tools of semiconductor manufacturers or distributors.

    Klaus
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    Re: 7Amp Heater and PWM using MOSFET

    just google logic level or look at element 14 website



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    Re: 7Amp Heater and PWM using MOSFET

    IRLZ24, IRLZ44
    These are logic level MOSFETs
    I use these for LED lighting regulation, my main working light is approx 75W which at 100% duty gives ~6,2A :)
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    Re: 7Amp Heater and PWM using MOSFET

    Quote Originally Posted by ZASto View Post
    IRLZ24, IRLZ44
    These are logic level MOSFETs
    I use these for LED lighting regulation, my main working light is approx 75W which at 100% duty gives ~6,2A :)
    Thank you zasto , i just tried IRLZ44 and it’s getting very hot . Can you please upload the circuit of it maybe i have something wrong in the connection.



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    Re: 7Amp Heater and PWM using MOSFET

    Even at 500Hz you might not be able to fully drive the MOSFET from a PIC output. The maximum current the PIC can drive is 20mA and even at that current it may not reach the required voltage to ensure full MOSFET conduction.
    Please try what I suggested in post #7.

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    Re: 7Amp Heater and PWM using MOSFET

    Quote Originally Posted by betwixt View Post
    Even at 500Hz you might not be able to fully drive the MOSFET from a PIC output. The maximum current the PIC can drive is 20mA and even at that current it may not reach the required voltage to ensure full MOSFET conduction.
    Please try what I suggested in post #7.

    Brian.
    Thank you Brian, I just tried your suggestion and it works well but when the transistor base is fluting the Mosfet still work, so if i put a 10k pull up resistor to the gate can this solve this problem?. or there is another better solution? , also is this circuit will work well with PWM or not?

    Thank you
    A.Boo

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    Re: 7Amp Heater and PWM using MOSFET

    Hi,

    If you have a scope, then show us V_GS measured directly at both Mosfet pins.

    With 5V drive voltage the Mosfet should have 28mOhms resistance.
    Low enough to easily drive a 7A load

    Try to lower PWM frequency. For a heater even 1Hz should work ... but it will decrease switching loss by a factor of 50.

    Klaus
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    Re: 7Amp Heater and PWM using MOSFET

    Hi,

    Why have a floating base? :) What about adding a 10k or even 100k to ground between the 220R and the NPN base.

    I agree with Klaus, e.g. best check the real value of the NMOS gate OFF voltage as it might not be getting turned fully off.



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    Re: 7Amp Heater and PWM using MOSFET

    I disagree.....

    To protect the MOSFET if the input is left floating, add a 100K resistor from the base of the NPN transistor to the +12V line, not to ground.
    If the base is pulled low, the MOSFET conducts which is exactly the opposite of what you need in a fail-safe condition.

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    Re: 7Amp Heater and PWM using MOSFET

    Quote Originally Posted by betwixt View Post
    I disagree.....

    To protect the MOSFET if the input is left floating, add a 100K resistor from the base of the NPN transistor to the +12V line, not to ground.
    If the base is pulled low, the MOSFET conducts which is exactly the opposite of what you need in a fail-safe condition.

    Brian.
    Yes it should be to the +12V not the ground I understand that .. I tried it and it's worked well .. But I didn't try it yet with pwm from uc..
    I hope to work with PWM too.

    Thank you



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    Re: 7Amp Heater and PWM using MOSFET

    Heaters (and their wiring, cables) have parasitic inductance, so the mosfet will see overvoltage spikes at switch-off, which can damage it. A fast-recovery diode across the heating element or a RC snubber across the mosfet D-S is used to prevent overvoltage spikes from damaging the MOSFET. You can use a scope to look at the drain voltage waveform and see how close to the 60V mosfet rating the spikes are.
    edit: HA210N06 is big TO-3P 210A 60V part, 5,800pF Ciss input capacitance, it will need a driver.



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    Re: 7Amp Heater and PWM using MOSFET

    There are now some isolating MOSFET drivers which ought
    to be interesting to the real world interfacing uC folks.

    https://www.google.com/search?client...ed+Gate+Driver

    Talking 5 bucks a pop, but what's non-popping your dev
    board worth? Lots of vendors to look through and the
    distributors too, behind that link.



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