Gate driver for mosfet problem

Discussion in 'General Electronics Chat' started by raychar, Nov 16, 2011.

  1. raychar

    Thread Starter Member

    Nov 8, 2011
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    Hello everybody,

    I try to use IR2117 gate driver to drive mosfet (IRF540 or IRFP240) in high side and not sucess. I can only get a little VB-Vs voltage, around 1.8V. I use BYV27-150 diode and I tuned different capacitor values from 0.5uf to 0.005uf. There is no VB-VS voltage when cap's value go larger.

    Does anyone have help in it, thanks,

    Raychar
     
  2. SgtWookie

    Expert

    Jul 17, 2007
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    Please attach a .png image of your schematic, exactly how you have it wired now, indicating all component values, part numbers (where applicable) and voltages applied.

    Use the "Go Advanced" button near the bottom, then "Manage Attachments" on the bottom of that screen.

    If you cannot create a .png image for some reason, then please post a .pdf format file.

    If you have the circuit in a schematic capture or simulation program like Cadsoft Eagle, ExpressSCH, LTSpice, then you can upload those files to the forum.

    The subject of the IR2110 driver comes up very frequently on the forums. In order to charge the boost cap on that driver, you must first turn ON the low-side MOSFET; or else there is no ground path for the boost capacitor(s).

    You can't leave the high-side MOSFET on indefinitely, as the boost cap will become discharged. Using an 0.1uF and a larger cap in parallel will help prolong the time you can leave it high, but you'll wind up with quite a peak current through your boost diode when you turn the low-side MOSFET on again - that's OK as long as it's rated for the current.
     
    Last edited: Nov 16, 2011
  3. raychar

    Thread Starter Member

    Nov 8, 2011
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    Please see the attached file (name 123).

    Thanks
     
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  4. raychar

    Thread Starter Member

    Nov 8, 2011
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    I missed to name the driver on the schematic, it is IR2117.
     
  5. SgtWookie

    Expert

    Jul 17, 2007
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    Datasheet:
    http://www.irf.com/product-info/datasheets/data/ir2117.pdf

    Ahh, I see - it's a high-side driver only.

    Are you certain that the motor always has continuity through it? If not, the cap won't charge - the motor wouldn't turn either.

    Try replacing the boost diode with a 1N4148 or 1N914; these are extremely fast switching diodes even though they have a low current rating.

    You need to have a 0.1uF cap AND a larger cap right next to the anode of the boost diode, and the Vcc terminal.

    I wouldn't use less than 0.1uF for the boost cap.

    If the boost cap voltage still won't go over ~1v or so, then try disconnecting the MOSFET gate from the driver, and connect the gate to the source terminal using a resistor; perhaps the MOSFET is shorted.
     
  6. raychar

    Thread Starter Member

    Nov 8, 2011
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    Hello,

    I haven't 1N4148 on hand and need to buy to test, I think the trouble is this boost diode. This one is faster than what I tried including STTA106 and BYV27, they are only around 20ns.

    I tried to connect a 100 ohm resistor between gate and source after disconnecting the driver, motor still don't run.
    The mosfet should't burn as I checked there is high mega ohm resistance between its pins.

    Can you detail the meaning of ".AND a larger cap right next to the anode of the boost diode, and the Vcc terminal." in your text? I already have 1uf cap on Vcc to ground and the boost cap (0.2~0.0XXuf). Actually, anode of diode connects to Vcc.

    Thanks
     
  7. praondevou

    AAC Fanatic!

    Jul 9, 2011
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    That would mean you turn the N-channel FET OFF.

    What motor is it?

    Where is the motor's ground connected to? Are the IR2117's ground and the motor ground seperate or did you connect them together?

    Have a look at figure 23 of AN-978. In your schematic, if the bootstrap capacitor is supposed to be charged by the left 15V power supply, then there needs to be a return path, through the motor back to the ground of the same power supply.
     
    Last edited: Nov 16, 2011
  8. raychar

    Thread Starter Member

    Nov 8, 2011
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    I am using general small d.c permanent magnet motor, diameter 1". This is for testing the circuit, I'll implement in a machine later.
    There is no connection between the motor ground and IR2117 ground. I suppose they shouldn't. As it is operated on floating voltage and ground.

    Thanks,
     
  9. praondevou

    AAC Fanatic!

    Jul 9, 2011
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    Just for testing purposes connect the two grounds together. I bet it works.
    There is no way you can charge the bootstrap capacitor if there is no return path to the power supply.

    If you had a look at the application note I posted you'll see that in a IR2110 for example the bootstrap cap is charged when the lower mosfet is ON. So the lower driver output power supply is used for upper and lower driver, it's always the same reference.

    Have a look at this image from this application note:

    [​IMG]
    Forget about Q2 and Rg2, you don't have them. So the only way to charge the bootstrap cap is through the load, when the upper MOSFET is OFF. You see it's the same reference.

    If you want the ground floating too you'll need a different power supply or use a different technology like the ones indicated on page 29 of AN978.
     
  10. raychar

    Thread Starter Member

    Nov 8, 2011
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    Yes, by connecting two grounds, the motor run, but slowly. The VB-S is 8V and still not sufficient? I applied to motor actually only 12V, I'll try to increase it by getting another power source, is this a matter for the reason of low VB-S??

    If I adopt the suggest schematic to have the floating ground, using IR2110 and two mosfets, the lower mosfet is just to provide the return charging path of boost cap? Will it'll be a waste to use a power mosfet in it?

    Thanks
     
  11. praondevou

    AAC Fanatic!

    Jul 9, 2011
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    It's Vgs - Gate - source voltage.

    How much the bootstrap cap will be charged depends on how long the upper MOSFET is in the OFF state, on the motor resistance and on bootstrap capacitance.
    Is there a specific reason why it needs to be a High-side driver?

    To put in a MOSFET only to provide the return path for a bootstrap capacitor doesn't make sense IMO.

    What will be the final application and motor voltage/power?
     
  12. raychar

    Thread Starter Member

    Nov 8, 2011
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    Oh, I burnt the mosfet driver again. How vulernable this IR2117 is!? I am sure I haven't make wrong connections nor short-circuit. I made change the motor supply voltage from 12V to 25V, it was done with all power down first.

    Is my sequence of turning on the circuit a matter? Power up input control circuit...Power up driver circuit...Power up the motor/Load. I sometimes reverse the sequence. Can anyone have knowledge of it.

    Thanks
     
  13. praondevou

    AAC Fanatic!

    Jul 9, 2011
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    It's ok this way, make sure the PWM is OFF when you connect the motor power. When exactly did the driver blow? Do you have a freewheeling diode on the motor terminals? Vs minimum is Vb - 25V. That means if you have 15Vb then you can have a negative peak of maximum -10V at Vs.

    What about the questions from my previous post?

    Did you connect the grounds together now? If you made any other changes please post a complete schematic with component values etc.
     
    Last edited: Nov 16, 2011
  14. raychar

    Thread Starter Member

    Nov 8, 2011
    82
    0
    Oh, the gate driver burnt out again, how vulnerable this IR211 is! For sure, I haven't make any wrong connections nor short-circuits. I made change on the motor power supply voltage from 12V to 25V with all power down first.

    Is the sequence of turning on the circuit a matter. First the control circuit power...then gate driver power....then motor power. I sometimes made reverse sequence. Does anyone have knowledge of this?

    Thanks,
     
  15. raychar

    Thread Starter Member

    Nov 8, 2011
    82
    0
    Oh, the gate driver burnt again, How vulnerable this IR2117 is! For sure, I haven't made any wrong connections nor short-circuits. I made change on motor power supply voltage from 12V to 25V with all powers down first.

    Is the sequence of power up a matter? First turning on the power of control circuit, then the power of driver, then the motor power. I sometimes make reverse sequence. Does anyone have knowledge of this.

    Thanks
     
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