A full bridge circuit using IR2110

Discussion in 'General Electronics Chat' started by DumbDummy77, Mar 21, 2010.

  1. DumbDummy77

    Thread Starter Member

    Jan 21, 2010
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    Hi

    Since I have built a full bridge circuit which is exactly same to the attached diagram. I have managed to get high and low output of square waveforms and I am pretty happy with this. Instead of applying 200V on the mosfet, I used 30V as part of test however I limited the current up to 500mA in order to protect the circuit. When powering my first PSU for two IR2110 driver circuit which was ok. Then I powered the second PSU for the MOSFET section, the current shot up to 500mA @ 1V and found out that Q4 of MOSFET was quite pretty warm while the rest of MOSFET were normal. I double-checked the circuit that I built and yet I could not pin-point the source of problem. I changed MOSFET for Q4 in case the first one was faulty. To my surprise, I still got the same result.

    Now I thought that my circuit could be wrong and I am not sure at the moment. Hoping to hear from you to help me to resolve this matter asap and looking forward to see a bipolar square waveform on the left side of full bridge circuit.

    Regards

    dd77
     
  2. rjenkins

    AAC Fanatic!

    Nov 6, 2005
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    I don't see anything obvious on the schematic which woudl cause problems.

    Double check all connections and make sure there are no mis-wires or shorts anywhere?

    Remember the High side drive will only work while the device has the proper high frequency Hi & Lo drive signals operating, to charge the cap on 'VB' through the diode.

    (For actual H-Bridge operation, the Hi & Lo drive should swap side to side, they are shown the same to both sides.)
     
  3. SgtWookie

    Expert

    Jul 17, 2007
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    Don't try to keep the high side MOSFET on for more than a few milliseconds. The high-side capacitor will drain, and the MOSFET will start heating.

    In your other thread, you were talking about low-side current sensing, but since you're using a high-side driver for four N-ch MOSFETs, you will have to PWM your high-side MOSFETs, and you will have problems trying to sense current on the low side, as the current being recirculated through the diode of the high-side MOSFET will not be accounted for.

    You will need to sense current on the high side. The easiest way to do that will be to use a Hall-effect sensor.
     
  4. DumbDummy77

    Thread Starter Member

    Jan 21, 2010
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    In regard to current sensing, it is not related to this project as I am doing two different projects. For current sensing circuit, I hold it for now and concentrate on full bridge circuit. However thank you for your inputs.

    I have discovered the waveforms on the resistor appear to be different! Yellow waveform highlights the right side of driver IC while the left waveform comes from right side of driver circuit. So I put a spare IR2110 on the right driver circuit and I still get the same result.

    It must be a faulty somewhere on the rifht side of driver circuit.....

    The current is 500mA at 1.3V - powring the full bridge circuit

    DD77
     
  5. SgtWookie

    Expert

    Jul 17, 2007
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    OK, so start by reading your Vgs levels.

    Vgs = voltage on the gate terminal when referenced to the source terminal; or the difference between the two.

    Your bridge supply will need to be isolated from the ground your 'scope is using, or you will have problems (like fried O-scope probes.)

    If Vgs=<1v, then the MOSFET should be off.
    You have not documented the MOSFETs that you are using. However, a standard N-ch MOSFET will be ON when Vgs=10v. A logic-level N-ch MOSFET will be ON when Vgs=5v.
     
  6. SgtWookie

    Expert

    Jul 17, 2007
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    You do not show a resistor anywhere in the circuit you posted.

    Therefore, the waveform does not make sense. We have no idea where you are taking the two readings from.
     
  7. DumbDummy77

    Thread Starter Member

    Jan 21, 2010
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    I am referring to RL which is in the middle of full bridge circuit which can be seen in my red diagram in the 1st post

    I am going to check the Vgs now

    DD77
     
  8. SgtWookie

    Expert

    Jul 17, 2007
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    I sit corrected. I don't know how I missed RsubL, it was there all the time. :confused:

    However, this sentence does not make sense:

    I think you meant to say:
    But even that does not make sense.

    Did you mean that the red trace was from the left side?
     
  9. DumbDummy77

    Thread Starter Member

    Jan 21, 2010
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    Hi again

    The Vgs on both high side and low side MOSFETs are approximately 10V and OV for on and off respectively.

    Here is another photo of my waveform :

    I have noticed that both waveform are slightly distorted and voltage drop to 25V roughly depsite powering at 30V.

    I admit I was expecting to see a bipolar square waveform instead of non-bipolar waveform.
     
  10. DumbDummy77

    Thread Starter Member

    Jan 21, 2010
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    Yes, red trace was from the left side and yellow trace was from the right side.

    In my last post, I was a bit puzzled with one thing, there was no current consumption when 30V applied.

    Another problem was the spike on both waveform and I believed it was down to the boot-strap capacitor and diode. I think the capacitor and diode need to be changed.

    DD77
     
  11. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    Like rjenkins said in post #2 you are driving both high side mosfets on at the same time. The load resistor is keeping it from being a short and blowing something.
     
  12. DumbDummy77

    Thread Starter Member

    Jan 21, 2010
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    Are you saying H bridge connection should be identical to Full bridge configuration?

    DD77
     
  13. rjenkins

    AAC Fanatic!

    Nov 6, 2005
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    With that drive setup, both ends of the load are driven high or both driven low.
    The load will not draw any current.

    To actually drive the load, you need to turn on the diagonally opposite devices.

    An 'H Bridge' is a full bridge - the 'H' represents the literal schematic with two vertical pairs of switching devices and the load across the two center points.
     
  14. DumbDummy77

    Thread Starter Member

    Jan 21, 2010
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    Indeed, it is what I have witnessed on my experiement as there was no current being drawn.

    Can you please kindly tell me a bit more about turning on the diagonally opposite devices? Maybe a visual diagram would be handy

    DD77
     
  15. SgtWookie

    Expert

    Jul 17, 2007
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    Refer to your schematic.

    You have:
    Q1 on the upper left of the bridge
    Q2 on the lower left of the bridge
    Q3 on the upper right of the bridge
    Q4 on the lower right of the bridge

    Start with Q1 through Q4 off.
    Turn on Q4 to supply a ground to the right side of RL.
    Turn on Q1 to supply +V to the left side of RL.
    You now have current flow through RL, and a voltage drop across it that is roughly equal to the supply voltage.

    Turn off Q1 and Q4
    Turn on Q2 and Q3
    You now have current flow in the opposite direction through RL, and the voltage drop will be in reverse polarity from the last experiment.
    Note that Q1 or Q3 cannot remain ON indefinitely, as your 0.47uF caps will rapidly become discharged. This will cause high power dissipation in the upper MOSFETs.
    I suggest that those 0.47uF caps should be 0.1uF metal poly with a 10uF cap in parallel. You will likely find that your high-side MOSFETs run cooler.

    If Q1 and Q2 are both ON, or Q3 and Q4 are both ON, you have the dreaded "shoot-through" condition, which shorts the power rails via the MOSFETs. Unpleasant things will happen.
     
  16. yeoh

    New Member

    May 17, 2010
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    how u do the invert pwm circuit ?
     
  17. yeoh

    New Member

    May 17, 2010
    3
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    How u do the invert PWM circuit ?
     
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