IR2110 definition

Discussion in 'General Electronics Chat' started by sean900911, Feb 13, 2013.

  1. sean900911

    Thread Starter Member

    Jan 28, 2013
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    Hi,
    Im doing my final project on H-bridge Mosfet and my supervisor ask me to used IR2110 to isolate the high and low side of the MOSFET. I had read a lot of the pdf and im still confuse of the application . Actually, what is the function of IR2110 .Why IR2110 is needed for H-bridge Mosfet ? Why the bootstrap circuit is only for high-side MOSFET? Please help and i really really appreciate your help..

    Thank you very much...
     
  2. praondevou

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    Jul 9, 2011
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    The function of a gate driver is to provide the high peak current necessary to charge and discharge the gate rapidly. Fast charging of the gate means decreasing switching losses, i.e. turn the MOSFET/IGBT on or off as fast as possible/feasible. (there are other considerations for the correct switching frequency)

    Let's have a look at a MOSFET halfbridge with a bus voltage of let's say 100V.

    Your driving signal can for example have a maximum level of 15V. The power supply of the 2110 is also 15V.

    The lower NFETs source terminal is connected to ground (the 0 of the 100V supply). Switching the gate of this FET requires only a voltage of 15V with respect to this 0V level.

    Now the upper (n-channel) Mosfet:
    If you want to make it conduct you need to apply a positive Gate-source voltage, right? The lower FET is now not conducting. The source of the upper FET cannot be connected to the 0V reference but it also needs a positive gate-source voltage to conduct. You need a independent power supply for the upper gate drive circuitry. That's the bootstrap part. It charges the upper bootstrap capacitor through a diode from the 2110s 15V power supply when the lower FET conducts.

    Read this App-note: http://www.irf.com/technical-info/appnotes/an-978.pdf
     
  3. sean900911

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    Jan 28, 2013
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    Hi , really Thank you so much for your reply . Erm , If u say IR2110 is used to perform as a fast switching gate drive, then why they say for isolation gate drive? I don't understand on this. Because if the bus voltage is about 300v and the high side of MOSFET will receive so much voltage as well . So, can IR2110 share the voltage from the high side to low side MOSFET so that high side of the MOSFET no need to support so much voltage? Let' s say for full bridge MOSFET, because my HIN and LIN is provide a signal by using micro controller (PWM) for the high and low side. Then, i had give a PWM signal to high and low side of the gate means that the duty cycle of PWM is the same for both as well . So, how the capacitor in high side is charge when both are turn on and off at the same time?

    Thank you so much for your helping. I really appreciate with your help..
    Please point my mistake if i was wrong. Thank you.
     
  4. praondevou

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    "both are turn on and off at the same time" = BOOM!

    If you turn on upper and lower MOSFET of the same leg you are shorting the main bus voltage.

    In a fulbridge the load is between the two legs where both FETs of one leg are connected.

    NEVER both FETs of one leg are ON at the same time. The bootstrap capacitor is charged when the lower FET is ON and the upper FET is OFF.
     
  5. shortbus

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    Sep 30, 2009
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    1. "If u say IR2110 is used to perform as a fast switching gate drive, then why they say for isolation gate drive?"
    The isolation of the high voltage is built into the inside of the chip.

    2. "So, can IR2110 share the voltage from the high side to low side MOSFET"
    The low side mosfet does not have it's high voltage on the IR2110, it only needs to supply the gate voltage to that mosfet.

    3. The H-bridge uses two IR2110, and four mosfets. The high side of one IR2110 is on when the low side of the other IR2110 is on. Both low and high of one IR2110 should NEVER be on at the same time! Doing so will cause a short circuit, and blow out the chip and probably the mosfets.
     
  6. sean900911

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    Jan 28, 2013
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    Hi, Thanks for your reply . So , actually, IR2110 is a driver that to provide the current and also drives the gates with an appropriate voltage level in order the MOSFET ?
     
  7. sean900911

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    Jan 28, 2013
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    Hi , Thanks for your reply. the bootstrap circuitry is only used to provide additional voltage in order to drive the mosfet?
     
  8. praondevou

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    Jul 9, 2011
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    Yes, it provides the necessary gate current and provides two independent gate signals. The voltage between these two gate signals can be as high as specified in the datasheet, i.e. 500V.
     
  9. sean900911

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    Jan 28, 2013
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    Thank you for your replay , What do you mean by two independent gate signals ? is that PWM high and low input signal ? About the bootstrap capacitor, i am using PWM to drive the gate MOSFET in 4 quadrant full bridge and the load that i am using is motor. This mean that I will drive 2 MOSFET at the same time which 1 is in the high side and another is in the low side . So, the PWM signal which I give to the high side of MOSFET cannot be same to the low side of MOSFET because it will BOOOM(like what u mention)and short circuit as well . Is that correct? Thank you so much for your reply.
     
  10. praondevou

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  11. sean900911

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    Jan 28, 2013
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    Hi , What do u mean about dead time?
     
  12. praondevou

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    Talking about the two MOSFETs of one leg of the H-bridge:

    Deadtime is the time between turning off one MOSFET and turning on the other one.

    When you discharge a gate, aka turn off the MOSFET, it is not immediately turned off. The deadtime garantees that there are never two FETs on at the same time.
     
  13. sean900911

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    Jan 28, 2013
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    Thank you for your reply . I want to ask about If i did not put a driver to the high side of MOSFET , what will gonna happend? it will burn my MOSFET? why?
     
  14. praondevou

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    Post a schematic please.

    What do you mean by not putting a driver? Leaving the gate terminal floating?
     
  15. sean900911

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    Jan 28, 2013
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    Can you give me ur email? i cannot post the schematic here , I mean if my mosfet gate is straight away connect to the microcontroller (PWM) without the driver , what is gonna be happen?
     
  16. praondevou

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    I think you have to first understand how a H-bridge works. Then you have to understand how it works with a bus voltage of 50V and a gate driver. Then you will see that you can not drive a H-bridge with 50V bus voltage directy with a microcontroller.

    You have to understand why the gate driver is necessary (not necessarily the IR2110) ... current drive capability and incresing the voltage level for the upper MOSFET with respect to ground.
     
  17. sean900911

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    Jan 28, 2013
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    Hi , actually i already the h-bridge function and the mosfet driver is needed because micro controller only provide small current and it take a while charge up the mosfet. During the time the gate is charging up, the mosfet is partially on and operating in its linear region. This will waste power and and could damage the mosfet if the mosfet Vsupply having a large voltage. That why we need a mosfet driver which can source a lot of current to charge the mosfet gate quickly as possible. Besides, it also perform isolation from the high side and low side of mosfet along with the microcontroller so that it would not damage the mosfet and the microcontroller . Am i right ?
     
  18. praondevou

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    Yes. Did you also understand why and how the upper MOSFET gate drive including bootstrap capacitor works?
     
  19. sean900911

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    Jan 28, 2013
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    Yes , the bootstrap capacitor is charge when the lower MOSFET is turn on and it is charge from the Vcc driver (12-15 V) . Then, it provide extra voltage to the gate of High side MOSFET in order to turn on the mosfet as fast as possible due to the lower current provided form microcontroller . This is because MOSFET VGS have a internal capacitor but the charging period is too slow and it might ruin the High side of MOSFET if the Vpower is too high due to the slow charging time. This is my understanding on High low side of MOSFET and Bootstrap circuitry . Thank you for so patient with me this few days and please point my mistake if i was wrong... Cheers ... Thank you
     
  20. praondevou

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    Actually any MOSFET will have a switching losses, every time you turn it fully on or off, so the low-side MOSFET as well.

    Apart from the higher current it can deliver the gate driver is really just there to make the upper gate drive signal independent from the zero reference. That's how you can use a much higher voltage on your H-bridge than would otherwise be possible.
     
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