IR2110 H-Bridge with uC, Shoot through?

Discussion in 'General Electronics Chat' started by Frakk, Nov 27, 2009.

  1. Frakk

    Thread Starter Active Member

    Jul 6, 2009
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    Hello,

    I am trying to build a H-Bridge with 2 IR2110's controlled by a microcontroller.

    Does the driver IC have shoot-through protection? I can't see anything mentioned about it in the datasheet, although I remember reading somewhere that it does. I plan on using logic gates to prevent it.

    What other precautions do I have to make to get everything to work reliably?

    Any advice or experiences would be greatly appreciated!
     
  2. SgtWookie

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    Jul 17, 2007
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    No.
    That's because it doesn't have it.
    I do that frequently when I've been reading lots of datasheets. It's easy to get features of one confused with features of another.

    Why? You're driving it from a microcontroller, right? You could compute the delay necessary, and build that into the program.

    This could be a long list of items.

    Well, you don't mention what you're using for MOSFETs, or the voltage/current being switched, type of load... a long list.

    It would help a great deal if you posted your schematic as it currently exists, and explain your project more completely.
     
  3. Frakk

    Thread Starter Active Member

    Jul 6, 2009
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    It will be a DC motor controller, 12V-24V up to 50-100A, maybe more depending on the MOSFET's and the motor. Currently I have IRFZ44N FET's but I would like to be able to swap to more powerfull ones, maybe use 2-4 in parallel if it doesn't add too much gate capacitance.

    Currently I only have a half-bridge on a breadboard to test the IC. 10uF cap and 1N5819 diode for the bootstrap, 0.1uF and 47uF for the supplies, 10ohm gate resistors.

    Thanks!
     
  4. SgtWookie

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    OK.

    Keep in mind that IRFZ44's have been around for a number of years now; they're nearly obsolete.

    You might want to have a look at a IXTH240N055T/IXTQ240N055T.
    Would you believe, Vdss=55,Rdson=3.6mOhms,Id=240A? :eek:
    http://parts.digikey.com/1/parts/1418716-mosfet-n-ch-55v-240a-247-ixth240n055t.html

    You would need to scab on rather large conductors to a board to carry that much current and carry away heat. I'm thinking heavy-gauge copper sheet folded into "L" or "U" shapes.

    If you're going to use PWM, and want the motor reversible, no sense in using PWM on both the high and low sides; just one or the other. That will eliminate the problem of shoot-through.

    Keep in mind that you should avoid sudden reversal of the motor. You can use the H-bridge to brake the motor rapidly by turning on both lower sides or both upper sides of the bridge at once until the motor is stopped.

    [eta]
    "scab on" might be taken out of context here. It's really a term used in the construction industry.
    In that context, it means to attach a piece of construction material (like another piece of wood or metal) to reinforce the original piece so that it can support more weight or stress.

    In the context I used, I meant to convey the idea of sweat-soldering a much thicker piece of conductive material (specifically, copper sheet) to a PCB trace, so that it would not only be able to conduct much higher current, but to carry away heat.
     
    Last edited: Nov 27, 2009
  5. Frakk

    Thread Starter Active Member

    Jul 6, 2009
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    Thank you for the recommendations!

    Very nice MOSFET! I didn't know the Z44 was obsolete, I can buy it from ret.hu no problems, I think I saw them on ebay as well. For 50c a piece I think they are a bargain.

    Do you mean turning the Low transistors completely on, PWM one of the upper FETs? I have seen that in App Notes but those were drivers with shoot through protect.
     
  6. SgtWookie

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    Sure, they're cheap. They're getting mighty "long in the tooth" though.

    With the amount of current you're switching, it would be a good idea to keep your switched circuit portions short and thick, for low resistance and inductance. If you're using a number of MOSFETs in parallel, that will be pretty hard to do.

    I mean turning just ONE of the low-side MOSFETs on continuously, and switching the high-side MOSFET on and off for PWM. You might have problems trying to keep a high-side MOSFET on continuously.

    The problems you'd have with shoot-through would only occur when you change the direction of the motor from forward to reverse or vice-versa. But if you turn the MOSFETs OFF and wait for a period of time sufficient to discharge the gate charge completely (not long; 1mS would likely be enough) then you could run the motor in the opposite direction.

    Be mindful about sudden motor reversal. This will place very heavy current demands on the bridge, much worse than if the rotor of the motor were locked (stalled).
     
  7. Frakk

    Thread Starter Active Member

    Jul 6, 2009
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    Thank you for your advices.

    This project is still in the planning and design stages as you probably figured. It will be a PID controller, more like a servo that moves from one position to an other. The uC will take care of all this control with a pot (or a rotary encoder later) as position feedback. It will interface to other devices by either I2C or SPI to get the position data stream and other communications I don't even know about yet.

    I know it is a lot of work and planning and it will take me quiet a while to complete, but slowly I'm getting more and more done.

    Thanks again!

    I just noticed that there is always a 1.4-1.7V on the Vs pin (also the source of the upper FET) when the upper side is OFF. When I turn it ON, this voltage rises to ~12V (supply) as it should. Is it normal that this voltage is there? What is it anyways?

    With a 10uF bootstrap cap I get about 0.5s ON time on the upper side. Is there a drawback using a large capacitor like this 10uF?
     
    Last edited: Nov 28, 2009
  8. SgtWookie

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    Can't tell ya. I have the datasheet for the driver IC, but that's it! Never used one.

    Well, generally the larger the cap you use, the higher the leakage rate.

    The logic inside the gate controller uses some current. That would tend to discharge the cap. You'll need to switch the high-side MOSFET off and back on to re-charge the driver cap. That's why I suggested previously that you'll have a hard time trying to keep those upper MOSFETs on continuously.

    You don't want to let those upper MOSFET gates to discharge slowly, or the high-side MOSFETs will dissipate a lot of power - as heat. Better to use a high duty cycle PWM on them, at a frequency high enough to keep the caps pretty well charged up.
     
  9. Frakk

    Thread Starter Active Member

    Jul 6, 2009
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    I know electrolytic caps have more leakage than ceramic, but it can't be that bad. If I use 25KHz for PWM or more, I think a 10uF cap will not get a chance to discharge, even a 1uF will be good. This is why I asked if I have to compromise anything to go with a 10uF? Is 30KHz too high for switching losses?

    I will PWM Ahi/turn ON Blo for forward, PWM Bhi/turn ON Alo for reverse. Between transitions from FWD-REV or vice-versa I will turn both Alo and Blo on until the Feedback Pot's position chinging (until the motor stops).

    I see a lot of designs use an anti-parallel resistor/diode on the gates. If I get the turn-on/off delay right within the uC, can I take these out for faster switching? Or is it better to use the resistor for a bit of turn-on delay?

    Thanks a lot!
     
  10. SgtWookie

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    You'll need to work through the math, and decide what's acceptable.
    Those MOSFETs have a rather large gate charge.
    Very generally, gate charge is a function of Rds(on), Vdss rating, and Id. The higher your PWM frequency, the more power you will use in charging/discharging the gates.

    That works for me. Or, you could just watch the pots until their rate of change gets low. If you want to get fancy, you could allow for a variable braking effect by PWMing just one of the low side MOSFETs during braking.

    You'll have to post an example of what you're looking at.

    Generally, you need some resistance in the gate charge/discharge path. Otherwise, the L of the path and the C of the gate will cause high frequency oscillations in the gate, which will cause problems. The R in series (as close to the MOSFET gate as possible) snubs this ringing.
     
  11. Frakk

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    Jul 6, 2009
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  12. SgtWookie

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    I see. A rapid discharge path.

    That brings up another point; what diodes are you using to charge your 10uF cap with?

    1N4148 diodes are fast, but have a limited current capacity (100mA), and a much higher Vf at their capacity (>1v) than a diode with a higher current rating.
     
  13. Frakk

    Thread Starter Active Member

    Jul 6, 2009
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    Right now I have a 1N5819 schottky diode in the circuit, 40V 1A, but I have 3A 1N5822 on hand as well. What are my best options?

    I would also considered using optocouplers for added safety. Is it worth the trouble?
     
  14. SgtWookie

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    The 1N5819 Schottky diodes will be fine.
     
  15. loop51

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    Jan 31, 2011
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    Hi, Im writing in this thread bcoz im basically trying to do the same thing with the same IR2110.... evn though itz an old thread...

    1) Like Frakk, Im also trying to make an H-Bridge to control a motor kinda like a servo... however I need to stop the motor without any drift velocity... my idea was that I would use HEXSENSE type of MOSFET to sense the current-- r8 after stop command I would reverse the H-Bridge nd when Eb(back emf is zero, so the motor has completely stopped) that means the Ia(armature current is very high) I would turn off the H-Bridge... is it practically feasible/possible.... what is the consequence of doing this.... my idea is the inductor of armature will contain some current-- what will happen if I reverse the H-Bridge?

    2) I need to keep the high side mosfet on for some indefinite time.... how do I do this.... like the thread suggests that I can use pwm to switch between AHi and ALo while I keep BLo on to keep the motor running in one direction.... and vice versa for the opposite direction
    but, I have another idea... I read AN978...[​IMG] nd it shows a circuit for continuous gate drive with IR2125(I dont hv it, so I want to try doing it with IR2110).... it also uses a 555 timer for charge pumping.... but after looking at the circuit carefully I see that the 555 timer isnt using the basic astable or the monostable circuit... and in fact the control voltage(pin5) and discharge(pin7) are not used... so basically I did not understand it's concept... how can I incorporate this concept with the IR2110...

    3) I see that sgtWookie suggests adding some gate resistance... what should be the gate resistance value.... I know that if I increase it too much I would be increasing the gate charging time which will increase the power dissipation of the MOSFET.... (lot of trouble)
    I am planning on using something around 10ohms.... do I have to care about the watt capacity of the resistance? like at turn on/off charging time a 10ohm with a 12V supply will dissipate 14.4watts.... so a standard quarter watt resistance should would fry in this conditions... but then again itz a switching thing... so my guess is if the switching frequency is 10Khz then the power dissipation would be alot less than 14.4W.... but how do I calculate this power dissipation... when I can calculate this... I can calculate exactly the watt requirement of the resistance...

    though I want to add here that my hunch is P= Fsw x Qg x Vcc -- now if I add a resistor in the gate-- does this P = the watt dissipated by the resistor?

    4) what kind of capacitor should I use for bootstrap operation....

    5) I understand that Vdd is the logic supply(?)... but in AN978 the Vcc is connected with Vdd....
    would it work if I supply the Vdd with 5v(the supply of my uc) and supply Vcc with 12V?
     
  16. SgtWookie

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    If you attempt to suddenly change the direction, you will wind up with very high current the moment you change the direction; as the motors' back-EMF will then be added to the voltage applied by the bridge; nearly doubled. Normally, the back-EMF plus the load is why the motor reaches a steady state RPM. This will be pretty hard on the motor and stress the H-bridge components as well. You might get away with it if you are running the motor at perhaps 2/3 it's rated voltage.

    The timer is configured with the OUT pin (3) charging/discharging the timing cap (1nF) via the 100k resistor. This winds up having a nearly 50% duty cycle with fewer components than a standard R1/R2/C1 astable circuit would have.

    If you do not have any resistance between the MOSFET gate and the IR2110 driver IC, you will most likely wind up with "ringing" on the gate, due to the L of the MOSFET pins and the length of the trace to the driver IC, and the C of the gate - you wind up with a series LC circuit that will ring like a struck bell. The resistor is necessary to stop the ringing quickly.

    Post your circuit. I don't know what MOSFETs you are using.

    though I want to add here that my hunch is P= Fsw x Qg x Vcc -- now if I add a resistor in the gate-- does this P = the watt dissipated by the resistor?[/QUOTE]
    That's about right.

    Use a 100nF poly metal film or ceramic cap, and use a larger aluminum electrolytic in parallel with it.

    That should work.
     
  17. loop51

    New Member

    Jan 31, 2011
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    Im probably going to use the same circuit for several motors.... some PMDC motor and some series dc motors.... the PMDC motors r rated 12/24Vdc-- Im planning on using 12V dc... so I guess it wont be much problem for them.... nd for the series dc motor itz rated at 48Vdc so I guess I hv to run this motor at 36Vdc....
    maybe if I place a 50ms delay between the reverse operation.... do u think I might be able to avoid this harsh breaking(for the motor).... is there some calculation I could use?
    what if I use another H-bridge in parallel with some series resistance.... to limit the current and reverse the polarity of dc supply of the motor for breaking.... (might make the circuit bulky... but just might work?)

    btw Im using IRF540.... so at 12V the Qc is around 55nC now if I use switching frequency of Fsw= 100KHz then Pdrv = Qc x Vcc x Fsw = (55nC) x 12 x (100K) = 0.066W... which is not even 1/4 watts? and if the resistance is 10ohm then transition time t = Qc/Ig would result in t= (55nC) / (1.2A) = 40ns... I got Ig = 1.2A from 12V/10ohm = 1.2A ..... ARE My CALCULATIONS CORRECT?

    now.... r8 after I posted... I found out that HEXSENSE IRC540 type of power mosfet r divested... so I dont think I can find them on my local market...

    can u suggest some alternative method? with an H-Bridge if I connect a series resistance(in milli ohm range) the polarity will change..... nd if I rectify it with some diodes before giving that as an input to my adc"--- the problem here is that diodes r temperature dependent..... I wont get an accurate result from this sort of topology...


    now... for the continuous high side gate drive? do u think the 555 timer topology is going to work.... bcoz if I use the pwm method to swap between AHi nd ALo..... dont u think 40ns would actually turn off the high side mosfet for some time... which would result in a pwm supply for the motor.....(I dont want variable speed here...)
     
  18. SgtWookie

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    Jul 17, 2007
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    The 2/3 rated voltage is simply a guess. Your mileage may vary considerably, depending upon how often you perform these sudden reversals.

    If you switch either both the high side or both the low side MOSFETs on at once, then that will act as a motor brake. It certainly won't stop it as quickly as reversing the voltage applied across the motor, but it won't be hard on it, either.

    You're starting to get unnecessarily complex here.

    I don't even know what your overall circuit is. Why don't you post your schematic, and include what your motor voltage and VA or wattage rating or current rating is, what you're using for Vcc and +V for your motor, etc.

    You should put your location in your profile, as we don't know where we might suggest that you can obtain parts.

    Click the "User CP" link near the top of this page, on the next page click "Edit Your Details", and on the next page, scroll down to "Location" and put your country and state or province in the box provided - then click the [Save Changes] button near the bottom.

    Well, not this evening. It's getting a bit late here, and I just finished a large dinner and am rather sleepy.

    Ahhh... where did you come up with 40nS?

    You're going to have to have some dead time between turning one side (high or low) off and the opposite side on. MOSFETs turn ON faster than they turn OFF. One way to do that is to use the resistor snubber as I was talking about; say around 22 Ohms or so, and then also have a fast diode like a 1N914/1N4148 with it's anode towards the gate to provide a fast gate discharge path. This "buys extra time" for the one to turn off, while the other is turning on.
     
    Last edited: Nov 20, 2011
  19. loop51

    New Member

    Jan 31, 2011
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    Im attaching my cicuit diagram(itz the basic concept I hv so far)

    1) Do I need diodes across drain source of the MOSFET in reverse bias? If so what kind of diode should I use(some model number would be helpful)

    2)
    I used this to get it
    the thing is Im not quite sure about this calculation....

    3) Im also not sure of the 555 timer thing to keep a continuous high side gate charge.... instincts tell me it might cause trouble.... Im not that savy with 555 timer nd specially this configuration of 555 timer....

    do u think it is going to work smoothly....

    4) then therez the problem and confusion is with the series dc motor.... what do u think? check the image series motor connection....
     
  20. SgtWookie

    Expert

    Jul 17, 2007
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    What is the voltage and current or VA or wattage rating of the motor?
     
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