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H-Bridge: Black Box or Are Details Important?

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William K.
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Platinum
Re: Hbridge
William K.   1/22/2014 10:07:04 AM
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Adding regeneration to any motor driving controller leads to another challenge, because aside from the additional controlling requirements there is now a need to put all of that energy someplace, which is no small matter. Most power supplies are single-quadrent devices, and so they can't handle it, a load resistor needs to be able to dissipate all of that power without failing, and a battery power source can only accept charge at some maximum rate. So the addition of regeneration adds a lot to the design effort.

And if you sometimes want to see just how much energy is stored in a rotating motor, just run one up to speed and then quickly disconnect the power source and short circuit the motor leads. But make sure that the motor can't roll off the bench before you do this, because most motors will attempt to roll over. It has always been an interesting demonstration for first year electrical technology students.

jhoagland
User Rank
Iron
Re: Hbridge
jhoagland   1/21/2014 11:29:13 PM
For background information, here's a video that shows different H-bridge configurations and also discusses regeneration:

 

http://youtu.be/UsA21W4v88I

William K.
User Rank
Platinum
Re: Hbridge
William K.   12/31/2013 4:49:48 PM
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tain yes, using graphics for the display of dircuits is certainly a lot more convenient, and able to provide a lot more details as well. The only reason that we used the text method was that then anybody with any operating system, and any file viewing program could read the circuit diagram. This was back in the day when ms was not the dominant OS provider, back before gates killled Dr.Dos  and the other OS companies. At one time we did have a choice with computer OSs.

taimoortariq
User Rank
Gold
Re: Hbridge
taimoortariq   12/31/2013 12:20:25 AM
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I rememner we used to make circuits from text in p spice software, but after that course we never ever used text. The graphical method is so much more convinient.

William K.
User Rank
Platinum
Re: Another flavor of H-Bridges
William K.   12/30/2013 8:09:44 PM
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a.saji, in a system that uses bipolar transistors as part of the higher current circuitry the saturation voltage drop often causes a larger amount of power dissipation than can be provided without additional heat sinking. While bipolar transistors can sometimes provide an advantage in these applications, a low effective "on" resistance is not one of those advantages. Thus a heat sink is sometimes required. 

I hope this answers the question that I think you were asking.

William K.
User Rank
Platinum
Re: Another flavor of H-Bridges
William K.   12/30/2013 7:58:34 PM
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Battar, you are certainly correct about switching speeds and generating EMI. That is always the challenge, since faster switching reduces power dissipation during the transition while it increases the high frequency components. The expensive solution is to use filtering and shielding, both of them add to cost without improving performance. So most designs are some form of compromise, which goes along exactly as you stated.

taimoortariq
User Rank
Gold
Re: Hbridge
taimoortariq   12/30/2013 11:56:03 AM
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I agree, but IC is not always the solution sometimes for your custom application you require a custom H Bridge, for that its important to know the in depth knowledge of H bridge, what parameters to select in it etc.

a.saji
User Rank
Silver
Re: Another flavor of H-Bridges
a.saji   12/30/2013 5:09:01 AM
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@William: Why do you need to fasten the system in that manner via motors ?   

Battar
User Rank
Platinum
Re: Another flavor of H-Bridges
Battar   12/29/2013 2:08:33 AM
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William,

            The downside is that if you switch motor currents too fast you are goinf to have EMC/EMI issues.

William K.
User Rank
Platinum
Those details can be quite vital
William K.   12/27/2013 11:06:36 PM
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For both the H-Bridge devices and op-amps, the intense pain can come from ignoring some details. Little things like maximum slew rate or input current versus any of a number of variables. And on H-Bridges, switching speed and drive requirements versus switching speed are the sort of thing that one might sometimes be lucky and get away with ignoring. But sometimes not. And unfortunately the higher the required performance the more that the details must be dealt with. That is the inconvenient reality. In some low performance applications one can sometimes get away without considering those details.

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