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[DPRG] Driving an H-Bridge with a switching power supply

Subject: [DPRG] Driving an H-Bridge with a switching power supply
From: David P. Anderson dpa at io.isem.smu.edu
Date: Tue Dec 23 09:35:02 CST 2003

Bob,

try

http://www.maxim-ic.com/quick_view2.cfm?qv_pk=1276

dpa

> 
> David,
> 
> The URL takes me to chipdocs. Apparently, it is
> a subscription only service.
> Do you have another URL for the Datasheet?
> 
> Thx!
> Bob
> 
> > Howdy
> >
> > On Using a Switching Power Supply to Drive an H_Bridge.
> >
> > One of the problems I've struggled with on the two-wheel
> > balancing robot is the change in behavior as the battery
> > drains.  I'm running the robot on 18 Nmh AA cells, at 1600
> > mAh.  Fully charged that's about 25 volts, and fully discharged
> > (at 1 volt per cell) is 18 volts.
> >
> > The robot balancing behavior is optimal at about 23 volts.
> > Higher than that, it is quite "jerky", and below about 22 volts
> > it is quite "loopy."   I can adjust it so that it is optimal
> > in any of these ranges, but then it works poorly in the others.
> >
> > On my other non-balancing robots, this problem is solved with
> > shaft encoders and a PID speed controller.  The speed controller
> > increases the pulse widths to compensate for the sagging battery
> > voltage, and the behaviors remain constant across the range of
> > the battery.
> >
> > For the balancing robot, this has proved more problematic.
> > I originally thought that I could deal with this by monitoring
> > the battery voltage, which I do, and adjusting the gain or gains
> > as the voltage drooped, but in practice this has proven very
> > difficult to do.
> >
> > About a month ago at one of the RBNOs at the warehouse, I was
> > demonstrating this behavior and the Most Excellent Brian Merritt
> > suggested that this problem might better be solved in hardware,
> > and thereafter gave me a pointer to a Dallas Semiconductor
> > Maxim MXL1074CT  --- here's a handy reference:
> >
> > http://www.chipdocs.com/pndecoder/datasheets/MAXIM/MXL1074CT.html
> >
> > So I ordered a couple of samples and after some consultation with Brian
> > and Ron Grant, made a trip to Tanners for the appropriate inductor
> > and a handful of capacitors, and built a little 23 volt, 5 amp
> > switching power supply.  I added three more AA cells to nBot's
> > battery pack and mounted the switcher between the power switch
> > and the H-Bridge.
> >
> > I've been running it for a couple of weeks now, and it works just
> > dandy!  The output remains at a steady 23 volts as the pack drains
> > from about 29 volts to about 25v.  I hung a 3amp load on the supply
> > and watched the output on the scope, it appears to regulate down to
> > within about 2.5 volts of the requested output voltage (which I can
> > adjust with a 10-turn pot).  There is a little bit of ringing on
> > the output waveform, but basically it's pretty clean.
> >
> > I'm now in the process of re-calibrating the robot, which is about
> > 1/2 done, but so far the performance is markedly improved.   Further,
> > during a two hour session of testing and calibrating, the behavior
> > remains consistent throughout.  As a result, it is easier to tune
> > the system, and the robot already seems more stable.
> >
> > This has made me wonder if this sort of thing might be a useful
> > addition to a non-balancing robot, as well.  And if so, if the
> > little switcher should just be part of the H-Bridge board to
> > begin with?  (It's only something like 5 components)
> >
> > Anybody have any similar experience?  How about with industrial
> > controllers?
> >
> > merry christmas,
> > dpa
> >
> >
> > _______________________________________________
> > DPRGlist mailing list
> > DPRGlist at dprg.org
> > http://nimon.ncc.com/mailman/listinfo/dprglist
> >
> 


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