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Fwd: DC-DC power supply recommendations?

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  • Jay Prince
    Dropped the list from the CC. ... From: Jay Prince Date: Fri, 4 Mar 2005 14:32:26 -0800 Subject: Re: DC-DC power supply recommendations?
    Message 1 of 3 , Mar 4, 2005
      Dropped the list from the CC.

      ---------- Forwarded message ----------
      From: Jay Prince <jayprince@...>
      Date: Fri, 4 Mar 2005 14:32:26 -0800
      Subject: Re: DC-DC power supply recommendations?
      To: Jeff Sampson <jsampson@...>


      Thanks to both of you for your recommendations. At the national site
      I found lots of potential solutions-- but also that they make some
      reasonably priced example boards, so I may not have to roll my own.

      At this point the general plan is:
      -- Main batteries run at 7.4V
      -- Motors are 12V motors, run at 7.4V
      -- Motor Controller runs as 7.4V (need to verify this--planning to use
      Traxxas XL1s, but if anyone has a recommendation for a $40 high-amp
      motor controller, I'm all ears.)
      -- DC-DC switching supply to provide 18V to main CPU
      -- 5V supply drawn from main CPU's regulated power supply. But if
      the total external load is too much, I'll get a DC-DC regulator to
      bring the 7.4V down to 5V.

      So, it looks like I may only need one DC-DC converter.


      On Fri, 04 Mar 2005 12:17:10 -0600, Jeff Sampson <jsampson@...> wrote:
      > First thing to consider when building a power system like this is to
      > look at the biggest power demand. In your case it is the motors. If you
      > can size your batteries to directly provide the motor power then you
      > don't have to convert that one up or down. So instead of a 60%-85%
      > conversion efficiency, you have a 100% conversion efficiency because you
      > just have a piece of wire. :-) Then you are left with generating the 18V
      > and 5V.
      >
      > But you have to determine if you can directly connect your battery to
      > your motor driver. ie. does it require a 12V +/-10% supply? Or will it
      > run on anything between 8V and 15V? (for instance).
      >
      > If something in the driver needs a regulated 12V then you can add a
      > small convertor just to generate that. But the big motor current can
      > come directly from the batteries. (Maybe you have mentioned what your
      > motor driver is, but I don't recall.)
      >
      > That would save you having to buy/build an expensive 120watt convertor.
      >
      > --
      > Jeff Sampson
      > http://tcrobots.org/members/jsamp.htm
      >
      > ________________________________________________________________________
      > > ________________________________________________________________________
      > >
      > > Message: 6
      > > Date: Tue, 1 Mar 2005 12:35:47 -0800
      > > From: Jay Prince <jayprince@...>
      > > Subject: DC-DC power supply recommendations?
      > >
      > > Hi..
      > >
      > > I've been pulling together a design for a robot that has a disparate
      > > set of components. Unfortunately, the different subsystems have
      > > differing power supply requirements. I'm looking for a power supply
      > > solution that will hopefully let me buy one item and supply them all.
      > >
      > > The voltages so far are:
      > >
      > > 18V ~3A Likely will not exceed 1A, in practice
      > > 12V High Amps (6? 10?) -- this will be driving the motors
      > > 5V ~1A
      > >
      > > I've got some NiCad 12V battery packs, and could wire them in series
      > > to get 24V, but I'm not sure about their capacity.
      > >
      > > I'd like to use Lithium-Ion Polymer battery packs, as I just don't
      > > want the weight of a SLA. But these come in 7.4, 11.1 and 14.4V.
      > >
      > > Can anyone recommend a supplier of DC power supplies, hopefully at
      > > reasnable cost, which will provide these three outputs? Maybe it will
      > > be better to buy three inexpensive ones, one of which is variable
      > > voltage. But I'm not sure.
      > >
      > > I could put in an inverter, and then use off the shelf AC power
      > > supplies, but that kinda offends me -- but then, maybe the inverter
      > > will be more efficient than a 7.4V to 12V DC-DC power supply? I have
      > > an inverter already, and enough AC power supplies to go this route
      > > without spending any money... and if its %80 efficient, then it
      > > doesn't really make sense to spend more than $50-$75 on a DC-DC
      > > supply-- I can buy more battery capacity with that money.
      > >
      > > Thanks a bunch!
      > >
      > > Jay
      > >
      > >
      > > ________________________________________________________________________
      > > ________________________________________________________________________
      > >
      > > Message: 7
      > > Date: Tue, 1 Mar 2005 14:10:41 -0800
      > > From: Steve Bennett <swbenn@...>
      > > Subject: Re: DC-DC power supply recommendations?
      > >
      > > Hi Jay
      > >
      > > You may want to look into rolling your own DC-DC using either the
      > > National simple switcher parts or the Linear tech parts. Both
      > > suppliers have plenty of documentation and app notes available to help
      > > the struggling designer get up and running in short order. LT's
      > > simulator is a great way to play with designs with a minimum of smoke.
      > >
      > > If you take a weekend's worth of robot tinkering time you should be
      > > able to come up with a couple of designs. Order up parts for from
      > > digikey and next weekend, build 'em up. Using simple boost or buck
      > > supplies you should be able to take the power you got and get the
      > > power you need. The one chip IC's out there today make it likely that
      > > you will get a usable design in a reasonable time.
      > >
      > >
      > > If you put some time in on switching supplies you will have an
      > > extremely useful brain tool when you're done.
      > >
      > > Here are some good places to start on the web:
      > >
      > > Switching Regulators for Poets
      > > A Gentle Guide for the Trepidatious
      > > http://www.linear.com/pc/downloadDocument.do?navId=H0,C1,C1154,C1002,P1209,D4120
      > >
      > > LT1070 Design Manual
      > >
      > > http://www.linear.com/pc/downloadDocument.do?navId=H0,C1,C1003,C1042,C1031,C1061,P1266,D4176
      > >
      > > The lt1070 series parts kick electron butt.
      > >
      > > If ya just want to plug in the numbers and get something out that will
      > > work check out the National semiconductor web site:
      > >
      > > http://www.national.com/appinfo/power/
      > >
      > > The web based design tool is quite helpful but keep an eye peeled, I
      > > have had odd results.
      > >
      > > Have fun
      > > Steve
      >
      >
    • tbrenke@verizon.net
      lm2675-5.0EVAL 7-40V in 5V @1A out the eval board is just about 1.5 times a 7805 regulate. and if memory serves, about $12 it is also self regulating. if you
      Message 2 of 3 , Mar 4, 2005
        lm2675-5.0EVAL
        7-40V in
        5V @1A out
        the eval board is just about 1.5 times a 7805 regulate.
        and if memory serves, about $12

        it is also self regulating. if you try to pull more then 1A from it the
        voltage lowers quickly instead op blowing up.

        DO not connect it backward.
        this will smoke it in no time at all.



        Jay Prince wrote:

        >Dropped the list from the CC.
        >
        >---------- Forwarded message ----------
        >From: Jay Prince <jayprince@...>
        >Date: Fri, 4 Mar 2005 14:32:26 -0800
        >Subject: Re: DC-DC power supply recommendations?
        >To: Jeff Sampson <jsampson@...>
        >
        >
        >Thanks to both of you for your recommendations. At the national site
        >I found lots of potential solutions-- but also that they make some
        >reasonably priced example boards, so I may not have to roll my own.
        >
        >At this point the general plan is:
        >-- Main batteries run at 7.4V
        >-- Motors are 12V motors, run at 7.4V
        >-- Motor Controller runs as 7.4V (need to verify this--planning to use
        >Traxxas XL1s, but if anyone has a recommendation for a $40 high-amp
        >motor controller, I'm all ears.)
        >-- DC-DC switching supply to provide 18V to main CPU
        >-- 5V supply drawn from main CPU's regulated power supply. But if
        >the total external load is too much, I'll get a DC-DC regulator to
        >bring the 7.4V down to 5V.
        >
        >So, it looks like I may only need one DC-DC converter.
        >
        >
        >On Fri, 04 Mar 2005 12:17:10 -0600, Jeff Sampson <jsampson@...> wrote:
        >
        >
        >>First thing to consider when building a power system like this is to
        >>look at the biggest power demand. In your case it is the motors. If you
        >>can size your batteries to directly provide the motor power then you
        >>don't have to convert that one up or down. So instead of a 60%-85%
        >>conversion efficiency, you have a 100% conversion efficiency because you
        >>just have a piece of wire. :-) Then you are left with generating the 18V
        >>and 5V.
        >>
        >>But you have to determine if you can directly connect your battery to
        >>your motor driver. ie. does it require a 12V +/-10% supply? Or will it
        >>run on anything between 8V and 15V? (for instance).
        >>
        >>If something in the driver needs a regulated 12V then you can add a
        >>small convertor just to generate that. But the big motor current can
        >>come directly from the batteries. (Maybe you have mentioned what your
        >>motor driver is, but I don't recall.)
        >>
        >>That would save you having to buy/build an expensive 120watt convertor.
        >>
        >>--
        >>Jeff Sampson
        >>http://tcrobots.org/members/jsamp.htm
        >>
        >> ________________________________________________________________________
        >>
        >>
        >>>________________________________________________________________________
        >>>
        >>>Message: 6
        >>> Date: Tue, 1 Mar 2005 12:35:47 -0800
        >>> From: Jay Prince <jayprince@...>
        >>>Subject: DC-DC power supply recommendations?
        >>>
        >>>Hi..
        >>>
        >>>I've been pulling together a design for a robot that has a disparate
        >>>set of components. Unfortunately, the different subsystems have
        >>>differing power supply requirements. I'm looking for a power supply
        >>>solution that will hopefully let me buy one item and supply them all.
        >>>
        >>>The voltages so far are:
        >>>
        >>>18V ~3A Likely will not exceed 1A, in practice
        >>>12V High Amps (6? 10?) -- this will be driving the motors
        >>>5V ~1A
        >>>
        >>>I've got some NiCad 12V battery packs, and could wire them in series
        >>>to get 24V, but I'm not sure about their capacity.
        >>>
        >>>I'd like to use Lithium-Ion Polymer battery packs, as I just don't
        >>>want the weight of a SLA. But these come in 7.4, 11.1 and 14.4V.
        >>>
        >>>Can anyone recommend a supplier of DC power supplies, hopefully at
        >>>reasnable cost, which will provide these three outputs? Maybe it will
        >>>be better to buy three inexpensive ones, one of which is variable
        >>>voltage. But I'm not sure.
        >>>
        >>>I could put in an inverter, and then use off the shelf AC power
        >>>supplies, but that kinda offends me -- but then, maybe the inverter
        >>>will be more efficient than a 7.4V to 12V DC-DC power supply? I have
        >>>an inverter already, and enough AC power supplies to go this route
        >>>without spending any money... and if its %80 efficient, then it
        >>>doesn't really make sense to spend more than $50-$75 on a DC-DC
        >>>supply-- I can buy more battery capacity with that money.
        >>>
        >>>Thanks a bunch!
        >>>
        >>>Jay
        >>>
        >>>
        >>>________________________________________________________________________
        >>>________________________________________________________________________
        >>>
        >>>Message: 7
        >>> Date: Tue, 1 Mar 2005 14:10:41 -0800
        >>> From: Steve Bennett <swbenn@...>
        >>>Subject: Re: DC-DC power supply recommendations?
        >>>
        >>>Hi Jay
        >>>
        >>>You may want to look into rolling your own DC-DC using either the
        >>>National simple switcher parts or the Linear tech parts. Both
        >>>suppliers have plenty of documentation and app notes available to help
        >>>the struggling designer get up and running in short order. LT's
        >>>simulator is a great way to play with designs with a minimum of smoke.
        >>>
        >>>If you take a weekend's worth of robot tinkering time you should be
        >>>able to come up with a couple of designs. Order up parts for from
        >>>digikey and next weekend, build 'em up. Using simple boost or buck
        >>>supplies you should be able to take the power you got and get the
        >>>power you need. The one chip IC's out there today make it likely that
        >>>you will get a usable design in a reasonable time.
        >>>
        >>>
        >>>If you put some time in on switching supplies you will have an
        >>>extremely useful brain tool when you're done.
        >>>
        >>>Here are some good places to start on the web:
        >>>
        >>>Switching Regulators for Poets
        >>>A Gentle Guide for the Trepidatious
        >>>http://www.linear.com/pc/downloadDocument.do?navId=H0,C1,C1154,C1002,P1209,D4120
        >>>
        >>>LT1070 Design Manual
        >>>
        >>>http://www.linear.com/pc/downloadDocument.do?navId=H0,C1,C1003,C1042,C1031,C1061,P1266,D4176
        >>>
        >>>The lt1070 series parts kick electron butt.
        >>>
        >>>If ya just want to plug in the numbers and get something out that will
        >>>work check out the National semiconductor web site:
        >>>
        >>>http://www.national.com/appinfo/power/
        >>>
        >>>The web based design tool is quite helpful but keep an eye peeled, I
        >>>have had odd results.
        >>>
        >>>Have fun
        >>>Steve
        >>>
        >>>
        >>
        >>
        >
        >
        >Visit the SRS Website at http://www.seattlerobotics.org
        >Yahoo! Groups Links
        >
        >
        >
        >
        >
        >
        >
        >
        >
        >
      • Dave Hylands
        I recently acquired a bunch of LM2671 s (5V @ 500 mA) along with a bunch of 47 uH inductors (DO3316-473). If anybody would like some, I can let them go for
        Message 3 of 3 , Mar 4, 2005
          I recently acquired a bunch of LM2671's (5V @ 500 mA) along with a bunch of
          47 uH inductors (DO3316-473).

          If anybody would like some, I can let them go for $0.50 for one of each (they
          retail at Digikey for about $4 for the pair).

          So if you'd like some, let me know.

          --
          Dave Hylands
          Vancouver, BC, Canada
          http://www.DaveHylands.com/

          > -----Original Message-----
          > From: tbrenke@... [mailto:tbrenke@...]
          > Sent: Friday, March 04, 2005 7:01 PM
          > To: SeattleRobotics@yahoogroups.com
          > Subject: Re: [SeattleRobotics] Fwd: DC-DC power supply
          > recommendations?
          >
          >
          >
          > lm2675-5.0EVAL
          > 7-40V in
          > 5V @1A out
          > the eval board is just about 1.5 times a 7805 regulate.
          > and if memory serves, about $12
          >
          > it is also self regulating. if you try to pull more then 1A
          > from it the
          > voltage lowers quickly instead op blowing up.
          >
          > DO not connect it backward.
          > this will smoke it in no time at all.
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