[TriEmbed] Need simple 1A controlled current power supply

[Robert Gasiorowski]

Can I suggest LM2576 based switcher? There are plenty of them on eBay for
$1-$1.25.
You can feed them 12V and get 1.25V @ 3A. Then use resistor if you need
even lower voltage.

Rob.

On Mon, Sep 26, 2016 at 8:29 AM, Rodney Radford via TriEmbed <
triembed at triembed.org> wrote:

> For the Southeastcon 2017 hardware robotics competition, one of the
> requirements is to be able to switch on and off a magnet field.
>
> The field is defined as number of turns, diameter, core, and the current -
> 1A - through it.  I need a simple (and cheap) way to implement this.  I
> will be building 8x of these for the competition and each school will be
> building one for their trial runs, so keeping it cheap and simple is better
> than elegant and higher cost.
>
> Initially I was planning on a very simple solution - a MOSFET switching
> current to the coil in series with a power resistor to drop the voltage.
> At first this was a 5 ohm, 5W power resistor (since the coil is below 0.1
> ohm), but then that changed to a 12 ohm, 12W power resistor as I switched
> over to using 12v to power everything since I needed that for the relays
> anyway (for another part of the design).
>
> This works, and is cheap and easy to build and if the coil is only on for
> a few seconds at a time, this is a great solution. However, a change in the
> contest stated that the coil is initially powered on (so robots can use it
> to navigate to the coil) and if the robot fails, it could be on for the
> full duration of the 5 minute competition.
>
> I tested this last night and it does work, but 12w through even a metal
> power resistor is HOT after about 30 seconds.  I would hate to use this for
> 5 minutes.  The cost is good - below $2 for the MOSFET and power resistor -
> but I am looking to see if there is a better solution.
>
> Some ideas considered:
> * use a lower voltage - would work, but I would need a lower voltage 1A
> supply
> * use a switched regulator - get the lower voltage *and* ability to
> control it
> * others?
>
> Any thoughts / suggestions?
>
> Btw, I will be bringing this in to the next meeting (next R&A/TAR and next
> Triembed) to show the progress on the hardware and software design. Most of
> it is done now and I hope to finish it in the next few days.
>
> On another issue - I watched a couple Eagle videos this weekend and was
> able to complete the schematic capture for the board and even routed a PCB.
> The routes were done with the auto-router and they were ugly, but
> functional. Not sure if I will just route it myself, or route some and let
> the autorouter finish, etc, but I need to investigate the design rules for
> the fab house first to verify I have spacings, hole sizes, trace widths,
> etc are correct before I dump too much more time into it.
>
> Thanx,
> Rodney
>
>
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