[TriEmbed] Need simple 1A controlled current power supply

[Rodney Radford]

Yes!  This is exactly the type of solution I was hoping to find.  I read
through several on/off regulator specs over the weekend, but did not find
one that could handle the 1A I needed (most were in the 100-200mA range).

This is a good solution and pre-built boards with the necessary passive
components are under $4 on eBay/Amazon.  I will order one to try out, but
open to other suggestions as well.

Thank you

On Mon, Sep 26, 2016 at 10:21 AM, Robert Gasiorowski <rgresume at gmail.com>
wrote:

> 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
>>
>>
>> _______________________________________________
>> Triangle, NC Embedded Computing mailing list
>> TriEmbed at triembed.org
>> http://mail.triembed.org/mailman/listinfo/triembed_triembed.org
>> TriEmbed web site: http://TriEmbed.org
>>
>>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.triembed.org/pipermail/triembed_triembed.org/attachments/20160926/42374820/attachment.htm>