Power adapters for FreeCalypso dev boards

Mychaela Falconia mychaela.falconia at gmail.com
Thu Aug 20 10:34:26 UTC 2020


Hello again everyone,

In addition to the USB to dual UART adapter covered in my previous post,
the other accessory needed for working with FCDEV3B boards is a 3.6 VDC
power supply.  It seems that most GSM modem evaluation boards (for
GTM900 etc) made by parties other than TI and FreeCalypso implement an
arrangement where external power input to the board is 5V nominal, and
there is an on-board LDO regulator that takes this 5V power input and
produces some battery-emulating voltage (from 3.5 to 4.2 V depending
on who designed each given board) to feed to the actual GSM chipset or
module - but on our FCDEV3B I implemented a different approach, the
same one which TI had on their own historical development boards: the
power input to the board goes directly to the VBAT rail, without any
on-board regulators or converters, and the user is responsible for
supplying battery-emulating power, 3.6 VDC nominal recommended.

It appears that some people have been unhappy with my choice of board
powering arrangement, for the obvious reason that power supplies
putting out 3.6 VDC are much less common than 5V ones.  My original
intent was to supply an ultra-compact universal AC to 3.6 VDC power
adapter with every FC development board kit, but the problem was that
I could not find any inexpensive ones.  The only such adapter I did
have to offer was expensive, putting prospective users in a difficult
position of either paying for an expensive PSU or having to provide
their own supply of an "oddball" DC voltage with high current rating
to support GSM Tx bursts.

As of yesterday this PSU accessory problem is finally solved: a month
ago I ordered a batch of 100 new power adapters custom-made for us,
and they arrived from China yesterday.  They look totally professional,
no different from a power adapter you would get for a laptop or
whatever, but they put out 3.6 VDC with 2.2 A rating just like our
previous scarce adapters, and they are just as compact.  I will ship
them fitted with Weidmuller connectors that plug into our dev boards,
and the total cost (before shipping) of one adapter is about $7, very
inexpensive.

If anyone has an FCDEV3B board but has no good power supply for it,
please ask, and I can send you one of our new power adapters for the
cost of shipping from USA.  No charge for the adapter itself - the
adapter cost is negligible compared to what you paid for the FCDEV3B.
All future kits will have these PSUs included as a standard accessory
at no extra cost.

Hasta la Victoria, Siempre,
Mychaela aka The Mother


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