Low voltage power supply unit


Dilshan Jayakody writes:

In this post we introduce simple and flexible, regulated low voltage power supply unit. This power supply has provision for 4 outputs such as 1.5V, 1.8V, 2.5V and 3.3V. We mainly build this low voltage power supply unit to test (and power-up) low voltage MCUs, CPLDs and radio receivers. For this power supply we choose 1.8V, 2.5V and 3.3V to get it compatible with most of the LVTTL/LVCMOS devices. Other than that, we include 1.5V because there are several analog ICs are available for that voltage level.
This power supply unit is based on LM1117/AMS1117 voltage regulator series and for this design we use AMS1117-1.5, AMS111-1.8, AMS1117-2.5 and AMS1117-3.3 fixed voltage regulators. Except to above regulators this board can be use with AMS1117-2.85 and AMS1117-5.0 regulators.

Project info at Dilshan Jayakody’s blog.

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  1. Hmmmm. Do I understand the schematic? Let’s see.

    There is this biiiiig switch with that single output port which can be set to 4 different voltages.

    Why not simply make 4 output ports and wire them directly? So you would have 4 powers the same time!!!!11eleven!

  2. One has to admire the solder-bodged unisolated brown mains wire going from the on/off switch to the transformer. Nothing to worry about if one believes in reincarnation and all that…

    1. just in case someone fails to touch the switch contacts, there’s a good chance that the mains wire gets into contact with the metal housing after some time. There’s no earthing at all…

    2. Admittedly the image resolution is a bit poor, but I can’t see any problem with that “unisolated” wire – it appears to be soldered to the pilot lamp’s terminal, so it’s not going to go anywhere and in the closed box it would be rather hard to touch. Same goes for the switch – this thing has a _cover_ (see other photo at the source); how exactly do you propose touching anything through it?!? Regarding earthing – sure, it’s always a nice plus, but to be fair in large parts of the world normal household outlets _don’t include an earthing pin at all_ and even when they do, houses are not wired with a third wire, except for one or two outlets meant for a washing machine or something similar that really, really needs it. Sure, new buildings are not wired like that anymore but many existing ones still are; an earth wire would be all but pointless in such an area. For reference, see https://en.wikipedia.org/wiki/AC_power_plugs_and_sockets#CEE_7.2F1_unearthed_sockets_and_CEE_7.2F2_unearthed_plugs

      On the other hand, the mains wire does not appear to be protected in any way as it comes into the box, and the edges of the metal hole will probably erode the cable in time; a mains fuse would have been a worthwhile addition; the transformer is only half-used since it does half-wave rectification – only one of the two windings is working at any given moment; and the input / output capacitors are a bit of a joke – 100nF? Really? Even if one considers the main 2200µF cap as the “input cap”, the very datasheet linked to by the author himself clearly states “The minimum output capacitance required by the LM1117 is 10µF, if a tantalum capacitor is used”…

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