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Multi-rail DC supply from a Wall-wart - (was How To: DC +/- Power Supply?)

Multi-rail DC supply from a Wall-wart

Warning - this circuit requires a little bit of electronic knowledge and some soldering skills. Please ask a knowledgeable person to help if you do not understand the circuit or risks as mains voltage circuitry is involved.

The circuit provides a 'high' current output at a nominal voltage as well as 'low' current auxiliary supplies at minus and at double the nominal output voltage (if only one auxiliary supply is required, the components for the other can be left off).

The 'low' current supplies have limited capability due to the half wave charge pump technique employed (50-100mA). The main supply should be limited to 60% of Wall-wart's rating as Wall-warts are normally heavily over rated. The power supply circuit normally forms part of the user's circuit.

This supply was quite popular in the late 70's. From a single transformer winding it provided 5v DC for a microprocessor circuit and +- supplies for analogue interface circuits and/or an RS-232 comms buffers (3-terminal regulators were used to regulate the outputs).

Start by buying one of the 4.5v to 12v DC switchable Wall-warts (>--o----|------o---|>|----o----|----o----- +V )( . | | | D4 | | | AC )( . | | |--|---|>|----' | | + )( . | | | | D5 | ===== Mains )( . | | | '---|>--|----o---o------|

Reply to
Gerhard v d Berg
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The plural police have flagged your sentence above as incorrect. The correction is as follows, "Nobody queried or corrected me - the hawks in the group are slipping up !"

:-)

Reply to
Lord Garth

Snip ...

Take 2 I left out two diodes in the charge-pump circuits. Nobody queried or corrected me - the hawks in the group is slipping up ! Maybe there is no interest :-/

I reposted the whole text and circuit with the corrections and add a reference.

- - -

Multi-rail DC supply from a Wall-wart.

This supply was quite popular in the late 70's. With regulators it provided 5v DC for microprocessor circuit and a +- supply for analogue interface circuits and/or an RS-232 comms buffers from a single transformer winding.

The circuit provides a 'high' current output at a nominal voltage as well as 'low' current auxiliary supplies at minus the nominal supply as well as a 'low' current supply at double the nominal voltage.

Buy one of these 4.5v to 12v DC switchable Wall-warts as it simplifies the selection of the correct output voltage(s). Also ensure that the Wall-wart's case can be opened as a small internal change is required. Open the case (do not plug it into socket while it is open !!!!

( MAINS VOLTAGE PRESENT INSIDE WALL-WART WHILE ) ( PLUGGED INTO MAINS SOCKET !!!!!! ( MAINS EASILY BLOWS HUMAN FUSE !!!!!! :-) ( Human fuse has prove to be very difficult to repair - ( replacement through cloning, is still in experimental stage)

Unsolder DC output wires across Wall-wart's smoothing capacitor (normally 1000uF 25v) and wire it directly across the transformer windings. Select windings to provide a suitable AC (Alternating current) output to generate the most suitable DC outputs for the circuit below.

I prefer to wire the output permanently to the correct transformer windings and not to the switch output. It avert problems when people adjust the switch and thus select a too low or high voltage. (View circuit using notepad or a fixed pitch font such as courier)

. Multi-rail DC supply . C1 || + . ,----||--------o----|>|-----o---------- +2V Wall-wart . | || | D2 | . | D1 | | . | +---|>|---' | + . | | ===== . | | | C3 . | | D3 | ------- ---->>--o----|------o---|>|----o----|----o----- +V )( . | | | D4 | | | AC )( . | | |--|---|>|----' | | + )( . | | | | D5 | ===== Mains )( . | | | '---|>--|----o---o------|

Reply to
Gerhard v d Berg

[clip]

There's always interest else there'd be no group!. I saw it but didn't notice any diodes missing. If a newcomer to electronics, then those diodes are very important but like many people here, over the years I've looked at literally 1000's of PSU circuits, hence will only casually 'scan' a circuit to see if any new idea has turned up. With experience it takes about 2 seconds to do this.

But ... From long and close familiarity with these things, it's just like reading a line of text. Words can be misspelt, whole words, characters, even sentences can be missing, yet the -meaning- still shines through. Simply a case of pattern recognition.

Occasionally, some weird novelty circuit comes along, at which point everything stops while pleasure is taken sucking the goodness out of it (may take an hour). The circuit is then no longer oddball and it and its variants (with and without crucial diodes etc) can henceforth be spotted and scanned quickly.

Reply to
john jardine

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