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multiple output power supply

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rupert kenna

New Member
I want to replace a power supply to a gadget, The gadget requires these inputs:
32 VDC 100mA
7.5 VDC 150mA
4.25 VAC 350mA
Please could you suggest best way to build such a supply both using
... mains 240 VAC input
and/or
... using 5VDC USB ideally with a pass thru battery
 

MikeMl

Well-Known Member
Most Helpful Member
Welcome,

Where are you located? That determines sources of supply..,

What is the "gadget"? (Any rf involved)?

Is the 0V of the 32Vdc supply common to the 0V of the 7.5Vdc supply or must they be isolated?

Is either end of the 4Vac supply common to the other two?

Starting from USB makes it hard, especially to get AC.

Hereabouts, there are hundreds of surplus wall-wart plug-pack power supplies available for less than the price of a cup 0f coffee in various thrift shops (typical price = 1$). I could find two DC wall-warts and an AC wall-wart and have this project done for $3 and a trip to town.

Come to think of it, I have seen some power supplies at the thrift shop that came with throwaway Inkjet printers that had multiple outputs near your requirements...
 
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ronsimpson

Well-Known Member
Most Helpful Member
Power line (220 vac) power supplies is a big project and involves high voltage. Too much for you.
For the moment lets not think about the battery.
You need to deliver about 6 watts. If your supply was 100% efficient that will pull 1.2A from the USB power supply.

So start out with a USB power supply that can deliver 2A.
For the 5V out, just pass the power through.
For the 32 and 7.5 get two of these:
http://www.ebay.com/itm/DC-DC-3-30V...548079?hash=item35de1a8aaf:g:QNkAAOxyTMhSALOn
OR search ebay.com for "DC-DC 3-30V to 4-35V LM2577 Boost DIY Mobile Phone Power Supply Module"
OR Look at the data sheet for the LM2577.
 

MikeMl

Well-Known Member
Most Helpful Member
Ron's idea will only work if the two dc supplies can share a common (ground, oV) at the "gadget" end, and even worse, that common will end up tied to the chassis of the PC from which you steal the USB 5V. You will still have to go looking for a wall-wart to get the AC.
 

rupert kenna

New Member
It powers an Oregon Scientific mirror clock MR238. Its old and power supply is damaged.

I thought a square wave may suffice for 5VAC if the USB can get flip flopped somehow.

So boost converter and AC adapter. ... I am in London UK but have some old trabsformers. I may even have old unkjet I can open up if it has this,
 

MikeMl

Well-Known Member
Most Helpful Member
If it is a clock, it likely is using the AC line frequency for the time reference. It would be hard to duplicate the accuracy of the time base starting from DC. (It can be done, but a big project). I just bought a ceiling projection clock for a bedroom that is synced with 60KHz WWVB radio transmissions for less than what you are likely to spend on getting yours going...

Starting from USB, you will have to keep the computer on 24/7 just to power a wall clock?
 
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ronsimpson

Well-Known Member
Most Helpful Member
Sorry I did not see "AC" for the 4.25V.
Is that RMS or peak.
Square is easy. Sign is not.

If the "AC" drives the clock then it should come from the power line.
A battery version requires a time source.
 
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MikeMl

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Most Helpful Member
Sorry I did not see "AC" for the 4.25V.
Is that RMS or peak.
Square is easy. Sign is not.
48 to 52Hz is easy; 50.000000Hz averaged over a month is not!
 

Les Jones

Well-Known Member
Most Helpful Member
When I saw the 4.5 volts AC my initial thought was that it feeds the filament of a vacuum fluorescent display. I googled "Oregon Scientific mirror clock MR238" and found the manual. It turns out that it does use this type of display and that is is radio controlled so the AC frequency is not critical. It does add another slight problem as the AC supply needs to be centre tapped and the tap is connected to a point a few volts positive of logic ground. I suspect that the 32 volts will only need to be a few mA as it probably only feeds the anodes on the display.

Edit. Link to info on VFD displays

Les.
 

spec

Well-Known Member
Most Helpful Member
Hi RK,

Supplying your power lines from a standard USB port would not be possible but a 2A USB wall wart or 2A USB hub (both 5V * 2A = 10W power capability) would have just about sufficient power- you can never get more power out of a system than you put in:
(1) 32 VDC 100mA = 3.2W
(2) 7.5 VDC 150mA= 1.125W
(3) 4.25 VAC 350mA= 1.35W
So the total power requirement is, 5.675W. Assume 60% efficiency, gives a total input power requirement of 5.675W/0.6 =9.46W
The two DC supplies would be straight-forward but the AC line would be more complex.

On the other hand, providing your supplies from the 240V 50 Hz UK mains supply would be simple:
(1) Off- line switch-mode power supply
(2) Off- line switch mode power supply
(3) 240V 50Hz to 4.5V transformer

All of the above items are available quite cheaply.

spec
 
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MikeMl

Well-Known Member
Most Helpful Member
If the UK time signal is like the one here in the US, there is no guarantee the clock will get updated every minute. In that case, you still want the 50Hz to come from the grid. Hereabouts, it takes an "atomic" clock up to 24hrs to lock-in and synchronize with the NIST 60kHz transmission from Ft Collins, CO.
 
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