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Need to make a power supply that generates +24V, +12V, -12V, +5V, +3.3V DC supply.

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Mar 15, 2010
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i need to make a power supply that generates +24V, +12V, -12V, +5V, +3.3V DC from 110/230VAC.
I Have 0 experience in power supply design.
Lets put questions one by one.
1. what type of supply i should go for? smps or linear power supply? and why?

1. Depends upon the current you require.
For no more than an amp or so, a linear supply would likely be preferable since it's simpler and lower noise.
Above that the dissipation in the regulator starts to get high enough to require a substantial heat-sink.

How many simultaneous voltage outputs do you want?

At the max 2 simultaneous outputs will work.
As far as i know the use of regulators will increase the heat dissipation. and bigger heat sinks will be needed.
Also consider this, What will happen to a linear supply which is designed for 230V and is given 110V?
The outputs will vary we will have to use high input linear regulators. that will again dissipate very much heat.

For someone who has zero experience in power supplies, I would go the linear route. They are far, far simpler for the novice.
A LM317, LM7912 pair would give you what you require. The LM337 you could switch voltage-setting resistors for the different voltages.

There are many transformers that have both 220/110 volt, 50/60 Hz primaries, you would only have to add a small selector switch in the back.

At the max 2 simultaneous outputs will work.
If you use a transformer with two separate (isolated) secondaries then you can use the same regulator circuit (such as the common LM317) for both outputs.
Whether the output becomes positive or negative then is simply determined by which output terminal you select to be common (with isolated transformer secondaries it makes no difference which side is considered ground).
I used that technique to build my own dual output lab supply.

Attached is the Schematic i generated from
I need the following information.

1. I need to tell the cost of transformer to the management. i really have no idea about what are the characteristics of the transformer and how to order it or find equivalent. I would like someone to help me out in the costing first.
The BOM Exported gave some characteristics of the transformer as give in pic below

2. As told to me this design will cost more because of multiple windings. So i am being suggested to generate a know voltage say +24V and then by using linear regulators generate +12V, -12V, 5V and 3.3V


  • schematic.pdf
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Take a PC power supply and attach a boost converter to boost from 12V to 24V. Keep the other voltages. Done.

Mr. ArticCynda, this project is for professional level so i cannot do that.
I need to design a power supply for each of ours engineers desk to be used upon.

You still haven't stated how much current you want from the supply.
That is the primary factor that determines the design and cost of the supply.

The design that i have attached above is for 1A fir each of voltage level generated.
Then I would go with a linear supply as it's simple, low cost, and has low noise electrical noise if you are powering sensitive analog circuits.

I suggest buying a transformer with two isolated outputs and built two identical series adjustable series regulator circuits using LM317s.

For 24Vdc maximum output you could use a transformer with two 20Vac, 1.6A windings (transformer rated for about 65VA total).

For a cheaper approach you could buy two 24Vdc, 1A wall-wort supplies and connect the LM317 regulators to them.
A direct connection would give 24Vdc output and the regulator would generate any voltages below that.
You could place the wall-worts inside the case along with the regulators and run a power extension cord inside the case if you want to avoid have to plug in two wall-worts externally.

That way you will have two independent (isolated) outputs that can be used for any combination of two voltages at the same time (both the same polarity or opposite polarity, depending upon how their outputs are connected externally).

You would need to heat-sink each LM317 to dissipate about 28W (24W with the wall-worts) maximum.
For that a fan-cooled heat-sink, such as used to cool PC CPUs should work well.

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