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Series Power Supplies

Wp100

Well-Known Member
Hi,

A question not for me, but not sure about the right answer ?

Referring to the typical power brick, eg 3A , can a 12v d cand 24v dc ones be tied together in series to provide 36v.

Have seen some reference to doing so with quality power supplies,.

Is it essential that both supplies are the same current rating and are there any downsides to this method ?
 

Diver300

Well-Known Member
Most Helpful Member
It's not essential that they are the same current rating but it is essential that there is a diode in parallel with each that is rated to the current rating of the other power supply or more.

The diode is reverse-biased by the power supply that it's in parallel with so it does nothing when the supply is operating normally. When the other power supply is providing more current, the diode prevents damage. One situation where one supply gives more current than the other is if one has no mains input or is turning of / on, so the diodes may be needed or one power supply dies on turn-on if there is a load.

Say you had a 24 V, 3 A supply and a 12 V, 5 A supply, and you fit diodes. If the load is <3 A, you get 36 V. If you take 4 A, the 24 V supply limits at 3 A, and the 12 V supply keeps going. If the 24 V supply continues to supply 3 A whatever, then you get 1 A flowing in the diode that is in parallel with the 24 V supply. If the 24 V supply shuts down, you get 4 A flowing in that diode. Without a diode, you can get -12 V across the 24 V supply which may damage it.
 

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