Combination of AC-DC Power supply and DC-DC Power Module

[Pramod P]

Hi ,
Can we combine the output's of two different Power units

example: 12V/8A from AC-DC Power supply and 12V/8A from DC-DC Power Module and best part is its inputs, which are AC-DC : Universal AC i/p and DC-DC: 36V-75Vdc

If this is possible, what will be the effect on switching frequency and isolations of PSU's.

please guide me.

 

[Les Jones]

You can connect them in series provided that neither the positive or negative outputs of at least one of the units is NOT connected to mains ground. If you connect them in parallel they all most certainly will not share the load equally as the output voltage and source resistance will be slightly different.

Les.

 

[Pramod P]

Thanks for the information,
But what about the input to output isolation of each power units, they will be different (For AC-DC Supply it is 4KV and for DC-DC module it is 2.2KV), so in this case what will be the isolation if we do series connection

 

[Les Jones]

The isolation will be that of the one with the lowest rating. In your case 2.2KV

Les.

 

[AnalogKid]

Are you connecting the two outputs in series (24 V at 8 A) or parallel (12 V at 16 A). Each way might have issues depending on how well the power supplies are designed.

With the series connection, the output noise will be greater. Also, at startup one of the supply outputs will come up before the other, and appear aw a reverse-connected power source driving the output stage of the later supply through the system load. That reverse connection might be seen as a fault and prevent the 2nd supply from starting up. To prevent this, put a power diode across each supply output reverse connected. This will prevent the reverse connection from exceeding 1 V, usually low enough that the 2nd supply does not see a fault.

With the parallel connection you can do what is called diode OR-ing or droop sharing. Connect the two +12V outputs together through power diodes. The diode's forward voltage drop acts as a ballast impedance. If you carefully adjust the two supply output to be the same voltage, you can get good (but not excellent) current sharing between the two supplies into the load. When we do this, we assume the sharing will never be better than 75%, and that is with the two diodes in one package so they are thermally connected. Output voltage regulation suffers, but you can combine almost any two supplies.

ak

 

[ronsimpson]

Hi ,
Can we combine the output's of two different Power units

example: 12V/8A from AC-DC Power supply and 12V/8A from DC-DC Power Module and best part is its inputs, which are AC-DC : Universal AC i/p and DC-DC: 36V-75Vdc

If this is possible, what will be the effect on switching frequency and isolations of PSU's.

Please draw a picture. I reread your post and there is too many different ways to understand.

One way to read is:
Output is 12V 8A.
Input1) 110 to 220VAC (4kv isolation)
Input2) 36 to 75VDC. (2kv isolation)
To be used with power line (110/220) and/or battery 36 to 75V

 

[Pramod P]

yes, what you have understood is correct.

 

[ronsimpson]

It is probably OK to connect the two supplies together.
You should have 4kv isolation to the power line. (If the DC supply is not connected.)
If the DC supply is connected you will have 2kV to the DC source. Most likely the DC is connected to ground and 2kv is good.
If both are connected at the same time; the power line could take a 4kv jolt and be good, but the DC line could only take 2kV.

If both are connected; likely one supply will supply most of the power but you can not know which one.
I think it will work.