# Isolated DC-DC converter in series

I am still unsure about connecting two DC-DC converters to achieve a higher output voltage. Regarding my question about this DC-DC converter. The answer I selected does not work when no load is connected, and therefore I want to use the answer below but I do not fully understand it.

Would connecting "Common pin" with Vout+/ Vout- via the load resistors not short the connection I want to make and only produce +15 V/-15 V between my ground?

If this schematic is correct, can I still produce the +15 V/-15 V between the midpoint of the circuit?

EDIT: After the comments I changed my schematic.

Am I correct, that the COM+ are now the GND connection for my devices that need +15 V?

• i dont understand, isnt this allready dual output (+/-) converter .. so u have +15 / common / -15 ? Mar 12, 2020 at 9:45
• +Vout = +15v common = GND -Vout = -15v why u need two converters Mar 12, 2020 at 9:54
• Because I need GND-30V and -30V-GND
– v3xX
Mar 12, 2020 at 10:40
• no u cant have (+ 30 and +15) of same node if i understand correctly your requirements remember (mid point is GND) its in the drawing Mar 12, 2020 at 10:44
• No, GND is your GND, COM+ and COM- are your +-15V. Mar 12, 2020 at 16:25

The answer I selected does not work when no load is connected

Those converters don't regulate very well at no load even when used on their own so the above is probably a red-herring: -

Below 10% load the regulation isn't guaranteed and this is quite common for many DC-DC converters (caveat emptor).

Would connecting "Common pin" with Vout+/ Vout- via the load resistors not short the connection I want to make and only produce +15V/-15V between my ground?

No. The voltages at all the nodes from the bottom to the top are -30, -15, 0 +15 and +30. This assumes you are using a TEL 3-xx23 device.

• These voltages are measured all against GND?
– v3xX
Mar 12, 2020 at 10:45
• I edited the labeling on my question. I am correctly interpreting the outputs?
– v3xX
Mar 12, 2020 at 11:11
• @v3xX if you are using the TEL 3-xx23 then yes. Mar 12, 2020 at 11:25
• I use 0523. Thank you very much, I will try a testrun in the evening
– v3xX
Mar 12, 2020 at 11:29
• @v3xX if this question is answered then you should formally accept one of the answers or, raise a new comment for clarification. Jul 16, 2022 at 9:25

Could you please ensure that GND on "Power Input" (left hand)side and GND on "Power Output" (right hand) side seperated?

Regarding to your schematics they are same Grounds! In this case it is not a right way to use Isolated DC-DC converter such like this... Grounds should be seperated first!

• I can not separate the Grounds. Why cant they share the same reference point?
– v3xX
Mar 13, 2020 at 14:23
• Regarding to the datasheet of Tracopower TEL 3-0523 DC-DC converter is an isolated converter. Mar 14, 2020 at 7:05
• İnput and output Side of converter is behaves as physicslly diffetent circuits. Mar 14, 2020 at 7:08
• Imagine that you are using a transformer which has regulated inputs and outputs. Isolated DC-DC converter is similar to transformers except it works on DC instead of AC. Mar 14, 2020 at 7:15