# DCDC converter in series

I need to convert 5V (main power supply) to +/- 30V. I have two +/-15V DCDC converters and was wondering if I can connect them in series to generate the +30V and -30V rail?

My simple schematic

I tried simulating this circuit using Mplab MINDI, but there are only DC power sources and I am not sure it is valid to connect them the way I use them. The result show +/-30V. (When I connect the DC source on both ends the Amplitude is split to +15V and -15V therefore I set the amplitude to 30V).

The datasheet for the converter is here (pdf, 224kB)

UPDATE: After the discussion in the comments I updated my circuit. This would mean I have the separate the supply GND from my circuit GND and also adding two more converters for -30V

• You'll have to provide a link to a spec in order to get a definitive answer, but I'm fairly certain it won't work as you've drawn it. The +15V and -15V outputs are usually relative to ground; with the grounds connected together as above, you'd be producing +15V, -15V, and a whole lot of wasted current--at least until something burned out. Commented Jan 24, 2020 at 13:14
• No. Connecting the 0V pins as you have, shorts one V+ to the other V-. But if the output sides are genuinely isolated (are they? check the datasheet) you can connect top V- and bottom V+ to 0V. Then top V+ is +30V, bottom V- is -30V.
– user16324
Commented Jan 24, 2020 at 13:15
• at.rs-online.com/web/p/dc-dc-wandler-isoliert/3965130/…
– v3xX
Commented Jan 24, 2020 at 13:17
• Depends, are the outputs floating/galvanically isolated from the input? Commented Jan 24, 2020 at 14:20
• then no, this will cause a short. its easy to see why. you connected 15V to -15V both relative to the same gnd Commented Jan 24, 2020 at 15:23

Per the datasheet these supplies have isolated outputs, so you can offset them from the input. All you need to do is avoid creating ground loops, and let the (nominal) 0V outputs float to the midpoint of the 30V rails each one produces.

• Would this not short the two outputs ( -Vout and +Vout)?
– v3xX
Commented Jan 24, 2020 at 16:08
• I've used isolated dual-voltage modules many times. But since the whole point of dual outputs is to have common ground, that is how I used them. I wonder, if connecting only positive and negative outputs to get single power source will affect output circuits regulation. Without even connecting two in series. Commented Jan 24, 2020 at 16:22
• might be helpful to label what the voltage output at the 0V pins would be. or it could make it more confusing, not sure Commented Jan 24, 2020 at 16:24
• @v3xX Not if they are isolated because then the outputs of the converters dont share any reference (except when you connect them to force them to share a reference). not sharing a reference means no shorted loop for current to flow Commented Jan 24, 2020 at 16:25
• @DKNguyen Actually "Yes", it will short them, because that's the whole point :) Commented Jan 24, 2020 at 16:25

I suspect leaving 0V outputs floating will result in unstable operation or oscillation. The datasheet seems to imply that minimum load for regulation is 10% of max current. Therefore I'd suggest adding small loads to the outputs. For example 1.5k for 10mA current.

• I will try the circuit from the post above (with schottky diodes) and measure the output behavior with different loads (between +/-30V). I will add the additional loads when necessary
– v3xX
Commented Jan 27, 2020 at 7:22

It depends on whether your 15v power supplies are isolated. Some are, most aren't.

If it's not isolated, then the -15v outputs of the PSUs are both at -15V in reference to the input ground, not just 30V below their own respective high rail.