Connecting two PSUs in series and parallel

So I have 2 identical 1W DC-DC converters (9V -> +/-5V). The converters are isolated to 6kV. The exact part is: XP IHA0109D05.

If I connect both (using the same battery for each one) in parallel will I get the same voltage at 2W (0.2A at max pd)?

And, in series, -10v -5v 0v 5v 10v at 1W (0.05A at max pd)?

Thanks.

• I understand these things have tiny transformers in, which means it should work? Feb 24 '21 at 17:11
• They are not ideally same so you may get different output currents. One of them may be overloaded and damaged. Feb 24 '21 at 17:20
• You should never connect power supplies in parallel unless they are designed to work this way or you have a special circuit that can properly balance them. Feb 24 '21 at 17:22

For that type of power supply it should be ok to parallel or series multiple devices to obtain more output.

IHA0109D05 Datsheet

As you can see from the graph on the top of page 4 of the datasheet the output voltage droops significantly with increase in load. This will allow the two units to share the load current.

Because of unit to unit variations two units in parallel will probably not share the load equally which will mean that you won't strictly get double the power output. If you had two units at the extremes with one at the high limit and the other at the low limit it could be as bad as a 10-90% split (eg if one was 5% high at full load and the other was 5% low at 10% load). It is extremely unlikely that would occur though.

Another point highlighted by @user263983 in the comments is that the graph is shown as "Voltage Accuracy". My interpretation of that is the graph is meant to cover all models of the device with varying voltage and current specifications.

If it included a regulated output where the output voltage remained constant they probably wouldn't share the load evenly when paralleled and the one with the slightly higher voltage would take al the load until it reached its maximum current, depending on how it responded to this overcurrent it might overload and fail while the other supply is doing nothing.

These supplies are commonly just a simple two transistor oscillator feeding a transformer with a bridge rectifier output, no regulation is provided.

One comment - the datasheet indicates the isolation voltage is 6kV not the 16kV that you state.

• Thanks for the in depth answer. I have corrected the main post regarding the 16kV value also. Feb 24 '21 at 17:32
• The gragh shows output voltage accuracy vs load current not voltage drop. They are not perfectly equal and with shared load currents are not equal. Feb 24 '21 at 18:15
• @user263983 - That's because the same graph applies to all models with different nominal output voltages. The important thing is that the voltage droops in a predictable fashion. It is not critical that the current be divided exactly equally but it is a point that is probably worth me pointing out. Feb 24 '21 at 18:48
• Accuracy means voltage drop may be different in some borders. But will it be 1% or 5% can be predicted with low probability. If output current not same, one can exceed the limit. Datasheet does not mention ability to work in parallel. Feb 24 '21 at 19:33