Why do we have an external PSU for S9 Series?

The overall goal of the S9 development team was to minimise both the size and the weight of the device that sits on the bed side table. By making the power supply external to the flow generator this provides users with the flexibility to place the PSU on the floor.
As with any medical device there are also regulatory and cost considerations that influence the design. If the PSU is placed internally, then the design must be such that the external surface of the flow generator does not exceed 50oC under ambient conditions of 35oC. This would have been very difficult to achieve with the S9 Series primarily due to the additional power requirements of the ClimateLine tube.

By placing the PSU external to the flow generator it is also far easier and to ensure the safety of the flow generator design (even under fault conditions) as the mains electricity supply is kept remote to the device and the PSU electronics can be easily and securely sealed to prevent water ingress (under spill conditions).