KNX communication Power supply for the smart home

Related Vendors

Phoenix Contact GmbH & Co. KG

FAULHABER Drive Systems

Wuxi InfiMotion Technology Co., Ltd.

Color display, an active choke, large input voltage range, and the usual slim design: These are the features of the Step-Power-KNX power supply from Phoenix Contact. The active choke not only increases efficiency but also ensures uninterrupted KNX communication up to 1,200 mA. The integrated color display ensures the necessary transparency of KNX status information and assists with commissioning and diagnosis, the advantage: simple KNX analysis.

Daniel Diekmann, Product Marketing, Phoenix Contact Power Supplies, Paderborn.

Nadine Schneider, Marketing Communication, Phoenix Contact Power Supplies, Paderborn.

KNX is a powerful and flexible standard for building automation. It enables seamless integration of various systems and devices to control lighting, heating, air conditioning, blinds, security systems, energy management, and more.

KNX has been an open standard for 34 years and allows products from different manufacturers to work together and communicate seamlessly.

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A KNX system consists of sensors and actuators. Sensors are field devices that are distributed decentrally in the building and gather information about the environment, such as temperature, light intensity, or movement. Actuators are usually central devices installed in the installation distributor on the mounting rail and react to the collected information from the sensors and perform actions, such as turning on lights or opening blinds.

For this communication to be available 24/7 without interruption or delay, a reliable KNX power supply is needed.

The heart of every KNX system

The power supply: An important and central aspect of building automation. It ensures that all components of the KNX system function properly and communicate with each other. The KNX bus is supplied by one or more power supplies with an integrated KNX choke and typically 30 V (operating range 28 to 31 V) DC voltage.

The choke separates the KNX bus from the active components of the power supply, thus enabling almost interference-free communication between the connected KNX participants.

For communication, the voltage is short-circuited for a minimal time by the addressed participants. Depending on the design and performance of the individual sensors and actuators, the current requirement is higher or lower—on average, around 10 mA is consumed per KNX participant. Typically, a KNX power supply with 640 mA is sufficient to supply a line with 64 bus participants and ensure smooth communication. However, if more powerful KNX devices like displays are installed in a line, this can quickly lead to higher power supply utilization. For this purpose, the KNX standard has defined an appropriate power reserve for each power supply in the guidelines—see KNX Standard 09_02 Basic and System Components Chapter 2.6 Electrical Features.

Full peak load up to 1,200 mA thanks to active KNX choke

The KNX standard specifies up to which operational range the different power variants of KNX power supplies must maintain the voltage and thus the KNX communication. The prescribed minimum voltage of 28 V must not be undershot. Additionally, a 640 mA power supply, for example, must maintain a power reserve up to 900 mA and ensure an overload current of 1,200 mA. Peak values like these can occur permanently with more powerful KNX sensors or temporarily through central functions or larger scenes when many KNX devices need to be addressed and communicate simultaneously. Therefore, attention should always be paid to the dimensioning or correct design of the power supply.

This means that the passive KNX choke commonly used on the market must withstand this load at the bus output without, for example, becoming magnetically saturated. The passive KNX chokes often use a ferrite core, such as an EI core with an air gap, for economic reasons. This can negatively impact the signal integrity of the KNX bus, so the operational range of the power supply up to 900 or 1,200 mA is not guaranteed and can lead to unexpected telegram losses or other transmission malfunctions.

With an active KNX choke, on the other hand, which operates with a toroidal core, the magnetic component and thus the saturation behavior can be avoided. The magnetization of a toroidal core can be executed more precisely depending on the material composition—through a homogeneous distribution of the material mixture, an air gap common in EI cores is distributed into many small individual air gaps. Negative effects of concentrated stray fields can thus be largely eliminated.

Another crucial advantage of the active choke circuit is that the required peak value is precisely adjustable. The required 1,200 mA of the 640 mA power supplies are thus available to the KNX bus without restrictions. For safety reasons, communication or the BUS output is actively switched off from 1,200 mA to ensure differentiation and clear delineation between KNX operation and short-circuit behavior. This makes a KNX system significantly more reliable in terms of system safety and availability and better plannable.

A KNX power supply ensures transparency

As the first KNX power supply, the Step Power facilitates work for the user via the integrated color display and provides an easy insight into the system directly on the device.

Through this transparency, the KNX bus gets a "face." The display not only reflects the current system state but also provides numerous pieces of information via the menu. These are primarily used for setting up, diagnosing, and expanding the KNX system. This way, the installer has all relevant KNX system information at a glance. This results in several relevant advantages for the user and system operator, such as:

• BUS and AUX outputs can be read separately, allowing for narrowed-down troubleshooting.

• A short circuit on the KNX line is indicated by a "black screen" or restarting.

• The temporal overload behavior is stored in the device and can be accessed via the display. This allows the electrical installer to determine why the device is defective, e.g., due to excessive temperatures in the distribution board.

• As soon as a reset of the KNX system has occurred, the runtime—but not the total runtime of the device—is reset to zero, allowing the exact time of the error to be determined.

After ten minutes of non-use, the display automatically turns off to maintain the efficiency of the power supply.

KNX power supply with color display and active KNX choke

Within the mere 3-unit width lies a lot of potential. The Step-Power-KNX power supply from Phoenix Contact offers users more transparency and communication security with the color display and active KNX choke. The device ensures secure communication without interruption thanks to the new choke circuit. The full 1,200 mA are available to the KNX bus. At the same time, the KNX system can be quickly and easily analyzed on-site— making the device also useful for temporary diagnostics in an existing system. All relevant system status information and historical values are always readable through the integrated menu. Thus, it is now possible for not only specialists to make a qualified statement about the system's behavior.

Efficiency and ecological balance also improve further. The active choke circuit dynamically adapts to the connected load, resulting in energy savings. Furthermore, network fluctuations are absorbed at the input, thanks to the wide AC and DC input voltage range, and have no impact on the 30 V KNX supply. Together with the active choke, this ensures a powerful and long-term stable secure KNX communication. (tk)

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