Power supply units: Your questions, our answers.

Various types of power supply units are used in measurement technology to provide electrical energy and operate electronic devices.

• Linear regulated power supply units: These power supply units generate a constant output voltage by regulating a higher input voltage down to the desired level. They usually offer good output voltage stability and noise suppression but are often less efficient than switching power supplies.
• Switching power supplies: In contrast to linear power supplies, switching power supplies use a switching circuit to modulate the input voltage and generate the output voltage. They are usually more efficient and can provide a wider range of output voltages but may be more susceptible to noise and have lower output stability.
• Programmable power supply units: These power supply units offer the option of remotely programming the output voltage and output current via a control interface such as USB, GPIB (General Purpose Interface Bus) or LAN. They are very flexible and enable precise control for specific measurement applications.
• DC voltage sources: They supply a constant DC voltage, which is required for many measurements in electronics.
• AC voltage sources: These power supply units generate a variable alternating voltage and are used for specific tests and measurements where alternating current is required.
• Battery chargers: Chargers for batteries can also be used in measurement technology to provide a constant or specific charging curve for battery tests.
• Multi-channel power supply units: These devices have several independent channels with different output voltages and output currents to fulfil different requirements for supplying several devices.

The output power of a power supply unit describes the maximum electrical power that the power supply unit can supply to the connected load. It is the product of the output voltage and the output current and is usually measured in watts (W).

The formula for calculating the output power is as follows: Output power = output voltage × output current

Laboratory power supply units and conventional power supply units differ in several aspects. Above all, laboratory power supplies offer greater functionality, accuracy and controllability for demanding applications and are often specially tailored to the needs of research and development. Conventional power supply units are designed more for general power supply requirements and everyday use. The most important differences in detail:

• Laboratory power supplies are generally more precise and offer greater accuracy in terms of output voltage and output current compared to conventional power supplies. This enables more precise control and measurement of electrical parameters for scientific, industrial or research purposes.
• Laboratory power supplies are often adjustable and programmable. They allow fine adjustment of output voltage, output current and other parameters via rotary knobs, buttons, or even digital interfaces such as USB, GPIB or LAN. These functions offer greater flexibility and precision in setting and controlling the output parameters compared to conventional power supply units.
• Laboratory power supplies usually offer higher output voltage stability and better noise suppression compared to conventional power supplies. This stability is important for precise measurements and applications that require a constant and stable power supply.
• Some laboratory power supply units have several independent output channels that make it possible to supply different output voltages and output currents simultaneously. This is particularly useful for applications that require multiple voltage sources.
• Laboratory power supply units offer protective functions such as overcurrent protection, overvoltage protection and short-circuit protection. They can also monitor and display parameters such as output power, voltage, current and other important measured values.

Other types of power supply units are:

19-inch power supply units

This special category of power supply units is designed to be accommodated in 19" racks. These racks are used in various industries and applications for the assembly of electronic devices, servers, audio and video equipment and other components. Standardisation refers to the width of the enclosure that is mounted in a rack. A typical 19" rack can accommodate various devices that can be mounted in this standardised width and height to enable a compact and structured arrangement of equipment. 19" power supply units are specially manufactured to fit into such racks. They can include different types of power supply such as power supply units, voltage converters, power supplies with different output voltages or special power supplies for specific applications. This type of power supply is often used in professional environments, data centres, laboratories and in industry, where a structured and standardised assembly of electronic devices is required. The 19" standard makes it easier to install, maintain and replace components, as they can simply be installed in the racks provided. 

Modular power supply units

A modular power supply unit consists of various modular components such as input modules, output modules, control modules, communication modules, etc. These modules can be replaced, added, or removed separately in order to change or expand the specifications of the power supply unit. The ability to combine or exchange modules means that modular power supply units can be adapted to changing requirements and to a wide range of voltage and current requirements - for example, by using modules with different output voltages or currents. In the event of a defect or maintenance, modules can be easily replaced without having to replace the entire power supply unit. Modular power supply units also often offer greater reliability, as failures of individual modules do not necessarily affect the functionality of the entire power supply unit. They can also offer improved energy efficiency as modules can be added or removed as required. Depending on the requirements, modular power supply units can adopt different configurations by combining modules to fulfil functions such as increased output power, multiple output voltages or special control and monitoring functions. Modular power supply units are used, for example, in industry, telecommunications, laboratories and test environments, as well as in applications where flexible and customisable power supply solutions are required.

Built-in power supply units

They are specially designed to be integrated into other devices, systems or structures. They often take the form of a housing or a packaged module and can be welded into a pre-assembled circuit board that can be inserted into the circuit. With built-in power supply units, some power supply units have a limited output voltage variance, for example: B. 11 V to 16 V. The power range is up to 5,000 W. These devices are very compact in order to save space.

DIN rail power supply units

These power supply units have been specially developed for mounting on DIN rails. DIN rails are standardised metal rails that are used in electrical enclosures, among other things, to mount electronic components, including power supply units. These power supply units are housed in compact, modular enclosures and are often used in industrial applications, control systems, automation solutions and other areas where a reliable power supply is required. Many DIN rail power supply units are designed for a wide range of input voltages in order to adapt to different electrical systems. They are available in several performance classes to meet different requirements. Some DIN rail power supply units have monitoring and protection functions such as overload protection, short-circuit protection and overvoltage protection.

Power supply units can be connected in series, but you should note the following:

Voltage compatibility

If you connect power supply units in series, the output voltages of the individual devices add up. Ensure that the total voltage is within the limits of the connected load and does not exceed the permissible operating voltages.

Current load

The total current flowing through the series-connected power supply units remains constant. Check the specifications to ensure that the current load of each individual power supply unit and the total current load do not exceed the permissible limits. 

Compatibility and stability

Not all power supply units are suitable for operation in series. Some devices may not function properly when connected in series due to differences in regulation or stability of the output voltage.

Safety

Check the safety standards and regulations to ensure that connecting power supply units in series does not pose any safety risks, such as exceeding voltage limits or the occurrence of faults that could damage the devices.

Always follow the instructions and specifications of the power supply unit manufacturer and consult your dataTec experts if you are unsure.

Power supply units can be connected in parallel to supply a higher total current. Please note the following:

• Voltage equality: The output voltages of the power supply units connected in parallel must be the same so that they can be successfully operated in parallel. Even small differences can lead to unwanted current flow between the power supply units, which can cause damage.
• Power distribution: Ensure that the power is distributed evenly between the parallel power supply units. Uneven load distribution can lead to overloading of individual power supply units.
• Current limitation and protection: The power supply units must have protective mechanisms to prevent overloading. Current limiting functions in the devices are important in order to limit the current to safe values in the event of a malfunction or overload.
• Synchronisation: It is crucial that the power supply units connected in parallel are synchronised in order to avoid undesirable phenomena such as phase shifts or interference that could lead to instability or damage.

Depending on the type and model, power supply units offer different programming options.

• Front panel control: Many power supply units have control panels with buttons, dials and displays that you can use to manually set parameters such as voltage, current and other desired values directly on the device.
• Software: Modern power supply units often have software that allows you to program them via a computer. This software can be connected to the power supply unit via an interface such as USB, Ethernet or GPIB (General Purpose Interface Bus). This allows you to make digital settings, monitor parameters and carry out automated tests.
• Programmable interfaces: Many power supply units offer programmable interfaces such as GPIB, USB, LAN (Ethernet), RS-232 or other protocols. You can send commands to the power supply unit using programming languages such as SCPI (Standard Commands for Programmable Instruments), LabVIEW and Python. This allows you to configure and control the output voltage, output current, protective functions, and other parameters.
• Remote control via the network: Some power supply units have functions for remote control via a network, such as Ethernet. You can access these devices via a special IP address and control them via the network, similar to the PC software, but via the network interface.

Laboratory power supplies offer a variety of interface options that allow them to be controlled, programmed, and connected to other devices or systems, including: 

• USB: USB interfaces enable direct connection to a computer and control of the power supply unit via special software or programmable commands.
• Ethernet / LAN: Laboratory power supply units can be integrated into a local network via Ethernet or LAN interfaces. This enables remote control and monitoring of the device via the network.
• GPIB (General Purpose Interface Bus): Also known as IEEE-488, GPIB is an older but still widely used interface for controlling laboratory measuring devices. It enables several devices to be connected via the same bus.
• RS-232: This serial interface is used for communication with other devices or computers. Although RS-232 is rather slow, it is still used as a control interface in some laboratory power supplies.
• LAN (Ethernet) with web browser control: Modern laboratory power supply units offer built-in web server functionality that enables the device to be controlled via a web browser. By entering the IP address of the power supply unit in the browser, the user can access a user interface to make settings and control the power supply unit.
  
• Wireless connectivity: Several laboratory power supplies also offer wireless connectivity options such as Wi-Fi or Bluetooth, which enable control and communication without cable connections.

You should ask yourself the following questions before buying a power supply unit:

• Which area of use and which application is involved?
• What output voltage, current and power are required?
• What type of current: AC or DC?
• Which design is required for the area of use and application?
• How many outputs / channels are required?
• Which communication interfaces are required?

The primary power supply specifications are the voltage and current output parameters. In terms of voltage, the power supply unit can have a fixed or variable output. If it has a fixed output, you can achieve the desired value with a small setting. If the power supply has a variable range, ensure that the power supply unit covers the required range. In terms of current, the power supply unit must be able to supply the required power. It should also have a certain amount of leeway beyond this minimum requirement. When calculating the requirements for the power supply specification, the so-called inrush current must be taken into account. When an appliance is switched on, a large current surge is initially drawn to charge capacitors. This inrush current can be a multiple of the normal operating current.

"Grid control" (also referred to as "mains voltage control" or "mains voltage tolerance") is a parameter in the specifications of power supply units that describes the ability of a power supply unit to provide a stable output voltage, regardless of fluctuations or variations in the input mains voltage. The grid control specifies how much the output voltage of the power supply changes when the input mains voltage changes. The grid control specification is normally given in millivolts for a specific input variation. It can also be quantified as a percentage of the output voltage. For most power supply units, it should be a few millivolts (e. g. 5 mV) or around 0.01 % of the maximum output voltage for a change in the mains voltage within the operating range.

Good grid control is important to ensure that the connected devices or circuits receive a stable and reliable supply of the required voltage, regardless of fluctuations or irregularities in the input mains voltage.

Load control is a parameter that is included in the specifications of power supplies. It indicates how much the output voltage of the power supply fluctuates when the connected load changes. Power fluctuations are normally expressed as millivolt fluctuations or as a percentage of the maximum output voltage. With a gradual load change from 0 to 100 %, this can be a few millivolts (e. g. 5 mV) or 0.01 %. It is normally specified as constant supply voltage and constant temperature. The voltage on the line from the power supply to the load may also drop. This can be reduced by using thicker wires with lower resistance.

With remote monitoring, the power supply unit is connected to the load, but additional wires are used to measure the voltage at the load. These wires carry almost no current. They are much thinner and there is almost no voltage drop along the wires. They detect the voltage at the load and feed this information back to the power supply unit so that the voltage regulator circuit regulates the voltage at the load instead of the output of the power supply unit. This function upgrades a power supply unit.