Modern distribution systems typically require complex combinations of isolated and non isolated AC/DC and DC/DC power converters. Isolation converters are mainly used to protect systems and users in the event of a single or multiple faults; It is also necessary to supply power to isolated sub functions to maintain signal integrity.
In principle, using advanced ICs can easily design low to medium power converters with a power of around 1000 watts, and different performance trade-offs can be achieved through different architectures. However, in reality, the development and validation of converters are far from simple. You must meet at least one basic set of functional performance requirements, including rated output voltage and current, efficiency, transient response, physical dimensions, and fault protection for circuits, loads, and power supplies.
Design challenges are not limited to basic knowledge. At present, it is necessary to comply with a series of mandatory regulatory requirements, covering safety performance, efficiency at different load levels, shutdown performance, thermal performance, electromagnetic interference (EMI) emission, and immunity. These attributes must be validated by a certified testing laboratory, which will significantly increase the design time. A simple independent research and development plan can quickly lead to extremely high risks, and you will soon find that when it comes to choosing between independent research and development or outsourcing, you will quickly lean towards the latter.
If you still have doubts, you may consider that the converter must also have electrical isolation function. Although this is a common requirement for almost all AC/DC converters, some DC/DC converters also require electrical isolation. This requirement introduces new regulations, mandatory safety and certification standards, making the decisions of self-developed and outsourced further inclined towards purchasing, regardless of the power supply specifications.
The good news is that circuit board mounted isolated and non isolated power converters have multiple rated voltages and currents to choose from. These products greatly simplify product design and deployment in application areas such as defense, communication, testing and measurement (isolated), and mobile robots (non isolated), and can be combined to achieve power distribution functions.
This type of converter realizes plug and play, can be plugged into the main printed circuit board (PC board), and the specific location is optimized for the distribution rail. In addition, this type of converter does not require independent support or bracket. Simply put, this type of product can serve as a closed, complete plug and play solution that directly achieves power functionality.
Basic knowledge of electrical isolation
Electrical isolation is an electrical barrier used to prevent the formation of a conductive ("Ohmic") path between the two ends of a signal or power path. However, this barrier still needs to allow energy and electricity to be transmitted through other means of transmission. The signal, power supply, or both need to be isolated, but it depends on the design. The isolation technology used depends on the specific specifications of the isolated current.
There are many reasons why electrical isolation is necessary. For signals, electrical isolation can improve the integrity of sensors, eliminate grounding loops, or protect users and circuits in the event of a fault, preventing current from flowing into the signal path.
In terms of power supply, the main purpose is to ensure user safety and prevent electric shock caused by accidental contact with AC wires or high-voltage DC power sources. Electrical isolation also meets the requirement for "floating" circuits used for non power signals, that is, not connected to the circuit ground.
Generally speaking, electrical isolation is a method of determining the direction of current flow based on Kirchhoff's current law (KCL). Any current flow must have a path back to the source, and the function of electrical isolation is to cut off this path. In the event of a possible electric shock, the isolation transformer in the power supply (Figure 1, right) will cut off the complete fault current path through the user and return to ground (Figure 1, left).
Figure 1: To prevent electric shock, the isolation transformer (right) in the power supply cuts off the fault current path that passes through the user and returns to ground (left). (Image source: Lumen Learning)
In a common electric shock scenario, when the insulation layer wears down, the live/heated power cord will directly come into contact with the metal casing of the equipment. Even if the device can still operate normally, if the grounding/grounding connection is disconnected (which is a common situation), the fault current will flow through the user to the ground instead of safely passing through the grounding wire, and the user may suffer electric shock at this time.
To control this risk, the isolation function in the power supply will cut off the current path between the original voltage source and the equipment. In this way, it can prevent the formation of a circuit between them, and even if there is a line fault, it can eliminate the risk of electric shock.
Please note that the risk voltage includes AC line voltage and equivalent DC voltage, such as the voltage of a multi-core battery pack. Most regulatory standards define hazardous voltage as voltage above 60 volts, depending on the actual situation and voltage type.
Power isolation is almost always achieved through magnetic coupling of transformers. Magnetic coupling has excellent electrical efficiency, strong technical practicality, flexible application, high reliability, easy customization, and can simultaneously meet regulatory and circuit requirements.
Reasons for choosing numerous high-quality solutions
Due to the use of multiple power rails in modern systems, there are many architectural choices in distribution planning. However, when certain parts of the circuit must be isolated while other parts do not require or prohibit isolation, choosing the appropriate power converter becomes extremely challenging.
In some cases, high-voltage AC/DC or DC/DC power rails do not require isolation, but isolation needs to be achieved further downstream in the distribution link. The decisions that designers must make include: whether to use a single large capacity isolated power supply or multiple small capacity isolated power supplies; And whether to only use isolated power sources in the required locations and non isolated power sources in other locations (Figure 2).
Figure 2: A complete system level distribution architecture typically requires a combination of isolated and non isolated AC/DC and DC/DC power converters. (Image source: TDK Lambda)
To meet these needs, TDK Lambda offers a variety of onboard buck/boost (buck/boost) isolated and non isolated AC/DC and DC/DC power converters, providing multiple input/output rated voltage and rated current options. Specifically, it includes:
The isolated AC/DC: PFE500F-28/T is a single output, 28 volt/18 ampere (A) converter used for 85 to 265 volt alternating current (VAC) input. This converter adopts a 122 × 70 × 12.7 mm fully enclosed brick module with 3000 volt VAC input and output isolation capability, suitable for environments where convection or forced air cooling is not possible.
The non isolated AC/DC: PF1500B-360 enclosed module is also full brick sized and can convert AC input into 360 VDC regulated output. It is suitable for distributed power systems equipped with isolated high-voltage DC/DC converters or loads that require high-voltage power supply. At an input voltage of 170 to 265 VAC, its rated power is 1512 watts; At an input voltage of 85 to 265 VAC, the rated power is 1008 watts. The power factor of this module is 0.98, with an efficiency of up to 96.5%.
Isolated DC/DC: GQA2W024A050V-007-R Isolated DC/DC converter is compact in size, packaged in a quarter brick, and has excellent performance. It can output 120 watts of power and has an input and output isolation voltage of up to 3000 VDC. The working input voltage range of this converter is 9 V to 36 V, and it can output 5 V current at 24 A. Its mechanical packaging provides various structural configurations such as bottom plate, sealed, and encapsulated (see Figure 3), which can be cooled by convection and conduction through external cold plates or heat sinks.
Figure 3: GQA2W024A050V-007-R converter offers multiple packaging configuration options, providing designers with high flexibility in overall packaging design and converter cooling. (Image source: TDK Lambda)
Non isolated DC/DC: I6A24014A033V-003-R Non isolated Point of Load (PoL) DC/DC converter is ideal for creating high current output voltage rails from 12 VDC or 24 VDC power sources. The input voltage range of this converter is 9 V to 40 V, with an output current of up to 14 A and an output regulation range of 3.3 V to 24 V. It is packaged in a compact 1/16 brick design.