Designing high-voltage isolated power supplies in this way easily achieves compact, low-EMI goals

In equipment applications such as medical or industrial plants, protecting personnel and equipment from high voltages is critical: wired patient monitors require continuous operation during defibrillation, and the associated high voltage transients can be a heavy burden; precise handling Modern high-speed communications used by robotic arms are subject to electrical noise interference from arc welding and other equipment, causing major safety production accidents; and so on. Therefore, to meet safety regulations and reduce noise, designers need to introduce isolation into high-voltage systems.

In equipment applications such as medical or industrial plants, protecting personnel and equipment from high voltages is critical: wired patient monitors require continuous operation during defibrillation, and the associated high voltage transients can be a heavy burden; precise handling Modern high-speed communications used by robotic arms are subject to electrical noise interference from arc welding and other equipment, causing major safety production accidents; and so on. Therefore, to meet safety regulations and reduce noise, designers need to introduce isolation into high-voltage systems.

Designing high-voltage isolated power supplies in this way easily achieves compact, low-EMI goals

However, this is often limited by latency, power consumption, cost, and size. Due to the extremely complex design of isolation, electromagnetic interference (EMI) is often generated when control power and data signals pass through the isolation barrier. These radiated emissions can negatively impact the performance of other Electronic systems and networks. Traditional methods typically use discrete circuits and transformers to transfer power, but this method is cumbersome and time-consuming, takes up valuable PCB space, and greatly increases cost. A more cost-effective solution is to integrate the transformer and required circuitry into a smaller form factor, such as a chip package, but doing so may introduce higher radiated emissions. In response to this situation, ADI, a high-performance analog circuit company, has introduced the groundbreaking isoPower® chip-scale integrated isolated power supply, which enables high-density, channel-to-channel isolation designs using multiple isolated power supplies, requiring fewer components and a smaller footprint.

How to balance small size and low cost with EMI suppression?this is a problem

Designing an isolated power supply can be one of the most challenging aspects of the design process. Building a solution involves weighing various design requirements and complying with regulatory requirements in many different regions of the world. The resulting sacrifices often have a negative impact on size, weight, and performance, or reduce the ability to meet EMC standards (EMC is the ability of an electronic system to function properly in its target environment without interfering with other In industrial, medical, communication and consumer environments, radiated emissions must generally comply with CISPR 11/EN 55011, CISPR 22/EN 55022 or FCC Part 15).

Designing high-voltage isolated power supplies in this way easily achieves compact, low-EMI goals

Electromagnetic Interference Standards

Integrating only the transformer and circuitry into a chip-scale package reduces component count, but radiated emission suppression techniques can complicate the PCB design (or require adding additional components) and may therefore offset the cost and cost savings of integrating the transformer. space. For example, a common approach to suppressing radiated emissions at the PCB level is to create a low impedance path for parasitic common mode (CM) currents from the secondary side to the primary side, thereby reducing the level of radiated emissions. To achieve this, bypass capacitors can be used between the primary and secondary sides. The bypass capacitor can be a discrete capacitor or an embedded interlayer capacitor. However, whether discrete or embedded, the use of bypass capacitors is not an ideal suppression technique. While it can help reduce radiated emissions, it comes at the cost of increased components, complex PCB layout, and increased transient susceptibility.

Designing high-voltage isolated power supplies in this way easily achieves compact, low-EMI goals

Internal PCB bypass capacitors formed between the center power and ground planes

Ideally, the integrated isolated power components should include measures to reduce the chip’s radiated emissions instead of adding additional complex designs externally. This allows components to pass rigorous radiated emission tests simply by placing them on a 2-layer board without having to make the board multiple times.

Innovative Low-E Radiation Technology Perfectly Meets Isolation Challenges

ADI’s next-generation isoPower® family uses innovative design techniques to avoid significant radiated emissions, even on 2-layer boards without bypass capacitors. The ADuM5020 and ADuM5028 can deliver 500 mW and 330 mW, respectively, across the isolation barrier while meeting the CISPR22/EN55022 Class B limits with substantial headroom.

Designing high-voltage isolated power supplies in this way easily achieves compact, low-EMI goals

ADuM5020/ADuM5028 Block Diagram

To reduce radiated emissions, the ADuM5020/ADuM5028 have excellent coil symmetry and coil drive circuitry to help minimize CM current transfer through the isolation barrier. Spread spectrum techniques are also used to reduce the noise density at a particular frequency and spread the radiated emission energy over a wider frequency band. The use of low-cost ferrite beads on the secondary side further reduces radiated emissions. These techniques can improve peak and quasi-peak measurement levels during radiated emissions compliance testing.

Designing high-voltage isolated power supplies in this way easily achieves compact, low-EMI goals

Concept ADuM5020 and Ferrite Characteristic Curve

The image above shows a ferrite bead placed on the secondary side close to the VISO and GNDISO pins. The ferrite used to collect the radiation emission map in the next paragraph is the Murata BLM15HD182SN1. These ferrites have high impedance over a wide frequency range (1800Ω at 100MHz, 2700Ω at 1GHz). These ferrites reduce the effective radiation efficiency of the dipole. As shown in the figure below, due to the impedance of the ferrite bead, the CM current loop is reduced, and the effective length of the dipole is significantly shortened, which reduces the dipole efficiency and reduces the radiation emission.

Designing high-voltage isolated power supplies in this way easily achieves compact, low-EMI goals

Use ferrite beads to reduce effective dipole

The ADuM5020/ADuM5028 provide a ready-to-use DC-DC power solution. The cost-effective, low-complexity, small footprint, and excellent radiated emission performance of this solution, if incorporated into the product design at the beginning of the design cycle, will help meet EMC regulations.

High measured margin for greater design flexibility

The ADuM5020/ADuM5028 were tested in a 10m half-wave anechoic chamber according to the CISPR22/EN55022 test guidelines. As specified by the standard, the ADuM5020/ADuM5028 evaluation PCB is placed on a non-conductive bench 10m away from the antenna calibration point. Make sure that there are no other conductive surfaces near the device under test (DUT), and no external equipment, metal planes, or cables that could interfere with the DUT’s radiated emissions testing. Also to test the ADuM5020/ADuM5028 evaluation boards, use a battery with an on-board low dropout regulator to keep the supply current loop small and eliminate unnecessary wiring.

Designing high-voltage isolated power supplies in this way easily achieves compact, low-EMI goals

Image and evaluation PCB of 10 m test room

The test results show that the ADuM5020 has passed the CISPR22/EN55022 test with a margin of more than 5dB when the output power is 5V (500mW) and the load is 100mA. This level of margin can provide great flexibility for design.

Designing high-voltage isolated power supplies in this way easily achieves compact, low-EMI goals

ADuM5020 meets CLASS B @ 100 mA load

Summarize

In today’s life-critical applications, smaller, lighter solutions are required while providing reliable high voltage protection for people and equipment. ADI’s next-generation isoPower family of products provides radiated emission suppression technology that meets EN55022/CISPR22 Class B requirements without bypass capacitors, making them ideal for compact, cost-effective isolation designs.

The Links:   MG50J2YS40 SKKH330-08E

“In equipment applications such as medical or industrial plants, protecting personnel and equipment from high voltages is critical: wired patient monitors require continuous operation during defibrillation, and the associated high voltage transients can be a heavy burden; precise handling Modern high-speed communications used by robotic arms are subject to electrical noise interference from arc welding…