How To Design for Low EMI in Miniature HV Supplies

When developing sensitive electronic systems for aerospace, scientific, or analytical applications, electromagnetic interference (EMI) is a considerable obstacle. The interference disrupts systems and compromises data integrity.

Engineers and system designers can improve the performance of their sensitive equipment. Learning how to design for low EMI in miniature HV supplies is necessary to sustain system performance and reliability. From shielding and filtering to thoughtful component selection and layout, these strategies will help you create a more stable and reliable electronic environment.

What Are Miniature High-Voltage (HV) Supplies?

A high-voltage power supply converts a low-voltage input into a high-voltage output that can reach thousands of volts. These devices are fundamental components in a variety of advanced applications, including mass spectrometers, electron microscopes, and night vision systems. Miniature versions of these supplies are particularly valuable in compact and portable devices where space is at a premium.

A miniature high-voltage power supply is ideal for devices with size and weight constraints. Their compact nature, however, can intensify challenges related to heat management and electromagnetic interference, requiring careful design and integration.

Understanding EMI in HV Supplies

Electromagnetic interference is an unwanted disturbance that affects an electrical circuit due to either electromagnetic induction or radiation emitted from an external source. In high-voltage power supplies, the high switching frequencies and rapid voltage changes create an environment where EMI is a common issue.

The Sources of EMI

The primary sources of EMI in switching HV supplies stem from their core operation. High-frequency switching of transistors and diodes generates rapidly changing electric and magnetic fields. These fields propagate through conduction along wires and traces or radiate through the air as electromagnetic waves, interfering with nearby components and systems. Parasitic capacitance and inductance within the circuit components can also contribute to unwanted oscillations and noise.

The Effects of EMI

The effects of EMI range from minor disturbances to complete system failure. In sensitive analytical instruments, electromagnetic interference can manifest as noise in the output signal. This could lead to inaccurate measurements and flawed data.

In communication systems, it may reduce signal clarity and increase error rates. For military and aerospace applications, EMI poses serious operational risks because it can disrupt navigation and control systems. Therefore, mitigating electromagnetic interference is a key objective in system design.

Design Techniques for Low EMI

Achieving low EMI requires a multifaceted approach that addresses interference at its source and blocks its transmission paths. Effective design integrates shielding, filtering, grounding, and careful component selection to create a quiet electrical environment.

Shielding

Shielding is a primary defense against radiated EMI. It involves enclosing the power supply or sensitive components within a conductive barrier, typically made of metal like steel or aluminum. The enclosure blocks external electromagnetic fields and contains internal fields generated by the power supply.

Effective shielding will occur with a continuous enclosure. Any gaps, seams, or holes for cables will act as antennas that permit electromagnetic interference to leak.

Filtering

Filtering addresses conducted EMI, which travels along power lines and signal traces. Input and output filters, composed of inductors and capacitors, suppress noise. An LC filter—composed of inductors and capacitors—smooths out voltage ripples and blocks high-frequency noise from entering or leaving the power supply.

• Capacitors should have low equivalent series resistance (ESR) to effectively shunt high-frequency noise to the ground.

• Inductors provide high impedance to the noise frequencies while allowing the desired DC or low-frequency signals to pass.

• Ferrite beads are useful for attenuating high-frequency noise on power lines.

Grounding

A well-designed grounding scheme provides a low-impedance path for noise currents to return to their source, preventing them from circulating through sensitive parts of the circuit. There are three primary types of grounding methods used in electrical systems: fully grounded, high resistance grounding, and ungrounded.

Fully-Grounded Systems

Fully-grounded systems directly connect the neutral point of the electrical system to the ground. It’s a simple and reliable approach that provides a clear path for fault currents to flow directly to the earth.

Fully-grounded systems are common in residential, commercial, and industrial settings because they effectively limit voltages during faults and improve personnel safety.

However, they may lead to higher fault currents, which require robust protective equipment to manage.

High-Resistance Grounding

High-resistance grounding involves connecting the electrical system to the ground through a resistor. It limits the magnitude of fault currents, reduces the likelihood of equipment damage, and minimizes system disruptions.

This design is frequently used in industrial applications where equipment continuity is critical, like in power plants or manufacturing processes. Controlling fault currents allows a system to continue operating even during single-phase faults, although it requires effective detection and monitoring systems.

Ungrounded Systems

Ungrounded systems, in contrast, do not have a direct connection between the electrical system and the ground. Instead, the system floats, which limits fault currents to very low levels during single-phase faults.

While ungrounded systems reduce the risk of equipment damage in certain situations, they can cause voltage instability and make fault detection more challenging. These systems are typically reserved for specialized applications, such as aboard ships and in isolated industrial facilities, where maintaining continuous operation outweighs the risks.

Component Selection

The choice of components can have a significant impact on EMI generation. Diodes with soft recovery characteristics produce slower current changes, reducing high-frequency noise. Transistors with controlled switching speeds can also help lower emissions. Using components with low parasitic capacitance and inductance minimizes unwanted resonances that can create noise. Additionally, selecting components with built-in shielding can further reduce radiated EMI.

Layout Considerations

A printed circuit board (PCB) layout is a critical factor in managing EMI. The physical arrangement of components and traces determines the paths that currents take and the extent of electromagnetic field generation. Placing high-frequency components close together minimizes the length of current loops, reducing radiated emissions.

Power supply traces should be short and wide to minimize inductance and resistance. Keep high-current switching loops as small as possible. Route sensitive signal traces away from noisy components, like switching transistors and transformers. Using a multilayered PCB with dedicated ground and power planes provides a low-impedance path for return currents and excellent shielding.

Achieve Superior Performance With HVM Technology

Mastering the design of low EMI in miniature HV supplies allows for the creation of more stable and precise electronic devices. For those seeking advanced solutions, HVM Technology offers a range of components tailored for high-performance applications. We have products like miniature high-voltage power supplies. Visit our website to explore our offerings or contact us to discuss how we can assist with your next project.