Understanding the Difference Between Latching and Non-Latching Relays

Relays remain a foundational component in modern electronic systems, enabling reliable control of circuits across industrial, commercial, and consumer applications. From HVAC systems and smart infrastructure to industrial automation and power management, relays provide a simple yet effective way to switch loads and isolate control signals. As system requirements continue to evolve toward greater efficiency and reliability, selecting the appropriate relay type has become increasingly important.

A non-latching relay remains activated only while current is continuously applied to its coil, whereas a latching relay holds its position even after power is removed. Because of these distinct operating principles, each relay type is better suited to specific applications. Understanding how and when to use each option allows engineers to optimize both performance and energy usage within their designs.

Both relay types play essential roles across industries, and Same Sky supports a wide range of relay solutions. This article outlines their core differences, advantages, limitations, and practical implementation guidance.

Relay basics: a quick refresher

Before comparing relay types, it helps to revisit how electromechanical relays function. A typical relay includes:

• A coil that generates a magnetic field when energized
• An armature that moves to open or close contacts
• A spring that returns the armature to its default position in non-latching designs

Contact configurations vary, including SPST (single-pole single-throw) and SPDT (single-pole double-throw) arrangements, allowing flexibility in circuit design. Because relays rely on mechanical motion, switching is not instantaneous. Several timing characteristics influence performance:

• Operate time: Delay between coil energization and contact movement
• Release time: Time required to return to the default state after power removal
• Contact bounce: Rapid, brief fluctuations during switching
• Minimum pulse width: Shortest pulse required to reliably actuate the relay

These parameters become especially important in fast-switching systems and in designs using latching relays.

Non-latching relays explained

Non-latching relays, also called monostable relays, have one stable state and depend on continuous coil current to stay actuated. When power is removed, the internal spring returns the contacts to their original position.

This behavior makes them a strong choice for safety-focused systems that must default to a known state during power loss. They are also easy to implement, as the drive circuitry is relatively simple and cost-effective. However, continuous coil energization increases power consumption. Over time, this can lead to heat buildup in the coil, which may impact longevity if not properly managed.

Figure 1: Cross-section of a typical non-latching relay. (Image source: Same Sky)

Latching relays explained

Latching relays, or bistable relays, retain their last switched state without requiring continuous power. They achieve this using either a permanent magnet or a mechanical latch to hold the armature in place. A short electrical pulse is used to change states.

This design offers significant efficiency advantages. Because the coil is only energized briefly, standby power consumption is minimized and thermal stress is reduced. Latching relays are especially valuable in applications where maintaining state during power interruptions is critical.

That said, these benefits come with trade-offs. Drive circuitry is more complex, particularly for single-coil designs that require polarity reversal. Additionally, designs that rely on permanent magnets may be sensitive to overcurrent or mechanical shock, which can affect reliability.

Figure 2: Cross-section of a typical latching relay. (Image source: Same Sky)

Within latching relays there are single-coil and double-coil latching designs, which both maintain their position without continuous power, but differ in how they are controlled.

• Single-coil designs use one coil for both setting and resetting the relay. Switching states require reversing the polarity of the applied voltage.
• Double-coil designs use two separate coils—one for setting and one for resetting.

While double-coil relays require additional pins and slightly more space, they simplify control circuitry by eliminating the need for polarity reversal.

Comparing latching and non-latching relays

Table 1 quickly summarizes the primary differences between the two relay types.

Table 1: Key differences between common relay designs. (Image source: Same Sky)

Best practices for reliable relay integration

Even high-quality relays require proper design practices to ensure long-term reliability. Thoughtful implementation can significantly improve system performance and lifespan.

For non-latching relays using DC coils, adding a flyback diode across the coil is essential. This helps suppress voltage spikes generated during de-energization, protecting surrounding electronics. Managing inrush current is also important, particularly when switching capacitive or magnetizing loads, which can draw large current surges at turn-on.

For latching relays, precise control of the actuation pulse is critical. In single-coil designs, using a dedicated driver IC or an H-bridge can simplify control and ensure consistent operation. Pulse timing must be carefully managed. Pulses that are too short may fail to actuate the relay, while overly long pulses waste energy and increase thermal stress. In applications exposed to vibration or shock, additional mechanical considerations may be necessary to prevent unintended switching.

General best practices apply to both relay types. These include derating contact loads, ensuring proper thermal management, and selecting sealed designs when operating in harsh environments with high humidity or dust.

Choosing the right relay for your application

Selecting between latching and non-latching relays starts with understanding system requirements. Key considerations include coil voltage, current availability, contact ratings, and environmental conditions. Proper derating should always be applied to avoid operating components at their maximum limits.

To simplify selection, consider these guiding questions:

• Should the system return to a default state after power loss? Non-latching
• Must the relay retain its state during power interruption? Latching
• Is minimizing standby power critical? Latching
• Is simple drive circuitry a priority? Non-latching

Conclusion

Choosing between latching and non-latching relays involves balancing efficiency, controlling complexity, and application requirements. Non-latching relays provide straightforward operation and inherent fail-safe behavior, while latching relays offer reduced power consumption and state retention.

Same Sky’s portfolio includes both relay types, giving engineers flexible options to meet a wide range of design needs. This includes signal relays for low-level current switching and power relays for high-level current switching.