Latching Relay

Many relay switch types require a continuous current or voltage input to maintain their current position. Latching relays, on the other hand, stay in their last energized state even after power is removed from the operating coil.

Learn more about latching relays, including how they work, types, and applications.

Types

There are a few main types of latching relay, including twin-coil, single-coil and bi-stable. A twin-coil type uses a magnet, coils and an iron core to retain the contacts in their operating position. A pulse to one coil turns the relay on, and a pulse to the opposite coil turns it off. This kind of relay is often used in Arduino projects.

A bi-stable latching relay has a remanent magnetic core that holds the contacts in their operating position, but needs a current pulse of opposite polarity to change them. This kind of relay is useful for applications where the contacts are likely to be changing frequently.

Latching relays do not require continuous current to hold their positions, which makes them more energy efficient than other switch types. This is especially important in situations where the relay is going to be in use for a long period of time, or when the switch is re-energized after each manual instruction.

The circuit wiring for a latching relay is very simple and easy to follow. A normally open (NO) button or contact is connected to connection A and a normally closed (NC) button or contact is connected to connection B. When the ‘Set’ button is pressed, the relay coil is energized and closes contact A to contact B. This remains the case until button-1 is pushed again. Latching relays are also able half bridge gate driver to’memorize’ which position they last were in, so they don’t need to be manually re-energized to return to that position.

Applications

Latching relays are used in electronic devices as a simple solution for switching high current loads. They have lower power consumption than conventional electromagnetic relays and can operate very quickly. They also tend to be less bulky and offer a longer lifespan. Latching relays can be used for many different applications, including home and office security systems.

The relay works by drawing a current from its operating coil through its contacts when it is energized. This current causes the armature IC VIDEO processing to be drawn against a spring tension and changes the state of the contact. The armature then stays in this new state until the supply of current from the operating coil is interrupted or reversed in polarity.

When the ‘Set’ switch is depressed, the armature of the relay will be pulled towards the operating coil against the spring tension, changing its state. Once the ‘Reset’ switch is pressed, the armature will be drawn away from the operating coil and the contacts return to their initial position.

This type of relay can be useful in battery-operated devices where continuous current is not an option. Conventional relays require a continual holding current to retain their operated states, which can be wasteful and cause a significant amount of heat. With a latching relay, only an opposite impulse or a small duration signal is needed to change the relay’s state. This provides energy savings and reduces overall cost.

Benefits

Latching relays are preferred by users that need the relay to remember its position and state and not switch to another position unless instructed to do so. This means no power is drawn whilst the relay is in its’set’ state and this can help to prevent heating from the coil and also reduce the risk of high power signals being routed to sensitive equipment.

The switching action of these devices tends to be more rapid and less bulky than that of mechanical relay switches and they can also offer a longer lifespan as their physical movement is very limited. They also require just one pulse of coil current to move the contacts in a single direction and only a brief change of the polarity of the applied voltage to reset them.

Latching relays can be supplied with various mounting options, including a printed circuit board (PCB) mount, panel mount or DIN rail mount. This means they can be integrated seamlessly into existing systems to achieve the desired functionality without compromising on space or cost. These units are available with either single or dual coils and can be powered by a wide range of input voltages. They are also highly reliable and can withstand repeated switching cycles. This makes them an ideal replacement for contactors in lighting circuits as they are more energy efficient than their metal counterparts.

Manufacturers

A number of manufacturers produce a range of latching relays. Among these are Panasonic, which may be more closely associated with consumer electronic ‘infotainment’ devices than industrial control equipment but also produces a wide range of other electromechanical switching products and components, including the latching relays. Another is TE Connectivity, which provides highly engineered connectivity, sensing and switching products to help power electric vehicles, digital factories, smart homes and efficient utility networks.

A standard electro magnetic relay operates by drawing armature current across one or more operating coils to move its contacts from open to closed state and vice versa. Once the contacts reach their operated position, a permanent magnet force holds them there, even if the operating coil is disconnected. A switch to an alternate coil re-energizes the armature to restore the original open or closed contacts, but these remain on or off until reset manually or through some other arrangement.

A key benefit of using a latching relay in place of a contactor within a lighting circuit is that no power is drawn whilst the relay contacts are held on or off. This can save 2W of energy for every relay, per year. A relay that is able to check its own contact status (as opposed to using an external auxiliary switch) can be even more energy efficient as this can reduce the amount of power needed to keep a relay or contactor in its operated position.