What is Latching Switch : Working & Its Applications

Generally, switches are categorized into two types based on performance & holding current conditions like latching and non-latching. There are different kinds of switches under different categories like electronic, normally open, normally closed, momentary, etc. The working of latching and non-latching switches are; once a latching switch is activated, it stays on until the pressure is disabled or removed whereas a non-latching switch turns ON only when pressed and turns OFF when removed. At present, most of the devices use these switches. This article discusses an overview of a latching switch – working with applications.

What is a Latching Switch?

A latching switch definition is; a switch that doesn’t require continuous compression to stay on. These types of switches are used in the home for light switches, on stereos, or central heating switches. The latching switch symbol is shown below.

As compared to other switches, these switches are turned ON and operate simply even after the pressure is removed on the switch. These switches are primarily used in alarms. Whenever alarms are activated, they stay on for an indefinite period, until the entire system is deactivated. These switches are normally made with metal or plastic material. These switches are available in a wide range of models, which are power-driven either by latching action.

How Does a Latching Switch Work?

The working of a latching switch is, once the pressure is applied on this switch, then it will be turned ON and it will be turned OFF unless the pressure is applied again to the switch by the user. So, these switches will be activated by the operator & then stay on until turned off again by the operator.

Latching Switch Circuit

The latching switch wiring using a transistor is shown below. This circuit can be built using different electronic components like 5V to 12V battery, PNP 2N4403 transistor, NPN 2N4401 transistor, relay, 1N4007, resistors like 1K, 10K, and 4.7K -2.

A latching circuit locks its output once an input signal is applied & keeps that position even after the input signal is detached. So this position will stay for an indefinite time until the power is reset otherwise some exterior signal is given to turn it off.

This circuit is very similar to Silicon Controlled Rectifier and is used whenever silicon controlled rectifier is not available. This circuit is applicable in alarm circuits. If the switch is triggered once, then the buzzer will generate a sound until someone removed the power manually.

In this circuit, the latch function can be performed by using transistors like 2N4401& 2N4403. Here, a relay switch is used at the o/p to control desired electronic device or application.

Working

This simple latching circuit can be operated with a 5V to 12 battery. In this circuit, two transistors are used NPN 2N4401 transistor denoted with Q1 and PNP 2N4403 transistor denoted with Q2. Once an input signal is provided at the base terminal of the Q1transistor, then this transistor will start conducting so that it connects the Q2 transistor’s base terminal to the ground. Thus, the Q2 transistor also starts conducting to enable the relay which is connected to the Q2 transistor’s collector terminal.

Here, a 4.7K resistor is connected from the Q2 transistor’s collector terminal to the Q1 transistor’s base terminal. So at the base terminal of the Q1 transistor, it provides a feedback voltage, to make the Q1 transistor continuously conduct until the power supply is detached. A 1N4007 diode in this circuit is mainly used for protecting from reverse current & voltage sparks.

This circuit is used in widespread applications like fire alarms, burglar alarms, and security systems for car theft and is used instead of SCR.

Types of Latching Switch

These switches are available in four types SPDT, DPDT, DPST, and SPST where each type and its specifications are discussed below.

SPST Latching Switch

These switches work with a 2A 250VAC rating and their operating life is up to 50,000 times compared to other switches. These types of switches are very famous for use in ticket dispensers, electronic kiosks & industrial-based applications.

The main features of this switch are; that they are made with metal, they are available waterproof, work in harsh conditions like -40C～+70C, avoid the penetration of dust, water, dirt, etc. These are corrosion-resistant and non-magnetic for indoor & outdoor utilization.

SPDT Latching Switch

This is one kind of latching switch and its specifications mainly include the following.

• The operation of the switch is latching.
• The mounting type is panel mount.
• The configuration of contact is SPDT (Single Pole Double Throw).
• The cutout size of the panel is 19.1 mm.
• The IP rating is IP67.
• The voltage rating is 250/125V ac.
• The current rating of contact is 16 A, 26 A.
• The shape of the actuator is flat.
• The type of actuator is a push button.
• The type of terminal is quick to connect.

DPDT Latching Switch

These switches are available with a high operating force so used in different foot control applications. The specifications of the DPDT switch mainly include the following.

• Switch operation is latching.
• The mounting type is PCB.
• Contact configuration is DPDT (Double Pole Double Throw).
• The cut-out size is12.2 mm.
• The diameter of the panel cut out is12.2mm.
• The current rating of contact is 2 A, 4 A.
• The shape of the actuator is the cylinder.
• DC voltage rating of contact is 12 V, 24 V.
• The type of terminal is solder lug.
• The type of actuator is a plunger cap.
• The voltage rating is 250V / 125V.

DPST Latching Switch

These switches are available with nonilluminated and suitable to use in Class II appliances. These switches include silver contacts with different switching formats. These switches are protected with a transparent cover from water ingression, dust, etc. The specifications of this switch include the following.

• Switch operation is latching.
• The type of mounting is panel mount.
• DPST contact configuration.
• The cut-out size of the panel is 30 x 22mm.
• An IP rating is IP40.
• The color of the actuator is green.
• The voltage rating is 230V ac.
• The current rating of contact is 16 A at 250 V ac.
• The shape of the actuator is rectangular.
• The type of terminal is a tab.

Momentary Switch Vs Latching Switch

The difference between a momentary switch and a latching switch includes the following.

Advantages

The advantages of the latching switch include the following.

• These switches are available in small sizes.
• It has a high load capacity.
• These are reliable, and secure including long service life.
• It replaces crossbar switches.
• It gives more comfort in control.
• It provides silent continuous operation.
• It requires very less time to connect to any device.

Disadvantages

The disadvantages of latching switch include the following.

• These are mainly used for low-risk applications where it would be extremely not convenient for the user to apply pressure manually to maintain the switch on. So it would be highly unsuitable to wait for a light switch to switch on.
• These switches are operated only manually.

Applications

The applications of latching switches include the following.

• The common application of this switch is a light switch.
• These switches are also used in different applications like computers, TV, and other electrical devices.
• These types of switches work in different ways, so suitable for different applications.
• Generally, these switches are used in the homes like light switches, on stereos, or central heating switches.
• These are used in different industries for spa operations & tattoo machines.
• Many devices function with latch switches, thus they have extensive application in different circuits.
• These are used in SCR circuits.

Thus, this is all about an overview of a latching switch – working with applications. This switch will stay in its place until pushed and it will not go back to its original condition until pushed again. These switches are also called maintained switches. Here is a question for you, what is a relay switch?