5 Device Applications Where You’ll Need Zero-Crossing SSR

5 Device Applications Where You'll Need Zero-Crossing SSR


5 Device Applications Where You’ll Need Zero-Crossing SSR. A Solid-State Relay (SSR) is an electronic switching device that controls the external voltage, either AC or DC, and connects across control terminals. They work in the same fashion as an electromechanical relay. However, a solid-state electronic component does not possess any moving parts and serves a longer operational period.

The majority of SSR devices contain MOS transistors with functions such as power-handling capability, voltage ratings, and current ratings used in SSR devices that match the developments in power FET technologies.

How Do SSRs Work?

First, it is best to understand SSR functions and their types better. When applied to control voltage, solid state relays work by using the AC SSR output to activate at the first zero crossing of the line voltage. Now, let’s deep dive into the kinds of SSRs.

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Types Of Solid-State Relays

There are a few types of SSRs: Zero Switching SSR (ZS), Instant-on switching (IO), Peak Switching SSR (PS), DC Switching SSR (DCS), Low Noise SSR (LN), System Monitoring SSR (SM), Analog Switching SSR (AS) and the Full Cycle SSR (FC). So, let’s tackle them one by one.

Zero Switching SSR (ZS) Solid State Relays

The ZS relay works on the applied control voltage by utilizing the AC SSR output to activate at the first zero crossing of the line voltage. They are also utilized in numerous applications that require resistive loads (temperature controls) and control of items such as incandescent bulbs.

These are the most commonly used SSRS. A few of their contributions include plastic molding machines, soldering machines, and packing machines. They are prominent in the food processing industry as well. In addition, the flexibility of ZS SSRs allows them to be in interfacing resistive loads or even lighting installations. Lastly, ZS has a high surge current and voltage blocking capabilities that function optimally in most inductive and capacitive loads.

Instant-on switching (IO) Solid State Relays

In the Instant-on switching SSRs, the output activates immediately once a control voltage is applied. The relay can turn on anywhere along the AC sinusoidal voltage curve. It is the best tool for applications requiring fast response time and phase angle control.

Peak Switching SSR (PS)

The peak switching SSR operates on the power output activation during the first line voltage peak applied to the control voltage. Similarly, after the first half period of operation or the inductive load, the PS SSR functions much like the ordinary ZS relay.

DC Switching SSR (DCS)

The DC Switching SSR works through a power semiconductor following the control input status. It is for resistive and inductive loads, which then manage the DC motors and valves. Switching inductive loads is a prerequisite to interconnecting a freewheeling diode surplus voltage that equals the load for protection.

Low Noise SSR (LN)

The Low Noise SSR (LN) is used in light industrial environments and fulfills the generic emission standards. The semiconductor’s switching mode is controlled to the peak level of the zero-voltage turn-on, reducing the noise generated.

LN SSRs are best suitable for electromagnetic noise applications to avoid interference with other equipment. In addition, it can be used for resistive and inductive loads.

System Monitoring SSR (SM)

This one provides an alarm output in the event of a circuit failure for internal circuits that monitor line voltage, load current, SSR input status, and correction function of the SSR. It is designed for the detection of faulty system parts.

Analog Switching SSR (AS)

The Analog Switching (AS) SSR is equipped with a built-in synchronization circuit to achieve phase angle control. The resultant output is equal to the input voltage or input current that is linear and reproducible. Therefore, it is best for closed-loop applications.

Full Cycle SSR (FC)

The Full Cycle SSR uses an analog switching principle that ensures that complete rounds generated are evenly distributed. So, the number of changed cycles during a specified time is equal to the control input applied to the SSR.

What Is A Zero-Crossing SSR?

The Zero Voltage Control (Zero-Cross Solid State Relay) is when a power switching takes place only during the beginning of the alternation from the point of control. The power switching component is only allowed around the zero crossing area. These relays are preferably used for resistive or capacitive loads. It limits the network’s disturbance and increases the lifetime and the load.

Device Applications That Use Zero-Crossing SSR

Heating Elements

The use of solid state relays on heating elements enables high-precision and high-frequency temperature control, as seen on residential heating, infrared heating, commercial food processing machines, drying, thermoforming, and soldering equipment.

Motor Starting

Application in motor starting is based on accurate measurement of the startup time of the motor or the influx of the current generated during use. SSR with zero-crossing detection maintains the AC output waveform state until it crosses zero on its own. This is the time that it can be shut on or off safely.


Incandescent lamps, halogen lamps, and similar devices produce a large inrush of current. SSRs regulate the peak value of the inrush current to prevent it from exceeding half the resistance of the SSR. These are useful in cinemas and theaters, airport runways, office spaces, and street and roadways lighting.

Medical And Healthcare

SSRs control motors in hospital beds, examination tables, and rehabilitation equipment in medical and healthcare applications. Also, they aid in sterilizing equipment, incubators, and blood warming units.

HVACS In Buildings

Heating, ventilation, and air conditioning (HVAC) are system units that regulate the flow of heat, air, and ventilation in a building. HVACs systems demand high-efficiency rates. It requires using specific products and system architectures with advanced controls that will ensure energy efficiency.

Key Takeaways

Solid state relay use and application have revolutionized energy efficiency and control aspects. SSRs regulate incoming electrical voltage, whether AC or DC, that travels across distinct control terminals. The best part of using SSRs is that it has no movable parts, which is attributed to their long operational period. Finally, the inclusion of MOS transistors in SSR devices further enhances power-handling capabilities, voltage ratings, and current ratings.

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