Electronic Load Relay ELR or Solid State Relay SSR

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With the use of conventional relays and contactors, one automatically accepts the disadvantages of mechanical switching, such as contact chatter, corrosion, welding of the switching contacts and a limited service life. But there is an alternative, namely electronic switching by using so-called solid-state relays.

Electronic Load Relay ELR or Solid-State Relay SSR - How it works

Common names: Electronic Load Relay ELRSolid-State Relay SSR or Semiconductor relay.

As already indicated, the electronic load relay has no moving parts. If you want to understand the structure and operation, you should know:

  • An optocoupler is used to fulfill the condition of galvanic isolation between control and load circuit as well as potential-free switching.
  • To be able to switch a high power on the output side, an electronic actuator is required. This can be a transistor, if a DC voltage is to be switched, or a TRIAC, which is also designed for AC voltage as well as for higher power.
  • Often, these electronic load relays are already equipped with overvoltage protection and protection against negative voltage peaks, which occur when switching off inductive loads.

Below is a simplified circuit of a semiconductor relay:

Electronic Load Relay ELR, Solid-State Relay SSR - structure and function (simplified)

Electronic Load Relay ELR, Solid-State Relay SSR - structure and function (simplified)

The following comparison of the advantages and disadvantages of a solid-state relay versus an electromagnetic relay is intended to help you make your decision (without claiming to be complete):

Electromagnetic RelaySolid State Relay
+ high switching capacity
+ high insulation resistance
+ high blocking voltage
+ fast switching times
+ high switching frequencies
+ long service life
+ noiseless switching
+ safe operation in case of vibrations and shocks
- Voltage drop from approx. 0.4V up to approx. 1.4V

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