Do solid state relays need resistors?

Do solid state relays need resistors?

Optocouplers and Solid-State Relays When using logic drive, an input resistor is usually required to limit current through the control LED to a recommended value. The recommended operating current for most SSRs is between 1 mA and 20 mA depending upon the application.

When would you use a solid state relay?

The most common application of solid state relays is in the switching of an AC load, whether that is to control the AC power for ON/OFF switching, light dimming, motor speed control or other such applications where power control is needed, these AC loads can be easily controlled with a low current DC voltage using a …

How is a solid state relay ( SSR ) different from a mechanical relay?

A Solid State Relay (SSR) is a re lay that does not have a moving contact. In terms of operation, SSRs are not very different fr om mechanical relays that have moving contacts. SSRs, however, employ semiconductor switching elements, such as thyristors, triacs, diodes, and transistors.

What are the shortcomings of solid state relays?

Lets say that the main shortcoming of SSRs in a design is that they generate more heat than an equivalent relay. Similarly, the main shortcoming of relays in the design is that they are at risk of mechanical failure due to arcing between the contacts every time they turn on.

What causes a relay to change its state?

Switching a relay during a peak in the mains voltage also causes an electric arc between the relay terminals, wearing them down and contributing to the mechanical failure of the relay. When using an SSR that supports zero-crossing detection, it will maintain its state until the AC output waveform crosses zero on its own.

How does a triac solid state relay work?

Second, a triac, silicon controlled rectifier, or MOSFET that switches the mains power using the output from the optocoupler. Finally, there is usually (but not always) a ‘zero-crossing detection circuit’. This causes the relay to wait until the current it is controlling reaches zero before shutting off.