Solid state relay

Solid state relay

A solid state relay (SSR) is an electronic switch, which, unlike an electromechanical relay, contains no moving parts. The types of SSR are photo-coupled SSR, transformer-coupled SSR, and hybrid SSR. A photo-coupled SSR is controlled by a low voltage signal which is isolated optically from the load. The control signal in a photo-coupled SSR typically energizes an LED which activates a photo-sensitive diode. The diode turns on a back-to-back thyristor, silicon controlled rectifier, or MOSFET transistor to switch the load.

Operation

Voltage applied to the control line of an SSR causes the LED to shine on the photo-sensitive diode. This produces a voltage between the MOSFET source and its gate, causing the MOSFET to turn on. An SSR based on a single MOSFET, or multiple MOSFETs in a paralleled array works well for DC loads.

There is an inherent substrate diode in all MOSFETs that conducts in the reverse direction. This means that a single MOSFET can't block current in both directions. For AC (bi-directional) operation, two MOSFETs are arranged back to back with their source pins tied together. Their drain pins are connected to either side of the output. The substrate diodes then are alternately reverse biased in order to block current when the relay is off. When the relay is on, the common source is always riding on the instantaneous signal level and both gates are biased positive relative to the source by the photo-diode.

It is common to provide access to the common source so that multiple MOSFETs can be wired in parallel if switching a DC load. There is also commonly some circuitry to discharge the gate when the LED is turned off, speeding the relay's turn-off.

Advantages over mechanical relays

*SSRs are faster than electromechanical relays; their switching time is dependent on the time needed to power the LED on and off, typically on the order of nanoseconds
*Increased lifetime due to the fact that there are no moving parts, and thus no wear
*Clean, bounceless operation
*Decreased electrical noise when switching
*Can be used in environments where a spark must not be generated during turn-on
*Totally silent operation
*Smaller than a corresponding mechanical relay.

Disadvantages

*Fail short more easily than electro-mechanical relays
*Increased electrical noise when conducting
*Higher impedance when closed (-> heat production)
*Lower impedance when open
*Reverse leakage current when open (µA range)
*Possibility of false switching due to voltage transients
*Often more expensive than comparable electromechanical relays

Images

External links

* [http://www.geofex.com/Article_Folders/ampprot/dcprot.htm A DC Fault Protection Circuit for Audio Amplifiers]
* [http://zone.ni.com/devzone/cda/tut/p/id/4125 Solid State Relays]
* [http://www.power-io.com/library/appnotes/solid-state-relay-terminology.htm Solid state relay glossary of terminology]
* [http://www.crydom.com/support/tips/amIusing.htm Am I using the right heatsink?]
* [http://www.crydom.com/support/tips/story.htm Solid State Relays - The Inside Story]


Wikimedia Foundation. 2010.

Игры ⚽ Поможем написать курсовую

Look at other dictionaries:

  • Solid-State Relay —   [engl.], Halbleiterrelais …   Universal-Lexikon

  • solid-state relay — bekontaktė relė statusas T sritis automatika atitikmenys: angl. contactless relay; solid state relay; static relay vok. kontaktloses Relais, n rus. бесконтактное реле, n pranc. relais sans contacts, m …   Automatikos terminų žodynas

  • Solid state — may refer to:In science:*Solid state chemistry *Solid state physics *Solid state laser *Solid matterIn electronics:*Solid state (electronics) are circuits that do not contain relays, vacuum tubes or, more currently, moving parts. *Solid state… …   Wikipedia

  • Solid State (Elektronik) — Mit solid state (englisch für fester Zustand bzw. fester Aggregatzustand) bezeichnet man in der Elektronik Bauteile oder Geräte, bei denen anstatt Elektronenröhren oder mechanischer Teile Halbleiterbauteile zum Einsatz kommen, die mit Hilfe der… …   Deutsch Wikipedia

  • Solid State Relais — Ein Relais [ʁəˈlɛː] (Pl.: Relais [ʁəˈlɛːs]) ist ein durch elektrischen Strom betriebener, meist elektromagnetisch wirkender, fernbetätigter Schalter mit in der Regel zwei Schaltstellungen. Das Relais wird über einen Steuerstromkreis aktiviert und …   Deutsch Wikipedia

  • Solid State Interlocking — (SSI) is the brand name of the first generation processor based interlocking developed in the 1980s by British Rail, GEC General Signal and Westinghouse Signals Ltd in the UK. Interlocking hardware SSI utilises a 2 out of 3 architecture, whereby… …   Wikipedia

  • Relay — This article is about the electrical component. For other uses, see Relay (disambiguation). Automotive style miniature relay, dust cover is taken off A relay is an electrically operated switch. Many relays use an electromagnet to operate a… …   Wikipedia

  • Digital protective relay — In electrical engineering of power systems, a digital protective relay uses a microcontroller with software based protection algorithms for the detection of electrical faults. Such relays are also termed as microprocessor type protective relays.… …   Wikipedia

  • contactless relay — bekontaktė relė statusas T sritis automatika atitikmenys: angl. contactless relay; solid state relay; static relay vok. kontaktloses Relais, n rus. бесконтактное реле, n pranc. relais sans contacts, m …   Automatikos terminų žodynas

  • static relay — bekontaktė relė statusas T sritis automatika atitikmenys: angl. contactless relay; solid state relay; static relay vok. kontaktloses Relais, n rus. бесконтактное реле, n pranc. relais sans contacts, m …   Automatikos terminų žodynas

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”