- Silicon-controlled rectifier
A silicon-controlled rectifier (or semiconductor-controlled rectifier) is a four-layer solid state device that controls current. The name "silicon controlled rectifier" or SCR is
General Electric's trade name for a type of thyristor. The SCR was developed by a team of power engineers led by Gordon Hall and commercialised by Frank W. "Bill" Gutzwiller in 1957.
Theory of operation
An SCR is a type of
rectifier, controlled by a logic gatesignal. It is a four-layer, three-terminal device. A p-type layer acts as an anodeand an n-type layer as a cathode; the p-type layer closer to the n-type(cathode) acts as a gate.
Modes of operation
In the normal "off" state, the device restricts current to the leakage current. When the gate to cathode voltage exceeds a certain threshold, the device turns "on" and conducts current. The device will remain in the "on" state even after gate current is removed so long as current through the device remains above the
holding current. Once current falls below the holding current for an appropriate period of time, the device will switch "off".
If the applied voltage increases rapidly enough,
capacitive couplingmay induce enough charge into the gate to trigger the device into the "on" state; this is referred to as "dv/dt triggering." This is usually prevented by limiting the rate of voltage rise across the device, perhaps by using a snubber. "dv/dt triggering" may not switch the SCR into full conduction rapidly and the partially-triggered SCR may dissipate more power than is usual, possibly harming the device.
SCRs can also be triggered by increasing the forward voltage beyond their rated
breakdown voltage(also called as breakover voltage), but again, this does not rapidly switch the entire device into conduction and so may be harmful so this mode of operation is also usually avoided. Also, the actual breakdown voltage may be substantially higher than the rated breakdown voltage, so the exact trigger point will vary from device to device.
SCRs are made with voltage ratings of up to 7500 volts, and with current ratings up to 3000 RMS amperes per device. Some of the larger ones can take over 50 kA in single-pulse operation. SCRs are used in
power switching, phase control, chopper, battery chargers, and inverter circuits. Industrially they are applied to produce variable DC voltages for motors (from a few to several thousand HP) from AC line voltage. They control the bulk of the dimmersused in stage lighting, and can also be used in some electric vehicles to modulate the working voltage in a Jacobson circuit. Another common application is phase control circuits used with inductive loads. SCRs can also be found in welding power supplies where they are used to maintain a constant output current or voltage. Large silicon-controlled rectifer assemblies with many individual devices connected in series are used in high-voltage DC converter stations.
Two SCRs in "inverse parallel" are often used in place of a
TRIACfor switching inductive loads on AC circuits. Because each SCR only conducts for half of the power cycle and is reverse-biased for the other half-cycle, turn-off of the SCRs is assured. By comparison, the TRIAC is capable of conducting current in both directions and assuring that it switches "off" during the brief zero-crossing of current can be difficult.
Typical electrostatic discharge (
ESD) protection structures in integrated circuits produce a parasitic SCR. This SCR is undesired; if it is triggered by accident, the IC can go into latchupand potentially be destroyed.
* [http://www.allaboutcircuits.com/vol_3/chpt_7/5.html SCR at AllAboutCircuits]
Wikimedia Foundation. 2010.
Look at other dictionaries:
silicon controlled rectifier — valdomasis silicio lygintuvas statusas T sritis radioelektronika atitikmenys: angl. silicon controlled rectifier vok. gesteuerter Siliziumgleichrichter, m rus. кремниевый управляемый выпрямитель, m pranc. redresseur commandé à silicium, m … Radioelektronikos terminų žodynas
silicon-controlled rectifier — (SCR) Electronic semiconductor which contains silicon. Controls current by timing pulses … Dictionary of automotive terms
silicon-controlled rectifier — noun a form of thyristor … Wiktionary
silicon-controlled rectifier — /ˌsɪləkən kəntroʊld ˈrɛktəfaɪə/ (say .siluhkuhn kuhntrohld rektuhfuyuh) noun a type of semiconductor switch often used in control circuits; thyristor. Abbrev.: SCR … Australian English dictionary
SCR — silicon controlled rectifier … Australian English dictionary
SCR — • silicon controlled rectifier • Special Casualty Representative (P&I) … Maritime acronyms and abbreviations
Diode — Figure 1: Closeup of a diode, showing the square shaped semiconductor crystal (black object on left) … Wikipedia
Vacuum tube — This article is about the electronic device. For experiments in an evacuated pipe, see free fall. For the transport system, see pneumatic tube. Modern vacuum tubes, mostly miniature style In electronics, a vacuum tube, electron tube (in North… … Wikipedia
Thyristor — The thyristor is a solid state semiconductor device with four layers of alternating N and P type material. They act as bistable switches, conducting when their gate receives a current pulse, and continue to conduct for as long as they are forward … Wikipedia
Opto-isolator — This article is about the electronic component. For the optical component, see optical isolator. Schematic diagram of an opto isolator showing source of light (LED) on the left, dielectric barrier in the center, and sensor (phototransistor) on… … Wikipedia