Light Activated SiliconControlled Rectifier LASCR

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Light Activated Silicon-Controlled
Rectifier(LASCR)

• Louella V. Tapongot

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LASCR

• it is an SCR whose state is controlled by the
  light falling upon a silicon semiconductor layer
  of the device.

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Basic Construction of LASCR
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Symbols
Anode
Anode
Gate
Gate
Cathode
Cathode
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• Some of the areas of application for the LASCR
  include optical light controls, relays, phase
  control, motor control and a variety of computer
  application
• The maximum currents (rms) and power (gate)
  ratings for LASCRs commercially available today
  are about 3A and 0.1W.
• One interesting application of an LASCR is in the
  AND and OR circuits

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AND
Load
LASCR1
Supply
LASCR2
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OR
Load
LASCR1
LASCR2
Supply
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• The LASCR is most sensitive to light when the
  gate terminal is open. Its sensitivity can be
  reduced and controlled somewhat by the insertion
  of the gate resistor.
• It is the semiconductor analog of the
  electromechanical relay.
• It offers complete isolation between input and
  switching element.
• The energizing current can be passed through a
  light-emitting diode or a lamp.

Ac or dc input
Dc input
S1
load
dc
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• The incident light will cause the LASCR to turn
  on and permit a flow of charge through the road
  as establish by the Dc supply. The LASCR can be
  turned off using the reset switch.
• This system offers the additional advantage over
  an electromechanical switch of long life
  microsecond response, small size, and the
  elimination of contact bounce.