Question

1)What is the LDR sensor and what is the effect of light on this device?

2)Name 4 physical phenomena that light can have on some devices, so these devices can be used as light sensor.

3)What is the main difference in structure of PIN Photodiode and standard PN photodiode (photovoltaic cell)? What is the advantage of PIN over PN?

Answer 1

1) LDR means Light Dependent Resistor. So, LDR has a variable resistance which changes with the amount of light falling on it. The value of the resistance decreases with increase in light intensity. Typical values of LDR varies from few hundred ohms (with bright light) to few Mega ohms (with no light). LDR sensor is mainly used as lighting switch.

2) Automatic street lights, To detect intrusion into rooms is one of the security application, security alarm system by photo electric sensor are important applications of LDR.

Photo Voltaic light sensor (Solar cell), Photo diodes (Infrared in remotes), Proximity light sensors, Photo Resistors, Photo conductive cells, Avalanche photo diodes etc

3) PN photodiode & PIN photodiode are the most common formats for photo diodes. A PIN-diode has a barrier height that is the same as for a PN-diode with the same doping concentrations for P and N-regions. A PIN-diode has a wider depletion region, so it has lower capacitance. The electric field is also weaker in a PIN diode due the wider depletion region which implies the breakdown voltage is larger.

The reveres bias in PIN photo diode offers better performance for high dynamic range applications. Also offers better performance for high bandwidth applications.