Transistor Switch

collector current is proportionally limited by its base current => current controlled switch
operating between cutoff and saturation
current move against direction of emitter arrow
advantage: small switch controlling high current load, true amplifier relatively low power signal to control a relatively large amount of power (actual power is from a source not the transistor signal current)
phototransistor which transitions when light in the near-infrared range (700nm - 1100nm) is detected by the phototransistor
called amplifier bz small current controlling large current
disconnected as the light is used to enable the current flow through the phototransistor. In some instances the base may be biased to set the required operating point.

Common Emitter transition from high state to a low state
Output created by connecting a resistor between supply and collector.
The output voltage is read at the terminal of the collector.
For three pin: base is input, collector is output, and emitter is common to both eg (attached to ground)



Common Collector transition from low state to a high state
output created by connectina a resistor between te emitter pin of the component and ground
output read at emitter terminal



Amplifier circuit load resistor is used to set the operation mode when no base connection is given
resistor value of 5kΩ or higher is adequate to operate the phototransistor in the switch mode.The high level output voltage in the switching mode should equal the supply voltage. The low level output voltage in the switching mode should be less than 0.8 Volts.

"Linear" or Active Mode the phototransistor generates a response proportional to the light received by the component up to a certain light level. When the amount of light surpasses that level, the phototransistor becomes saturated and the output will not increase even as the light level increases. used for light comparison
V_CC > R_L * I_CC

Switch Mode phototransistor will either be ”off” (cut-off) or ”on” (saturated) in response to the light. for detecting objects, sending data or encoder sensing
V_CC < R_L * I_CC

Links

Design Fundamentals for Phototransistor Circuits: http://www.fairchildsemi.com/an/AN/AN-3005.pdf
Phototransistor Symbol and Circuit Configurations: http://www.radio-electronics.com/info/data/semicond/phototransistor/photo-transistor-circuits-symbols.php
Basic Design ideas for emitters and sensors: http://www.er-online.co.uk/minisumo/pdf/App%20Note%20213.pdf
Phototransistor switching time analysis: http://www.cel.com/pdf/appnotes/an3009.pdf
Photodiodes and Phototransistors: http://hades.mech.northwestern.edu/index.php/Photodiodes_and_Phototransistors
Phototransistor and IRED: http://www.hofoo.com.cn/uploadfiles/phototransistor-ired%20data%20book.pdf
Temperature Compensation
Using Lamp: http://www.vishay.com/docs/80085/measurem.pdf
Using Current Source: www.avagotech.com/docs/5963-7544EN
Temperature compensation built-in IC: (for project EE SY410 (Light on model)) http://www.omron-ap.com/FAQ/FAQ01127/index.asp

Connecting Optoreflective Sensor

emitter = LED, sensor or detector = phototransistor
assembly for good photo-coupling

Power LED:

• forward voltge (change with desired current and ambient temperature) V_f = minimum voltage required to turn on OPTEK Tcchnology OP240 1.8v
• forward current (select a safe range typically) I_f OPTEK Tcchnology OP240 20mA
  
  • current is typically controlled by current limiting resistor (either on cathode side or anode side, calculate remaining voltage drop and power dissipated
    
    

Pulse Driven

R_D = (V_CC - V_LED - V_CE) / I_D
V_CE (Collector-Emitter Saturation Voltage) = 0.4V
V_LED 1.8V
V_CC 1.9V pulsed output from 3.1V
I_D current through resistor 20mA
R_D = - 0.3/20m (negative value) so V_cc should be increased so that R_D = 0 (no power wastage) => requires additional 0.7V

R_L = (V_CC - V_CE) / I_L
R_L = (1.9 - 0.4) / 0.25m = 60 Ohm
P_RL= 0.25² * 60 = 37.5 mW

LED to pwm supply

• mbed pin voltage 3.1V, LED V_F = 1.8V => Duty Cycle = V_F / V_pin = 0.58064%
  • results in V_avg = 1.9V

Phototransistor:

• minimum I_C(on) OP550 0.25mA
• saturation voltage V_ce OP550 0.4V
  • Calculate R_C(min) = (V_CC - V_sat) / I_c(on)min
    
    

Phototransistor

emitter = LED, sensor or detector = phototransistor
assembly for good photo-coupling

R_C(min) = (1.8 - 0.4) / 0.00025 = 5.6 KOhm
R_C(min) = (1.9 - 0.4) / 0.00025 = 6 KOhm
P = I² * R_C = ) = 0.375 mW
Switch Mode
V_CC (1.9) < R_L * I_CC (1.5) 1.9 < Standard Resistor:
http://www.daycounter.com/Calculators/Standard-Resistor-Value-Calculator.phtml
SCHEMATICS - INFRARED EMITTER DETECTOR:
http://www.societyofrobots.com/schematics_infraredemitdet.shtml