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What is Operational Amplifier? Operational Amplifier is an electronic devices which amplifies small ac or dc signal and perform basic operation as addition, subtraction multiplication and so on. Fig. Operational amplifier (LM741)
Operational Amplifier Op Amp has 2 inputs Voltage Output Inverting Input +V _ Vin1 V out + V in2 -V Non-Inverting Input Inverting Input- the input where output will change to the opposite sign. Non-Inverting Input- the input where output will not change to the opposite sign.
Operational Amplifier Op Amp has voltage supply, +V and -V Positive (+) supply voltage +V _ Vin1 V out + V in2 -V Negative (-) supply voltage
What is the use of Operational Amplifier? Operational Amplifier -amplifies small AC or DC Signal. Operational Amplifier can also do basic operation : add, subtract, multiply (amplify) etc.
+V V out _ Vin1 + V in2 V out = A x (Vin2 – Vin1) -V Gain (A) = V out V in Open Loop Gain = 100,000 x
Op Amp as Comparator. Op Amp compares Vin1 and Vin2: If Vin 2 > Vin1 therefore: V out = +V If Vin1 > Vin2 V out = -V
Op Amp as Comparator. Op Amp compares Vin1 and Vin2: If Vin 2 > Vin1 therefore: V out = +V If Vin1 > Vin2 V out = -V Example: The +V= 15V and; If Vin1= 4mV and –V = -15V Vin2 = 6 mV Therefore: Vin2 > Vin2 So, Vout= 15V
Other uses of Op Amp. Inverting Amplifier Non inverting amplifier Summing Amplifier Differential amplifier Voltage follower Integrator Differentiator
Revision Question ________________is an electronic devices which amplifies small ac or dc signal and perform basic operation as addition, subtraction multiplication and so on. ________________- input of Op Amp where the output is changed to opposite sign. ________________ the open loop gain of Op Amp. ________________ use of an Op Amp with no feedback. where it compares Vin2 and Vin2. ________________ the arrangement of Pin of an integrated circuit of IC. ________________is the Pin number of the output of a LM741 operational amplifier.
Project- automatic fan controller Do you understand now the purpose of the operational amplifier in this circuit? Answer: To Compare input pin 3 and pin 2.
What is NTC? NTC is a Thermistor or Thermal Resistor that converts Temperature to Change in Resistance. It has two (2) types; NTC and PTC NTC – Negative Temperature Coefficient. As temp increses, resistance Decrease. PTC – Positive Temperature Coefficient. As tempincrease, resistance increases. Resistance , ohm Resistance , ohm Temperature, deg C Temperature, deg C NTC PTC
Voltage Divider… Vcc The voltage VC changes the resistance of the Thermistor changes. A R1 B VB = Vcc x RNTC . R1 + RNTC C
Revision Question ________________ a circuit that divided the voltage proportionally with the value of resistors connected in series. _______________ a thermal resistor that converts temperature in change in resistance. _______________ use of an Op Amp with no feedback. where it compares Vin2 and Vin2. ________________ the arrangement of Pin of an integrated circuit of IC.
Voltage Divider… Vcc Vc = Vcc x RNTC . R1 + RNTC A R1 B If R1 = 10,000 RNTC = 10,000 @ 30 deg C VB = 10V x ( 10,000/20,000) VB = 5V C
Voltage Divider… Vcc = 10V If R1 = 10,000 RNTC = 10,000 @ 30 deg C VB = 10V x ( 10,000/20,000) VB = 5V If RNTC = 8,000 @ 50 deg C VB = 10V x (8,000/ 18,000) VB = 4.44 V A R1 B C
Voltage Output IN THIS FIGURE ONLY So, if Vin2 > Vin3 = Vout = +12V The Vout = +12V will activate the Driver Transistors
What is Transistor? BJT? Transistor is derived from the combination of two words, “Transfer-Resistance”. It means that it is a device, which transfers a low resistance into a circuit having high resistance BJT - is a three-terminal semiconductor device, whose operation depends upon the flow of electric charge carriers within the solid.
Transistor ID. Low Power Small Packages Medium Power Medium Packages High Power big Packages
The base is 0.7V (or slightly more) positive of its emitter The base is 0.7V (or slightly more) positive of its emitter The base is 0.7V (or slightly more) positive of its emitter Transistor Action… • Its emitter is its negative terminal. • The collector is several volts positive of its emitter. • The base is 0.7V (or slightly more) positive of its emitter
Use of Transistor. • Transistor is used as: • Switch • Amplifier. Will Turn ON the Transistor Small Base Current
Transistor as switch… When switch is closed: Small base current is applied to the base. LED B is DIM (small current) Transistor is turned ON allowing emitter-collector current which is bigger. LED C will have a bright light (big current)
Voltage Output IN THIS FIGURE ONLY So, if Vin2 > Vin3 = Vout = +12V The Vout = +12V will activate the Driver Transistors
R Base So if the output of the OP Amp is Hi, it will provide base current to the transistor making it ON thus Energizing the Relay.
What is a Relay? Relay – an electrically operated switch. It is made of coil and set of contacts, NO NC.
AC power Supply Small Current Med Current R Base Big current
Conclusion We Learned About: Application of Semiconductor Devices: transistor diode, etc.. Learned the operation of transistor WE learn operational amplifier and it uses. We make use of LED as indicator of current.
