An operational amplifier (op-amp) is a DC-coupled high-gain electronic voltage amplifier with a differential input and, usually, a single-ended output. (WIKIPEDIA)
Amplifier is a device which takes small voltage in input terminal and spits out large voltages in output terminal...
the gain of amplifier is the amount multiplied with input to produce the desired output...
for example if u take a 1V input and get 5v output then the gain of amlifier is =5
an OP-AMP has generally 5 important pins
i> inverting input
ii> non-inverting input
iii> +Vcc
iv> -Vcc
v> OUTPUT
in input terminal only use signals ...
OP-AMPS can't creat voltage out of nothing!!! so we have to use a bit larger supply volatage than the desired output voltage
so if i have to get a 10V oupput then i have to use atleast 12V supply voltages... dont try to apply high voltage it may damage your device so always reffer the DATA SHEET
if your supply voltage s very less then you will get clipped OUTPUTS
smooth voltage sources are important for a amplifier to give a uniform output signal so use two suopply batteries, hooked up in series with capacitors given below :
CLASSIC NON-INVERTING AMPLIFIER:
here we use a LM324 OPAMP with max current rating = 20mA
you can set the gain using resistors ...
the circuit diagram is given below
THE GAIN FORMULA :
for simplicity use R1=1k (fixed) and then choose R2 according to you gain......
CLICK HERE for the derivation of the gain formula ( find it in thr 9th page )
APPLICATION:
SPY-MICROPHONE
a simple small microphone has a output signal of 20mV
and to run a EAR-BUD we need atleast 2V
so gain must be 100
using gain fomula r2= 100k
so gain= 101 nearly equal to 100
OK TIME TO UNDERSTAND THE CIRCUIT BLOCK BY BLOCK :
BLOCK A
use 9V supply to power up the mic and use R1 to limit the current
BLOCK B
is a high pass filter and the capacitor blocks the supplied 9v DC and passes the signal
BLOCK C
r2 and r1 is set to a gain of 100
so in output pin we get a 2V signal
BLOCK D
10K variable resistor is used to change the supply voltage of LS(ear-bud) to control the volume
2V output is sufficient to run the earbuds but can't run a LOUD SPEAKER as a loudspeaker needs high power supply which will kill the LM324 ..... so i have googled for a home theater OPAMP and found LM1875 OPAMP, which is great for loud sounds in your home.....you can supply more voltages and use high valued resistors to get LOOUUDDDDD SOUNDDDDDD!!!!!!!!!! the circuit diagram is same for both LM324 N' LM1875
DERIVATION OF GAIN( NON INVERTING)
*video will be uploaded soon
