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Posted by BitesizePhysicsTeacher (U15165682) on Tuesday, 29th January 2013
The second type of op-amp circuit is the differential mode operational amplifier -
+ TWO input voltages, V1 , to the inverting input (-), via resisitor R1 and V2 to the non-inverting input (+) via resistor R2.
+ feedback resisitor, Rf, connects output, Vo , to the inverting input
+ resistor R3 connects the non-inverting input to 0 V
+ the ratios of the resistors for a differentail mode op-amp will always be such that Rf/R1 = R3/R2
circuit diagram can be found here - www.bbc.co.uk/bitesi...
For all differential mode op-amps, the output is given by the formula -
Vo = - Rf/R1 x (V2 - V1)
** N.B. this type of amplifier amplifies the DIFFERENCE between the two input voltages **
** if the calculated value of Vo is greater than Vs, the supply voltage, then the output will SATURATE, as no amplifier can produce a voltage larger than its supply. **