Inverting amplifier using NPN transistor

An inverting amplifier is a circuit in which output is out of the phase of the input. Using inverting condition limits the gain of the circuit but the stability of the circuit is much higher than a non-inverting one. Circuits such as differentiator, integrators etc. are preferred to be constructed on an inverting amplifier mode. It is due to prime importance in applicative and developmental areas that inverting configuration is a must for every electronic enthusiast and covering the basics of the inverting amplifier is this electronic circuit tutorial. IC 741 is used most of the time to play the role of the amplifier. This is a comparator IC and can be used in non-inverting configuration too depending upon how the power supply is connected.

The project demonstrates the principle behind the operation of an inverting amplifier. In this circuit input to output voltage effect is reversed i.e., an increasing input voltage results in decreasing output voltage.

The project is based on the npn transistor 2N2222 (T1). A variable preset of 100K (VR1) is connected across the power supply to provide a variable voltage source. VR1 is connected to base of transistor T1 via a resistance

of value 100k. The collector is connected to Vcc through a resistance of 10k. The emitter is grounded. The circuit operates on 12V.

The circuit has large voltage gain. A small change in input voltage results in large change in output voltage. The operation of the circuit can be observed by moving the preset. As the voltage at the base of transistor T1 increases, the output across the transistor decreases. The table below describes the results obtained by varying the preset VR1.

S. No.	Vin	Vout
1.	0.28	11.2
2.	0.55	10.88
3.	0.96	6.97
4.	1.64	0.16
5.	2.54	0.07
6.	6.05	0.03

This circuit is temperature sensitive, i.e. for same position of potentiometer if temperature changes, the base diode characteristics change resulting in different base current for same input voltage, this then turns collector current and thus affecting output voltage, such errors or changes can be minimised by using signal feedback.