An amplifier is a device that can amplify the voltage or power of an input signal, and is composed of tubes or transistors, power transformers and other electrical components. Widely used in communications, broadcasting, television, automation control, radar and other devices.
Amplifiers Applications
Difference Between Operational Amplifier and Power Amplifier
According to the usage, the common amplifiers are operational amplifiers and power amplifiers. Both can amplify small signals, the difference lies in the output capability. The operational amplifier is integrated, and the output capability of ordinary operational amplifiers is limited, and it is only suitable for loads with relatively high impedance. The power amplifier can be composed of ordinary discrete components, with strong output capability, and is suitable for outputting higher power with loads with relatively low impedance.
The operational amplifier can process analog models with high precision and can be used as a DC amplifier to perform various addition, subtraction, multiplication, and division operations. The main purpose of power amplifiers is to output high current and high voltage to drive heavier loads without high precision, so most power amplifiers cannot be used as DC amplifiers.
In circuit applications, there is no such clear distinction between the two. Ordinary operational amplifiers can increase the output current to drive a low-resistance load by expanding the current of the tube with external power, so as to achieve the function of a power amplifier. With the development of semiconductor technology, many precision integrated power amplifiers such as LM3886, LM1875, etc. TI Amplifiers can even perform DC amplification.
How to test if an operational amplifier is damaged？
Operational amplifiers play an important role in analog circuits. They can form various circuits such as amplification, addition, subtraction, and conversion. When there is an abnormality in the circuit, what are the methods to check whether it is the cause of the damage to the operational amplifier? You can analyze the circuit through the virtual short and virtual break of the op amps, and make judgments with some tips.
Virtual Short
The virtual short refers to ideally, the potentials of the two input terminals being equal, which can be regarded as the two input terminals being shorted together. Since there is no actual short circuit, it is called virtual short. The trigger condition is that the op-amp introduces deep negative feedback.
Due to the large voltage amplification factor of the operational amplifier, the open-loop voltage amplification factor of general-purpose operational amplifiers is above 80 dB. The output voltage of the op-amp is limited, generally between 10 V and 14 V. Therefore, the differential mode input voltage of the op-amp is less than 1 mV, and the two input terminals are approximately equal potential, which is equivalent to a short circuit. The greater the magnification of the open-loop voltage, the closer the potentials of the two input terminals are to the same.
Virtual Break
A virtual break means that because the input resistance of an ideal operational amplifier is infinite, the current flowing into the input terminal of the integrated operational amplifier is 0, which is equivalent to a state of the open circuit between the two input terminals. Since there is no actual open circuit, it is called a virtual break.
Because the differential mode input resistance of the operational amplifier is very large, the input resistance of general-purpose operational amplifiers is more than 1MΩ. Therefore, the current flowing into the input terminal of the op amp is often less than 1uA, which is much smaller than the current of the circuit outside the input terminal. Therefore, the two input terminals of the op-amp can usually be regarded as an open circuit, and the greater the input resistance, the closer the two input terminals are to an open circuit.
According to the principle of the virtual short of the amplifier, if the operational amplifier operates linearly, the voltages at its non-inverting and inverting inputs are almost equal (there may be a slight difference). In some high input impedance circuits, the internal resistance of the multimeter will affect the voltage test. Generally, it will not exceed 0.2V. If it exceeds 0.5V, it can be determined that the amplifier is damaged.
In many instruments and meters, integrated op amps are used for small signal amplification. It is more easily damaged than other integrated blocks and components, so being able to quickly judge whether it is good or bad can be said to be a shortcut for instrument repair. Many of the integrated blocks in more complex instruments are directly welded on the printed circuit board, the circuit board is inserted into the socket, and the distance between the circuit boards is also very small, so it is difficult to measure the voltage directly. Some simple and practical methods for judging integrated operational amplifier blocks are proposed below.
A. Touch the temperature of the integrated op-amp block by hand after power on for a period of time. If the temperature is greater than 50℃, it should be suspected whether it is damaged.
B. Measure its DC current, which should be within a few milliamps. Otherwise, it is damaged.
C. The integrated operational amplifier has a combination of a single operational amplifier and several operational amplifiers and should be familiar with its power supply, input, and output pins. The resistance between the input pins of the integrated operational amplifier should be relatively large (generally greater than 10 MΩ). When the measured value is small, the diode with infinite value at the input should be observed, otherwise, it can be determined to be damaged.
D. The input voltage of online measurement should be relatively small. Generally below 0.1 V. Touch the input end with your hand, the voltage should change at the output end, or touch the two ends of the feedback resistor with your hand (equivalent to a resistor in parallel), and the output will change accordingly.