An integrated operational amplifier is an operational amplifier, which has two input terminals, in-phase and inverting, an output terminal and positive and negative power supply terminals. When the voltage of the non-inverting input terminal increases slightly, the voltage of the output terminal will increase greatly; and when the voltage of the inverting input terminal increases slightly, the voltage of the output terminal will greatly decrease. Taking advantage of this feature, integrated operational amplifiers are widely used in industrial and agricultural instrumentation, power electronic equipment, and also have a place in children's toys and middle school physics experiments.
There are many varieties of integrated operational amplifiers, and people have summarized many practical control circuits in long-term practice, such as the switching power supply circuit composed of uA741. as the picture shows.
The stable voltage of the Zener diode VS is 12V, which is used as the reference voltage of this circuit. When the output voltage is 2mV lower than the reference voltage (because the response sensitivity of uA741 is 2mV), it will react to the inverting input terminal (pin 2) of uA741, so that pin 6 outputs a high voltage, VT1 and VT2 are turned on, and a large current is used to supply The load and related filter capacitors C2, C3 and other supplementary power. The output voltage will soon rise to 12V, that is, the potentials of pins 2 and 3 of uA741 are equal. At this time, pin 6 outputs a low voltage (about 2V), VT1 and VT2 are turned off, and the supplementary energy is suspended. With the increase of time, the output voltage gradually decreases, and the above process is repeated again and again, and the power supply continues to be on and off, and the output voltage is always stabilized at 12V.
