Familiar with the electronic element- Operational amplifier

An operational amplifier is a DC-coupled high-gain electronic voltage with a differential input and, usually, a single-ended output. In this configuration, an op-amp produces an output potential that is typically hundreds of thousands of times larger than the potential difference between its input terminals.

Op-amps are among the most widely used electronic devices today, being used in a vast of consumer, industrial, and scientific devices. There are two kinds of packages: chip, and plug-in. The operational amplifier can be divided into several categories, single operational amplifier(LM321), twin operational amplifier(lm358), and four operation amplifiers (LM324). In a flyback power supply circuit, we usually use an LM358 operational amplifier.

Principle

Here is an input and negative feedback circuits, the circuits composed of different linear or nonlinear elements, when the circuits access to the operational amplifier, it can achieve various specific function relationships flexibly.

  • Operation of signal in a circuit, just like: add, subtract, proportion, logarithm, index, integral, differential, etc.
  • Signal operation circuit, just like: active filter, a precision rectifier circuit, voltage comparator, sample and hold circuit.
  • Signal generation circuit, just like: create a square wave, sawtooth wave.

In a flyback power supply circuit, we only a simple operational amplifier, voltage comparator.

LM358 is a twin operational amplifier, single power supply for DC 3V-30V.

LM358
  1. First operational amplifier output terminal.
  2. First operational amplifier inverting input terminal.
  3. First operational amplifier noninverting input terminal.
  4. GND
  5. Second operational amplifier noninverting input terminal.
  6. Second operational amplifier inverting input terminal.
  7. Second operational amplifier output terminal.
  8. VCC

Operation condition

  • Voltage(3 pin) > Voltage(2 pin),  Voltage(1 pin): the high level was outputted.
  • Voltage(3 pin) < Voltage(2 pin),  Voltage(1 pin): the low level was outputted.
  • Voltage(5 pin) > Voltage(6 pin),  Voltage(1 pin): the high level was outputted.
  • Voltage(5 pin) < Voltage(6 pin),  Voltage(1 pin): the low level was outputted.

Output high level Voltage: VDD = 1.5V

Output low level Voltage: VDD = 0.2V

Mobile phone detector using LM358