The working principle of an industrial frequency converter and switching power supply unit
The working principle of industrial frequency transformer is relatively simple, from the primary coil input frequency AC voltage into a magnetic field, through the magnetic conductive material (usually silicon steel sheet) transmitted to the secondary coil induced voltage. Output for the frequency and input frequency is the same, the voltage in accordance with the initial stage of the coil turns than the reduced voltage (if the number of turns of the secondary is more boost). As the transformer output is alternating current, and most of the electrical circuits used for direct current, the transformer output voltage also needs to be rectified, filtered, regulated and other circuits, into a relatively smooth and stable voltage for the load circuit part of the work.
Switching power supply is still the core of the transformer component, and also follow the rules of the voltage ratio is equal to the number of turns ratio. Unlike industrial transformers, switching power supplies need to increase the operating frequency, that is, the need to change the low-frequency AC voltage into high-frequency AC voltage, which requires additional control circuitry to achieve. Because the circuit requires DC power to operate, the input AC voltage has to be rectified and changed to DC voltage before it can be controlled by the circuit behind it. Below is an example of a commonly used mobile phone charger circuit to briefly understand the working principle of switching power supply.
Input 220V AC voltage after rectification and filtering, will become about 310V DC voltage (that is, 220V AC voltage peak), the following need to turn this DC into high-frequency alternating current. Want to turn this voltage into high-frequency alternating current, the simplest way is to use a switch, so that the switch quickly disconnect and close, so that the DC power into a high-speed pulse DC voltage, to achieve the switch component is a transistor. Transistors, including commonly used transistors and field effect tubes, etc., these two components can be used as an electronic switch, that is, through the voltage control of a pin (the base of the transistor as well as the gate of the field effect tube), you can make the other two pins to achieve the on-off control.
With the switch, the next need to control the switch circuit, the role of this circuit is to output high-speed switching signals to control the switching tube on and off, this circuit is called oscillator circuit. This circuit is called oscillation circuit. Switching power supply oscillation circuit is divided into many kinds of, no matter which one, the role is to provide control signals to the switching tube. After the control circuit control, the input voltage from the low-frequency alternating current into a high-frequency pulsed DC voltage, input to the transformer for step-down, the transformer output voltage will also be rectified. The output voltage from the transformer is also rectified and filtered into a DC output, which is provided to the load. The difference with the industrial frequency transformer is that the switching power supply also has an additional Part of the voltage detection circuit, which will output the voltage signal through the detection and feedback to the transformer primary control circuit for voltage regulation, which makes the switching power supply This makes the stability of the output voltage of the switching power supply is improved, and can have a wide range of input voltage. So the working process of switching power supply is actually from AC - DC, DC - AC, and then through the AC - AC
DC - AC, and then through the AC - DC several processes to achieve.
