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Talking about the control principle and classification of switching power supply

chipmall.com | Adafruit | 29/12/2020

What is a switching power supply? What is a switching power supply use for? A switching power supply is a voltage conversion circuit. Its main work content is to increase and decrease pressure. It is widely used in modern electronic products. Because the switching transistor always works in "on" and "off" states, it is called a switching power supply. The switching power supply is essentially an oscillating circuit. This method of converting electrical energy is not only used in power circuits, but also widely used in other circuits, such as LCD backlight circuits, fluorescent lamps, etc. Compared with transformers, switching power supplies have high efficiency, good stability and small size. The disadvantage of the switching power supply is that the power is relatively small, which will cause high-frequency interference to the circuit, and the circuit is complicated and difficult to maintain.

There are three control principles of switching power supply:

 


The first is a constant switching cycle at the end of the pulse width adjustment, and the empty ratio is changed by changing the pulse width;

The second is the pulse frequency adjustment, the on-pulse width is constant, and the duty cycle is changed by changing the frequency of the switch;

The third method is to mix and adjust the on-pulse width and the switching operating frequency, both of which are not fixed and can be changed. It is to mix the above two control methods.

 

Switching power supply classification:


1. According to the technology, the connection method of the switching tube, and the power supply technology, the switching power supply can be divided into series switching power supply and parallel switching power supply. The switch tube of the series switching power supply is connected in series between the input voltage and the output load, which is a step-down regulator circuit; while the switching tube of the parallel switching power supply is connected in parallel between the input voltage and the output load, similar to redundancy The power supply is a step-up regulator circuit.

2. According to the excitation mode, the switching power supply can be divided into self-excited and other excitation. In the self-excited switching power supply, a positive feedback loop is formed by the switch tube and transformer technology ""high-frequency transformer, which is similar to the intermittent oscillator; while the other-excited switching power supply must add an oscillator to oscillate The switching pulse generated by the switch is applied to the switching tube to control the on and off of the switching tube, so that the switching circuit works and has a DC voltage output.

3. According to the modulation method, switching power supplies like server power supplies can be divided into pulse width modulation (PWM) and pulse frequency modulation (PFM). PWM is a way to control the output voltage stability by changing the switching pulse width, while PFM is when the output voltage changes, through sampling and comparison, the error value is amplified and then the switching pulse period (ie frequency) is controlled to stabilize the output voltage.

4. According to the output DC value, the switching power supply can be divided into step-up switching power supply and step-down switching power supply, and can also be divided into high-voltage switching technology "high-voltage switching power supply and low-voltage switching power supply.

5. According to the output waveform, the switching power supply can be divided into rectangular wave and sine wave circuits.

6. According to output performance, switching power supply can be divided into constant voltage and constant frequency and variable voltage and frequency conversion circuits.

7. According to the number of switching tubes and the connection mode, switching power supplies can be divided into single-ended, push-pull, half-bridge and full-bridge, etc. The single-ended type uses only one switch tube, the push-pull type and half-bridge type use two switch tubes, and the full-bridge type uses four switch tubes.

8. Switching power supplies can be divided into forward and flyback according to the energy transfer mode.

9. According to the soft switching method, the switching power supply has current resonance type, voltage resonance type, E type and quasi E type resonance type and partial resonance type.

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power supply

switching power supplies

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