Principle of switching power supply composition of

2022-07-22
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With the development and innovation of power electronics technology, the design technology of switching power supply is constantly innovating. At present, switching power supply is widely used in almost all electronic equipment with the characteristics of small size, light weight and high efficiency. It is an indispensable power supply mode for the rapid development of electronic information industry

switching power supply is to use electronic switching devices (such as transistors, field effect tubes, thyristors, etc.) to make electronic switching devices constantly “ Connect ” And “ Turn off ”, Let the electronic switching device pulse modulate the input voltage, so as to realize dc/ac, dc/dc voltage conversion, and the output voltage can be adjusted and stabilized automatically. Next, I will introduce the principle and composition of switching power supply

principle of switching power supply

the working principle of switching power supply is different from that of linear power supply. Linear power supply makes the power transistor work in linear mode, while switching power supply makes the power transistor work in two working states: on and off. In other words, through “ Chopping ”, That is, the amplitude of the input DC voltage is chopped into a pulse voltage equal to the amplitude of the input voltage. This working principle of switching power supply makes the volt ampere product added to the power transistor very small (in the on state, the voltage is low and the current is large; in the off state, the voltage is high and the current is small), that is, the loss generated on the power transistor is very small

switching power supply composition

1. Main circuit

impulse current limiting: limit the impulse current at the input side at the moment of power on

input filter: its function is to filter the clutter existing in the power grid and prevent the clutter generated by the machine from being fed back to the power grid

rectification and filtering: the AC power supply of the power grid is directly rectified into smoother DC

inverter: convert the rectified DC into high-frequency AC, which is the core of high-frequency switching power supply

output rectification and filtering: provide stable and reliable DC power supply according to load needs

2. Control circuit

on the one hand, take samples from the output end, compare with the set value, and then control the inverter to change its pulse width or pulse frequency to stabilize the output. On the other hand, according to the data provided by the test circuit, through the identification of the protection circuit, provide the control circuit with various protection measures for the power source

3. Detection circuit

provides various parameters and instrument data in operation in the protection circuit

4. The auxiliary power supply

realizes the software (remote) startup of the power supply and supplies power for the operation of the protection circuit and the control circuit (PWM and other chips)

reasons for low output voltage of switching power supply

1. The working voltage provided by 220V AC voltage input circuit and rectifier filter circuit to the switch tube is not enough, which is beyond the control range of pulse width modulation circuit

2. The over-current in the load circuit causes the load of the switching power supply to increase and the output voltage to drop

3. The on/off interface circuit is in the standby state, so that the switching power supply works in the low-frequency oscillation state, and its output voltage is the degree in the standby state. This kind of fault should only be caused by the model without standby power supply, and the working voltage of CPU in standby state is provided by switching power supply

4. The end of the on/off interface circuit works in the state between startup or standby for some reason, resulting in the working frequency of the switching power supply between standby and startup, resulting in the output voltage of the switching power supply being higher than the standby value and lower than the startup value

5. The protection circuit terminal works in the on state due to fault, which makes the power supply enter the weak vibration narrow pulse power supply, causing the output voltage of the switching power supply to drop

6. The diode, filter capacitor and current limiting resistor in the rectifier output circuit are damaged, causing the output voltage to become low

7. There is a problem with the pulse width modulation circuit, which cannot make a tangent response to the change of the output voltage of the switching power supply, and the adjustment direction of the base voltage of the power switch is wrong, resulting in the low output voltage of the switching power supply

8. The positive feedback resistance in the positive feedback circuit becomes larger, the performance of the discharge diode becomes worse, and the positive feedback is insufficient, resulting in a longer oscillation period. The oscillation frequency decreases, resulting in low output voltage of switching power supply

9. The output voltage of the externally excited switching power supply is low because it works below the low-frequency state because it has not been inverted

editor's summary: This is the introduction of the principle and composition of switching power supply. I hope it will be helpful to you. If you want to know more about it, you can pay attention to the information

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