The working principle of series switching power supply
The simplest working principle diagram of a series switching power supply is the working voltage of the switching power supply, that is, the DC input voltage; K is the control switch, R is the load. When the control switch K is turned on, the switching power supply outputs a pulse voltage Up with a width of Ton and an amplitude of Ui to the load R; When the control switch K is turned off, it is equivalent to the switching power supply outputting a pulse voltage of Toff width and 0 amplitude to the load R. In this way, the control switch K continuously "turns on" and "off", and a pulse modulated output voltage uo can be obtained at both ends of the load.
The waveform of the output voltage of the series switching power supply, the output voltage uo of the control switch K, is a pulse modulated square wave. The pulse amplitude Up is equal to the input voltage Ui, and the pulse width is equal to the turning on time Ton of the control switch K. From this, the average value Ua of the output voltage uo of the series switching power supply can be obtained as:
In the formula, Ton is the time when the control switch K is turned on, and T is the working cycle of the control switch K. By changing the ratio of the on time Ton of the control switch K to the off time Toff, the average value Ua of the output voltage uo can be changed. Generally, people refer to it as the duty cycle, represented by D, which is:
The amplitude Up of the output voltage uo of a series switching power supply is equal to the input voltage Ui, and the average value Ua of its output voltage uo is always smaller than the input voltage Ui. Therefore, series switching power supplies generally use the average value Ua as the variable output voltage. Therefore, the series module power supply belongs to the step-down switching power supply.
The series switching power supply, also known as a chopper, is widely used in output power control due to its simple working principle and high efficiency. For example, the speed controller of electric motorcycles and the power controller of lighting power supply all belong to the application of series switching power supply. If the series switching power supply is only used for power output control, the voltage output can directly provide power output to the load without being connected to a rectifier filter circuit; But if used for stable output, it must undergo rectification and filtering.
The disadvantage of series switching power supply is that the input and output share the same ground, which can easily cause EMI interference and electrification of the base plate. When the input voltage is the mains rectified output voltage, it can easily cause electric shock and be unsafe for personal safety
