Working principle of series-connected switching power supply
The simple operating schematic diagram of a series-connected switching power supply shows the operating voltage of the switching power supply, i.e., the DC input voltage; K is the control switch and R is the load. When the control switch K on, the switching power supply to the load R output a pulse width of Ton, the amplitude of Ui pulse voltage Up; when the control switch K off, and equivalent to the switching power supply to the load R output a pulse width of Toff, the amplitude of 0 pulse voltage. In this way, the control switch K constantly "on" and "off", in both ends of the load can get a pulse modulated output voltage uo.
Series switching power supply output voltage waveform, as seen in the figure, the control switch K output voltage uo is a pulse modulated square wave, pulse amplitude Up is equal to the input voltage Ui, the pulse width is equal to the control switch K on time Ton, which can be obtained as the average value of the series switching power supply output voltage uo Ua:
Where Ton is the control switch K turn-on time, T is the control switch K operating cycle. Changing the ratio of the control switch K turn-on time Ton to the turn-off time Toff, you can change the average value of the output voltage uo Ua . This is generally referred to as the duty cycle (Duty) and is expressed in terms of D, i.e.:
The amplitude Up of the output voltage uo of the series-connected 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, so the series-connected switching power supply generally outputs the voltage with the average value Ua as the variable output voltage. Therefore, series-connected modular power supply belongs to buck-type switching power supply.
Series-connected switching power supply is also called chopper by some people, because of its simple working principle and high efficiency, so its application in output power control is very wide. For example, electric motorbike speed controllers and lighting power controllers power controllers, etc., are applications belonging to the series switching power supply. If the series switching power supply is only used for power output control, the voltage output can not be connected to the rectifier filter circuit, and directly to the load to provide power output; but if used for regulating the output voltage, it must be rectified and filtered.
The disadvantage of series switching power supply is that the input and output share a common ground, so it is easy to produce EMI interference and the base plate charged, when the input voltage for the utility rectifier output voltage, easy to cause electric shock, personal insecurity.
