Principles of Linear Power Supplies vs. Switching Power Supplies
Linear power supply is the first AC power through the transformer voltage, and then through the rectifier circuit rectifier filter to get unstable DC voltage, to achieve high precision DC voltage, must be adjusted through the voltage feedback output voltage. From the main performance, this power supply technology is very mature, can achieve a high degree of stability, ripple is also very small, and no switching power supply has the interference and noise. Voltage feedback circuit is working in a linear state, there is a certain voltage drop on the adjustment tube, in the output of a larger operating current, the power consumption of the adjustment tube is too large, low conversion efficiency.
Linear power supply means that the tubes used for voltage adjustment work in the linear region. Corresponding to the switching power supply is used for voltage regulation of the tube working in the saturation and cut-off region, that is, the switching state.
Linear power supply generally samples the output voltage and sends it to a comparative voltage amplifier with the reference voltage, and the output of this voltage amplifier is used as the input of the voltage regulator to control the regulator so that the junction voltage changes according to the change of the input to adjust the output voltage. However, a switching power supply changes the output voltage by changing the on and off time of the regulator, i.e., the duty cycle.
Comparison of switching power supply: switching power supply mainly includes input grid filter, input rectifier filter, inverter, output rectifier filter, control circuit, protection circuit. Their functions are:
1, input grid filter: eliminate interference from the power grid, such as motor starting, switching of electrical appliances, lightning strikes, etc., and also prevent the high-frequency noise generated by the switching power supply from spreading to the power grid.
2,Input rectifier filter: rectify and filter the grid input voltage to provide DC voltage for the converter.
3, inverter: is the key part of the switching power supply. It converts the DC voltage into high-frequency AC voltage and isolates the output part from the input grid.
4, the output rectifier filter: the converter output high-frequency AC voltage rectifier filter to get the required DC voltage, but also to prevent high-frequency noise on the load interference.
5, the control circuit: detect the output DC voltage, and compare it with the reference voltage, amplification. Modulate the pulse width of the oscillator to control the converter to keep the output voltage stable.
6, protection circuit: when the switching power supply occurs over-voltage, over-current short circuit, the protection circuit makes the switching power supply to stop working to protect the load and the power supply itself.
Switching power supply is the first AC rectifier into DC, DC reverse into AC, in the rectifier output into the required DC voltage. This switching power supply eliminates the transformer and the voltage feedback circuit in the linear power supply. The inverter circuit in the switching power supply is completely digital adjustment, also can achieve very high adjustment accuracy.
The main working principle of the switching power supply is that the Mos tubes of the upper and lower bridges conduction in turn, firstly, the current flows through the Mos tube of the upper bridge, using the storage function of the coil, the power will be gathered in the coil, and finally close the Mos tube of the upper bridge, open the Mos tube of the lower bridge, the coil and the capacitor continue to supply power to the outside. Then the lower bridge Mos tube is turned off again, and the upper bridge is turned on again to let the current in, and so it repeats, and because the Mos tubes have to be switched on and off in turn, it is called a switching power supply.
The linear power supply is not the same, because there is no switching intervention, making the upper pipe has been in the discharge, if there is more, it will leak out, which is what we often see in some linear power supply Mos tube heat is very large, inexhaustible power, all converted into heat. From this point of view, the conversion efficiency of the linear power supply is very low, and when the heat is high, the life of the components is bound to decline, affecting the final use of the results.
