Push-pull switching power supply working principle
Rectified output push-pull transformer switching power supply, due to the two switching tubes take turns to work alternately, the equivalent of two switching power supply output power at the same time, its output power is about twice as much as the output power of a single switching power supply. Therefore, push-pull transformer switching power supply output power is very large, high efficiency, by the bridge rectifier or full-wave rectifier, only a very small filtering inductance and capacitance, its output voltage ripple can be very small.
Push-pull circuit in two switches S1 and S2 alternately on, in the winding N1 and N'1 respectively, the formation of the two ends of the phase of the opposite AC voltage, change the duty cycle can change the output voltage. s1 on, the diode VD1 in the on state, the inductor L of the current rises gradually. s2 on, the diode VD2 is in the on state, the inductor L of the current rises gradually. When the two switches are off, VD1 and VD2 are in the on state, each sharing half of the current, S1 and S2 off state of the peak voltage are 2 times Ui. S1 and S2 at the same time, equivalent to the primary side of the transformer windings short-circuited, so should be avoided at the same time to avoid two switches on. The duty cycle of each switch should not exceed 50%, but also leave a dead band.
As the push-pull transformer switching power supply in the two control switches K1 and K2 alternating work in turn, its output voltage waveform is very symmetrical, and the switching power supply in the entire operating cycle to provide power output to the load, therefore, its output current instantaneous response speed is very high, the voltage output characteristics are very good. Push-pull transformer switching power supply is the switching power supply with the highest voltage utilisation among all switching power supplies, which can still maintain a large power output at very low input voltage, so push-pull transformer switching power supply is widely used in DC/AC inverter or DC/DC converter circuits with low input voltage.
Push-pull switching power supply by the bridge rectifier or full-wave rectifier, the output voltage of the voltage pulsation coefficient Sv and current pulsation coefficient Si are very small, only a very small value of energy storage filter capacitor or energy storage filter inductor, you can get a voltage ripple and current ripple are very small output voltage. Therefore, the push-pull switching power supply is a switching power supply with very good output voltage characteristics.
In addition, push-pull switching power supply transformer belongs to the bipolar magnetic polarisation, the magnetic induction variation range is more than twice as much as the unipolar magnetic polarisation, and the transformer core does not need to leave an air gap, therefore, push-pull switching power supply transformer core permeability than the unipolar magnetic polarisation of the positive excitation or inverse switching power supply transformer core permeability is many times higher; in this way, push-pull switching power supply transformer primary and secondary coil turns can be compared to Unipolar magnetic polarisation transformer primary and secondary coil turns less than double. Therefore, the leakage inductance of the push-pull switching power supply transformer as well as the copper resistance loss are much smaller than the unipolar magnetic polarisation transformer, and the efficiency of the switching power supply is very high.
Push-pull switching conversion circuit, the energy conversion by the two tubes alternately controlled, when the output of the same power, the current is only half of the single-ended switching power supply tubes, so the switching loss is reduced, the efficiency is improved.
