One of the basic topologies in push-pull switching power supply design
Push-pull circuit is two different polarity transistors connected to the output circuit. Push-pull circuit using two power BJT tube or MOSFET tube with the same parameters, in a push-pull manner in the circuit, each responsible for the positive and negative half-week waveform amplification task, the circuit works, two symmetrical power tubes each time there is only one conduction, so the conduction loss is small and high efficiency. The push-pull output can either pour current into the load or draw current from the load.
If the output stage has two transistors, always in a conduction, a cut-off state, that is, two transistors connected to the push-pull, such a circuit structure is called push-pull circuit or totem pole (Totem-pole) output circuit.
Push-pull transformer has two transistors in the alternating switch, has reached more than a single-tube operating circuit output power, due to the primary coil of the centre of the tap connected to the positive pole of the input power supply, so that when one side of the transistor conduction, the other side of the transistor to withstand the voltage and twice the supply voltage, which is a higher requirement for the transistor. Advantages: simple structure, high utilisation of the switching transformer core, push-pull circuit, two symmetrical power switching tubes each time only one conduction, so the conduction loss is small. Disadvantages: transformer with a centre tap, and the switching tube withstand voltage is higher; due to the presence of the transformer primary leakage inductance, power switching tube off moment, the leakage inductance pole will produce a large voltage spike, in addition to the input current ripple is larger, and thus the size of the input filter is larger.
Mainstream IC SG3525 is the U.S. Silicon General Semiconductor Corporation introduced a high-performance, full-featured and versatile monolithic integrated PWM control chip, it is simple, reliable, convenient and flexible, the output drive I push-pull output form, increasing the drive capability; internal undervoltage lockout circuit, soft-start control circuits, PWM latches, with overcurrent protection, frequency adjustable, and at the same time can limit the maximum Duty cycle. IR2110 is a driver produced by the U.S. IR Corporation. It has the advantages of optocoupler isolation (small size) and electromagnetic isolation (fast speed), and it is the first choice of driver for small and medium power converter devices. UC3846 adopts fixed frequency current mode control, which improves the line voltage regulation rate and load response characteristics of the system and simplifies the design of the control loop. IR2112S is a push-pull driver from IR, which is a high-voltage, high-amplification MOSFET and a push-pull amplifier with a stand-alone, in order to bootstrap the mode of operation, the gate driver power supply range from 10V to 20V.
