Advantages and disadvantages of half bridge transformer switching power supply
The half bridge transformer switching power supply is similar to the push-pull transformer switching power supply. Due to the alternating operation of two switch tubes, it is equivalent to two switch power supplies outputting power simultaneously, and its output power is approximately twice the output power of a single switch power supply. Therefore, the half bridge transformer switching power supply has a large output power and high working efficiency. After bridge rectification or full wave rectification, the voltage ripple coefficient Sv and current ripple coefficient Si of the output voltage are both very small. With only a small filtering inductance and capacitor, the output voltage ripple and current ripple can be very small.
The biggest advantage of a half bridge transformer switching power supply is that the withstand voltage requirement for two switching devices can be reduced by half compared to a push-pull transformer switching power supply. Because the working voltage of the two switching devices of the half bridge transformer switching power supply is only half of the input power supply Ui, and its maximum withstand voltage is equal to the sum of the working voltage and the back electromotive force, which is about twice the power supply voltage. This result is exactly half of the withstand voltage of the two switching devices of the push-pull transformer switching power supply. Therefore, the half bridge transformer switching power supply is mainly used in situations with high input voltage. Generally, high-power switching power supplies with a grid voltage of AC 220V are mostly powered by half bridge transformer switching power supplies.
The transformer primary coil of a half bridge switching power supply only requires one winding, which is also its advantage. This brings some convenience to the winding of the coil of a low-power switching power supply transformer. However, there is no advantage in winding the coils of high-power switching power transformers, as the coils of high-power switching power transformers require multiple strands of wire to be wound.
The main drawback of a half bridge transformer switching power supply is its low power utilization rate. Therefore, the half bridge transformer switching power supply is not suitable for applications with low working voltage. In addition, the connection between the two switching devices in the half bridge transformer switching power supply does not have a common ground, which is more troublesome to connect to the driving signal.
The biggest drawback of a half bridge switching power supply is that when two control switches K1 and K2 are in alternating switching mode, both switching devices will simultaneously experience a short period of semi conducting region, that is, both control switches are in the on state at the same time. This is because when the switching device starts to conduct, it is equivalent to charging the capacitor, and it requires a transition process from the cut-off state to the fully conducting state; When the switching device transitions from the on state to the off state, it is equivalent to discharging the capacitor, and it also requires a transition process from the on state to the fully off state.
When two switching devices are respectively in the transition process of conduction and cutoff, that is, when both switching devices are in a semi conduction state and semi conduction state, it is equivalent to two control switches being turned on simultaneously, which will cause a short circuit to the power supply voltage; At this point, a large amount of current will appear in the series circuit of the two control switches, and this current does not pass through the transformer load. Therefore, during the transition period of both control switches K1 and K2, the two switching devices will generate significant power losses. In order to reduce the losses caused by the transition process of control switches, it is generally intentional to stagger the on and off times of two control switches for a short period of time in a half bridge switching power supply circuit.
The advantage of a single capacitor half bridge transformer switching power supply is that it saves one capacitor compared to a double capacitor half bridge transformer switching power supply. In addition, when the single capacitor half bridge transformer switching power supply first started working, the output voltage was almost twice that of the double capacitor half bridge transformer switching power supply. This feature is most suitable for use as a fluorescent lamp power supply, such as energy-saving lamps or fluorescent lamps, as well as backlights for LCD display screens.
Fluorescent lamps generally require a high voltage when they start to light up, ranging from a few hundred to a few thousand volts. However, after lighting up, the working voltage only needs to be a few tens to over one hundred volts. Therefore, almost all energy-saving lamps use a single capacitor half bridge transformer switching power supply.
The single capacitor half bridge transformer switching power supply also has a disadvantage, which is that the voltage withstand requirement of the switching device is higher than that of the dual capacitor half bridge transformer switching power supply.
