Advantages and disadvantages of half bridge transformer power supply
The half-bridge transformer switching power supply is the same as the push-pull transformer switching power supply. Since the two switching tubes work alternately, it is equivalent to the output power of two switching power supplies at the same time, and its output power is about twice that of a single switching 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 very small, and only a small filter is required. Inductors and capacitors, the output voltage ripple and current ripple can be very small.
The biggest advantage of the half-bridge transformer switching power supply is that the withstand voltage requirements for the two switching devices can be reduced by half compared with the push-pull transformer switching power supply for the two switching devices. 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, its highest 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 the push-pull type Transformer switching power supply is half of the withstand voltage of the two switching devices. Therefore, the half-bridge transformer switching power supply is mainly used in occasions where the input voltage is relatively high. Generally, most high-power switching power supplies with a grid voltage of 220 volts of AC power supply use a half-bridge transformer switching power supply.
The transformer primary coil of the half-bridge switching power supply only needs one winding, which is also its advantage, which brings some convenience to the coil winding of the small-power switching power supply transformer. However, there is no advantage for coil winding of high-power switching power supply transformers, because the coils of high-power switching power supply transformers need to be wound with multi-strand wires.
The main disadvantage of the half-bridge transformer switching power supply is that the power utilization rate is relatively low. Therefore, the half-bridge transformer switching power supply is not suitable for occasions with low working voltage. In addition, the two switching devices in the half-bridge transformer switching power supply are not connected to a common ground, so it is troublesome to connect with the driving signal.
The biggest disadvantage of the half-bridge switching power supply is that when the two control switches K1 and K2 are in the alternate switching state, the two switching devices will simultaneously appear in a short-term semi-conducting region, that is, the two control switches are in the same state at the same time. connected state. This is because when the switching device starts to conduct, it is equivalent to charging the capacitor, and it needs a transition process from the off state to the fully on state; and when the switching device switches from the on state to the off state, it is equivalent to charging the capacitor Discharge, it also needs a transition process from the conduction state to the complete cut-off state.
When the two switching devices are in the conduction and cut-off transition process respectively, that is, when the two switching devices are in the semi-conducting state, when the two switching devices are in the semi-conducting state, it is equivalent to the two control switches being turned on at the same time. Short circuit; At this time, a large 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 process of the two control switches K1 and K2 at the same time, the two switching devices will generate a large power loss. In order to reduce the loss caused by the transition process of the control switch, generally in the half-bridge switching power supply circuit, the turn-on and turn-off times of the two control switches are deliberately staggered for a short period of time.
The single-capacitor half-bridge transformer switching power supply saves one capacitor than the double-capacitor half-bridge transformer switching power supply, which is its advantage. In addition, when the single-capacitor half-bridge transformer switching power supply starts to work, the output voltage is almost twice as high as that of the double-capacitor half-bridge transformer switching power supply. This feature is most suitable as a fluorescent lamp power supply, for example, energy-saving lamps or Fluorescent lamps and backlights for LCD displays, etc.
Fluorescent lamps generally require a high voltage when they start to light up, about several hundred volts to several thousand volts, and after they are lit, the working voltage needs tens of volts to more than 100 volts. Therefore, almost all energy-saving lamps use Single capacitor half bridge transformer switching power supply.
The single-capacitor half-bridge transformer switching power supply also has a disadvantage, that is, the withstand voltage requirement of the switching device is higher than that of the double-capacitor half-bridge transformer switching power supply.
