Advantages and disadvantages of half-bridge transformer switching power supplies
Half-bridge transformer switching power supply and push-pull transformer switching power supply, as the two switching tubes take turns to work alternately, equivalent to two switching power supply output power at the same time, its output power is about equal to a single switching power supply output power twice. Therefore, half-bridge transformer switching power supply output power is very large, high efficiency, 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 need for filtering inductance and capacitance, the output voltage ripple and current ripple can be achieved very small.
Half-bridge transformer switching power supply is the biggest advantage of the two switching device voltage requirements than push-pull transformer switching power supply on the two switching device voltage requirements can be reduced by half. Because, the half-bridge transformer switching power supply two switching device operating voltage is only half of the input power supply Ui, its maximum withstand voltage is equal to the operating voltage and the sum of the reverse electromotive force, about twice the power supply voltage, this result is exactly half of the push-pull transformer switching power supply two switching device withstand voltage. Therefore, half-bridge transformer switching power supply is mainly used for input voltage is relatively high occasions, the general grid voltage of 220 volts AC power supply most of the high-power switching power supply is a half-bridge transformer switching power supply.
Half-bridge switching power supply transformer primary coil only needs a winding, which is also its advantage, which is more or less for small power switching power supply transformer coil winding to bring some convenience. But there is no advantage for coil winding of high power switching power supply transformer because, the coil of high power switching power supply transformer needs to be wound with multi-stranded wire.
The disadvantage of the half-bridge transformer switching power supply is mainly that the power utilisation is relatively low, therefore, the half-bridge transformer switching power supply is not suitable for use in occasions where the operating voltage is low. In addition, half-bridge transformer switching power supply in the two switching devices connected to no common ground, and drive signal connection is more troublesome.
The biggest disadvantage of the half-bridge switching power supply is that when the two control switches K1 and K2 are in the alternating switching operating state, the two switching devices will appear at the same time a short period of time half-conducting region, that is, the two control switches at the same time in the on state. This is because the switching device in the beginning of conduction, equivalent to the capacitor charging, it is from the cut-off state to the full conduction state requires a transition process; and switching device from the conduction state to the cut-off state is equivalent to the capacitor discharge, it is from the conduction state to the full cut-off state also requires a transition process.
When the two switching devices are in the on and off transition process, that is, the two switching devices are in the semi-conducting state when the semi-conducting state, equivalent to two control switches on at the same time, they will cause a short circuit on the supply voltage; at this time, in the two control switches in the series circuit there will be a very large current, 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 losses generated by the transition process of the control switches, generally in the half-bridge switching power supply circuit, are intended to let the two control switches on and off time staggered for a small period of time.
A single capacitor half-bridge transformer switching power supply has the advantage of saving a capacitor over a dual capacitor half-bridge transformer switching power supply. In addition, the output voltage of a single-capacitor half-bridge transformer switching power supply is almost twice as high as that of a dual-capacitor half-bridge transformer switching power supply when it first starts to work, which is most suitable for use as a power supply for fluorescent lamps such as energy-saving lamps or fluorescent lamps as well as backlighting for LCD displays.
Fluorescent lamps generally start to light up when the need for a very high voltage, about several hundred volts to several thousand volts, and light up after the working voltage only need a few tens of volts to more than 1 hundred volts, therefore, almost all of the energy-saving lamps are not the use of a single-capacitor half-bridge transformer switching power supply.
Single-capacitor half-bridge transformer switching power supply also has a disadvantage, that is, the switching device voltage requirements than the double-capacitor half-bridge transformer switching power supply high voltage.
