Advantages and Disadvantages of Half-bridge Switching Power Sources

High power output and great efficiency of half-bridge switching Power Source make them rather popular. Their design characteristics, nonetheless, also provide certain difficulties. Their benefits and constraints will be discussed in this paper to enable designers to make more wise decisions.

Z3PW Power Source

1 The output power of the half-bridge transformer switching Power Source is large and the working efficiency is high

The push-pull transformer switching Power Source corresponds with the half-bridge transformer switching Power Source. The two switching tubes operate alternately, hence their output power is roughly twice the output power of a single switching Power Source. It is comparable to the two switching Power Sources outputting electricity at the same time. Consequently, the half-bridge transformer switching Power Source boasts great working efficiency and a great output power. Following bridge rectification or full-wave rectification, the voltage ripple coefficient Sv and current ripple coefficient Si of the output voltage are extremely small and only small filter inductors and capacitors are needed; so, the output voltage ripple and current ripple can be really modest.

2 The withstand voltage value of the switching tube of the half-bridge switching Power Source is relatively low

The half-bridge transformer switching Power Source offers the largest benefit in that it allows the two switching devices’ withstand voltage requirement to be halved relative to that of the push-pull transformer switching Power Source. The two switching devices of the half-bridge transformer switching Power Source only half of the input Power Source Ui, thus their maximum withstand voltage is equal to the sum of the working voltage and the back electromotive force, roughly twice the Power Source voltage. This outcome precisely half of the two push-pull transformer switching device withstand voltage of the two switching devices. Consequently, the half-bridge transformer switching Power Source is mainly applied in situations involving somewhat high input voltage. Generally speaking, half-bridge transformer switching Power Sources are used by most high-power switching power sources running a 220 volts AC grid voltage.

3 Transformer primary coil of half-bridge switching Power Source

The half-bridge switching Power Source’s advantage—that it requires just one winding—also adds some convenience to the coil winding of the transformer of the small-power switching Power Source. However, as the transformer of the high-power switching Power Source must be coiled with several strands of wire, it has no benefit in the coil winding of the transformer.

4 The main disadvantage of the half-bridge transformer switching Power Source is the relatively low power utilization rate

Low operating voltage situations call for a different kind of half-bridge transformer switching Power Source. Furthermore more difficult to link with the driving signal is the two switching devices in the half-bridge transformer switching Power Source, which are coupled without a common ground.

5 The disadvantage of the half-bridge switching Power Source is that there will be a semi-conduction area, which has large losses

The main drawback of the half-bridge switching Power Source is that, in the alternating switching working state, the two switching devices will concurrently appear in a very short semi-conduction area, that is, the two control switches are in the on state at the same time. This is so because, when the switching device starts to operate, it is like charging the capacitor; hence, it requires a transition process from the off state to the totally on state; and when the switching device moves from the on state to the off state, it is like discharging the capacitor.
This is equivalent to that the two control switches are turned on simultaneously, which will cause a short circuit to the Power Source voltage; at this time, a great current will appear in the series circuit of the two control switches, and this current does not pass through the transformer load. When the two switching devices are in the conduction and cutoff transition state, that is, when both switching devices are in the semi-conducting state, Consequently, the two switching devices will cause a significant power loss during the period when the two control switches K1 and K2 are in the transition process concurrently. Usually in the half-bridge switching Power Source circuit, the turn-on and turn-off times of the two control switches are deliberately staggered for a brief period of time to help to lower the loss created by the transition process of the control switch.

6 Single capacitor half-bridge transformer switching Power Source and dual capacitor half-bridge transformer switching Power Source

Its advantage is that the single capacitor half-bridge transformer switching Power Source saves one capacitor as compared to the dual capacitor half-bridge transformer switching Power Source. Furthermore, the output voltage is merely twice as high as the output voltage of the dual-capacitor half-bridge transformer switching Power Source when the single-capacitor half-bridge transformer switching Power Source starts running. This function is best appropriate for fluorescent lamp Power Source, like energy-saving lamps or fluorescent lamps and LCD display backlights.
Usually starting at hundreds of volts to thousands of volts, fluorescent lamps need a very high voltage when they turn on; the working voltage only requires tens of volts to more than 100 volts after lighting up. Consequently, single-capacitor half-bridge transformer switching Power Source are used practically exclusively in energy-saving lighting.

7 Disadvantages of single-capacitor half-bridge transformer switching Power Sources

The switching device’s withstand voltage need is larger than that of the dual-capacitor half-bridge transformer switching Power Source.

The issues of high withstand voltage requirements, significant semi-conduction losses and low power use in its design cannot be overlooked even if the half-bridge switching Power Source performs well in high power output and efficiency. Selecting an appropriate Power Source solution calls for thorough examination of these elements to guarantee the best performance of the system of Power Source.