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Advantages and Disadvantages of Half-bridge Switching Power Transformers
Mar 08, 2017



 Advantages and Disadvantages of Half-bridge Switching Power Transformers


The half-bridge switching power supply transformer is the same as a push-pull transformer switching power supply. Since the two switching tubes alternately work in turn, the two switching power supplies are equivalent to output power at the same time, and their output power is approximately 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 factor Sv and the current ripple factor Si of the output voltage are small, requiring only very small filtering. Inductance and capacitance, the output voltage ripple and current ripple can be achieved very small.

 

The biggest advantage of the half-bridge switching power transformer is that the withstand voltage requirements of the two switching devices can be reduced by half compared to the voltage requirements of the push-pull transformer switching power supply for the two switching devices. Because the operating voltage of the two switching devices of the half-bridge transformer switching power supply is only half that of the input power Ui, the maximum withstand voltage is equal to the sum of the operating voltage and the back-EMF, which is approximately twice the supply voltage. This result is just a push-pull type. Transformer switching power supply two switching devices half the voltage. Therefore, the half-bridge transformer switching power supply is mainly used in applications where the input voltage is relatively high, and most of the high-power switching power supplies with a power supply voltage of 220 volts AC are mostly half-bridge transformer switching power supplies.

 

The disadvantage of the half-bridge transformer switching power supply is mainly the relatively low power utilization rate. Therefore, the half-bridge transformer switching power supply is not suitable for applications with low operating voltage. In addition, the two switching devices in the half-bridge transformer switching power supply have no common ground connection and are troublesome to connect with the driving signal.

 

The transformer primary coil of the half-bridge switching power supply requires only one winding, which is also its advantage. This brings about some convenience for winding the coil of the low-power switching power supply transformer. However, there is no advantage for the coil winding of the high-power switching power supply transformer because the coil of the high-power switching power supply transformer needs to be wound with multiple strands.



The biggest drawback of the half-bridge switching power supply is that when the two control switches K1 and K2 are in the alternate switching operation state, the two switching devices will simultaneously have a semi-conducting area for a short time, that is, the two control switches are at the same time. On state. This is because when the switching device starts conducting, it is equivalent to charging the capacitor. It needs a transition from the off state to the fully on state. When the switching device switches from the on state to the off state, it is equivalent to the capacitor. Discharge, it also requires a transition from the on-state to the complete off-state.

 

When two switching devices are in the turn-on and turn-off transients respectively, that is, when both switching devices are in the semi-conductive state, they are half-conductive, which means that two control switches are turned on at the same time. They will cause a voltage to the power supply. A short circuit occurs; 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 where both control switches K1 and K2 are at the same time, the two switching devices will generate a large power loss. In order to reduce the loss caused by controlling the transition process of the switch, generally, in the half-bridge switching power supply circuit, it is intended to make the two control switches to be turned on and off for a short period of time.

 

The single-capacitor half-bridge transformer switching power supply saves one capacitor compared to 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 is started, the output voltage is almost twice as high as the output voltage of the double-capacitor half-bridge transformer switching power supply. This feature is most suitable for use as a fluorescent lamp power supply, for example, an energy-saving lamp or Fluorescent lamps and LCD display backlights, etc.

 

When a fluorescent lamp generally starts to light, it needs a very high voltage, which is about several hundred volts to several thousand volts, and it takes several tens of volts to more than one hundred volts for the working voltage to be turned on. Therefore, almost all energy-saving lamps are used. Single-capacitor half-bridge transformer switching power supply.

 

The single-capacitor half-bridge switching power supply transformer is also disadvantageous, that is, the withstand voltage requirement of the switching device is higher than that of the double-capacitor half-bridge transformer switching power supply.


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