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Advantages and Disadvantages of Half Bridge Transformer Switching Power Supply


Release time:

2017-02-16

Half-bridge transformer switching power supply and push-pull transformer switching power supply, because the two switches work alternately, equivalent to two switching power supply at the same time output power, the output power is about twice the output power of a single switching power supply.

Advantages and Disadvantages of Half Bridge Transformer Switching Power Supply

Half-bridge transformer switching power supply and push-pull transformer switching power supply, because the two switches work alternately, equivalent to two switching power supply at the same time output power, the output power is about twice the output power of a single switching power supply. Therefore, the output power of the half-bridge transformer switching power supply is very large, and the working efficiency is very high. 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 inductor and capacitor are required, and the output voltage ripple and current ripple can be very small.

The advantage of half-bridge transformer switching power supply is that the voltage requirement of the two switching devices can be reduced by half compared to the voltage requirement 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 of the input power supply Ui, and its high withstand voltage is equal to the sum of the operating voltage and the back electromotive force, which is about twice the power supply voltage. This result is exactly half the withstand voltage of the two switching devices of the push-pull transformer switching power supply. Therefore, half-bridge transformer switching power supply is mainly used for high input voltage occasions, the general grid voltage for AC 220 volts power supply of high-power switching power supply are mostly half-bridge transformer switching power supply.

Half-bridge switching power supply transformer primary coil only needs one winding, which is also its advantage, which brings some convenience to the coil winding of small power switching power supply transformer. However, there is no advantage for the winding of the coil 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 main disadvantage of half-bridge transformer switching power supply is that the power utilization rate is relatively low. Therefore, 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 connected without a common ground, which is troublesome to connect with the driving signal.

The big disadvantage of the half-bridge switching power supply is that when the two control switches K1 and K2 are in the alternately switching working state, the two switching devices will have a half-conducting region for a short time at the same time, that is, the two control switches are in the on state at the same time. This is because when the switching device starts to turn on, it is equivalent to charging the capacitor, and it needs a transition process from the off state to the full on state; and when the switching device switches from the on state to the off state, it is equivalent to discharging the capacitor, and it also needs a transition process from the on state to the full off state.

When the two switching devices are in the on and off transition process respectively, that is, when the two switching devices are in the half-on state, it is equivalent to that the two control switches are turned on at the same time, and they will cause a short circuit to the power supply voltage. At this time, a large current will appear in the series loop of the two control switches, and this current does not pass through the transformer load. Therefore, during the transition 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 on and off times of the two control switches are intentionally staggered for a short period of time.

The single-capacitor half-bridge transformer switching power supply saves a capacitor compared with 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 the output voltage of the double-capacitor half-bridge transformer switching power supply. This feature is suitable for use as a fluorescent lamp power supply, for example, energy-saving lamps or fluorescent lamps and backlights for LCD displays.

Fluorescent lamps generally need a high voltage when they start to light up, about several hundred volts to several thousand volts, and the working voltage only needs tens of volts to more than 100 volts after lighting up. Therefore, almost all energy-saving lamps use single-capacitor half-bridge transformer switching power supply.

Single-capacitor half-bridge transformer switching power supply also has shortcomings, that is, the voltage resistance of switching devices is higher than that of double-capacitor half-bridge transformer switching power supply.

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