Synchronous rectification drive circuit and synchronous rectification method of switching power supply

Abstract

The invention discloses a synchronous rectification drive circuit and a synchronous rectification method of a switching power supply, and particularly relates to the synchronous rectification drive circuit and the synchronous rectification method with fly-back topology. Voltage Vds between the drain electrode and the source electrode of a switch tube of the fly-back topology switching power supply is transmitted to the secondary side of the switching power supply through an isolated drive capacitor, the voltage is distributed through the isolated drive capacitor, a grid electrode-source electrode G-S junction capacitor of a synchronous rectification MOS and a common mode capacitor Y, and voltage Vgs which is obtained after voltage distribution is provided for the synchronous rectification MOS for drive. The synchronous rectification drive circuit applied to the switching power supply has the advantages that the circuit is simple, cost is low, the size is small, drive pulse signals have no negative voltage, and the input voltage range of the synchronous rectification drive circuit suitable for the switching power supply is wide.

Description

technical field [0001] The invention relates to a synchronous rectification driving circuit and a synchronous rectification method of a switching power supply, and is particularly suitable for the application field of a switching power supply with a wide input voltage range, small power supply volume and low no-load power consumption. Background technique [0002] With the rapid development of semiconductor devices and VLSI, the demand for high-current, low-voltage, and low-cost isolated switching power supplies has also increased significantly. The Schottky diode with a forward voltage drop of only 0.3V-0.7V rectifies, and the large conduction loss becomes the bottleneck of the miniaturization of the switching power supply. In order to improve the efficiency of low-voltage, high-current switching power supplies, synchronous rectification technology is used for output rectification. In the prior art, two driving methods are generally used, the transformer winding self-driven...

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Problems solved by technology

[0004] 1. Synchronous rectification drive waveform has negative voltage, resulting in large drive loss

[0005] 2. The synchronous rectification drive waveform negative voltage is proportional to the input voltage of the switching power supply, and the Vgs voltage of the general MOS tube is only ±20V, so the switching power supply in a wide input voltage range cannot be applied; while in the application field of the module power supply, the input voltage The range has 2:1 input voltage range and 4:1 input voltage range, this circuit cannot be applied in the 4:1 input voltage range

[0006] like figure 2 Shown is another synchronous rectification isolation drive technology in the prior art. The drive signal comes from the drive signal of the primary side switch, and is provided to the synchronous rectification MOS tube of the secondary side through the synchronous primary and secondary side drive capacitors and isolation transformers. Although the input The voltage range is relatively wide, and the driving level has no negative voltage, etc., but it uses an isolation transformer, which increases the cost and volume of the capacitor, and is difficult to apply in a small-volume, high-power-density module power supply.

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