Synchronous rectifier control circuit, method and switching power supply provided with same

A synchronous rectification and control circuit technology, which is applied in the direction of electrical components, output power conversion devices, AC power input conversion to DC power output, etc., can solve problems such as back-feeding current, improve reliability and prevent damage Effect

Inactive Publication Date: 2016-06-22
MORNSUN GUANGZHOU SCI & TECH
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

[0011] In view of this, the present invention provides a synchronous rectification control circuit, a method and a switching power supply using it to solve the problem of back-feeding current generated during the start-up process of the self-driven synchronous rectification of the transformer winding

Method used

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  • Synchronous rectifier control circuit, method and switching power supply provided with same
  • Synchronous rectifier control circuit, method and switching power supply provided with same
  • Synchronous rectifier control circuit, method and switching power supply provided with same

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Embodiment 1

[0039] Figure 4 It shows the synchronous rectification drive control circuit of Embodiment 1 of the present invention, including a transformer winding self-driven synchronous rectification circuit 1, an output variation voltage sampling circuit 2 and a drive control circuit 3; the transformer winding self-driven synchronous rectification circuit 1 includes two synchronous rectification circuits MOS tubes Q1 and Q2; the input end of the output change voltage sampling circuit 2 is connected to the output voltage Vo of the switching power supply, and the output end is connected to the input end of the drive control circuit; the two output ends of the drive control circuit are respectively connected to two synchronous rectification MOS tubes Gates of Q1 and Q2;

[0040] Compared with the prior art, the transformer winding self-driven synchronous rectification circuit also includes a drive capacitor C1 and a drive capacitor C2; one end of the drive capacitor C1 is connected to one...

Embodiment 2

[0049] Figure 6 It shows the synchronous rectification driving control circuit of the second embodiment of the present invention, the difference from the first embodiment is:

[0050] The output change voltage sampling circuit adds a discharge diode D1, and its connection relationship is that the cathode of the discharge diode D1 is connected to the connection point of the sampling capacitor C3 and the current limiting resistor R1, and the anode of the discharge diode D1 is connected to the secondary reference point GND of the switching power supply.

[0051] The working principle of this embodiment is analyzed as follows:

[0052] Such as Figure 4 In the circuit of Embodiment 1 shown, when the output voltage drops when the power is turned off, upper positive and lower negative voltages are generated on the sampling capacitor C3, and the voltage will be maintained for a short time after the power is turned off. During the re-starting process of the switching power supply, ...

Embodiment 3

[0054] Figure 7 It shows the synchronous rectification drive control circuit of the third embodiment of the present invention, the difference from the second embodiment is:

[0055] The current limiting resistor R1 of the output variation voltage sampling circuit is removed, and the sampling resistor R1 is connected in parallel at both ends of the discharge diode D1.

[0056] The triode Q3 of the driving control circuit is replaced by a MOS transistor Q3, the gate of the MOS transistor Q3 is the input terminal of the driving control circuit, the source of the MOS transistor Q3 is connected to the secondary reference point GND of the switching power supply, and the drain of the MOS transistor Q3 is connected to The cathodes of the isolation diode D2 and the isolation diode D3, and the anodes of the isolation diode D2 and the isolation diode D3 are the two output terminals of the drive control circuit.

[0057] The working principle of this embodiment is slightly different fro...

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PUM

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Abstract

The invention discloses a synchronous rectification control circuit, a method and a switching power supply using the same. The input terminal of the output variable voltage sampling circuit collects the variable voltage output by the switching power supply, generates sampling current and provides it to the input of the drive control circuit through its output terminal terminal, the output terminal of the drive control circuit outputs a control signal; when the switching power supply is turned on or off, the control signal pulls down the drive level of the synchronous rectifier tube, and during the start-up process or after a delay for a period of time after start-up, the synchronous rectifier will be rectified within this time period The tubes are all working in their body diode rectification state; when the switching power supply enters the steady state, the drive control circuit is in the off state. Therefore, the energy stored in the output capacitor of the switching power supply is prevented from being poured back into the power supply when it is started or shut down, and the operation of the self-driven synchronous rectification circuit of the transformer winding is not affected when the switching power supply enters a steady state operation.

Description

technical field [0001] The invention relates to a synchronous rectification control circuit, a method and a switching power supply using the same, in particular to the control and application of the synchronous rectification self-driven by a transformer winding. 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 type and the control chip external drive type. [0003] Such as figure ...

Claims

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Application Information

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IPC IPC(8): H02M7/217
CPCH02M7/217
Inventor 李绍兵
Owner MORNSUN GUANGZHOU SCI & TECH
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