A MOSFET control circuit for a switching power supply

Abstract

This invention relates to the field of rectifier circuit technology, specifically to a MOSFET control circuit for a switching power supply. The circuit includes a MOSFET, the drain (D) of which is connected to the secondary winding of a transformer (T). The source (S) of the MOSFET is connected to one end of a capacitor (C2) and the output via an inductor (L2). The switching of the primary winding of the transformer (T) is controlled by a switch. When the switch is on, the voltage control circuit pulls the voltage at the gate (G) of the MOSFET higher than the voltage at the drain (D), turning the MOSFET on. When the switch is off, the voltage control circuit pulls the voltage at the gate (G) of the MOSFET lower than the voltage at the source (S), turning the MOSFET off. This invention cleverly connects the MOSFET and the voltage control circuit, ensuring a simple voltage control circuit structure while achieving precise control of the MOSFET's on and off states. Using the MOSFET control circuit proposed in this invention for circuit rectification provides the functionality of a rectifier diode while significantly reducing power dissipation.

Description

Technical Field

[0001] This invention relates to the field of rectifier circuit technology, and more specifically to a MOS (Metal-Oxide-Semiconductor) control circuit for a switching power supply. Background Technology

[0002] Traditionally, diodes are used to implement circuit rectification. When the diode is forward-biased, the voltage drop generally remains relatively stable. However, when the current is large, the power dissipation of the diode is large, which reduces the power supply efficiency. Moreover, as the current increases, the voltage drop of the diode increases, which further increases the heat loss of the diode and reduces the power supply efficiency.

[0003] In some designs, transistors are used instead of diodes, and their resistance is adjusted by regulating the voltage difference across the transistor. However, transistors are often in a non-switching state, and their voltage drop is not smaller than that of diodes, so energy consumption cannot be reduced. In addition, the circuit structure design for controlling the precise conduction and cutoff of transistors is relatively complex, and there is a lack of simple, reliable, and easy-to-implement control circuit structures and regulation methods. Summary of the Invention

[0004] To address the problems existing in the prior art, the purpose of this invention is to provide a MOSFET control circuit for a switching power supply, which solves the problems of high power dissipation and complex control circuits for conduction and cutoff in existing rectifier circuits.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] This invention proposes a MOSFET control circuit for a switching power supply, comprising a MOSFET, wherein the drain D of the MOSFET is connected to the secondary coil of a transformer T, the source S is connected to one end of a capacitor C2 and the output via an inductor L2, and the gate G is connected to a voltage control circuit, with the other end of the capacitor C2 grounded; the voltage control circuit includes a conduction control circuit and a cutoff control circuit, wherein the switching of the circuit containing the primary coil of the transformer T is controlled by a switch; when the switch is on, the conduction control circuit pulls the voltage of the gate G of the MOSFET higher than the voltage of the drain D, and the MOSFET is turned on; when the switch is off, the cutoff control circuit pulls the voltage of the gate G of the MOSFET lower than the voltage of the source S, and the MOSFET is turned off.

[0007] Furthermore, the conduction control circuit includes a capacitor C1, one end of which is connected to the gate G and drain D of the MOSFET, and the other end of which is connected to the end of the inductor L2 away from the MOSFET.

[0008] Furthermore, the capacitance of capacitor C1 is ≤0.01μF.

[0009] Furthermore, the capacitor C1 is connected to the drain D of the MOSFET through the inductor L1.

[0010] Furthermore, a diode D2 is provided between the inductor L1 and the drain D of the MOS transistor. The anode of the diode D2 is connected to the drain D of the MOS transistor, and the cathode is connected to the end of the inductor L1 away from the capacitor C1.

[0011] Furthermore, the cutoff control circuit includes a transistor U, the base of which is connected to the end of the inductor L2 away from the MOSFET, the emitter of which is connected to the drain D of the MOSFET, and the collector of which is connected to the gate G of the MOSFET.

[0012] Furthermore, when the switch is turned off, the cutoff control circuit pulls the voltage of the gate G of the MOS transistor down to a level lower than the voltage of the source S, and the voltage of the gate G is 0.1~0.3V higher than the voltage of the drain D.

[0013] Furthermore, it also includes a diode D1, the anode of which is grounded and the cathode is connected to the source S of the MOS transistor.

[0014] Compared with the prior art, the technical solution provided by the present invention has the following beneficial effects:

[0015] (1) In the MOS transistor control circuit proposed in this invention, the MOS transistor is connected to the secondary coil of the switching power supply transformer. The MOS transistor operates in a switching state. The voltage control circuit connected to the gate G can accurately control the MOS transistor to realize the function of the switching circuit. When the switch is turned on, the voltage control circuit pulls the voltage of the gate G of the MOS transistor to a higher voltage than the drain D, so that the MOS transistor is turned on. When the switch is turned off, the voltage control circuit pulls the voltage of the gate G of the MOS transistor to a lower voltage than the source S, so that the MOS transistor is turned off. In this way, the MOS transistor can act as a diode. Since the resistance of the MOS transistor is low when it is turned on (up to milliohms), the MOS transistor control circuit proposed in this invention can be used for circuit rectification. While having the function of a rectifier diode, it can significantly reduce power dissipation and improve power efficiency.

[0016] (2) The voltage control circuit structure and method for controlling the conduction and cutoff of the MOS transistor in this invention are simple. By cleverly connecting the MOS transistor with the conduction control circuit and the cutoff control circuit, and setting a capacitor C1 and an inductor L1 at a specific position in the conduction control circuit, the voltage of the gate G of the MOS transistor can be driven to be higher than the voltage of the drain D when the switch is turned on, thereby turning on the MOS transistor. In the cutoff control circuit, only a transistor U is set, and the voltage of the gate G of the MOS transistor can be driven to be lower than the voltage of the source S when the switch is turned off, thereby turning off the MOS transistor.

[0017] (3) The capacitor C1 selected in this invention has a small capacitance (≤0.01μF). Since one end of the capacitor C1 is connected to the gate G and drain D of the MOS transistor, it can ensure that when the switch is turned on, the voltage of the capacitor C1 rises rapidly, thereby quickly driving the voltage of the gate G of the MOS transistor to be higher than the voltage of the drain D, so that the MOS transistor can be turned on quickly. Attached Figure Description

[0018] The accompanying drawings are incorporated in and form part of this specification, and together with the description serve to explain the principles of the invention.

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a schematic diagram of the MOS transistor control circuit of the present invention;

[0021] Figure 2 This is a specific MOS transistor control circuit diagram of the present invention. Detailed Implementation

[0022] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numbers in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present invention. Rather, they are merely examples of apparatuses consistent with some aspects of the invention as detailed in the appended claims.

[0023] To enable those skilled in the art to better understand the technical solutions of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Example

[0024] refer to Figure 1 and Figure 2This example proposes a MOSFET control circuit for a switching power supply, including a MOSFET. The drain (D) of the MOSFET is connected to the secondary winding of a transformer T. The source (S) is connected to one end of a capacitor C2 and the output via an inductor L2. The gate (G) is connected to a voltage control circuit, and the other end of capacitor C2 is grounded. The voltage control circuit includes a turn-on control circuit and a turn-off control circuit. The primary winding of the transformer T is connected to an energy storage capacitor after AC rectification. The on / off state of the circuit containing the primary winding of the transformer T is controlled by a switch. When the switch is on, the turn-on control circuit pulls the voltage of the MOSFET's gate (G) higher than the voltage of the drain (D), and the voltage difference between the gate (G) and the drain (D) is greater than the turn-on voltage of the MOSFET, thus turning on the MOSFET. When the switch is off, the turn-off control circuit pulls the voltage of the MOSFET's gate (G) lower than the voltage of the source (S), thus turning off the MOSFET.

[0025] In this embodiment, the MOSFET operates in a switching state. During MOSFET operation, the turn-on control circuit and the turn-off control circuit can precisely control the MOSFET to achieve the function of a switching circuit. When the switch is on, the current flows from left to right and increases, and the voltage at the drain (D) of the MOSFET is positive. At this time, the turn-on control circuit pulls the voltage at the gate (G) of the MOSFET higher than the voltage at the drain (D), turning the MOSFET on. The current flows from left to right through the MOSFET to charge capacitor C2 and provide current for the output. When the switch is off, the current flows from left to right and decreases, and the voltage at the drain (D) of the MOSFET is negative. At this time, the turn-off control circuit pulls the voltage at the gate (G) of the MOSFET lower than the voltage at the source (S), turning the MOSFET off. Since the resistance of the MOSFET is low when it is on (down to milliohms), using the MOSFET control circuit proposed in this invention for circuit rectification can significantly reduce power dissipation and improve power efficiency while possessing the function of a rectifier diode. In this embodiment, the start-up voltage of the MOSFET is 1~2.2V, and the voltage difference between the gate (G) and the drain (D) of the MOSFET when it is on is 2.8V. To allow inductor L2 to freewheel when the MOSFET is off, a diode D1 can be placed in the MOSFET control circuit. The anode of the diode D1 is grounded, and the cathode is connected to the source S of the MOSFET.

[0026] refer to Figure 2In the above embodiments, the conduction control circuit includes a capacitor C1. One end of the capacitor C1 is connected to the gate G and drain D of the MOSFET, respectively. The capacitor C1 is connected to the drain D of the MOSFET through an inductor L1. The other end of the capacitor C1 is connected to the end of the inductor L2 away from the MOSFET. When the switch is turned on, the current flows through the inductor L1 to charge the capacitor C1, causing the voltage of the capacitor C1 to rise sharply to a level higher than the voltage of the drain D, thereby pulling up the voltage of the gate G of the MOSFET. To ensure unidirectional current flow in the conduction control circuit, a diode D2 can also be placed between the inductor L1 and the drain D of the MOSFET. The anode of the diode D2 is connected to the drain D of the MOSFET, and the cathode is connected to the end of the inductor L1 away from the capacitor C1.

[0027] The cutoff control circuit includes a transistor U. The base of transistor U is connected to the end of inductor L2 furthest from the MOSFET. The emitter of transistor U is connected to the drain D of the MOSFET. The collector of transistor U is connected to the gate G of the MOSFET. When the switch is off, the voltage at the base of transistor U is greater than the voltage at its emitter, causing it to quickly conduct and pull the voltage at the gate G of the MOSFET down to a level lower than the voltage at the source S, thus cutting off the MOSFET.

[0028] As can be seen from the above embodiments, the structure and control method of the MOS transistor control circuit proposed in this invention are relatively simple.

[0029] In the above examples, when the switch is off, in order to further enable the MOSFET to cut off the current in the circuit more completely, the cutoff control circuit pulls the voltage of the MOSFET's gate G down to a level lower than the voltage of the source S. Preferably, the voltage of the gate G is 0.1~0.3V higher than the voltage of the drain D. In this way, the voltages of the MOSFET's gate G and drain D are close to each other and much lower than the voltage of the source S.

[0030] In the above embodiments, the capacitance of capacitor C1 is preferably ≤0.01μF. The small capacitance of capacitor C1 can ensure that when the switch is turned on, the voltage of capacitor C1 rises rapidly, thereby quickly driving the voltage of the gate G of the MOSFET to be higher than the voltage of the drain D, thus accelerating the conduction of the MOSFET. In this example, the capacitance of capacitor C1 is 0.01μF.

[0031] The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement the present invention. Various modifications to the above embodiments will be readily apparent to those skilled in the art, such as replacing the N-type MOS transistor in the above embodiments with a P-type MOS transistor; the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention.

[0032] It should be understood that the present invention is not limited to the content already described above, and various modifications and changes can be made without departing from its scope. The scope of the present invention is limited only by the appended claims.

Claims

1. A MOSFET control circuit for a switching power supply, characterized in that, The MOS tube is connected with the secondary coil of the transformer T, the source S is connected with one end of the capacitor C2 and the output through the inductor L2 respectively, the gate G is connected with the voltage control circuit, and the other end of the capacitor C2 is grounded; the voltage control circuit comprises a conduction control circuit and a cutoff control circuit, the on-off of the loop where the primary coil of the transformer T is located is controlled by a switch, when the switch is on, the conduction control circuit pulls up the voltage of the gate G of the MOS tube to be higher than the voltage of the drain D, and the MOS tube is turned on; when the switch is off, the cutoff control circuit pulls down the voltage of the gate G of the MOS tube to be lower than the voltage of the source S, and the MOS tube is turned off; The conduction control circuit comprises a capacitor C1, one end of the capacitor C1 is connected with the gate G and the drain D of the MOS tube respectively, and the other end of the capacitor C1 is connected with one end of the inductor L2 away from the MOS tube; The capacitor C1 is connected with the drain D of the MOS tube through the inductor L1; A diode D2 is further arranged between the inductor L1 and the drain D of the MOS tube, the anode of the diode D2 is connected with the drain D of the MOS tube, and the cathode is connected with one end of the inductor L1 away from the capacitor C1; The cutoff control circuit comprises a triode U, the base of the triode U is connected with one end of the inductor L2 away from the MOS tube, the emitter of the triode U is connected with the drain D of the MOS tube, and the collector of the triode U is connected with the gate G of the MOS tube.

2. The MOSFET control circuit for a switching power supply of claim 1, wherein, The capacity of the capacitor C1 is less than or equal to 0.01 microfarad.

3. The MOSFET control circuit for a switching power supply of claim 1, wherein, When the switch is off, the cutoff control circuit pulls down the voltage of the gate G of the MOS tube to be lower than the voltage of the source S, and the voltage of the gate G is 0.1-0.3V higher than the voltage of the drain D.

4. The MOSFET control circuit for a switching power supply of claim 1, wherein, A diode D1 is further arranged, the anode of the diode D1 is grounded, and the cathode is connected with the source S of the MOS tube.

Images