CN102223069A - Self-driven synchronous buck converter circuit - Google Patents

Abstract

The present invention provides a self-driven synchronous step-down converter circuit, which includes an input port, a main power MOS transistor M1, a freewheeling MOS transistor M2, a filter capacitor C and a filter inductor L, and the filter inductor L includes a mutually coupled main topology output filter Inductor coil and freewheeling MOS tube drive coil, terminals 1 and 3 of the filter inductor L are terminals with the same name, the drain of the main power MOS tube M1 is connected to the input port, the source of the main power MOS tube M1 is connected to terminal 1 of the filter inductor L Connection, the 2 ends of the filter inductor L are connected to one end of the filter capacitor C, the other end of the filter capacitor C is grounded, the drain of the freewheeling MOS transistor M2 is connected to the first end of the filter inductor L, and the source of the freewheeling MOS transistor M2 is grounded , the source and gate of the freewheeling MOS transistor M2 are respectively connected to terminals 3 and 4 of the filter inductor L. The beneficial effect of the invention is that the low-side driving chip is omitted, and the freewheeling MOS tube can be driven auxiliaryly by the freewheeling MOS tube driving coil of the filter inductor, thereby simplifying the circuit and reducing the cost.

Description

A Self-Driven Synchronous Buck Converter Circuit

technical field

The present invention relates to a synchronous step-down converter circuit, in particular to a self-driven synchronous step-down converter circuit with a semiconductor switch in a half-bridge configuration in a high-frequency DC/DC converter and controlled by a complementary driving signal.

Background technique

At present, the use of power converters is becoming more and more common. In order to obtain lower output voltage, higher current, and faster transient response, designers have begun to use synchronous rectification technology.

The circuit diagram of the existing synchronous step-down converter circuit is shown in Figure 1. Compared with the traditional step-down converter, the synchronous step-down converter replaces the freewheeling diode with a controllable MOS tube, and utilizes the low on-resistance of the MOS tube And fast switching characteristics, in higher power applications, lower output voltage, higher efficiency and faster transient response can be obtained.

As shown in Figure 1, a synchronous buck converter usually uses a dedicated driver chip to control the high-side and low-side MOS transistors. The working process is as follows:

After the input terminal of the synchronous step-down converter is powered, the control chip and the driver chip start to work, and the control chip sends a master control pulse signal to the driver chip, and the driver chip applies two sets of complementary gate drives to the power MOS transistors M1 and M2 respectively. pulse. When the power MOS transistor M1 is turned on, the power MOS transistor M2 is turned off. At this time, the main power flows in from the power MOS transistor M1, passes through the filter inductor L and the filter capacitor C, and then is transmitted to the load resistor R. During this process, the inductor L and the capacitor C are charged. When the power MOS transistor M1 is turned off, the power MOS transistor M2 is turned on, and the energy stored in the inductor L is released through the power MOS transistor M2, the filter capacitor C and the load resistor R. If the circuit works in discontinuous mode, then the inductance L will reverse the freewheeling flow.

Therefore, each power MOS transistor in this synchronous step-down converter circuit must have a dedicated drive device to drive them to work, which can be a separate high-side drive chip and low-side drive chip, or both can be integrated. The driver chip leads to a more complex circuit, a larger number of components, and a higher cost.

Contents of the invention

In order to solve the problems in the prior art, the present invention provides a self-driven synchronous buck converter circuit.

The present invention provides a self-driven synchronous step-down converter circuit, including an input port for receiving an input voltage, a main power MOS transistor M1, a freewheeling MOS transistor M2, and a high-side drive chip for driving the main power MOS transistor M1 , a filter capacitor C and a filter inductance L, wherein the filter inductance L includes two groups of coils, wherein one group of coils is a main topology output filter inductance coil with terminals 1 and 2, and the other group of coils is a freewheeling coil with terminals 3 and 4 MOS tube drive coil, the main topology output filter inductor coil is coupled with the freewheeling MOS tube drive coil, terminals 1 and 3 of the filter inductor L are terminals with the same name, and the drain of the main power MOS tube M1 is connected to the drain of the main power MOS tube M1. The input port is connected, the source of the main power MOS transistor M1 is connected to terminal 1 of the filter inductor L, terminal 2 of the filter inductor L is connected to one end of the filter capacitor C, and the filter capacitor C The other end of the freewheeling MOS transistor M2 is connected to the ground, the drain of the freewheeling MOS transistor M2 is connected to terminal 1 of the filter inductor L, the source of the freewheeling MOS transistor M2 is grounded, and the source of the freewheeling MOS transistor M2 is connected to the The three terminals of the filter inductor L are connected, and the gate of the freewheeling MOS transistor M2 is connected to the four terminals of the filter inductor L.

As a further improvement of the present invention, an inductance L _add is connected in series between the source of the freewheeling MOS transistor M2 and the three terminals of the filter inductor L, and the inductance L _add is used to prevent the main power MOS transistor M1, The freewheeling MOS transistor M2 is turned on instantaneously.

As a further improvement of the present invention, one end of the inductor L _add is connected to the source of the freewheeling MOS transistor M2, and the other end is connected to the intersection of the main power MOS transistor M1 and the first end of the filter inductor L.

As a further improvement of the present invention, the filter capacitor C is connected with a load resistor R in parallel.

As a further improvement of the present invention, the TG end of the high-side driver chip is connected to the gate of the main power MOS transistor M1, and the TS end of the high-side driver chip is connected to the source of the main power MOS transistor M1 .

The beneficial effects of the present invention are: through the above scheme, the low-side drive chip is omitted, and the freewheeling MOS transistor can be driven by the freewheeling MOS transistor driving coil of the filter inductor, which simplifies the circuit and reduces the cost.

Description of drawings

FIG. 1 is a circuit diagram of an existing synchronous buck converter circuit;

Fig. 2 is a circuit diagram of a self-driven synchronous step-down converter circuit of the present invention;

Fig. 3 is a schematic diagram of topological work when the main power MOS tube M1 of the self-driven synchronous step-down converter circuit of the present invention is turned on;

Fig. 4 is the working diagram when the inductance of the self-driven synchronous step-down converter circuit of the present invention is freewheeling;

Fig. 5 is the working diagram when the inductance of the self-driven synchronous step-down converter circuit of the present invention reverses freewheeling;

FIG. 6 is a waveform diagram of driving signals of the main power MOS transistor M1 and the freewheeling MOS transistor M2 of the self-driven synchronous buck converter circuit of the present invention.

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

As shown in Figure 2, a self-driven synchronous buck converter circuit includes an input port for receiving a DC input voltage, an output port for providing a regulated DC output voltage, a main power MOS transistor M1, a freewheeling MOS Tube M2, a high-side drive chip for driving the main power MOS tube M1, a filter capacitor C, and a filter inductor L, wherein the filter inductor L includes two sets of coils, and one set of coils is a main topology with 1 and 2 terminals Output filter inductance coil, another set of coils is a freewheeling MOS tube drive coil with terminals 3 and 4, the main topology output filter inductance coil is coupled with the freewheeling MOS tube drive coil, and 1, 2 of the filter inductance L Terminal 3 is the terminal with the same name, the drain of the main power MOS transistor M1 is connected to the input port, the source of the main power MOS transistor M1 is connected to terminal 1 of the filter inductor L, and the filter inductor L Terminal 2 is connected to one terminal of the filter capacitor C, the other terminal of the filter capacitor C is grounded, the drain of the freewheeling MOS transistor M2 is connected to terminal 1 of the filter inductor L, and the freewheeling MOS transistor M2 The source of the freewheeling MOS transistor M2 is connected to terminal 3 of the filter inductor L, and the gate of the freewheeling MOS transistor M2 is connected to terminal 4 of the filter inductor L.

As shown in Fig. 2, an inductance L _add is connected in series between the source of the freewheeling MOS transistor M2 and the three ends of the filter inductor L, and the inductance L _add is used to prevent the main power MOS transistor M1, continued The flow MOS tube M2 is turned on instantaneously. Wherein, the inductance L _add is an inductance with a small inductance.

As shown in FIG. 2 , one end of the inductor L _add is connected to the source of the freewheeling MOS transistor M2 , and the other end is connected to the intersection of the main power MOS transistor M1 and terminal 1 of the filter inductor L .

As shown in FIG. 2 , the filter capacitor C is connected with a load resistor R in parallel.

As shown in FIG. 2 , the TG terminal of the high-side driver chip is connected to the gate of the main power MOS transistor M1 , and the TS terminal of the high-side driver chip is connected to the source of the main power MOS transistor M1 .

The operating principle of a self-driven synchronous step-down converter circuit provided by the present invention is:

1. When the high-side driver chip drives the main power MOS transistor M1 to turn on, as shown in Figure 3, the main topology output filter inductor coil 1 of the filter inductor L induces a positive voltage. According to the voltage relationship at the end of the same name, the filter inductor L The 3 terminals of the freewheeling MOS tube drive coil also induce a positive voltage, and the 4 terminals of the freewheeling MOS tube drive coil of the filter inductor L induce a negative voltage, and the freewheeling MOS tube drive coil of the filter inductor L will make the freewheeling MOS tube M2 The gate of the gate is subjected to negative voltage, so that the freewheeling MOS transistor M2 is turned off, and the input DC level is sequentially transmitted to the load resistor R through the main power MOS transistor M1, filter inductor L, and filter capacitor C;

2. When the high-side driver chip drives the main power MOS transistor M1 to turn off, as shown in Figure 4, a negative voltage is induced at terminal 1 of the freewheeling inductor L. According to the voltage relationship at the end of the same name, the freewheeling MOS transistor of the filter inductor L drives the coil Negative voltage is also induced at terminal 3 of filter inductor L, and positive voltage is induced at terminal 4 of the freewheeling MOS tube drive coil of filter inductor L. The drive coil of the freewheeling MOS tube of the filter inductance L will cause the gate of the freewheeling MOS tube M2 to bear the forward voltage, so that the freewheeling MOS tube M2 will be turned on, and the filter inductance L will pass through the filter capacitor C, the load resistor R, and the continuous current in turn. Flow MOS tube M2 and inductor L _add complete freewheeling;

3. If the load is light and the inductor current works intermittently, as shown in Figure 5, then the freewheeling inductor continues to flow in the opposite direction, and the 2 terminals of the filter inductor L still induce a positive voltage, and the 1 terminal induces a negative voltage, and the filter inductor L Negative voltage is still induced at terminal 3 of the freewheeling MOS tube driving coil, positive voltage is induced at terminal 4 of the freewheeling MOS tube driving coil of the filter inductor L, the gate of the freewheeling MOS tube M2 bears positive voltage, and the freewheeling MOS tube The tube M2 is still conducting, providing a path for the reverse freewheeling of the inductor.

In summary, it can be seen that the driving signals of the main power MOS transistor M1 and the freewheeling MOS transistor M2 are opposite, as shown in FIG. 6 , so as to ensure the normal operation of the circuit. However, such a situation may occur, when the freewheeling MOS transistor M2 is turned on, terminal 1 of the filter inductor L is a negative voltage, and terminal 2 is a positive voltage. If the main power MOS tube M1 is suddenly turned on, the positive voltage has not been sensed at the terminal 1 of the filter inductor L at this time, and the freewheeling MOS tube M2 cannot be turned off immediately, resulting in the main power MOS tube M1 and the freewheeling MOS tube M2 At the same time conduction, resulting in a short circuit at the input port.

In order to avoid this phenomenon, it is necessary to connect an inductance L _{add with} a small inductance value in series with the drain of the freewheeling MOS transistor M2, and the inductance L _add will momentarily block the current, so that the main power MOS transistor M1 and the freewheeling MOS transistor M2 will not Immediately pass through to allow time for the change of the induced voltage of the filter inductor L, so as to ensure that the freewheeling MOS transistor M2 is reliably turned off.

Compared with the traditional synchronous step-down converter circuit, the self-driven synchronous step-down converter circuit provided by the present invention has the advantages of simple circuit structure, high efficiency and low cost.

The above content is a further detailed description of the present invention in conjunction with specific preferred embodiments, and it cannot be assumed that the specific implementation of the present invention is limited to these descriptions. For those of ordinary skill in the technical field of the present invention, without departing from the concept of the present invention, some simple deduction or replacement can be made, which should be regarded as belonging to the protection scope of the present invention.

Claims (5)

1. self-driven synchronous buck converter circuit, it is characterized in that: comprise the input port that is used to receive input voltage, main power MOS pipe M1, afterflow metal-oxide-semiconductor M2, drive the flash chip for driving of described main power MOS pipe M1, filter capacitor C and filter inductance L, wherein, described filter inductance L comprises two groups of coils, wherein one group of coil is for having 1, the topological output inductor coil of the master of 2 ends, another group coil is for having 3, the afterflow metal-oxide-semiconductor drive coil of 4 ends, topological output inductor coil of described master and described afterflow metal-oxide-semiconductor drive coil intercouple, 1 of described filter inductance L, 3 ends are end of the same name, the drain electrode of described main power MOS pipe M1 is connected with described input port, the source electrode of described main power MOS pipe M1 is connected with 1 end of described filter inductance L, 2 ends of described filter inductance L are connected with the end of described filter capacitor C, the other end ground connection of described filter capacitor C, the drain electrode of described afterflow metal-oxide-semiconductor M2 is connected with 1 end of described filter inductance L, the source ground of described afterflow metal-oxide-semiconductor M2, the source electrode of described afterflow metal-oxide-semiconductor M2 is connected with 3 ends of described filter inductance L, and the grid of described afterflow metal-oxide-semiconductor M2 is connected with 4 ends of described filter inductance L.

2. self-driven synchronous buck converter circuit according to claim 1 is characterized in that: be in series with inductance L between the source electrode of described afterflow metal-oxide-semiconductor M2 and 3 ends of described filter inductance L _Add, described inductance L _AddBe used to avoid described main power MOS pipe M1, afterflow metal-oxide-semiconductor M2 moment conducting.

3. self-driven synchronous buck converter circuit according to claim 2 is characterized in that: described inductance L _AddAn end be connected with the source electrode of described afterflow metal-oxide-semiconductor M2, the other end is connected with the intersection point of 1 end of described filter inductance L with described main power MOS pipe M1.

4. self-driven synchronous buck converter circuit according to claim 1 is characterized in that: described filter capacitor C is parallel with load resistance R.

5. self-driven synchronous buck converter circuit according to claim 1, it is characterized in that: the TG end of described flash chip for driving is connected with the grid of described main power MOS pipe M1, and the TS end of described flash chip for driving is connected with the source electrode of described main power MOS pipe M1.

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