A self-excited BUCK circuit

Abstract

The present invention discloses a self-excited BUCK circuit, including a main power circuit, a driving circuit, a starting circuit and a negative feedback control circuit. The main power circuit includes a switch tube TR1, wherein: it also includes a switch tube TR2 and a driving circuit of the switch tube TR2, the drain of the switch tube TR2 serves as the output voltage negative electrode of the main power circuit, and at the same time, the switch tube TR2 and the switch tube TR1 maintain an open and a conduction state. The present invention adopts a topological structure in which two switch tubes are complementary-conducted, which can achieve higher energy efficiency under low current levels, thereby reducing the loss in the self-excited BUCK circuit.

Description

Technical Field

[0001] The invention relates to a self-excited BUCK circuit, in particular to a self-excited BUCK circuit using switch tubes for complementary conduction. Background Art

[0002] In the field of power electronics, the switching power supply is an important component of the power supply of electronic equipment, and its performance directly affects the stability and efficiency of the entire system. Buck circuit, as a widely used DC-to-DC step-down circuit, is widely used in many fields due to its high efficiency and flexibility. Buck circuit, also known as step-down circuit, realizes the conversion of input voltage to output voltage by controlling the on and off of the switch tube. In the Buck circuit, MOSFET (metal oxide semiconductor field effect transistor) is usually used as the switch tube. When the MOSFET is turned on, the input voltage supplies power to the load through the inductor and charges the capacitor at the same time; when the MOSFET is turned off, the inductor discharges the lower tube MOSFET through the freewheeling diode or in the synchronous Buck circuit to maintain the stability of the output voltage.

[0003] Chinese patent document CN206389278U discloses a self-excited switching power supply circuit. The self-excited switching power supply circuit includes a main power circuit, a driving circuit, a driving time-limiting circuit, a starting circuit, a positive feedback control circuit and a negative feedback control circuit. The driving circuit effectively drives the main power switch tube to increase the switching speed of the main power switch tube, thereby improving the efficiency of the entire circuit; the driving time-limiting circuit can limit the opening time of the main power switch tube to achieve the purpose of limiting the peak current of the main power inductor, so that the circuit can work reliably under a higher input voltage; the negative feedback control circuit monitors the output voltage so that the circuit works in an "intermittent mode" when it is unloaded or lightly loaded, thereby reducing the power consumption of the entire circuit. The utility model has a simple circuit structure, high cost performance, high reliability, and is easy to mass produce. When the self-excited switching power supply circuit in the prior art is applied to the auxiliary power supply of the motor, due to the use of a diode freewheeling method, the energy efficiency is also low when the current level is low. Summary of the invention

[0004] In order to solve the technical problem that the existing self-excited BUCK circuit using diode freewheeling has low energy efficiency when the current level is low, the present invention provides a self-excited BUCK circuit, including a main power circuit, a drive circuit, a start circuit and a negative feedback control circuit. The main power circuit includes a switch tube TR1, wherein: it also includes a switch tube TR2 and a drive circuit of the switch tube TR2. The drain of the switch tube TR2 serves as the negative electrode of the output voltage of the main power circuit. At the same time, the switch tube TR2 and the switch tube TR1 maintain an open and a conducting state.

[0005] Note: In this solution, at the same time, the switch tube TR2 and the switch tube TR1 maintain an on and off state, which means that when the switch tube TR1 is turned on, the drive circuit of the switch tube TR2 drives the switch tube TR2 to turn off, and when the switch tube TR1 is turned off, the drive circuit of the switch tube TR2 drives the switch tube TR2 to turn on.

[0006] In the prior art, since the diode needs to consume part of the power to make the diode conduct before the freewheeling operation can be performed, and the voltage drop when the diode is turned on will cause a large amount of power consumption, especially when the current level is low, it will greatly reduce the energy efficiency. Therefore, compared with the topology of diode freewheeling in the prior art, this solution adopts a topology structure of two switching tubes for complementary conduction. Since the on-resistance of the switching tube is smaller, it can achieve higher energy efficiency at a lower current level, thereby reducing the loss in the self-excited BUCK circuit.

[0007] Preferably, a dead zone cut-off circuit is further included, and when the switch tube TR1 is turned on, the dead zone cut-off circuit accelerates the turn-off of the switch tube TR2. In order to avoid a short circuit in the self-excited BUCK circuit, the dead zone cut-off circuit is used in this solution to accelerate the turn-off of the switch tube TR2, which can further ensure that the two switch tubes are not turned on at the same time, so as to avoid a short circuit in the self-excited BUCK circuit.

[0008] Preferably, the main power circuit also includes an inductor L1, the source of the switch tube TR1 is connected to the positive electrode of the input voltage Vin, the drain of the switch tube TR1 is connected to one end of the inductor L1, the other end of the inductor L1 serves as the positive electrode of the output voltage of the main power circuit, and is connected to one end of the output capacitor C3, and the other end of the output capacitor C3 is connected to the source of the switch tube TR2.

[0009] Preferably, the driving circuit of the switch tube TR2 includes a resistor R4, a resistor R7, a diode D3, a voltage regulator tube Z1 and a filter capacitor C1, one end of the resistor R4 is connected to the positive electrode of the input voltage Vin, the other end of the resistor R4 is respectively connected to the cathode of the diode D3, one end of the resistor R7 and one end of the filter capacitor C1, the other end of the filter capacitor C1 is connected to the source of the switch tube TR2, the cathode of the voltage regulator tube Z1 is respectively connected to one end of the resistor R7, the anode of the diode D3 and the gate of the switch tube TR2, and the anode of the voltage regulator tube Z1 is connected to the source of the switch tube TR2.

[0010] Preferably, the dead zone cut-off circuit includes a resistor R5, a resistor R6, a transistor Q5 and a diode D1, one end of the resistor R5 is connected to the drain of the switch tube TR1, the other end of the resistor R5 is respectively connected to one end of the resistor R6, the anode of the diode D1 and the base of the transistor Q5, the emitter of the transistor Q5 is connected to the other end of the resistor R6 and the cathode of the diode D1 and is grounded, and the collector of the transistor Q5 is connected to the drive circuit of the switch tube TR2.

[0011] Preferably, the driving circuit includes a transistor Q1, a resistor R1, a resistor R3, a diode D2, a transistor Q2 and a transistor Q3, the emitter of the transistor Q1 is connected to the gate of the switch tube TR1 and the anode of the diode D2, one end of the resistor R1 is connected to the source of the switch tube TR1 and the collector of the transistor Q1, the cathode of the diode D2 is respectively connected to the base of the transistor Q1, the other end of the resistor R1, the collector of the transistor Q2 and the collector of the transistor Q3, the emitter of the transistor Q2 is connected to the base of the transistor Q3, and the emitter of the transistor Q3 is connected to the starting circuit.

[0012] Preferably, the starting circuit includes a resistor R2, a transistor Q4 and a transistor Q7, one end of the resistor R2 is respectively connected to the emitter of the transistor Q3, the base of the transistor Q4 and the base of the transistor Q7, the emitter of the transistor Q4 is connected to the emitter of the transistor Q7 and the other end of the resistor R2, and then connected to the negative electrode of the input voltage Vin, and the collector of the transistor Q4 is connected to the drive circuit of the switch tube TR2.

[0013] Preferably, the negative feedback control circuit includes a voltage regulator tube Z2, a resistor R8, a transistor Q6, a resistor R9 and a capacitor C2, the cathode of the voltage regulator tube Z2 is connected to the positive electrode of the output voltage, the anode of the voltage regulator tube Z2 is connected to one end of the resistor R8, the other end of the resistor R8 is respectively connected to one end of the resistor R9, one end of the capacitor C2 and the base of the transistor Q6, the other end of the capacitor C2 is connected to the other end of the resistor R9 and the emitter of the transistor Q6 and is grounded, and the collector of the transistor Q6 is connected to the drive circuit.

[0014] The present invention has the following beneficial effects:

[0015] 1. The present invention adopts a topological structure in which two switch tubes are complementary to each other, replacing the topological structure in which diode freewheeling is used in the prior art, and can achieve higher energy efficiency at a lower current level;

[0016] 2. The design of the dead zone cut-off circuit in the present invention can accelerate the turn-off of the switch tube TR2, and can solve the short circuit problem caused by the simultaneous conduction of the two switch tubes during the complementary conduction of the two switch tubes;

[0017] 3. The present invention controls the circuit by means of self-excitation feedback, does not require an additional controller, and can reduce the cost of the product. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 A circuit schematic diagram of an embodiment of a self-excited BUCK circuit of the present invention;

[0019] Figure 2 for Figure 1 Circuit structure partition diagram;

[0020] Figure 3 shows Figure 1 Schematic diagram of the working principle. DETAILED DESCRIPTION

[0022] The following is further described in detail through specific implementation methods:

[0023] 1. Definition

[0024] Current level: The current level is usually divided according to the intensity of the current, mainly including microcurrent, milliampere current and ampere current.

[0025] Dead zone cutoff: refers to the state where the diode cannot conduct electricity under low voltage. When the voltage of the diode is lower than a certain value, the current cannot pass through, and this area is called dead zone cutoff. Because at low voltage, the carrier concentration of the diode is too low to form enough charge carriers, so the current cannot pass through and the diode is cut off.

[0026] 2. The reference numerals in the drawings of the specification include: drive circuit 301, drive circuit ①302 of switch tube TR2, dead zone cut-off circuit 303, negative feedback control circuit 304, start-up circuit 305, drive circuit ②306 of switch tube TR2.

[0027] The embodiment is basically as follows Figure 1 and Figure 2As shown: a self-excited BUCK circuit, including a main power circuit, a driving circuit 301, a starting circuit 305, a dead zone cut-off circuit 303 and a negative feedback control circuit 304. The main power circuit is a BUCK conversion circuit, including a switch tube TR1, a switch tube TR2 and an inductor L1. The source of the switch tube TR1 is connected to the positive electrode of the input voltage Vin, the drain of the switch tube TR1 is connected to one end of the inductor L1, and the other end of the inductor L1 is used as the positive electrode of the output voltage of the main power circuit and is connected to one end of the output capacitor C3. The other end of the output capacitor C3 is connected to the source of the switch tube TR2. The drain of the switch tube TR2 is used as the negative electrode of the output voltage of the main power circuit. When the switch tube TR1 is turned on, the driving circuit of the switch tube TR2 drives the switch tube TR2 to turn off. When the switch tube TR1 is turned off, the driving circuit of the switch tube TR2 drives the switch tube TR2 to turn on. The switch tube TR1 is a PMOS, and the switch tube TR2 is an NMOS.

[0028] When the switch tube TR1 is turned on, the dead zone cut-off circuit 303 accelerates the switch tube TR2 to turn off. The dead zone cut-off circuit 303 includes a resistor R5, a resistor R6, a transistor Q5 and a diode D1, one end of the resistor R5 is connected to the drain of the switch tube TR1, the other end of the resistor R5 is respectively connected to one end of the resistor R6, the anode of the diode D1 and the base of the transistor Q5, the emitter of the transistor Q5 is connected to the other end of the resistor R6 and the cathode of the diode D1 and is grounded, and the collector of the transistor Q5 is connected to the drive circuit of the switch tube TR2.

[0029] The driving circuit 301 includes a transistor Q1, a resistor R1, a resistor R3, a diode D2, a transistor Q2 and a transistor Q3. The emitter of the transistor Q1 is connected to the gate of the switch tube TR1 and the anode of the diode D2. One end of the resistor R1 is connected to the source of the switch tube TR1 and the collector of the transistor Q1. The cathode of the diode D2 is respectively connected to the base of the transistor Q1, the other end of the resistor R1, the collector of the transistor Q2 and the collector of the transistor Q3. The emitter of the transistor Q2 is connected to the base of the transistor Q3. The emitter of the transistor Q3 is connected to the start-up circuit 305.

[0030] The starting circuit 305 includes a resistor R2, a transistor Q4 and a transistor Q7. One end of the resistor R2 is connected to the emitter of the transistor Q3, the base of the transistor Q4 and the base of the transistor Q7 respectively. The emitter of the transistor Q4 is connected to the emitter of the transistor Q7 and the other end of the resistor R2 and then connected to the negative electrode of the input voltage Vin. The collector of the transistor Q4 is connected to the driving circuit of the switch tube TR2.

[0031] The negative feedback control circuit 304 includes a voltage regulator tube Z2, a resistor R8, a transistor Q6, a resistor R9 and a capacitor C2. The cathode of the voltage regulator tube Z2 is connected to the positive electrode of the output voltage, the anode of the voltage regulator tube Z2 is connected to one end of the resistor R8, the other end of the resistor R8 is respectively connected to one end of the resistor R9, one end of the capacitor C2 and the base of the transistor Q6, the other end of the capacitor C2 is connected to the other end of the resistor R9 and the emitter of the transistor Q6 and is grounded, the collector of the transistor Q6 is connected to the drive circuit 301, and the collector of the transistor Q6 is connected to the base of the transistor Q2.

[0032] It also includes a driving circuit of the switch tube TR2, and the driving circuit of the switch tube TR2 includes two parts: a driving circuit ①302 of the switch tube TR2 and a driving circuit ②306 of the switch tube TR2. The driving circuit of the switch tube TR2 includes a resistor R4, a resistor R7, a diode D3, a voltage regulator Z1 and a filter capacitor C1. One end of the resistor R4 is connected to the positive electrode of the input voltage Vin, and the other end of the resistor R4 is respectively connected to the collector of the transistor Q5, the cathode of the diode D3, one end of the resistor R7 and one end of the filter capacitor C1. The other end of the filter capacitor C1 is connected to the source of the switch tube TR2. The cathode of the voltage regulator Z1 is respectively connected to one end of the resistor R7, the anode of the diode D3 and the gate of the switch tube TR2. The anode of the voltage regulator Z1 is connected to the source of the switch tube TR2 and the emitter of the transistor Q4.

[0033] The specific implementation process is as follows: From the start-up to the normal operation of the self-excited BUCK circuit in this embodiment, the circuit operation is divided into two major processes: the switching process and the voltage stabilization process. Figure 3 As shown, the above two major processes are broken down step by step as follows:

[0034] 1) Switching process:

[0035] Step 1: Start the machine, the input voltage +Vin is added to the base of transistor Q2 through resistor R3, generating current i1. After being amplified by transistor Q2 and transistor Q3, the voltage at point b drops, the voltage at point a drops, the parasitic capacitance Cgs of switch tube TR1 is discharged, and switch tube TR1 starts to turn on;

[0036] Step 2: The voltage at point c rises, transistor Q4 turns on, and the voltage at point e drops; the gate voltage of switch tube TR2 drops, and switch tube TR2 turns off;

[0037] Step 3: During the turning-on process of the switch tube TR1, the voltage at point d gradually rises, the voltage at point f rises, the transistor Q5 is turned on, forming a positive feedback, accelerating the turning-off of the switch tube TR2;

[0038] Step 4: After the switch tube TR1 is turned on, the input voltage +Vin stores energy in the inductor L1;

[0039] Step 5: Under the action of ib, iq surges, and iq flows through the resistor R2 to increase the voltage at point c. As the voltage at point c increases, current flows through the emitter junction of transistor Q7, and transistor Q7 is turned on to generate current i3, which is in a downward direction, causing ib to decrease.

[0040] Step 6: ib decreases, iq decreases, the voltage at point c drops, and transistors Q4 and Q7 are turned off;

[0041] Step 7: When the voltage at point b rises to a certain level, transistor Q1 turns on, accelerating the rise of the voltage at point a and turning off the accelerating switch TR1;

[0042] Step 8: The switch tube TR1 is turned off, the voltage at point d is clamped to about -0.7V, the voltage at point f drops, the transistors Q5 and Q4 are both turned off, the voltage at point e increases, and the switch tube TR2 is turned on;

[0043] Step 9: After the inductor L1 has finished freewheeling, the voltage at point d rises, the voltage at point f rises, the transistor Q5 turns on, the voltage at point e decreases, the switch tube TR2 starts to turn off, and at the same time the diode D3 turns on, accelerating the turn-off speed of the switch tube TR2;

[0044] Step 10: At this time, transistor Q4 and transistor Q7 are turned off, the circuit returns to the initial state, and the next switching cycle begins;

[0045] 2) Voltage stabilization process:

[0046] Step 11: The circuit will charge the output capacitor C3 in each switching cycle. After several cycles, the voltage at point f rises, breaking down the voltage regulator Z2 and generating current iz.

[0047] Step 12: iz acts on transistor Q6, transistor Q6 is turned on, making ib current decrease, thereby preventing Step 1 process and turning off switch TR1; during the turning off process of TR1, the voltage at point d gradually decreases, and the current of inductor L1 first flows through the body diode of switch TR2. When switch TR1 is completely turned off, the voltage at point d drops to -0.7V, transistor Q5 is turned off, switch TR2 is turned on, and the current is transferred from the body diode of switch TR2 to the MOS tube;

[0048] Step 13: After that, the current of inductor L1 is gradually consumed, the voltage at point d rises, transistor Q5 is turned on again, and at the same time, the output voltage drops, iz decreases, and transistor Q6 is turned off;

[0049] Step 14: i1 regains the advantage and re-enters Step 1.

[0050] The self-excited switching power supply circuit using diode freewheeling in the prior art and the self-excited BUCK circuit using complementary conduction in this embodiment were tested, with an input voltage of 50V, an output voltage of 12V, and a full-load output of 12V, 1A. The output currents of the two circuits were measured and the efficiencies were calculated, and the results are shown in the following table.

[0051] Load current Diode freewheeling Complementary conduction Improve efficiency 0.10 43％ 45％ 2％ 0.20 58.50％ 61.50％ 3％ 0.30 66.70％ 70.60％ 4％ 0.40 71.60％ 76.20％ 5％ 0.50 75％ 80％ 5％ 0.60 77.40％ 82.30％ 5％ 0.70 79.20％ 85.70％ 6％ 0.80 80.70％ 86.40％ 6％ 0.90 82.40％ 88.50％ 6％ 1.00 84％ 90.30％ 6％

[0052] It can be seen from the above table that, compared with the prior art, the complementary conduction self-excited BUCK circuit of the present invention can improve the efficiency by 6% under the condition of full load output.

[0053] The above is only an embodiment of the present invention. The common sense such as the known specific structure and characteristics in the scheme is not described in detail here. The ordinary technicians in the relevant field know all the common technical knowledge in the technical field of the invention before the application date or priority date, can obtain all the existing technologies in the field, and have the ability to apply the conventional experimental means before that date. The ordinary technicians in the relevant field can improve and implement this scheme in combination with their own abilities under the enlightenment given by this application. Some typical known structures or known methods should not become obstacles for ordinary technicians in the relevant field to implement this application. It should be pointed out that for those skilled in the art, without departing from the structure of the present invention, several deformations and improvements can be made, which should also be regarded as the protection scope of the present invention, which will not affect the effect of the implementation of the present invention and the practicality of the patent. The protection scope required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims

1. A self-excited BUCK circuit, comprising a main power circuit, a drive circuit, a start-up circuit and a negative feedback control circuit, wherein the main power circuit comprises a switch tube TR1, and is characterized in that: It also includes a switch tube TR2 and a driving circuit of the switch tube TR2. The drain of the switch tube TR2 serves as the negative electrode of the output voltage of the main power circuit. At the same time, the switch tube TR2 and the switch tube TR1 maintain an open and a conducting state.

2. The self-excited BUCK circuit according to claim 1, characterized in that: It also includes a dead zone cut-off circuit. When the switch tube TR1 is turned on, the dead zone cut-off circuit accelerates the switch tube TR2 to turn off.

3. The self-excited BUCK circuit according to claim 2, characterized in that: The main power circuit also includes an inductor L1, the source of the switch tube TR1 is connected to the positive electrode of the input voltage Vin, the drain of the switch tube TR1 is connected to one end of the inductor L1, the other end of the inductor L1 serves as the positive electrode of the output voltage of the main power circuit, and is connected to one end of the output capacitor C3, and the other end of the output capacitor C3 is connected to the source of the switch tube TR2.

4. The self-excited BUCK circuit according to claim 3, characterized in that: The driving circuit of the switch tube TR2 includes a resistor R4, a resistor R7, a diode D3, a voltage regulator tube Z1 and a filter capacitor C1. One end of the resistor R4 is connected to the positive electrode of the input voltage Vin, and the other end of the resistor R4 is respectively connected to the cathode of the diode D3, one end of the resistor R7 and one end of the filter capacitor C1. The other end of the filter capacitor C1 is connected to the source of the switch tube TR2. The cathode of the voltage regulator tube Z1 is respectively connected to one end of the resistor R7, the anode of the diode D3 and the gate of the switch tube TR2, and the anode of the voltage regulator tube Z1 is connected to the source of the switch tube TR2.

5. The self-excited BUCK circuit according to claim 4, characterized in that: The dead zone cut-off circuit includes a resistor R5, a resistor R6, a transistor Q5 and a diode D1. One end of the resistor R5 is connected to the drain of the switch tube TR1, and the other end of the resistor R5 is respectively connected to one end of the resistor R6, the anode of the diode D1 and the base of the transistor Q5. The emitter of the transistor Q5 is connected to the other end of the resistor R6 and the cathode of the diode D1 and is grounded. The collector of the transistor Q5 is connected to the drive circuit of the switch tube TR2.

6. The self-excited BUCK circuit according to claim 5, characterized in that: The driving circuit includes a transistor Q1, a resistor R1, a resistor R3, a diode D2, a transistor Q2 and a transistor Q3. The emitter of the transistor Q1 is connected to the gate of the switch tube TR1 and the anode of the diode D2. One end of the resistor R1 is connected to the source of the switch tube TR1 and the collector of the transistor Q1. The cathode of the diode D2 is respectively connected to the base of the transistor Q1, the other end of the resistor R1, the collector of the transistor Q2 and the collector of the transistor Q3. The emitter of the transistor Q2 is connected to the base of the transistor Q3. The emitter of the transistor Q3 is connected to the start-up circuit.

7. The self-excited BUCK circuit according to claim 6, characterized in that: The starting circuit includes a resistor R2, a transistor Q4 and a transistor Q7, one end of the resistor R2 is respectively connected to the emitter of the transistor Q3, the base of the transistor Q4 and the base of the transistor Q7, the emitter of the transistor Q4 is connected to the emitter of the transistor Q7 and the other end of the resistor R2, and then connected to the negative electrode of the input voltage Vin, and the collector of the transistor Q4 is connected to the drive circuit of the switch tube TR2.

8. The self-excited BUCK circuit according to claim 7, characterized in that: The negative feedback control circuit includes a voltage regulator tube Z2, a resistor R8, a transistor Q6, a resistor R9 and a capacitor C2. The cathode of the voltage regulator tube Z2 is connected to the positive electrode of the output voltage, the anode of the voltage regulator tube Z2 is connected to one end of the resistor R8, the other end of the resistor R8 is respectively connected to one end of the resistor R9, one end of the capacitor C2 and the base of the transistor Q6, the other end of the capacitor C2 is connected to the other end of the resistor R9 and the emitter of the transistor Q6 and is grounded, and the collector of the transistor Q6 is connected to the drive circuit.

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