A high voltage buck circuit

Abstract

The application relates to a high-voltage Buck circuit, which comprises a main Buck circuit and a control circuit for controlling the operation of the main Buck circuit, wherein the control circuit comprises a control chip, a first freewheeling circuit, a voltage dividing circuit and a soft-start control circuit; the soft-start control circuit comprises a switching device, one end of the switching device being connected with a feedback voltage sampling pin of the control chip; and a charge-discharge circuit, the other end of the switching device and the main Buck circuit being connected with the charge-discharge circuit respectively, so that the switching device is turned on to raise the voltage collected by the feedback voltage sampling pin, and then the energy output by the control chip is reduced. The application has the advantages that the soft-start control circuit can compensate for the shortage of the internal soft driving time of the chip, and can avoid the phenomenon of output voltage overshoot in the power-on process when a larger capacitive load is connected to the output.

Description

Technical Field

[0001] This invention relates to the field of switching power supply technology, and in particular to a high-voltage Buck circuit. Background Technology

[0002] The Buck circuit, also known as a step-down circuit, has the following basic structure: Figure 1 As shown, it mainly includes AC input L / N, rectifier bridge (composed of first diode VD1, second diode VD2, third diode VD3 and fourth diode VD4), first capacitor C1, MOSFET M1, fifth diode VD5, inductor L1, second capacitor C2 and first resistor R1. The first capacitor C1 is used to store the rectified energy, the fifth diode VD5 is a freewheeling diode; the second capacitor C2 is the output filter capacitor, used to stabilize the output voltage; the first resistor R1 acts as a load.

[0003] In practical circuits, Figure 1 The MOSFET M1 and control circuit in the circuit will be replaced by integrated circuits and peripheral circuits. The replaced circuit is as follows: Figure 2 As shown, integrated chip N1 has a built-in NMOS transistor. The Drain pin is the drain of the NMOS transistor; the Source pin is the source of the NMOS transistor; the control circuit inside integrated chip N1 uses the Source pin as a reference ground; VCC is the power supply port; the FB pin is the feedback voltage sampling point; the inductor L1 in the Buck circuit has a freewheeling function. When the NMOS transistor inside integrated chip N1 is turned on, the current in inductor L1 gradually increases; when the NMOS transistor is turned off, the current in inductor L1 has three freewheeling paths operating simultaneously: inductor L1 - second capacitor C2 - fifth capacitor C2. The circuit consists of diode VD5, inductor L1, sixth diode VD6, third capacitor C3, inductor L1, seventh diode VD7, and fourth capacitor C4. In other words, under steady-state conditions, if the voltage drops across diodes VD5, VD6, and VD7 are not considered, the voltages across the second capacitor C2, third capacitor C3, and fourth capacitor C4 are equal. The voltage across the third capacitor C3 passes through the two voltage divider resistors R2 and R3 and then enters the FB pin of integrated chip N1. The voltage across the third capacitor C3 reflects the voltage value across the second capacitor C2. Capacitor C4 is used to stabilize the power supply voltage of integrated chip N1.

[0004] This circuit integrates a soft-start function within the integrated chip N1. Soft-start prevents output voltage overshoot during power-up. However, since the soft-start time within integrated chip N1 is fixed, if the capacitance of the second capacitor C2 is very large after the soft-start time ends, the voltage across C2 may still not reach the set value. In this case, integrated chip N1, by detecting the voltage on the FB pin, may mistakenly interpret this as a large load and continue to increase the output power, ultimately causing the Buck circuit to experience output voltage overshoot. Therefore, further improvements are needed. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a high-voltage Buck circuit that can effectively prevent output voltage overshoot compared with the above-mentioned prior art.

[0006] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows: a high-voltage Buck circuit, including a main Buck circuit and a control circuit for controlling the operation of the main Buck circuit, wherein the control circuit includes:

[0007] The control chip has a built-in switching transistor and a power supply pin and a feedback voltage sampling pin.

[0008] The first freewheeling circuit has one end connected to the main Buck circuit and the other end connected to the power supply pin of the control chip through the seventh diode; it is used to provide voltage to the control chip by turning off the freewheeling circuit when the switching transistor in the control chip turns off the freewheeling circuit.

[0009] The voltage divider circuit has its first terminal connected to the seventh diode, its second terminal connected to the reference ground of the control chip, and its voltage divider output terminal connected to the feedback voltage sampling pin of the control chip.

[0010] Its characteristic is that it further includes a soft-start control circuit disposed within the control circuit, the soft-start control circuit comprising:

[0011] A switching device, one end of which is connected to the feedback voltage sampling pin of the control chip; and

[0012] The charging and discharging circuit is connected to the other end of the switching device and the main Buck circuit, respectively, to turn on the switching device and raise the voltage collected by the feedback voltage sampling pin, thereby reducing the energy output by the control chip.

[0013] Furthermore, the charging and discharging circuit includes a fifth capacitor and a fifth resistor connected in series with the fifth capacitor.

[0014] Preferably, the switching device is a transistor, with the emitter of the transistor serving as one end of the switching device for connection to the feedback voltage sampling pin of the control chip, and the base of the transistor serving as the other end of the switching device for connection to the fifth resistor. The collector of the transistor is connected to the first end of the voltage divider circuit through a current-limiting resistor.

[0015] Furthermore, the main Buck circuit includes a fifth diode, an inductor, and a second capacitor. The cathode of the fifth diode is connected to the inductor, the other end of the inductor is connected to the second capacitor, and the other end of the second capacitor is connected to the anode of the fifth diode.

[0016] Preferably, the control chip has a built-in MOSFET as the switching transistor, so that the control chip has a drain pin and a source pin. The drain pin of the control chip is connected to one end of the external power supply, and the source pin of the control chip is connected to the second end of the voltage divider circuit as a reference ground, and is connected between the inductor and the fifth diode.

[0017] To stabilize the base-emitter junction voltage of the transistor and prevent false turn-on due to low voltage, the soft-start control circuit includes a sixth capacitor and a sixth resistor connected in parallel with it. One end of the sixth capacitor and the sixth resistor is connected to the base of the transistor, and the other end is connected to the source pin of the control chip. This sixth capacitor stabilizes the base-to-ground voltage of the transistor, thereby indirectly stabilizing the base-emitter junction voltage. The sixth resistor is only used to discharge the sixth capacitor after the external power supply fails.

[0018] The first freewheeling circuit includes a sixth diode and a third capacitor. The cathode of the sixth diode is connected to one end of the third capacitor and is also connected to the power supply pin of the control chip. The anode of the sixth diode and the other end of the third capacitor are respectively connected to the two ends of the inductor. The freewheeling effect of the inductor is used to charge the third capacitor when the MOSFET built into the control chip is turned off, so that the voltage on the third capacitor, after passing through a voltage divider circuit, enters the feedback voltage sampling pin of the control chip.

[0019] To prevent the transistor from conducting during normal operation, the soft-start control circuit also includes a second freewheeling circuit connected to the main Buck circuit and the charging / discharging circuit respectively. The second freewheeling circuit includes an eighth diode, a seventh capacitor, and a seventh resistor. The eighth diode and the seventh capacitor are connected in series and then in parallel with the third capacitor. One end of the seventh resistor connected in parallel with the seventh capacitor is connected to the other end of the fifth capacitor.

[0020] It also includes a rectifier bridge, which comprises a first diode, a second diode, a third diode, and a fourth diode. The cathode of the third diode and the anode of the first diode are connected together and then connected to the live wire of the mains power. The cathode of the fourth diode and the anode of the second diode are connected together and then connected to the neutral wire of the mains power. The cathodes of the first diode and the second diode are connected together and then connected to the drain pin of the control chip. The anodes of the third diode and the fourth diode are connected together and then connected to the anode of the fifth diode.

[0021] Preferably, the voltage divider circuit includes a second resistor and a third resistor connected in series with the second resistor. The other end of the second resistor serves as the first end of the voltage divider circuit; the other end of the third resistor serves as the second end of the voltage divider circuit; and the area between the second resistor and the third resistor serves as the voltage divider output terminal of the voltage divider circuit, which is used to connect to the feedback voltage sampling pin of the control chip.

[0022] Compared with existing technologies, the advantages of this invention are as follows: Through the switching devices and charging / discharging circuit in the soft-start control circuit, the switching devices are driven to conduct during the power-on process of the charging / discharging circuit due to voltage rise. This causes the output voltage detected by the control chip through the feedback voltage sampling pin to be higher than the actual output voltage, thereby reducing the output energy of the control chip. Therefore, this soft-start control circuit can compensate for the insufficient soft-drive time inside the chip, avoiding output voltage overshoot during power-on when connected to a large capacitive load. The circuit is simple and achieves good results. Attached Figure Description

[0023] Figure 1 This is a basic circuit diagram of a Buck circuit in the prior art;

[0024] Figure 2 This is an actual circuit diagram of a Buck circuit in the prior art;

[0025] Figure 3 This is a circuit diagram of the Buck circuit in an embodiment of the present invention. Detailed Implementation

[0026] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0027] like Figure 3 As shown, the high-voltage Buck circuit in this embodiment includes a rectifier bridge 5, a main Buck circuit 1, and a control circuit for controlling the operation of the main Buck circuit 1. The two input terminals of the rectifier bridge 5 are connected to the mains power, and the two output terminals of the rectifier bridge 5 are respectively connected to the control circuit and the main Buck circuit 1.

[0028] The control circuit includes a control chip N1, a first freewheeling circuit 2, and a voltage divider circuit 3. The control chip N1 has a built-in switching transistor and a power supply pin VCC and a feedback voltage sampling pin FB. In this embodiment, the built-in switching transistor of the control chip N1 is a MOSFET, so that the control chip N1 has a drain pin Drain and a source pin source. The drain pin Drain of the control chip N1 is connected to one output terminal of the rectifier bridge 5. One end of the first freewheeling circuit 2 is connected to the main Buck circuit 1, and the other end is connected to the power supply pin VCC of the control chip N1 through the seventh diode VD7. It is used to provide voltage to the control chip N1 by turning off the freewheeling transistor in the control chip N1. The first end of the voltage divider circuit 3 is connected to the seventh diode VD7, and the second end of the voltage divider circuit 3 is connected to the source pin source. The source pin source serves as the reference ground of the voltage divider circuit 3. The voltage divider output terminal of the voltage divider circuit 3 is connected to the feedback voltage sampling pin FB of the control chip N1.

[0029] In this embodiment, the main Buck circuit 1 includes a fifth diode VD5, an inductor L1, and a second capacitor C2. The cathode of the fifth diode VD5 is connected to the inductor L1, and the other end of the inductor L1 is connected to the second capacitor C2. The other end of the second capacitor C2 is connected to the anode of the fifth diode VD5. The first freewheeling circuit 2 includes a sixth diode VD6 and a third capacitor C3. The cathode of the sixth diode VD6 is connected to one end of the third capacitor C3 and connected to the power supply pin VCC of the control chip N1 through a seventh diode VD7. The anode of the sixth diode VD6 and the other end of the third capacitor C3 are respectively connected to the two ends of the inductor L1. The voltage divider circuit 3 includes a second resistor R2 and a third resistor R3 connected in series with the second resistor R2. The other end of the second resistor R2 serves as the first terminal of the voltage divider circuit 3. The other end of the third resistor R3 serves as the second terminal of the voltage divider circuit 3. The area between the second resistor R2 and the third resistor R3 serves as the voltage divider output terminal of the voltage divider circuit 3, which is connected to the feedback voltage sampling pin FB of the control chip N1.

[0030] The aforementioned rectifier bridge 5 includes a first diode VD1, a second diode VD2, a third diode VD3, and a fourth diode VD4. The cathode of the third diode VD3 and the anode of the first diode VD1 are connected together and then connected to the live wire of the mains power. The cathode of the fourth diode VD4 and the anode of the second diode VD2 are connected together and then connected to the neutral wire of the mains power. The cathodes of the first diode VD1 and the second diode VD2 are connected together and then serve as the first output terminal of the rectifier bridge 5, which is connected to the drain pin of the control chip N1. The anodes of the third diode VD3 and the fourth diode VD4 are connected together and then serve as the second output terminal of the rectifier bridge 5, which is connected to the anode of the fifth diode VD5.

[0031] To compensate for the insufficient soft-start time of the control chip N1 and avoid output voltage overshoot during power-on when connected to a large capacitive load, the aforementioned control circuit also includes a soft-start control circuit 4. The soft-start control circuit 4 includes a switching device and a charging / discharging circuit 41. One end of the switching device is connected to the feedback voltage sampling pin FB of the control chip N1. The charging / discharging circuit 41 is connected to the other end of the switching device and the main Buck circuit 1, respectively, to turn on the switching device and raise the voltage sampled by the feedback voltage sampling pin FB, thereby reducing the energy output of the control chip N1. In this embodiment, the charging / discharging circuit 41 includes a fifth capacitor C5 and a fifth resistor R5 connected in series with the fifth capacitor C5. The switching device is a transistor V1. The emitter of the transistor V1 serves as one end of the switching device connected to the feedback voltage sampling pin FB of the control chip N1, and the base of the transistor V1 serves as the other end of the switching device connected to the fifth resistor R5. The collector of the transistor V1 is connected to the first end of the voltage divider circuit 3 through a current-limiting resistor R4. The fifth resistor R5 is used to adjust the charging current through the fifth capacitor C5 and the charging time of the fifth capacitor C5; the current-limiting resistor R4 is used to adjust the current on the collector of the transistor V1 when it is turned on.

[0032] The soft-start control circuit 4 also includes a sixth capacitor C6, a sixth resistor R6 connected in parallel with the sixth capacitor C6, and a second freewheeling circuit 42 connected to the main Buck circuit 1 and the charging and discharging circuit 41. One end of the sixth capacitor C6 and the sixth resistor R6 is connected to the base of the transistor V1, and the other end is connected to the source pin of the control chip N1. The sixth capacitor C6 is used to stabilize the voltage between the base of the transistor V1 and the reference ground Source, thereby indirectly stabilizing the voltage of the BE junction of the transistor V1 and preventing small voltage spikes from causing the BE junction to conduct erroneously. The sixth resistor R6 is a large-value resistor and is only used to discharge the sixth capacitor C6 after the mains power L / N fails.

[0033] The second freewheeling circuit 42 includes an eighth diode VD8, a seventh capacitor C7, and a seventh resistor R7. The eighth diode VD8 is connected in series with the seventh capacitor C7 and then in parallel with the third capacitor C3. One end of the seventh resistor R7, connected in parallel with the seventh capacitor C7, is connected to the other end of the fifth capacitor C5. Utilizing the unidirectional conductivity of the eighth diode VD8, the seventh capacitor C7 rises from 0V to near the output voltage during power-on (if the voltage drop of the eighth diode VD8 is not considered, the voltage of the seventh capacitor C7 is equivalent to the voltage of the third capacitor C3). During normal operation, the voltage across the seventh capacitor C7 is relatively stable, preventing the transistor V1 from conducting during normal operation. The seventh resistor R7 is a large-value resistor, and it is only discharged from the mains power after the L / N circuit is switched off. During normal operation, the power consumption of the seventh resistor R7 is minimal. The energy consumed by the seventh capacitor C7 in the seventh resistor R7 can be recharged by the new freewheeling path L1-VD6-VD8-C7 during L1 freewheeling.

[0034] The working principle of the high-voltage Buck circuit described above is as follows: Before power-on, the voltage of the fifth capacitor C5 is 0. As the mains power L / N is applied, current flows through the fifth capacitor C5, causing its voltage to rise and eventually stabilize at its highest point. Part of the current flowing through the fifth capacitor C5 passes through the BE junction of transistor V1, turning on transistor V1 and thus raising the voltage across the third resistor R3. This allows the output voltage detected by the control chip N1 via the feedback voltage sampling pin FB to be higher than the actual output voltage, thereby reducing the output energy of the control chip N1 and ultimately preventing output voltage overshoot when connected to a large capacitive load.

[0035] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A high-voltage Buck circuit comprising a main Buck circuit (1) and a control circuit for controlling the operation of the main Buck circuit (1), the control circuit comprising: a control chip (N1) having a built-in switching tube and having a power supply pin (VCC) and a feedback voltage sampling pin (FB); a first freewheeling circuit (2) connected at one end to the main Buck circuit (1) and connected at the other end to the power supply pin (VCC) of the control chip (N1) through a seventh diode (VD7), for providing voltage to the control chip (N1) after the switching tube in the control chip (N1) is turned off; a voltage dividing circuit (3) having a first end connected to the seventh diode (VD7) and a second end connected to a reference ground of the control chip (N1), and having a voltage dividing output end connected to the feedback voltage sampling pin (FB) of the control chip (N1); characterized in that it further comprises a soft-start control circuit (4) arranged in the control circuit, the soft-start control circuit (4) comprising: a switching device having one end connected to the feedback voltage sampling pin (FB) of the control chip (N1); and a charge-discharge circuit (41) connected to the other end of the switching device and to the main Buck circuit (1), respectively, for turning on the switching device to raise the voltage collected by the feedback voltage sampling pin (FB) and thereby reducing the energy output by the control chip (N1); wherein the switching device is a triode (V1), the emitter of the triode (V1) serving as the one end of the switching device for being connected to the feedback voltage sampling pin (FB) of the control chip (N1), the base of the triode (V1) serving as the other end of the switching device for being connected to the charge-discharge circuit (41), and the collector of the triode (V1) being connected to the first end of the voltage dividing circuit (3) through a current-limiting resistor (R4); wherein the soft-start control circuit (4) comprises a second freewheeling circuit (42) connected to the main Buck circuit (1) and the charge-discharge circuit (41), respectively, the second freewheeling circuit (42) comprising a seventh capacitor (C7) having one end connected to the charge-discharge circuit (41) and the other end connected to the main Buck circuit (1); and wherein the charge-discharge circuit (41) comprises a fifth capacitor (C5) and a fifth resistor (R5), one end of the fifth capacitor (C5) being connected to one end of the fifth resistor (R5), and the charge-discharge circuit (41) being connected to the base of the triode (V1) through the other end of the fifth resistor (R5). ​ ​ ​ ​ ​ ​ ​ ​ 2. The high voltage Buck circuit of claim 1, wherein: ​ 3. The high voltage Buck circuit of claim 2, wherein: The main Buck circuit (1) includes a fifth diode (VD5), an inductor (L1) and a second capacitor (C2), the cathode of the fifth diode (VD5) is connected with one end of the inductor (L1), the other end of the inductor (L1) is connected with one end of the second capacitor (C2), the other end of the second capacitor (C2) is connected with the anode of the fifth diode (VD5).

4. The high voltage Buck circuit of claim 3, wherein: The switch tube built in the control chip (N1) is a MOS tube, so that the control chip (N1) has a drain pin (Drain) and a source pin (source), the drain pin (Drain) of the control chip (N1) is connected with one end of an external power supply, the source pin (source) of the control chip (N1) is connected with the second end of the voltage dividing circuit (3) as a reference ground, and is connected with the connection point of the inductor (L1) and the fifth diode (VD5).

5. The high voltage Buck circuit of claim 4, wherein: The soft start control circuit (4) further includes a sixth capacitor (C6) and a sixth resistor (R6) connected in parallel with the sixth capacitor (C6), one end of the sixth capacitor (C6) and the sixth resistor (R6) is connected with the base of the triode (V1), and the other end is connected with the source pin (source) of the control chip (N1).

6. The high voltage Buck circuit of claim 5, wherein: The first freewheeling circuit (2) includes a sixth diode (VD6) and a third capacitor (C3), the cathode of the sixth diode (VD6) and one end of the third capacitor (C3) are connected and connected with the power supply pin (VCC) of the control chip (N1), the anode of the sixth diode (VD6) is connected with one end of the inductor (L1), and the other end of the third capacitor (C3) is connected with the other end of the inductor (L1).

7. The high voltage Buck circuit of claim 6, wherein: The second freewheeling circuit (42) further includes an eighth diode (VD8) and a seventh resistor (R7), the eighth diode (VD8) is connected in series with the seventh capacitor (C7) and then connected in parallel with the third capacitor (C3), and one end of the seventh resistor (R7) connected in parallel with the seventh capacitor (C7) is connected with the other end of the fifth capacitor (C5).

8. The high voltage Buck circuit of claim 4, wherein: It also includes a rectifier bridge (5), the rectifier bridge (5) includes a first diode (VD1), a second diode (VD2), a third diode (VD3) and a fourth diode (VD4), the cathode of the third diode (VD3) and the anode of the first diode (VD1) are connected in common and connected with the live wire of the mains, the cathode of the fourth diode (VD4) and the anode of the second diode (VD2) are connected in common and connected with the zero line of the mains, the cathode of the first diode (VD1) and the cathode of the second diode (VD2) are connected in common and connected with the drain pin (Drain) of the control chip (N1), and the anode of the third diode (VD3) and the anode of the fourth diode (VD4) are connected in common and connected with the anode of the fifth diode (VD5).

9. The high voltage Buck circuit according to any one of claims 1 to 8, characterized in that: The voltage dividing circuit (3) comprises a second resistor (R2) and a third resistor (R3), one end of the second resistor (R2) is connected with one end of the third resistor (R3), the other end of the second resistor (R2) is taken as the first end of the voltage dividing circuit (3); the other end of the third resistor (R3) is taken as the second end of the voltage dividing circuit (3); the connection point of the second resistor (R2) and the third resistor (R3) is taken as the voltage dividing output end of the voltage dividing circuit (3), which is used for being connected with the feedback voltage sampling pin (FB) of the control chip (N1).

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