Boost circuit of switching power supply

Abstract

The utility model belongs to the technical field of power supplies, and relates to a switching power supply booster circuit, which comprises a transformer, and a first voltage output branch and a second voltage output branch are arranged on the secondary side of the transformer. The first voltage output branch comprises a first diode and a first capacitor; the second voltage output branch comprises a second capacitor, a third capacitor, a fourth capacitor, a fifth capacitor, a second diode and a third diode; one end of the second capacitor is connected with the secondary winding, one end of the third capacitor is connected with the negative electrode of the first diode, the common end of the second capacitor and the third capacitor is connected with the positive electrode of the third diode through the fourth capacitor, and the fifth capacitor is connected with the negative electrode of the third diode. A secondary boost branch is added on the basis of a flyback circuit, the branch charges a boost capacitor by using peak voltage at the switching moment, the voltage is easily boosted to driving voltage required by a controllable switching device, and the circuit is simple in structure, efficient, low in cost and small in size.

Description

Technical Field

[0001] The utility model belongs to the technical field of power supplies, and particularly relates to a switching power supply boost circuit. Background Art

[0002] When a charger performs a charging operation, it is necessary to detect whether a battery is connected to avoid no-load, and at the same time, it is also necessary to cut off the power in time for possible abnormal situations during the charging process. The most direct way to do this is to set a controllable switching device (such as an MOS transistor, a thyristor, etc.) controlled by a charger chip at the power output end of the charger. Generally, the driving voltage required by the controllable switching device is higher than the charging output voltage. Therefore, it is necessary to design the boost circuit of the charger. The conventional method is to add windings or use multi-tap windings on the secondary side of the transformer in the boost circuit. However, this structure will obviously increase the volume of the circuit, and the added coils (equivalent to inductors) are also not conducive to EMC / EMI testing. Summary of the Utility Model

[0003] In view of the problems mentioned in the background art, the utility model provides a switching power supply boost circuit to meet the requirements of charging voltage output and driving voltage output, which is specifically achieved by the following technical means:

[0004] The switching power supply boost circuit of the utility model includes a transformer, and a first voltage output branch and a second voltage output branch are arranged on the secondary side of the transformer;

[0005] The first voltage output branch includes a first diode and a first capacitor. The positive electrode of the first diode is connected to the secondary winding of the transformer, and its negative electrode is connected to the output end of the first voltage output branch. The first capacitor is connected to the negative electrode of the first diode;

[0006] The second voltage output branch includes a second capacitor, a third capacitor, a fourth capacitor, a fifth capacitor, a second diode and a third diode; one end of the second capacitor is connected to the secondary winding, and the other end is connected to the third capacitor; one end of the third capacitor is connected to the negative electrode of the first diode, and the common end of the second capacitor and the third capacitor is connected to the positive electrode of the third diode through the fourth capacitor. The negative electrode of the third diode is connected to the output end of the second voltage output branch. The fifth capacitor is connected to the negative electrode of the third diode; the positive electrode of the second diode is grounded or connected to the positive electrode of the first capacitor, and its negative electrode is connected to the fourth capacitor.

[0007] In one or more embodiments of the utility model, one end of the fifth capacitor is connected to the negative electrode of the third diode, and the other end is grounded.

[0008] In one or more embodiments of the utility model, one end of the fifth capacitor is connected to the negative electrode of the third diode, and the other end is connected to the positive electrode of the first capacitor.

[0009] Compared with the prior art, the advantages of the present utility model are as follows: A secondary boost branch is added on the basis of the flyback circuit. This branch utilizes the peak voltage at the moment of switching to charge the boost capacitor, easily raising the voltage to the driving voltage required by the controllable switching device. Moreover, the circuit structure is simple, efficient, low-cost, and small in size, and is easy to implement. At the same time, this branch obtains the peak voltage through three capacitors in a divided mode, has better electrical isolation compared to the original secondary-side output circuit, is not prone to generating interference ripples, and abandons the traditional technical habit of increasing the winding coil to raise the electrical bias, maximizing the avoidance of inductive devices in the branch, which is conducive to passing the EMC / EMI test. Description of the Drawings

[0010] Figure 1 It is the circuit schematic diagram of Embodiment 1 of the present utility model.

[0011] Figure 2 It is the circuit schematic diagram of Embodiment 2 of the present utility model.

[0012] Figure 3 It is the circuit schematic diagram of Embodiment 3 of the present utility model.

[0013] Figure 4 It is the circuit schematic diagram of Embodiment 4 of the present utility model.

[0014] Figure 5 It is the circuit schematic diagram of Embodiment 5 of the present utility model.

[0015] Figure 6 It is the schematic diagram of the application principle framework of the present utility model in the charger circuit. Detailed Embodiments

[0016] The following further describes the solution of the present application in conjunction with the drawings:

[0017] Embodiment 1

[0018] See the appendix Figure 1, the switching power supply boost circuit includes a transformer T1A, diodes D1, D2, D3, capacitors C1, C2, C3, C4, C5, a resistor R1 and a resistor R2; the primary winding of the transformer T1A is connected to the DC source VBUS (such as the positive pole of the primary side input capacitor) and the drain MOS_D of the MOS transistor, and one end of the secondary winding of the transformer T1A is connected to the positive pole of the diode D1, and the other end is grounded; the negative pole of the diode D1 is connected to the positive pole of the capacitor C1, and the negative pole of the capacitor C1 is grounded; the diode D1 and the capacitor C1 form a first voltage output branch, and the charging voltage VA for charging the subsequent battery is output from the positive pole of the capacitor C1. The capacitors C2, C3 and C4 are star-connected. One end of the capacitor C2 is connected to the secondary winding of the transformer T1A to obtain the induced voltage VB. One end of the capacitor C3 is connected to the negative pole of the diode D1 through the resistor R1, and one end of the capacitor C4 is connected to the positive pole of the diode D3. The positive pole of the diode D2 is grounded, and the other end is connected to the capacitor C4; one end of the capacitor C5 is connected to the negative pole of the diode D3, and the other end is grounded; the diode D2, the diode D3, the capacitors C2, C3, C4, C5, the resistor R1 and the resistor R2 form a second voltage output branch. One end of the capacitor C5 is connected to the output end of the second voltage output branch, and the other end is grounded. The capacitor C5 outputs the driving voltage VC for supplying power to the subsequent switching device.

[0019] The current flyback circuit is more used for bucking, and there are very few for boosting. Based on the flyback buck topology, this circuit adds a secondary boost branch (i.e., the second voltage output branch) on the basis of the flyback topology. This branch uses the spike voltage (the spike component in the induced voltage VB) generated by the secondary winding of the transformer T1A at the moment of switching to charge the capacitor C5 (boost capacitor), so as to easily raise the voltage to the driving voltage required by the controllable switching device. Specifically, on the basis of the secondary absorption resistor R1 and the capacitor C2, the circuit is improved. This branch obtains the spike voltage by dividing the mode through the capacitors C2, C3 and C4, that is, the capacitors C2 and C3 are first connected in series, and the voltage ratio of the common end of the two is controlled by designing the capacitance values of the capacitors C2 and C3, and then the capacitor C4 obtains and charges the capacitor C5 through the diode D3. This structure connected by capacitors makes the second voltage output branch have better electrical isolation from the first voltage output branch, and it is not easy to generate interfering voltage ripples with each other. Moreover, the capacitor C3 and the resistor R1 play a role in voltage division on the one hand, and on the other hand, they also take into account the function of peak clipping of the output voltage of the diode D1, filtering out the spike components that are not beneficial to the first voltage output branch, protecting the first voltage output branch and making its output stable; in addition, this second voltage output branch abandons the traditional technical habit of increasing the winding coil to raise the electrical bias, and maximally avoids using inductive devices in the branch, which is beneficial to passing the EMC / EMI test.

[0020] Due to the one-way conduction of diode D3, the charge of capacitor C4 will be fully charged after several cycles and cannot be charged continuously, resulting in the circuit being unable to work continuously. Therefore, diode D2 is added as the discharge circuit of capacitor C4 to balance the charge of capacitor C4.

[0021] In this embodiment, diode D1 is the first diode, diode D2 is the second diode, diode D3 is the third diode, capacitor C1 is the first capacitor, capacitor C2 is the second capacitor, capacitor C3 is the third capacitor, capacitor C4 is the fourth capacitor, capacitor C5 is the fifth capacitor, and resistor R1 is the first resistor.

[0022] Based on the principle of Embodiment 1, the present utility model also proposes Embodiments 2-5 for fine-tuning the circuit structure.

[0023] Embodiment 2

[0024] See the appendix Figure 2 The switching power supply boost circuit includes transformer T1A, diodes D1, D2, D3, capacitors C1, C2, C3, C4, C5, resistor R1 and resistor R2; the primary winding of transformer T1A is connected to the DC source VBUS (such as the positive pole of the input capacitor on the primary side) and the drain MOS_D of the MOS transistor, and one end of the secondary winding of transformer T1A is connected to the positive pole of diode D1, and the other end is grounded; the negative pole of diode D1 is connected to the positive pole of capacitor C1, and the negative pole of capacitor C1 is grounded; diode D1 and capacitor C1 form the first voltage output branch, and the charging voltage VA for charging the subsequent battery is output from the positive pole of capacitor C1. Capacitors C2, C3 and C4 are star-connected. One end of capacitor C2 is connected to the secondary winding of transformer T1A to obtain the induced voltage VB. One end of capacitor C3 is connected to the negative pole of diode D1 through resistor R1. One end of capacitor C4 is connected to the positive pole of diode D3. Diode D2 is used to balance the charge amount of capacitor C4. The positive pole of diode D2 is connected to the positive pole of capacitor C1, and the negative pole of diode D2 is connected to capacitor C4; one end of capacitor C5 is connected to the negative pole of diode D3, and the other end is grounded; diode D2, D3, capacitors C2, C3, C4, C5, resistor R1 and resistor R2 form the second voltage output branch. One end of capacitor C5 is connected to the output end of the second voltage output branch, and the other end is grounded. Capacitor C5 outputs the driving voltage VC for supplying power to the subsequent switching device.

[0025] In this embodiment, diode D1 is the first diode, diode D2 is the second diode, diode D3 is the third diode, capacitor C1 is the first capacitor, capacitor C2 is the second capacitor, capacitor C3 is the third capacitor, capacitor C4 is the fourth capacitor, capacitor C5 is the fifth capacitor, and resistor R1 is the first resistor.

[0026] Embodiment 3

[0027] See the appendix Figure 3 As shown in the figure, the boost circuit of the switching power supply includes transformer T1A, diodes D1, D2, D3, capacitors C1, C2, C3, C4, C6, resistors R1 and R2; the primary winding of the transformer T1A is connected to the DC source VBUS (such as the positive pole of the input capacitor on the primary side) and the drain MOS_D of the MOS transistor, one end of the secondary winding of the transformer T1A is connected to the positive pole of the diode D1, and the other end is grounded; the negative pole of the diode D1 is connected to the positive pole of the capacitor C1, and the negative pole of the capacitor C1 is grounded; the diode D1 and the capacitor C1 form the first voltage output branch, and the charging voltage VA for charging the subsequent battery is output from the positive pole of the capacitor C1. The capacitors C2, C3 and C4 are star-connected. One end of the capacitor C2 is connected to the secondary winding of the transformer T1A to obtain the induced voltage VB. One end of the capacitor C3 is connected to the negative pole of the diode D1 through the resistor R1. One end of the capacitor C4 is connected to the positive pole of the diode D3. The positive pole of the diode D2 is grounded, and the other end is connected to the capacitor C4 to balance the charge amount of the capacitor C4; one end of the capacitor C5 is connected to the negative pole of the diode D3, and the other end is grounded; the second voltage output branch is composed of the diodes D2, D3, capacitors C2, C3, C4, C6, resistor R1 and resistor R2. The capacitor C6 outputs the driving voltage VC for supplying power to the subsequent switching device, and both ends of the capacitor C6 are respectively connected between the output ends of the first voltage output branch and the second voltage output branch. The capacitor C6 stabilizes the voltage difference between the voltage VA and the voltage VC.

[0028] In this embodiment, diode D1 is the first diode, diode D2 is the second diode, diode D3 is the third diode, capacitor C1 is the first capacitor, capacitor C2 is the second capacitor, capacitor C3 is the third capacitor, capacitor C4 is the fourth capacitor, capacitor C5 is the fifth capacitor, and resistor R1 is the first resistor.

[0029] Embodiment 4

[0030] See the appendix Figure 4, the boost circuit of the switching power supply includes a transformer T1A, a diode D1, a diode D2, a diode D3, a capacitor C1, a capacitor C2, a capacitor C3, a capacitor C4, a capacitor C6, a resistor R1 and a resistor R2; the primary winding of the transformer T1A is connected to the DC source VBUS (such as the positive pole of the input capacitor on the primary side) and the drain MOS_D of the MOS transistor, and one end of the secondary winding of the transformer T1A is connected to the positive pole of the diode D1, and the other end is grounded; the negative pole of the diode D1 is connected to the positive pole of the capacitor C1, and the negative pole of the capacitor C1 is grounded; the diode D1 and the capacitor C1 form a first voltage output branch, and the charging voltage VA for charging the subsequent battery is output from the positive pole of the capacitor C1. The capacitors C2, C3 and C4 are star-connected. One end of the capacitor C2 is connected to the secondary winding of the transformer T1A to obtain the induced voltage VB. One end of the capacitor C3 is connected to the negative pole of the diode D1 through the resistor R1. One end of the capacitor C4 is connected to the positive pole of the diode D3. The diode D2 is used to balance the charge amount of the capacitor C4. The positive pole of the diode D2 is connected to the positive pole of the capacitor C1, and the negative pole of the diode D2 is connected to the capacitor C4; one end of the capacitor C5 is connected to the negative pole of the diode D3, and the other end is grounded; the diode D2, the diode D3, the capacitor C2, the capacitor C3, the capacitor C4, the capacitor C6, the resistor R1 and the resistor R2 form a second voltage output branch. The capacitor C6 outputs the driving voltage VC for supplying power to the subsequent switching device, and both ends of the capacitor C6 are respectively connected between the output terminals of the first voltage output branch and the second voltage output branch. The capacitor C6 stabilizes the voltage difference between the voltage VA and the voltage VC.

[0031] In this embodiment, the diode D1 is the first diode, the diode D2 is the second diode, the diode D3 is the third diode, the capacitor C1 is the first capacitor, the capacitor C2 is the second capacitor, the capacitor C3 is the third capacitor, the capacitor C4 is the fourth capacitor, the capacitor C5 is the fifth capacitor, and the resistor R1 is the first resistor.

[0032] Embodiment 5

[0033] See Appendix Figure 5, the boost circuit of the switching power supply includes a transformer T1A, a diode D1, a diode D2, a diode D3, a capacitor C1, a capacitor C2, a capacitor C3, a capacitor C4, a capacitor C5, a capacitor C6, a resistor R1 and a resistor R2; the primary winding of the transformer T1A is connected to the DC source VBUS (such as the positive pole of the input capacitor on the primary side) and the drain MOS_D of the MOS transistor, and one end of the secondary winding of the transformer T1A is connected to the positive pole of the diode D1, and the other end is grounded; the negative pole of the diode D1 is connected to the positive pole of the capacitor C1, and the negative pole of the capacitor C1 is grounded; the diode D1 and the capacitor C1 form a first voltage output branch, and the charging voltage VA for charging the subsequent battery is output from the positive pole of the capacitor C1. The capacitors C2, C3 and C4 are star-connected. One end of the capacitor C2 is connected to the secondary winding of the transformer T1A. One end of the capacitor C3 is connected to the negative pole of the diode D1 through the resistor R1. One end of the capacitor C4 is connected to the positive pole of the diode D3. The diode D2 is used to balance the charge amount of the capacitor C4. The positive pole of the diode D2 is connected to the positive pole of the capacitor C1, and the negative pole of the diode D2 is connected to the capacitor C4; one end of the capacitor C5 is connected to the negative pole of the diode D3, and the other end is grounded; the diode D2, the diode D3, the capacitor C2, the capacitor C3, the capacitor C4, the capacitor C5, the capacitor C6, the resistor R1 and the resistor R2 form a second voltage output branch, and the driving voltage VC for supplying power to the subsequent switching device is jointly output by the capacitors C5 and C6. One end of the capacitor C5 is connected to the output end of the second voltage output branch, and the other end is grounded. The two ends of the capacitor C6 are respectively connected between the output ends of the first voltage output branch and the second voltage output branch. This dual-capacitor structure plays a positive role in stabilizing the voltages VA and VC.

[0034] In this embodiment, the diode D1 is the first diode, the diode D2 is the second diode, the diode D3 is the third diode, the capacitor C1 is the first capacitor, the capacitor C2 is the second capacitor, the capacitor C3 is the third capacitor, the capacitor C4 is the fourth capacitor, the capacitors C5 and C6 are equivalent to the fifth capacitor, and the resistor R1 is the first resistor.

[0035] In the charger product to which this patent is applied, the output control module of the charger generally consists of two NMOS transistors back to back, and its function is defined as: when the NMOS transistor does not receive an effective control signal, it blocks the current flow from the VA terminal to the battery and also blocks the battery current from flowing to VA. When the MCU of the charger detects that the battery is connected and there is no abnormality, it is necessary to control the output control module to conduct to form a current loop from the VC terminal - the output control module - the VA terminal - the capacitor C5 - the VC terminal, that is, the Figure 6 operating current shown by the current I in the figure.

[0036] In the above-mentioned Embodiments 4 and 5, a discharge loop is composed of resistor R1, capacitors C2, C3, C4, and C5 (capacitor C6). Since the drive current required when the NMOS transistor is working is very small (at the μA level), a resistor of 20K - 100K is generally placed between the gate and source to ensure that the MOS transistor remains off when there is no drive. Taking a drive voltage of 10V as an example, the current I should at least ensure 0.5mA.

[0037] 1) Selection of capacitor C3 and resistor R1

[0038] In the flyback circuit, capacitor C3 and resistor R1 are placed across diode D1 to reduce the spikes across diode D1. The specific values of capacitor C3 and resistor R1 are balanced and selected based on the actual winding of transformer T1A, the selection of the breakdown voltage of diode D1, as well as losses and temperature rise.

[0039] 2) Selection of capacitor C4

[0040] Since the average charging current of capacitor C4 should be ≥ I to ensure the drive voltage, it was found in the experiment that when the capacitance value of capacitor C4 is equal to that of capacitor C3, it can ensure that the voltage at the VC terminal is at least 8V higher than the voltage at the VA terminal. Therefore, increasing the capacitance of C4 can obtain a higher VC voltage.

[0041] Since the flyback circuit adjusts the output voltage by adjusting the duty cycle, the forward average current flowing through capacitor C4 will be different under different output loads, different switching frequencies, and different diode D1 models. Therefore, the value of capacitor C4 and the voltage difference between the VC terminal and the VA terminal are determined by actual circuit debugging.

[0042] 3) Selection of capacitor C2

[0043] The main function of capacitor C2 is to reduce the breakdown voltage ratings of capacitors C4 and C3. That is, the star topology composed of capacitors C2, C3, and C4 can make the circuit suitable for using capacitor components with low breakdown voltage ratings, thereby balancing circuit cost and performance.

[0044] The above preferred embodiments should be regarded as illustrative examples of the implementation modes of the present application. All technical deductions, substitutions, improvements, etc. that are identical, similar to, or based on the present application should be regarded as within the protection scope of this patent.

Claims

1. A switching power supply boost circuit, comprising a transformer, characterized in that: A first voltage output branch and a second voltage output branch are provided on the secondary side of the transformer; The first voltage output branch includes a first diode and a first capacitor, the positive electrode of the first diode is connected to the secondary winding of the transformer, the negative electrode thereof is connected to the output end of the first voltage output branch, and the first capacitor is connected to the negative electrode of the first diode; The second voltage output branch includes a second capacitor, a third capacitor, a fourth capacitor, a fifth capacitor, a second diode and a third diode; one end of the second capacitor is connected to the secondary winding, and the other end thereof is connected to the third capacitor; one end of the third capacitor is connected to the cathode of the first diode, a common end of the second capacitor and the third capacitor is connected to the anode of the third diode via the fourth capacitor, the cathode of the third diode is connected to the output end of the second voltage output branch, and the fifth capacitor is connected to the cathode of the third diode; The anode of the second diode is grounded, and the cathode of the second diode is connected to the fourth capacitor.

2. The switching power supply boost circuit according to claim 1, characterized in that: One end of the fifth capacitor is connected to the cathode of the third diode, and the other end is grounded.

3. The switching power supply boost circuit according to claim 1, characterized in that: One end of the fifth capacitor is connected to the cathode of the third diode, and the other end is connected to the anode of the first capacitor.

4. A switching power supply boost circuit, comprising a transformer, characterized in that: A first voltage output branch and a second voltage output branch are provided on the secondary side of the transformer; The first voltage output branch includes a first diode and a first capacitor, the positive electrode of the first diode is connected to the secondary winding of the transformer, the negative electrode thereof is connected to the output end of the first voltage output branch, and the first capacitor is connected to the negative electrode of the first diode; The second voltage output branch includes a second capacitor, a third capacitor, a fourth capacitor, a fifth capacitor, a second diode and a third diode; one end of the second capacitor is connected to the secondary winding, and the other end thereof is connected to the third capacitor; one end of the third capacitor is connected to the cathode of the first diode, a common end of the second capacitor and the third capacitor is connected to the anode of the third diode via the fourth capacitor, the cathode of the third diode is connected to the output end of the second voltage output branch, and the fifth capacitor is connected to the cathode of the third diode; The anode of the second diode is connected to the anode of the first capacitor, and the cathode of the second diode is connected to the fourth capacitor.

5. The switching power supply boost circuit according to claim 4, characterized in that: One end of the fifth capacitor is connected to the cathode of the third diode, and the other end is grounded.

6. The switching power supply boost circuit according to claim 4, characterized in that: One end of the fifth capacitor is connected to the cathode of the third diode, and the other end is connected to the anode of the first capacitor.

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