Synchronous rectification circuit, switching power supply and power supply adapter equipment

Abstract

The utility model provides a synchronous rectification circuit, which comprises a transformer, a primary side circuit and a plurality of secondary side circuits, and the secondary side circuits are sequentially connected in series. The transformer comprises a magnetic coupler, the primary side winding is connected with the secondary side windings in the secondary side circuits through the magnetic coupler, and the number of turns of the secondary side windings is equal. Under the condition that the primary side circuit inputs the same input voltage and a secondary side rectifying tube with a high withstand voltage parameter is not replaced, the output voltage of the synchronous rectifying circuit is improved by connecting and coupling a plurality of secondary side circuits in series, the design cost of the circuit is greatly saved, and the current-sharing and voltage-sharing functions of a plurality of groups of secondary side circuits are realized. The utility model also provides a switching power supply and a power supply adaptive device using the synchronous rectification circuit, and the switching power supply and the power supply adaptive device have the advantages of low cost, high voltage conversion efficiency and stable output voltage, and can be suitable for various electronic device fast charging scenes.

Description

Technical Field

[0001] The utility model belongs to the technical field of power supply circuits, and particularly relates to a synchronous rectification circuit, a switching power supply and a power adapter device. Background Art

[0002] Synchronous rectification technology is a new technology that uses a synchronous rectification tube with an extremely low on-resistance to replace a rectifier diode with a relatively high on-voltage drop in the output circuit to improve the conversion efficiency of the circuit. By adopting synchronous rectification technology in a switching power supply, the output efficiency of low-voltage and large-current can be significantly improved. Synchronous rectification circuits are widely used in fast charging scenarios of electronic devices such as mobile phones and laptop computers.

[0003] However, due to the selection of synchronous rectification tubes and cost limitations of synchronous rectification circuits, the output voltage of power adapter devices equipped with synchronous rectification circuits on the market is currently limited, and it is difficult to further improve the voltage conversion efficiency. Summary of the Utility Model

[0004] The technical object of the utility model is to provide a synchronous rectification circuit and a power adapter device, aiming to solve the problem that the output voltage of the power adapter device of the synchronous rectification circuit is limited by cost.

[0005] To solve the above technical problems, the utility model is implemented as follows. A synchronous rectification circuit includes a transformer, a primary circuit and a plurality of secondary circuits, and each of the secondary circuits is connected in series in turn;

[0006] The primary circuit includes a primary winding, an input voltage terminal, a primary rectifier diode, a protection circuit and a ground terminal, and the input voltage terminal, the primary winding, the primary rectifier diode and the ground terminal are connected in series in turn; the protection circuit is connected in parallel at both ends of the primary winding;

[0007] Each of the secondary circuits includes a secondary winding, a secondary rectifier diode, an output capacitor, a positive output terminal and a negative output terminal; the positive output terminal, the secondary winding, the secondary rectifier diode and the negative output terminal are connected in series in turn, the output capacitor is connected across the positive output terminal and the negative output terminal, and the negative output terminal of the previous secondary circuit is electrically connected to the positive output terminal of the next secondary circuit;

[0008] The transformer includes a magnetic coupler, the primary winding is connected to the secondary windings in each of the secondary circuits through the magnetic coupler, and the number of turns of each of the secondary windings is equal.

[0009] Further, the turn ratio of the primary winding to a single secondary winding is greater than or equal to 10:1.

[0010] Further, two secondary circuits are included in the synchronous rectification circuit, and the source of the secondary rectifier diode of one secondary circuit is electrically connected to the positive output terminal of the other secondary circuit, so that the two secondary circuits are connected in series.

[0011] Further, the breakdown voltage parameter of the secondary rectifier diode is 20V - 60V.

[0012] Further, the breakdown voltage parameter of the primary rectifier diode is 600V - 700V.

[0013] Further, the input voltage at the input voltage terminal is 240V - 270V, and the output voltage of the secondary circuit is 20V - 40V.

[0014] Further, the first ends of the primary winding and the protection circuit are electrically connected to the input voltage terminal, the second ends of the primary winding and the protection circuit are electrically connected to the drain of the primary rectifier diode, the gate of the primary rectifier diode is used to be electrically connected to the drive circuit, and the source of the primary rectifier diode is connected to the ground terminal.

[0015] Further, the protection circuit includes a resistor, an input capacitor and a diode; the input voltage terminal is electrically connected to the first end of the resistor, the second end of the resistor is electrically connected to the negative electrode of the diode, the positive electrode of the diode is electrically connected to the drain of the primary rectifier diode, and the input capacitor is connected in parallel with the resistor.

[0016] The present invention also provides a switching power supply, including a drive circuit, a load and the synchronous rectification circuit as described above;

[0017] The drive circuit is electrically connected to the gates of the primary rectifier diode and the secondary rectifier diode in the synchronous rectification circuit. The primary circuit of the synchronous rectification circuit is used to input a power supply voltage, and the output terminal of the secondary circuit of the synchronous rectification circuit is electrically connected to the load.

[0018] The present invention also provides a power adapter device, including the synchronous rectification circuit as described above.

[0019] Compared with the prior art, the beneficial effects of the synchronous rectification circuit, the flyback switching power supply and the power adapter device in the present invention are as follows:

[0020] Under the condition of inputting the same input voltage to the primary side circuit and not replacing the secondary side rectifier diode with high withstand voltage parameters, the utility model improves the output voltage of the synchronous rectification circuit by serially coupling multiple secondary side circuits, greatly saving the circuit design cost. And because the turn ratio of the primary side winding to each secondary side winding is the same, the primary side winding and the secondary side windings are coupled to the magnetic coupler of the same transformer, and the current and output voltage of each of the serially connected multiple secondary side circuits are the same, so that the current sharing and voltage equalization functions of multiple groups of secondary side circuits can be realized.

[0021] The switching power supply and the power adapter device using this synchronous rectification circuit have low cost, high voltage conversion efficiency, and stable output voltage, and can be applied to fast charging scenarios of various electronic devices. Brief Description of the Drawings

[0022] Figure 1(a) is a schematic circuit diagram of the rectification circuit of a conventional flyback switching power supply in the related art;

[0023] Figure 1(b) is a schematic circuit diagram of the synchronous rectification circuit of a flyback switching power supply in the related art;

[0024] Figure 2 is a schematic circuit diagram of the synchronous rectification circuit in this embodiment;

[0025] Figure 3 is a schematic circuit diagram of another synchronous rectification circuit in the related art;

[0026] Figure 4 is a circuit block diagram of the switching power supply in this embodiment. Detailed Embodiments

[0027] In order to make the objectives, technical solutions and advantages of the present utility model clearer, the present utility model will be further described in detail below with reference to the accompanying drawings and embodiments, where the same or similar reference numerals represent the same or similar elements or elements with the same or similar functions throughout. It should be understood that the specific embodiments described herein are only used to explain the present utility model and are not used to limit the present utility model. In addition, the technical features involved in the various embodiments of the present utility model described below can be combined with each other as long as they do not conflict with each other.

[0028] In the related art, as shown in FIG. 1(a), the rectifier circuit of a conventional flyback switching power supply includes a primary circuit and a secondary circuit. Among them, the secondary circuit includes a diode D1 and an output capacitor C1. FIG. 1(b) shows the synchronous rectifier circuit of the flyback switching power supply, and its secondary circuit includes a synchronous rectifier tube Q1 and an output capacitor C1. The diode D1 is replaced by the synchronous rectifier tube Q1. Since the conduction loss of the synchronous rectifier tube Q1 is lower than that of the diode D1, the efficiency of the overall power supply can be significantly improved, especially more obvious under high load. And the diode will generate extra heat when conducting. When using the rectifier current of the conventional flyback switching power supply, usually additional heat dissipation measures need to be provided, and the required cost is relatively high.

[0029] The synchronous rectifier tube Q1 in the synchronous rectifier circuit in FIG. 1(b) is a secondary rectifier tube, and the primary rectifier tube is not shown in the figure. It should be known that the platform voltage stress formulas of the secondary rectifier tube and the primary rectifier tube are as follows:

[0030] The platform voltage stress formula of the secondary rectifier tube is Vds_syn =Vin / n+Vo;

[0031] The platform voltage stress formula of the primary rectifier tube is Vds_pr =Vin +Vo×n;

[0032] Among them, n is the turn ratio of the primary winding and the secondary winding of the transformer, Vin is the input voltage of the primary circuit, and Vo is the output voltage of the secondary circuit.

[0033] It can be understood that the platform voltage stress of the secondary rectifier tube is inversely proportional to the turn ratio n, and the platform voltage stress of the primary rectifier tube is directly proportional to the turn ratio n. It should also be known that when the input voltage Vin remains unchanged, the turn ratio n is directly proportional to the output voltage Vo.

[0034] Without considering the cost, reducing the turn ratio n is beneficial to reducing the platform voltage stress of the primary rectifier tube, but this increases the platform voltage stress of the secondary rectifier tube, and a secondary rectifier tube with a higher withstand voltage parameter needs to be selected. And the output voltage Vo will also decrease, and it is often difficult to meet the requirements of the output voltage;

[0035] Increasing the turn ratio n is beneficial to reducing the platform voltage stress of the secondary rectifier tube and increasing the output voltage Vo, but it will increase the platform voltage stress of the primary rectifier tube, and a synchronous rectifier tube with a higher withstand voltage needs to be selected as the primary rectifier tube.

[0036] However, the higher the breakdown voltage of the synchronous rectifier tube, the relatively higher its cost. Due to cost limitations, power adapter devices with synchronous rectifier circuits on the market usually use conventional power semiconductors as synchronous rectifier tubes. Among them, in common switching power supplies and power adapter devices with a relatively high output voltage level, such as an output voltage of 24V or 48V, the breakdown voltage parameter of the primary rectifier tube is usually 650V - 700V, the breakdown voltage parameter of the secondary rectifier tube is about 100V, and the output voltage is usually 20V. If you want to increase the output voltage on the basis of the original synchronous rectifier circuit, the selection cost of the synchronous rectifier tube will increase significantly. Correspondingly, the improvement in voltage conversion efficiency is very small.

[0037] Therefore, please refer to Figure 2 , an embodiment of the present invention provides a synchronous rectifier circuit, including a transformer, a primary circuit, and a plurality of secondary circuits, and the secondary circuits are connected in series in sequence;

[0038] The primary circuit includes a primary winding, an input voltage terminal, a primary rectifier tube, a protection circuit, and a ground terminal. The input voltage terminal Vbus, the primary winding, the primary rectifier tube, and the ground terminal are connected in series; the protection circuit is connected in parallel with the primary winding;

[0039] Each secondary circuit includes a secondary winding, a secondary rectifier tube, an output capacitor, a positive output terminal, and a negative output terminal; the positive output terminal, the secondary winding, the secondary rectifier tube, and the negative output terminal are connected in series, and the positive output terminal, the output capacitor, and the negative output terminal are connected in series;

[0040] The transformer includes a magnetic coupler, and the primary winding and the secondary windings in each secondary circuit are connected through the magnetic coupler, and the number of turns of each secondary winding is equal.

[0041] In this embodiment, when the same input voltage is input to the primary circuit and the secondary rectifier tubes with high breakdown voltage parameters are not replaced, the turns ratio of the primary winding to each secondary winding is the same. The primary winding and the secondary windings are coupled to the magnetic coupler of the same transformer. The current and output voltage of each of the multiple series-connected secondary circuits are the same. By connecting multiple secondary circuits in series, the output voltage of the synchronous rectifier circuit is increased, greatly saving the circuit design cost. The multiple groups of secondary circuits also have functions of current sharing and voltage equalization, and the output voltage is stable, which can be applied to fast charging scenarios of various electronic devices.

[0042] As an example, as Figure 2 shown, the synchronous rectifier circuit includes two secondary circuits. The source electrode of the secondary rectifier tube QSR1 in one secondary circuit is electrically connected to the positive output terminal of the other secondary circuit, so that the two secondary circuits are connected in series in sequence.

[0043] Set the turn ratio n of the primary rectifier diode Q1 to the single secondary rectifier diode QSR1 / QSR2 to 14:1. The voltage input to the primary circuit is 270V. At this time, each secondary circuit can output a voltage of 27V. It is more appropriate to select the secondary rectifier diodes OSR1 and OSR2 with a breakdown voltage parameter of 60V.

[0044] As Figure 3 shown in the circuit schematic diagram of another synchronous rectification circuit provided in the related art, which shows the case where only one secondary circuit is used in the synchronous rectification circuit. In this circuit, the turn ratio n of the primary rectifier diode Q1 to the secondary rectifier diode QSR is set to 7:1. The voltage input to the primary circuit is also 270V. At this time, the secondary circuit can output a voltage of 55V. It is more appropriate to select the secondary rectifier diode OSR with a breakdown voltage parameter of 100V.

[0045] It can be seen that Figure 2 for the synchronous rectification circuit shown and the synchronous rectification circuit of this embodiment, when the input voltages are the same and the output voltages are similar, Figure 2 the breakdown voltage parameter required for the secondary rectifier diode QSR in the shown synchronous rectification circuit is relatively high, and the circuit cost is relatively high. While in this embodiment, multiple secondary rectifier diodes QSR1 / QSR2 with lower breakdown voltage parameters have a lower cost.

[0046] It can be understood that the synchronous rectification circuit including two secondary circuits in this embodiment is only a preferred example in the fast charging application scenario of electronic devices. The synchronous rectification circuit can also be provided with three, four or more secondary circuits to be applied to more usage scenarios.

[0047] The turn ratio n of the primary winding to the single secondary winding in the synchronous rectification circuit of this embodiment being 14:1 is also a preferred example. In other embodiments, the turn ratio n of the primary winding to the single secondary winding being greater than 10:1 is sufficient.

[0048] Correspondingly, other embodiments are not limited to only selecting the secondary rectifier diodes with a breakdown voltage parameter of 60V. When the number of secondary circuits is increased or the turn ratio n of the primary winding to the single secondary winding is changed, the secondary rectifier diodes with a breakdown voltage parameter of 20V to 60V can be adaptively selected, such as 20V, 30V, 40V or other breakdown voltage parameter secondary rectifier diodes. The secondary rectifier diodes with a breakdown voltage parameter of 20V to 60V are usually used in low voltage or light load application scenarios and have a lower cost. Therefore, the above settings reduce the cost of the synchronous rectification circuit while ensuring a high output voltage, the selection of secondary rectifier diodes is more flexible, and multiple secondary rectifier diodes can also dissipate heat, which is beneficial to the heat dissipation management of the synchronous rectification circuit.

[0049] In addition, in this embodiment, the breakdown voltage parameter of the primary rectifier diode is set to 600V - 700V. The selection of this primary rectifier diode can ensure that the synchronous rectification circuit has good stability and service life. The input voltage at the input voltage terminal is 240V - 270V, and the output voltage of the secondary circuit is 20V - 40V. It has a high voltage conversion efficiency, a stable output voltage, and can be applied to fast charging scenarios of various electronic devices.

[0050] As Figure 2 shown, in this embodiment, the first ends of the primary winding and the protection circuit are electrically connected to the input voltage terminal, the second ends of the primary winding and the protection circuit are electrically connected to the drain of the primary rectifier diode Q1, the gate of the primary rectifier diode Q1 is used to be electrically connected to the drive circuit, and the source of the primary rectifier diode Q1 is connected to the ground terminal.

[0051] The protection circuit includes a resistor Rn, an input capacitor Cn, and a diode Dn; the input voltage terminal Vbus is electrically connected to the first end of the resistor Rn, the second end of the resistor Rn is electrically connected to the negative electrode of the diode Dn, the positive electrode of the diode Dn is electrically connected to the drain of the primary rectifier diode Q1, and the input capacitor Cn is connected in parallel with the resistor Rn.

[0052] As Figure 4 shown, in this embodiment, a switching power supply is also provided, including a drive circuit, a load, and the synchronous rectification circuit as above;

[0053] The drive circuit is electrically connected to the gates of the primary rectifier diode and the secondary rectifier diode in the synchronous rectification circuit. The primary circuit of the synchronous rectification circuit is used to input the power supply voltage, and the output terminal of the secondary circuit of the synchronous rectification circuit is electrically connected to the load. The switching power supply in this embodiment is a flyback switching power supply, and the drive circuit externally drives the conduction and cut-off of the primary rectifier diode and the secondary rectifier diode in the synchronous rectification circuit.

[0054] In this embodiment, a power adapter device is also provided, including the synchronous rectification circuit as above.

[0055] The switching power supply and the power adapter device in this embodiment both include the synchronous rectification circuit in the above embodiment, and have similar effects to the synchronous rectification circuit, which will not be elaborated here. The embodiments in the content of the present utility model are all described in a progressive manner. Each embodiment focuses on the differences from other embodiments. The same or similar parts among the various embodiments can be referred to each other.

[0056] It should also be noted that in the content of the present utility model, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, such that a process, method, article or device comprising a series of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "comprising an..." does not exclude the presence of additional identical elements in the process, method, article or device comprising the said element.

[0057] The above description of the disclosed embodiments enables those skilled in the art to implement or use the content of the present utility model. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined in the content of the present utility model can be implemented in other embodiments without departing from the spirit or scope of the content of the present utility model. Therefore, the content of the present utility model will not be limited to these embodiments shown in the content of the present utility model, but rather to the broadest scope consistent with the principles and novel features disclosed in the content of the present utility model.

Claims

1. A synchronous rectification circuit, characterized in that: It includes a transformer, a primary circuit and a plurality of secondary circuits, wherein the secondary circuits are connected in series in sequence; The primary circuit comprises a primary winding, an input voltage terminal, a primary rectifier, a protection circuit and a ground terminal, wherein the input voltage terminal, the primary winding, the primary rectifier and the ground terminal are sequentially connected in series; the protection circuit is connected in parallel to both ends of the primary winding; Each of the secondary circuits comprises a secondary winding, a secondary rectifier, an output capacitor, a positive output terminal and a negative output terminal; the positive output terminal, the secondary winding, the secondary rectifier and the negative output terminal are sequentially connected in series, the output capacitor is connected across the positive output terminal and the negative output terminal, and the negative output terminal of the previous secondary circuit is electrically connected to the positive output terminal of the next secondary circuit; The transformer comprises a magnetic coupler, the primary winding and the secondary winding in each secondary circuit are connected via the magnetic coupler, and the number of turns of each secondary winding is equal.

2. The circuit according to claim 1, characterized in that The turns ratio of the primary winding to the single secondary winding is greater than or equal to 10:

1.

3. The circuit according to claim 2, characterized in that The synchronous rectification circuit includes two secondary circuits, and the source of the secondary rectifier tube of one secondary circuit is electrically connected to the positive output end of the other secondary circuit, so that the two secondary circuits are connected in series.

4. The circuit according to claim 3, characterized in that The withstand voltage parameter of the secondary rectifier tube is 20V~60V.

5. The circuit according to claim 3, characterized in that The withstand voltage parameter of the primary rectifier tube is 600V~700V.

6. The circuit according to claim 1, characterized in that The input voltage of the input voltage end is 240V~270V, and the output voltage of the secondary circuit is 20V~40V.

7. The circuit according to claim 1, characterized in that The first end of the primary winding and the protection circuit is electrically connected to the input voltage end, the second end of the primary winding and the protection circuit is electrically connected to the drain of the primary rectifier tube, the gate of the primary rectifier tube is used to electrically connect to the drive circuit, and the source of the primary rectifier tube is electrically connected to the ground end.

8. The circuit according to claim 1, characterized in that The protection circuit includes a resistor, an input capacitor and a diode; the input voltage end is electrically connected to the first end of the resistor, the second end of the resistor is electrically connected to the cathode of the diode, the anode of the diode is electrically connected to the drain of the primary rectifier, and the input capacitor is connected in parallel with the resistor.

9. A switching power supply, characterized in that: A synchronous rectification circuit comprising a driving circuit, a load and the synchronous rectification circuit according to any one of claims 1 to 8; The driving circuit is electrically connected to the gates of the primary rectifier and the secondary rectifier in the synchronous rectifier circuit, the secondary circuit output end of the synchronous rectifier circuit is electrically connected to the load, and the primary circuit of the synchronous rectifier circuit is used to input the power supply voltage.

10. A power adapter device, characterized in that: The invention comprises the synchronous rectification circuit as claimed in any one of claims 1 to 8.

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