A power adapter circuit with synchronous rectification

Abstract

The utility model discloses a kind of power adapter circuits with synchronous rectification, it includes transformer, synchronous rectification circuit, output filter circuit, feedback circuit and controller, synchronous rectification circuit includes first resistance, second resistance, third resistance, first field effect transistor, second field effect transistor and synchronous rectification chip, the first end of first resistance is electrically connected with the grid of first field effect transistor, the second end of first resistance is electrically connected with the source of second field effect transistor. The first end of second resistance is electrically connected with the source of second field effect transistor, the second end of second resistance is electrically connected with the grid of second field effect transistor. The first end of third resistance is electrically connected with the first end of transformer's first secondary coil, the second end of third resistance is electrically connected with the third foot of synchronous rectification chip. The source of first field effect transistor is grounded, the drain of first field effect transistor is electrically connected with the first end of transformer's second secondary coil. The utility model has the advantages of simple structure, low cost and high reliability.

Description

Technical Field

[0001] This utility model relates to the field of power adapter technology, and in particular to a power adapter circuit with synchronous rectification. Background Technology

[0002] Power adapter circuits typically include a flyback DC-DC converter circuit. In this circuit, secondary-side rectification is usually performed using diodes. However, using diodes for secondary-side rectification has some significant drawbacks:

[0003] First, diodes have a forward voltage drop when they are conducting, typically 0.6-0.7V (for ordinary silicon diodes) or 0.3-0.4V (for Schottky diodes). This voltage drop causes power loss, especially at high current outputs, where the loss becomes more significant. For example, at an output current of 1A, a diode with a forward voltage drop of 0.7V will generate 0.7W of power loss, which is converted into heat, reducing the efficiency of the entire conversion circuit.

[0004] Secondly, due to the power losses mentioned above, diodes generate heat during operation. If this heat cannot be dissipated in time, the diode temperature will rise, affecting its performance and lifespan. In high-power-density applications, additional heat dissipation measures may be required, such as adding heat sinks or fans, which increases system complexity and cost.

[0005] Third, the reverse recovery time of a diode is a critical parameter. During the switching process of a flyback converter, the diode needs to quickly switch from the conducting state to the blocking state. However, the reverse recovery time of ordinary diodes is relatively long, which can lead to current and voltage spikes at the moment of switching, affecting the dynamic response performance of the converter and potentially having an adverse impact on the electromagnetic compatibility of the circuit.

[0006] Finally, the forward voltage drop of a diode is fixed, which means that at low voltage outputs, the diode's voltage drop accounts for a larger proportion of the output voltage, further reducing efficiency. For example, when the output voltage is 3.3V, the 0.7V diode voltage drop accounts for 21% of the output voltage, making diode rectification less efficient in low-voltage output applications.

[0007] Therefore, it suffers from drawbacks such as low efficiency, complex thermal management, poor dynamic performance, and limitations in high-frequency applications, leading to its gradual replacement by more advanced technologies such as synchronous rectification in applications requiring high efficiency, high power density, and high performance. However, existing power adapter circuits with synchronous rectification are complex and costly. Utility Model Content

[0008] The technical problem solved by this utility model is to provide a power adapter circuit with synchronous rectification that is simple in structure and low in cost.

[0009] This utility model provides a power adapter circuit with synchronous rectification, including a transformer, a synchronous rectification circuit, an output filter circuit, a feedback circuit, and a controller. The synchronous rectification circuit includes a first resistor, a second resistor, a third resistor, a first field-effect transistor (FET), a second field-effect transistor (FET), and a synchronous rectification chip. The first end of the first resistor is electrically connected to the gate of the first FET, and the second end of the first resistor is electrically connected to the source of the second FET. The first end of the second resistor is electrically connected to the source of the second FET, and the second end of the second resistor is electrically connected to the gate of the second FET.

[0010] The first end of the third resistor is electrically connected to the first end of the first secondary coil of the transformer, and the second end of the third resistor is electrically connected to the third pin of the synchronous rectifier chip; the source of the first field-effect transistor is grounded, and the drain of the first field-effect transistor is electrically connected to the first end of the second secondary coil of the transformer; the source of the second field-effect transistor is electrically connected to the fourth pin of the synchronous rectifier chip, and the gate of the second field-effect transistor is electrically connected to the first pin of the synchronous rectifier chip; the output filter circuit is electrically connected to the second end of the first secondary coil of the transformer and the second end of the second secondary coil of the transformer; the feedback circuit is electrically connected to the output filter circuit and the controller.

[0011] In one embodiment, the synchronous rectification circuit further includes a fourth resistor, the first end of which is electrically connected to the gate of the first field-effect transistor, and the second end of which is electrically connected to the eighth pin of the synchronous rectification chip.

[0012] In one embodiment, the synchronous rectification circuit further includes a rectifier diode, the anode of which is electrically connected to the first end of the third secondary coil of the transformer, the cathode of which is electrically connected to the seventh pin of the synchronous rectification chip, and the second end of the third secondary coil of the transformer is grounded.

[0013] In one embodiment, the synchronous rectification circuit further includes a first capacitor, a first terminal of which is electrically connected to the cathode of the rectifier diode, and a second terminal of which is grounded.

[0014] In one embodiment, the source of the first field-effect transistor is electrically connected to and grounded to the fifth pin of the synchronous rectifier chip.

[0015] In one embodiment, the feedback circuit includes a fifth resistor, a sixth resistor, a second capacitor, a first Zener diode, a second Zener diode, and an optocoupler. The first terminal of the fifth resistor is electrically connected to the anode of the first Zener diode, and the second terminal of the fifth resistor is electrically connected to the first terminal of the optocoupler. The first terminal of the sixth resistor is electrically connected to the output filter circuit, and the second terminal of the sixth resistor is electrically connected to the first terminal of the second capacitor. The second terminal of the second capacitor is electrically connected to the control terminal of the second Zener diode. The cathode of the first Zener diode is electrically connected to the first terminal of the sixth resistor. The anode of the second Zener diode is grounded, and the cathode of the second Zener diode is electrically connected to the second terminal of the optocoupler.

[0016] In one embodiment, the feedback circuit further includes a seventh resistor, the first end of which is electrically connected to the second end of the second capacitor, and the second end of the seventh resistor is grounded.

[0017] In one embodiment, the feedback circuit further includes an eighth resistor, the first end of which is electrically connected to the first end of the fifth resistor, and the second end of which is electrically connected to the cathode of the second Zener diode.

[0018] In one embodiment, the feedback circuit further includes a ninth resistor, a tenth resistor, and a third capacitor. The first end of the ninth resistor is electrically connected to the cathode of the second Zener diode, the second end of the ninth resistor is electrically connected to the first end of the third capacitor, and the second end of the third capacitor is electrically connected to the second end of the second capacitor. The first end of the tenth resistor is electrically connected to the second end of the third capacitor, and the second end of the tenth resistor is electrically connected to the first end of the sixth resistor.

[0019] In one embodiment, the feedback circuit further includes a fourth capacitor, the first end of which is electrically connected to the first end of the ninth resistor, and the second end of which is electrically connected to the first end of the tenth resistor.

[0020] This invention offers the following advantages: The synchronous rectification circuit comprises a first resistor, a second resistor, a third resistor, a first field-effect transistor (FET), a second FET, and a synchronous rectification chip. The first terminal of the first resistor is electrically connected to the gate of the first FET, and the second terminal of the first resistor is electrically connected to the source of the second FET. Similarly, the first terminal of the second resistor is electrically connected to the source of the second FET, and the second terminal of the second resistor is electrically connected to the gate of the second FET. The first terminal of the third resistor is electrically connected to the first terminal of the first secondary coil of the transformer, and the second terminal of the third resistor is electrically connected to the third pin of the synchronous rectification chip. Therefore, driven by the synchronous rectification chip, it achieves synchronous rectification, offering advantages such as simple structure, low cost, and high reliability. Attached Figure Description

[0021] Figure 1 This is a schematic block diagram of the power adapter circuit with synchronous rectification according to this utility model.

[0022] Figure 2 This is a circuit diagram showing the transformer, output filter circuit, feedback circuit, and controller of the power adapter circuit with synchronous rectification of this utility model. Detailed Implementation

[0023] The present invention will now be described in detail with reference to the accompanying drawings and embodiments. It should be noted that, unless otherwise specified, embodiments of the present invention and the various features thereof can be combined with each other, all of which are within the protection scope of the present invention.

[0024] Please see Figure 1 and Figure 2 This utility model provides a power adapter circuit with synchronous rectification, including an input rectifier and filter circuit 1, a power factor correction circuit 2, an LLC converter circuit 3, a transformer 4, a synchronous rectifier circuit 5, an output filter circuit 6, a feedback circuit 7, and a controller 8. The input rectifier and filter circuit 1 is electrically connected to the power factor correction circuit 2, and the LLC converter circuit 3 is electrically connected to the power factor correction circuit 2 and the transformer 4. The feedback circuit 7 is electrically connected to the output filter circuit 6 and the controller 8.

[0025] The synchronous rectification circuit 5 includes a first resistor R1, a second resistor R2, a third resistor R3, a first field-effect transistor Q1, a second field-effect transistor Q2, and a synchronous rectification chip U. The first end of the first resistor R1 is electrically connected to the gate of the first field-effect transistor Q1, and the second end of the first resistor R1 is electrically connected to the source of the second field-effect transistor Q2. The first end of the second resistor R2 is electrically connected to the source of the second field-effect transistor Q2, and the second end of the second resistor R2 is electrically connected to the gate of the second field-effect transistor Q2.

[0026] The first terminal of the third resistor R3 is electrically connected to the first terminal of the first secondary coil of the transformer 4, and the second terminal of the third resistor R3 is electrically connected to the third pin of the synchronous rectifier chip U. The source of the first field-effect transistor Q1 is grounded, and the drain of the first field-effect transistor Q1 is electrically connected to the first terminal of the second secondary coil of the transformer 4. The source of the second field-effect transistor Q2 is electrically connected to the fourth pin of the synchronous rectifier chip U, and the gate of the second field-effect transistor Q2 is electrically connected to the first pin of the synchronous rectifier chip U. The output filter circuit 6 is electrically connected to the second terminal of both the first and second secondary coils of the transformer 4. The source of the first field-effect transistor Q1 is electrically connected to the fifth pin of the synchronous rectifier chip U and grounded.

[0027] Because the on-resistance of a field-effect transistor (FET) is much lower than the forward voltage drop of a conventional diode, the heat generated during operation is significantly reduced. This not only reduces the complexity and cost of heat dissipation design but also improves circuit reliability and extends lifespan. Furthermore, the switching speed of an FET is much faster than that of a conventional diode. FET switching times are typically on the order of nanoseconds, while those of a conventional diode may be on the order of microseconds. This rapid switching characteristic allows the synchronous rectifier circuit 5 to be better suited for high-frequency switching power supply applications.

[0028] The synchronous rectification circuit 5 also includes a fourth resistor R4, a first capacitor C1, and a rectifier diode D. The first terminal of the fourth resistor R4 is electrically connected to the gate of the first field-effect transistor Q1, and the second terminal of the fourth resistor R4 is electrically connected to pin 8 of the synchronous rectification chip U. The first terminal of the first capacitor C1 is electrically connected to the cathode of the rectifier diode D, and the second terminal of the first capacitor C1 is grounded to filter the current output by the rectifier diode D. The anode of the rectifier diode D is electrically connected to the first terminal of the third secondary coil of the transformer 4, the cathode of the rectifier diode D is electrically connected to pin 7 of the synchronous rectification chip U, and the second terminal of the third secondary coil of the transformer 4 is grounded.

[0029] Feedback circuit 7 includes a fifth resistor R5, a sixth resistor R6, a second capacitor C2, a first Zener diode ZD1, a second Zener diode ZD2, and an optocoupler ZD3. The first terminal of the fifth resistor R5 is electrically connected to the anode of the first Zener diode ZD1, and the second terminal of the fifth resistor R5 is electrically connected to the first terminal of the optocoupler ZD3. The first terminal of the sixth resistor R6 is electrically connected to the output filter circuit 6, and the second terminal of the sixth resistor R6 is electrically connected to the first terminal of the second capacitor C2. The second terminal of the second capacitor C2 is electrically connected to the control terminal of the second Zener diode ZD2. The cathode of the first Zener diode ZD1 is electrically connected to the first terminal of the sixth resistor R6. The anode of the second Zener diode ZD2 is grounded, and the cathode of the second Zener diode ZD2 is electrically connected to the second terminal of the optocoupler ZD3. This circuit can output a stable and reliable feedback voltage. The controller 8 controls the output voltage of the transformer 4 in real time based on the voltage fed back from the feedback circuit 7 to achieve output voltage stability.

[0030] Feedback circuit 7 also includes a seventh resistor R7 and an eighth resistor R8. The first terminal of the seventh resistor R7 is electrically connected to the second terminal of the second capacitor C2, and the second terminal of the seventh resistor R7 is grounded. The first terminal of the eighth resistor R8 is electrically connected to the first terminal of the fifth resistor R5, and the second terminal of the eighth resistor R8 is electrically connected to the cathode of the second Zener diode ZD2. The required output voltage is set by the cooperation of the seventh resistor R7 and the eighth resistor R8.

[0031] Feedback circuit 7 also includes a ninth resistor R9, a tenth resistor R10, and a third capacitor C3. The first terminal of the ninth resistor R9 is electrically connected to the cathode of the second Zener diode ZD2, and the second terminal of the ninth resistor R9 is electrically connected to the first terminal of the third capacitor C3. The second terminal of the third capacitor C3 is electrically connected to the second terminal of the second capacitor C2. The first terminal of the tenth resistor R10 is electrically connected to the second terminal of the third capacitor C3, and the second terminal of the tenth resistor R10 is electrically connected to the first terminal of the sixth resistor R6. Furthermore, optocoupler ZD3 is also connected to an eleventh resistor R11 and a third Zener diode ZD3. Optocoupler ZD3 is electrically connected to controller 8 through the eleventh resistor R11.

[0032] Feedback circuit 7 also includes a fourth capacitor C4. The first terminal of fourth capacitor C4 is electrically connected to the first terminal of the ninth resistor R9, and the second terminal of fourth capacitor C4 is electrically connected to the first terminal of the tenth resistor R10, thus improving stability. Output filter circuit 6 includes multiple fifth capacitors C5 connected in parallel. The first terminal of fifth capacitor C5 is grounded, and the second terminal of fifth capacitor C5 is electrically connected to the second terminals of the first and second secondary coils of transformer 4. It is understood that the synchronous rectifier chip U can be a synchronous rectifier chip from Chipmax Microelectronics, model LPXXR100FN or LP35118L. Of course, it can also be other models of chips from other companies; no specific limitation is made here.

[0033] In summary, the synchronous rectification circuit 5 of this utility model includes a first resistor R1, a second resistor R2, a third resistor R3, a first field-effect transistor Q1, a second field-effect transistor Q2, and a synchronous rectification chip U. The first end of the first resistor R1 is electrically connected to the gate of the first field-effect transistor Q1, and the second end of the first resistor R1 is electrically connected to the source of the second field-effect transistor Q2. The first end of the second resistor R2 is electrically connected to the source of the second field-effect transistor Q2, and the second end of the second resistor R2 is electrically connected to the gate of the second field-effect transistor Q2. The first end of the third resistor R3 is electrically connected to the first end of the first secondary coil of the transformer 4, and the second end of the third resistor R3 is electrically connected to the third pin of the synchronous rectification chip U. Therefore, under the drive of the synchronous rectification chip U, it achieves synchronous rectification, and has the advantages of simple structure, low cost, and high reliability.

[0034] The power adapter circuit with synchronous rectification provided by this utility model has been described in detail above. Specific examples have been used to illustrate the principle and implementation of this utility model. The descriptions of the embodiments above are only for the purpose of helping to understand the method and core idea of ​​this utility model. Furthermore, those skilled in the art will recognize that, based on the idea of ​​this utility model, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification is only an embodiment of this utility model and does not limit the patent scope of this utility model. Any equivalent structural or procedural transformations made using the content of this utility model specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of this utility model and should not be construed as a limitation of this utility model.

Claims

1. A power adapter circuit with synchronous rectification, characterized in that, The system includes a transformer, a synchronous rectification circuit, an output filter circuit, a feedback circuit, and a controller. The synchronous rectification circuit includes a first resistor, a second resistor, a third resistor, a first field-effect transistor (FET), a second field-effect transistor (FET), and a synchronous rectification chip. The first terminal of the first resistor is electrically connected to the gate of the first FET, and the second terminal of the first resistor is electrically connected to the source of the second FET. The first terminal of the second resistor is electrically connected to the source of the second FET, and the second terminal of the second resistor is electrically connected to the gate of the second FET. The first end of the third resistor is electrically connected to the first end of the first secondary coil of the transformer, and the second end of the third resistor is electrically connected to the third pin of the synchronous rectifier chip; the source of the first field-effect transistor is grounded, and the drain of the first field-effect transistor is electrically connected to the first end of the second secondary coil of the transformer; the source of the second field-effect transistor is electrically connected to the fourth pin of the synchronous rectifier chip, and the gate of the second field-effect transistor is electrically connected to the first pin of the synchronous rectifier chip. The output filter circuit is electrically connected to the second end of the first secondary coil of the transformer and the second end of the second secondary coil of the transformer; the feedback circuit is electrically connected to the output filter circuit and the controller.

2. The power adapter circuit with synchronous rectification as described in claim 1, characterized in that, The synchronous rectification circuit further includes a fourth resistor, the first end of which is electrically connected to the gate of the first field-effect transistor, and the second end of which is electrically connected to the eighth pin of the synchronous rectification chip.

3. The power adapter circuit with synchronous rectification as described in claim 1 or 2, characterized in that, The synchronous rectification circuit also includes a rectifier diode. The anode of the rectifier diode is electrically connected to the first end of the third secondary coil of the transformer, the cathode of the rectifier diode is electrically connected to the seventh pin of the synchronous rectification chip, and the second end of the third secondary coil of the transformer is grounded.

4. The power adapter circuit with synchronous rectification as described in claim 3, characterized in that, The synchronous rectification circuit further includes a first capacitor, the first terminal of which is electrically connected to the cathode of the rectifier diode, and the second terminal of which is grounded.

5. The power adapter circuit with synchronous rectification as described in claim 1 or 2, characterized in that, The source of the first field-effect transistor is electrically connected to the fifth pin of the synchronous rectifier chip and grounded.

6. The power adapter circuit with synchronous rectification as described in claim 1 or 2, characterized in that, The feedback circuit includes a fifth resistor, a sixth resistor, a second capacitor, a first Zener diode, a second Zener diode, and an optocoupler. The first terminal of the fifth resistor is electrically connected to the anode of the first Zener diode, and the second terminal of the fifth resistor is electrically connected to the first terminal of the optocoupler. The first terminal of the sixth resistor is electrically connected to the output filter circuit, and the second terminal of the sixth resistor is electrically connected to the first terminal of the second capacitor. The second terminal of the second capacitor is electrically connected to the control terminal of the second Zener diode. The cathode of the first Zener diode is electrically connected to the first terminal of the sixth resistor. The anode of the second Zener diode is grounded, and the cathode of the second Zener diode is electrically connected to the second terminal of the optocoupler.

7. The power adapter circuit with synchronous rectification as described in claim 6, characterized in that, The feedback circuit also includes a seventh resistor, the first end of which is electrically connected to the second end of the second capacitor, and the second end of the seventh resistor is grounded.

8. The power adapter circuit with synchronous rectification as described in claim 6, characterized in that, The feedback circuit further includes an eighth resistor, the first end of which is electrically connected to the first end of the fifth resistor, and the second end of which is electrically connected to the cathode of the second Zener diode.

9. The power adapter circuit with synchronous rectification as described in claim 6, characterized in that, The feedback circuit further includes a ninth resistor, a tenth resistor, and a third capacitor. The first end of the ninth resistor is electrically connected to the cathode of the second Zener diode, the second end of the ninth resistor is electrically connected to the first end of the third capacitor, and the second end of the third capacitor is electrically connected to the second end of the second capacitor. The first end of the tenth resistor is electrically connected to the second end of the third capacitor, and the second end of the tenth resistor is electrically connected to the first end of the sixth resistor.

10. The power adapter circuit with synchronous rectification as described in claim 9, characterized in that, The feedback circuit further includes a fourth capacitor, the first end of which is electrically connected to the first end of the ninth resistor, and the second end of which is electrically connected to the first end of the tenth resistor.

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