A reverse flow prevention circuit

Abstract

This utility model discloses an anti-backflow circuit, which is integrated into the transformer-stage circuit of the charging circuit. The core components include diode D8, resistor R53, capacitor C11, resistor R52, transistor Q3, bias resistor R25, MOS switch Q2, and gate protection resistor R27. Its working principle is as follows: When the charger is working normally, the transformer secondary winding outputs a forward voltage. This voltage is sampled by diode D8, stored in capacitor C11, and divided by resistor R52, driving transistor Q3 to conduct. This, in turn, turns on MOS switch Q2, allowing the subsequent circuit to normally deliver power to the USB output. When the charger stops working, the secondary winding has no output. Capacitor C11 discharges, causing transistor Q3 to turn off. MOS switch Q2 is reliably turned off under the action of resistor R27, cutting off the path between the output terminal and the subsequent circuit, thus blocking voltage backflow and reverse discharge.

Description

Technical Field

[0001] This utility model relates to the field of charging technology, specifically to an anti-backflow circuit. Background Technology

[0002] In the field of charging technology, the following technical pain points often exist in the connection scenarios between chargers and products being charged (such as charging packs, electronic devices, etc.): When the charger is not in operation (such as not connected to mains power, or a fault in the front-end circuit), if the product being charged still maintains a physical connection with the charger (such as being plugged into a charging pack), a voltage reverse flow phenomenon may occur because the product itself has energy storage components (such as batteries). That is, the voltage at the product end flows backward into the charger's subsequent circuit, causing damage to the charger's internal power module. At the same time, the reverse flow process may also cause the product being charged to discharge in reverse, resulting in product power loss, and even affecting the product's lifespan due to unstable discharge current.

[0003] Existing charger circuits mostly focus only on achieving forward charging functionality, lacking anti-reverse current design for non-operating states, or using a single diode rectification for anti-reverse current, resulting in problems such as large on-state voltage drop, high power consumption, and narrow applicable current range, failing to meet the requirements of efficient and safe charging. Therefore, there is an urgent need for a simple, highly reliable, and low-power anti-reverse current circuit to solve the aforementioned voltage reverse current and reverse discharge problems. Utility Model Content

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide an anti-backflow circuit. By setting an intelligent switch control module after the transformer in the charging circuit, the circuit can achieve the function of "conducting when charging and turning off when not charging", effectively blocking the voltage backflow path, reducing circuit power consumption, and ensuring equipment safety.

[0005] To solve the above-mentioned technical problems, this utility model provides an anti-backflow circuit, which is installed in a charging circuit. The charging circuit includes a transformer pre-stage circuit and a transformer post-stage circuit. The transformer pre-stage circuit is connected to mains power, and after filtering and rectification, the power is fed into the primary winding of transformer T1. The transformer post-stage circuit is connected to the secondary winding of transformer T1, and the power is sequentially fed through a filter circuit and a rectification circuit to the USB circuit output. The anti-backflow circuit is located in the transformer post-stage circuit and includes: Diode D8, the positive terminal of which is connected to the T+ terminal of the secondary winding, and the T- terminal of the secondary winding is grounded to RTN2; Resistor R53, the first end of which is connected to the negative terminal of diode D8; Capacitor C11 is used for energy storage. Its first end is connected to the second end of resistor R53, and its second end is connected to the V-output circuit. Resistor R52, the first end of which is connected to the first end of capacitor C11; The base of transistor Q3 is connected to the second terminal of resistor R52, and its emitter is connected to the V- output circuit. Resistor R25 has its first end connected to the base of transistor Q3, and its second end connected to the V- output circuit; The gate G of the MOS switch Q2 is connected to the collector of the transistor Q3, and its drain D is connected to the output terminal of the rectifier circuit. A resistor R27 is connected between the source S and the gate G of the MOS switch Q2, and the source S of the MOS switch Q2 is connected to the V+ output circuit.

[0006] Furthermore, the resistor R25 is a bias resistor, which prevents the transistor Q3 from malfunctioning.

[0007] Furthermore, the resistance value of the resistor R27 is sufficient to prevent the MOS switch Q2 from being broken down by current.

[0008] Furthermore, the filter circuit includes an RC filter circuit with a diode D6 connected in parallel for rectification. The RC filter circuit includes a resistor R19 and a capacitor C8 connected in series. The first end of the resistor R19 is connected to the T+ terminal of the secondary winding and the positive terminal of the diode D6.

[0009] Furthermore, after filtering, the RC filter circuit stores energy through a polarized capacitor EC3. The positive terminal of the polarized capacitor EC3 is connected to the negative terminal of the diode D6, and its negative terminal is connected to the T- terminal of the secondary winding. The T-terminal of the secondary winding is also connected to the first terminal of resistor R20. A polarized capacitor EC4 is connected between the second terminal of resistor R20 and the negative terminal of diode D6. A resistor R7 is connected in parallel with the polarized capacitor EC4. The negative terminal of the polarized capacitor EC4 is connected to the second terminal of the resistor R20.

[0010] Furthermore, the negative terminal of the diode D6 is also connected to the first end of the first winding of the common-mode inductor LF3, and the second end of the first winding of the common-mode inductor LF3 is connected to the drain of the MOS switch Q2. The first end of the second winding of the common-mode inductor LF3 is connected to the second end of the resistor R20, and the second end of the second winding is connected to the V-output circuit.

[0011] Compared with the prior art, the beneficial effects of this utility model are: 1. The anti-backflow circuit of this utility model has high reliability in preventing backflow: through the three-level control logic of "diode sampling + transistor driving + MOSFET main switch", the main circuit is only turned on when the charger is working normally (the secondary winding has output), and is completely turned off when not working, thus physically blocking the backflow path and avoiding power supply damage or reverse discharge.

[0012] 2. The anti-backflow circuit of this utility model has the functions of low power consumption and low loss: the anti-backflow circuit uses a MOS switch as the main switching element, which has a small on-resistance (far lower than that of traditional diodes) and negligible on-state voltage drop, thus greatly reducing circuit power consumption and improving charging efficiency.

[0013] 3. The anti-backflow circuit of this utility model has strong anti-interference capability: the bias resistor R25 prevents the transistor Q3 from malfunctioning, the common mode inductor LF3 suppresses common mode interference, and the combination of RC filter and polarized capacitor improves voltage stability, ensuring that the circuit can still work reliably under voltage fluctuation and external interference environment.

[0014] 4. The anti-backflow circuit of this utility model has a simple structure and low cost: the core components are all conventional discrete components, without the need for complex integrated circuits, which are easy to purchase and mass-produce, and are compatible with various low-cost charging devices.

[0015] 5. The anti-backflow circuit of this utility model has wide compatibility: it can be directly integrated into the transformer stage of the existing USB charging circuit without major modification to the front stage circuit, and is suitable for various charging scenarios such as mobile phone chargers, charging packs, and small home appliances. Attached Figure Description

[0016] Figure 1 This is the circuit diagram of the transformer front-end of this utility model.

[0017] Figure 2 This diagram shows the filter circuit, rectifier circuit, and anti-backflow circuit of the transformer's subsequent stage circuit of this utility model.

[0018] Figure 3 This is the USB circuit diagram of this utility model.

[0019] Figure 4 This is a diagram of the amplifier circuit and switching circuit of this utility model. Detailed Implementation

[0020] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments, so that the advantages and features of the present utility model can be more easily understood by those skilled in the art, thereby making a clearer and more definite definition of the protection scope of the present utility model. Obviously, the embodiments described in this utility model are only some embodiments of the present utility model, and not all embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present utility model.

[0021] Furthermore, the technical features involved in the different embodiments of this utility model described below can be combined with each other as long as they do not conflict with each other.

[0022] Example 1: The specific structure of this utility model is as follows: Please refer to the appendix. Figure 1-4 This utility model discloses an anti-backflow circuit, which is installed in a charging circuit. The charging circuit includes a transformer pre-stage circuit and a transformer post-stage circuit. The transformer pre-stage circuit is connected to the mains power supply, and the power is fed into the primary winding of transformer T1 after filtering and rectification. The transformer post-stage circuit is connected to the secondary winding of transformer T1, and the power is output to the USB circuit after passing through a filter circuit and a rectification circuit. The anti-backflow circuit is located in the transformer post-stage circuit and includes: Diode D8, the positive terminal of which is connected to the T+ terminal of the secondary winding, and the T- terminal of the secondary winding is grounded to RTN2; Resistor R53, the first end of which is connected to the negative terminal of diode D8; Capacitor C11 is used for energy storage. Its first end is connected to the second end of resistor R53, and its second end is connected to the V-output circuit. Resistor R52, the first end of which is connected to the first end of capacitor C11; The base of transistor Q3 is connected to the second terminal of resistor R52, and its emitter is connected to the V- output circuit. Resistor R25 has its first end connected to the base of transistor Q3, and its second end connected to the V- output circuit; The gate G of the MOS switch Q2 is connected to the collector of the transistor Q3, and its drain D is connected to the output terminal of the rectifier circuit. A resistor R27 is connected between the source S and the gate G of the MOS switch Q2, and the source S of the MOS switch Q2 is connected to the V+ output circuit.

[0023] The resistor R25 is a bias resistor, which prevents the transistor Q3 from malfunctioning.

[0024] The resistance of resistor R27 is sufficient to prevent the MOS switch Q2 from being damaged by current.

[0025] The filter circuit includes an RC filter circuit with a diode D6 connected in parallel for rectification. The RC filter circuit includes a resistor R19 and a capacitor C8 connected in series. The first end of the resistor R19 is connected to the T+ terminal of the secondary winding and the positive terminal of the diode D6.

[0026] After filtering, the RC filter circuit stores energy through a polarized capacitor EC3. The positive terminal of the polarized capacitor EC3 is connected to the negative terminal of the diode D6, and its negative terminal is connected to the T- terminal of the secondary winding. The T-terminal of the secondary winding is also connected to the first terminal of resistor R20. A polarized capacitor EC4 is connected between the second terminal of resistor R20 and the negative terminal of diode D6. A resistor R7 is connected in parallel with the polarized capacitor EC4. The negative terminal of the polarized capacitor EC4 is connected to the second terminal of the resistor R20.

[0027] The negative terminal of the diode D6 is also connected to the first end of the first winding of the common-mode inductor LF3, and the second end of the first winding of the common-mode inductor LF3 is connected to the drain of the MOS switch Q2. The first end of the second winding of the common-mode inductor LF3 is connected to the second end of the resistor R20, and the second end of the second winding is connected to the V-output circuit.

[0028] Example 2:

[0029] The following is the working principle of the anti-backflow circuit of this utility model: The anti-backflow circuit of this utility model achieves the anti-backflow function through the logic of "sampling the secondary winding output signal → driving the switching element → controlling the on / off state of the main circuit". The specific working process is divided into two scenarios: Scenario 1: The charger is working normally (the secondary winding has an output). When the transformer's front circuit is connected to the mains and is working normally, the secondary winding of transformer T1 outputs a positive voltage (T+ terminal is positive, T- terminal is grounded): the positive voltage of the secondary winding charges capacitor C11 through diode D8 (unidirectional conduction) and resistor R53 (current limiting), so that a stable voltage is established across capacitor C11. The voltage across capacitor C11 is divided by resistor R52, providing a positive drive voltage to the base of transistor Q3. At this time, the base-emitter junction of transistor Q3 meets the conduction condition (Vbe > conduction voltage), and transistor Q3 is turned on. After transistor Q3 is turned on, its collector potential is pulled down to near the potential of the V- output circuit (low level). The gate G of MOS switch Q2 is grounded through transistor Q3, and a positive voltage (Vgs > turn-on voltage) is formed between the gate and source. MOS switch Q2 is turned on. After the MOS switch Q2 is turned on, the electrical energy processed by filtering and rectification in the transformer's downstream circuit is delivered to the V+ output circuit through the MOS switch Q2, and finally, normal charging output is achieved through the USB circuit.

[0030] Scenario 2: The charger stops working (no output from the secondary winding). When the transformer's front-end circuit is disconnected from the mains power or malfunctions (such as power failure or short circuit), the secondary winding of transformer T1 has no positive output (no voltage at the T+ terminal): diode D8 is cut off due to the lack of positive voltage, and capacitor C11 discharges through resistor R52 and the base-emitter circuit of transistor Q3, causing the voltage at both ends to gradually decrease.

[0031] When the voltage across capacitor C11 drops to a level that can no longer keep transistor Q3 on (Vbe < on-voltage), transistor Q3 will turn off. After transistor Q3 is turned off, the gate G of MOS switch Q2 loses its discharge path. At this time, resistor R27 (between gate and source) plays a role: on the one hand, it prevents sudden changes in gate voltage, and on the other hand, it discharges to gate G through source S, so that Vgs voltage drops rapidly below the turn-on voltage, and MOS switch Q2 is reliably turned off.

[0032] After the MOS switch Q2 is turned off, the path between the output terminal (V+, V-) of the charging circuit and the subsequent circuit is cut off. The voltage at the end of the product being charged cannot flow back into the transformer's subsequent circuit, thus completely blocking voltage backflow and reverse discharge, protecting the charger and the product being charged.

[0033] In summary, the anti-backflow circuit of this utility model has high reliability in preventing backflow: through the three-level control logic of "diode sampling + transistor driving + MOSFET main switch", the main circuit is only turned on when the charger is working normally (the secondary winding has output), and is completely turned off when not working, thus physically blocking the backflow path and avoiding power supply damage or reverse discharge.

[0034] This utility model anti-backflow circuit has the functions of low power consumption and low loss: the anti-backflow circuit uses a MOS switch as the main switching element, which has a small on-resistance (far lower than that of traditional diodes) and negligible on-state voltage drop, which greatly reduces circuit power consumption and improves charging efficiency.

[0035] This utility model's anti-backflow circuit has strong anti-interference capabilities: it avoids malfunction of transistor Q3 by using bias resistor R25, suppresses common-mode interference by using common-mode inductor LF3, and improves voltage stability by combining RC filter and polarized capacitor, ensuring that the circuit can still work reliably under voltage fluctuations and external interference environments.

[0036] This utility model's anti-backflow circuit has a simple structure and low cost: the core components are all conventional discrete components, without the need for complex integrated circuits, making it easy to purchase and mass-produce, and adaptable to various low-cost charging devices.

[0037] This utility model's anti-backflow circuit has wide compatibility: it can be directly integrated into the transformer stage of existing USB charging circuits without requiring significant modifications to the pre-stage circuit, and is suitable for various charging scenarios such as mobile phone chargers, charging packs, and small household appliances.

[0038] The above description is only a preferred embodiment of the present utility model and does not limit the patent scope of the present utility model. Any equivalent structural or procedural transformations made based on the contents of the present utility model specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present utility model.

Claims

1. An anti-backflow circuit, wherein the anti-backflow circuit is disposed in a charging circuit, the charging circuit comprising a transformer pre-stage circuit and a transformer post-stage circuit, the transformer pre-stage circuit being connected to mains power, and the power is fed into the primary winding of transformer T1 after filtering and rectification; the transformer post-stage circuit being connected to the secondary winding of transformer T1, and the power is output to a USB circuit after passing through a filter circuit and a rectification circuit in sequence, characterized in that, The backflow prevention circuit is located in the downstream circuit of the transformer and includes: Diode D8, the positive terminal of which is connected to the T+ terminal of the secondary winding, and the T- terminal of the secondary winding is grounded to RTN2; Resistor R53, the first end of which is connected to the negative terminal of diode D8; Capacitor C11 is used for energy storage. Its first end is connected to the second end of resistor R53, and its second end is connected to the V-output circuit. Resistor R52, the first end of which is connected to the first end of capacitor C11; The base of transistor Q3 is connected to the second terminal of resistor R52, and its emitter is connected to the V- output circuit. Resistor R25 has its first end connected to the base of transistor Q3, and its second end connected to the V- output circuit; The gate G of the MOS switch Q2 is connected to the collector of the transistor Q3, and its drain D is connected to the output terminal of the rectifier circuit. A resistor R27 is connected between the source S and the gate G of the MOS switch Q2. The source S of the MOS switch Q2 is connected to the V+ output circuit. The resistor R25 is a bias resistor, which prevents the transistor Q3 from malfunctioning. The resistance value of resistor R27 is sufficient to prevent the MOS switch Q2 from being broken down by current. The filter circuit includes an RC filter circuit with a diode D6 connected in parallel for rectification. The RC filter circuit includes a resistor R19 and a capacitor C8 connected in series. The first end of the resistor R19 is connected to the T+ terminal of the secondary winding and the positive terminal of the diode D6. After filtering, the RC filter circuit stores energy through a polarized capacitor EC3. The positive terminal of the polarized capacitor EC3 is connected to the negative terminal of the diode D6, and its negative terminal is connected to the T- terminal of the secondary winding. The T-terminal of the secondary winding is also connected to the first terminal of resistor R20. A polarized capacitor EC4 is connected between the second terminal of resistor R20 and the negative terminal of diode D6. A resistor R7 is connected in parallel with the polarized capacitor EC4. The negative terminal of the polarized capacitor EC4 is connected to the second terminal of the resistor R20; The negative terminal of the diode D6 is also connected to the first end of the first winding of the common-mode inductor LF3, and the second end of the first winding of the common-mode inductor LF3 is connected to the drain of the MOS switch Q2. The first end of the second winding of the common-mode inductor LF3 is connected to the second end of the resistor R20, and the second end of the second winding is connected to the V-output circuit.

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