A two-stage isolated switching power supply with capacitor and a starting method

Abstract

The present invention provides a two-stage isolated switching power supply with capacitor and a startup method, wherein the two-stage isolated switching power supply with capacitor includes a primary circuit, a transformer T1, a secondary circuit, and a sampling control circuit; the sampling control circuit includes a primary capacitor C1, voltage-dividing resistors R2 and R3, one end of the primary capacitor C1 is connected to the positive input end of the rectifier bridge, the voltage-dividing resistor R2 and the voltage-dividing resistor R3 are connected in series and then connected in parallel with the primary capacitor C1, and the node between the voltage-dividing resistors R2 and R3 is used as a sampling end for sampling voltage; the sampling control circuit calculates the initial duty cycle and then outputs a control signal to the gate of each power tube to complete the startup. The present invention effectively reduces the backflow current, and there is no need to add an additional anti-backflow circuit in the switching power supply. Single-side sampling also reduces the design of the isolated sampling circuit at the output and input ends of the switching power supply, reduces the number of components, improves the integration of the product, and effectively reduces the manufacturing cost.

Description

Technical Field

[0001] The present invention mainly relates to the technical field of switching power supplies, and in particular to a two-stage isolated switching power supply with capacitors and a starting method thereof. Background Art

[0002] During the use of the switching power supply, the input voltage may be turned off, but the output capacitor or capacitive load may not be fully discharged, that is, there is residual voltage on the output side of the system, forming a bias voltage. In traditional analog power supplies, the driving duty cycle usually does not consider the bias voltage, and usually starts to increase from 0. However, due to the existence of the bias voltage, the traditional analog power supply is prone to current backflow when starting, resulting in harsh working conditions and damage to the power supply components. In general analog two-stage isolation circuits, the common treatment method is to add an anti-backflow circuit on the output side, but adding an anti-backflow circuit will increase the design and manufacturing cost of the circuit and occupy layout space. Summary of the invention

[0003] The technical problem to be solved by the present invention is to provide a two-stage isolated switching power supply with capacitor and a startup method to avoid current backflow when the switching power supply is started.

[0004] In order to solve the above technical problems, in the first aspect, the present invention provides a two-stage isolated switching power supply with capacitor, including a primary circuit, a transformer T1, a secondary circuit, and a sampling control circuit, wherein the primary circuit includes: a power tube S1, a power tube S2, an inductor L1, and a rectifier bridge composed of a power tube S3, a power tube S4, a power tube S5, and a power tube S6; the drain of the power tube S1 is connected to the positive electrode of the input power supply, and the source of the power tube S1 is connected to one end of the inductor L1; the other end of the inductor L1 is connected to the positive input end of the rectifier bridge; the drain of the power tube S2 is connected to the source of the power tube S1, and the source of the power tube S2 is connected to the negative electrode of the input power supply; the secondary circuit includes a power tube S7 and a power tube S8, and the drain of the power tube S7 is connected to the positive electrode of the transformer T1. The first positive output terminal of the power tube S7 is connected to the drain of the power tube S8 and the positive electrode of the load respectively; the source of the power tube S8 is connected to the negative output terminal of the transformer T1; the transformer T1 also includes a second positive output terminal, and the second positive output terminal is connected to the negative electrode of the load; the second positive input terminal is arranged at the middle position of the secondary coil of the transformer T1; the sampling control circuit includes a primary capacitor C1, a voltage dividing resistor R2 and a voltage dividing resistor R3, one end of the primary capacitor C1 is connected to the positive input terminal of the rectifier bridge, the voltage dividing resistor R2 and the voltage dividing resistor R3 are connected in series and then connected in parallel with the primary capacitor C1, and the node between the voltage dividing resistor R2 and the voltage dividing resistor R3 is used as a sampling terminal for sampling voltage; the sampling control circuit also outputs a control signal to the gate of each power tube.

[0005] Optionally, a filter capacitor C3 is connected in parallel to the voltage-dividing resistor R3.

[0006] Optionally, the secondary circuit further includes a secondary capacitor C2, one end of the secondary capacitor C2 is connected to the positive electrode of the load R1, and the other end of the secondary capacitor C2 is connected to the negative electrode of the load R1.

[0007] In a second aspect, the present invention provides a method for starting a two-stage isolated switching power supply with a capacitor, which is applied to the two-stage isolated switching power supply with a capacitor as described in the first aspect, and includes: setting the working state of the switching power supply, disconnecting the load and the power tube S1, controlling the power tube S7 and the power tube S8 to be alternately turned on with a fixed duty cycle, controlling one path of the rectifier bridge to be turned on when the power tube S7 is turned on, and controlling another path of the rectifier bridge to be turned on when the power tube S8 is turned on, so that the bias voltage of the secondary circuit is transmitted from the secondary side of the transformer T1 to the primary circuit; obtaining a sampling voltage; obtaining the output voltage of the primary circuit through the sampling voltage; calculating the initial duty cycle through the output voltage of the primary circuit and the input voltage of the primary circuit; generating a control signal according to the initial duty cycle, and the control signal controls the primary circuit and the secondary circuit to complete the startup of the switching power supply.

[0008] Optionally, the initial duty cycle Dinitial is: Dinitial= Vc1 / Vin; wherein Vin is the primary circuit input voltage, and Vc1 is the voltage on the primary capacitor C1.

[0009] Optionally, the primary circuit output voltage V_c1 is:

[0010]

[0011] Wherein, Vsingle is the sampling voltage.

[0012] Optionally, the fixed duty cycle is 50%.

[0013] Compared with the prior art, the present invention has the following beneficial effects: adding a primary capacitor to the primary side of the voltage, obtaining the voltage of the primary capacitor through a sampling circuit and then calculating the initial duty cycle of the start-up signal, effectively reducing the backflow current, and no additional anti-backflow circuit is needed in the switching power supply. Single-sided sampling also reduces the design of the isolated sampling circuit at the output and input ends of the switching power supply, reduces the number of components, improves the integration of the product, and effectively reduces the manufacturing cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The accompanying drawings are included to provide a further understanding of the present invention, and they are included and constitute a part of the present invention. The accompanying drawings illustrate embodiments of the present invention and together with the specification serve to explain the principles of the present invention. In the accompanying drawings:

[0015] Figure 1 It is a schematic diagram of the principle of a two-stage isolated switching power supply with capacitor according to an embodiment of the present invention;

[0016] Figure 2 It is a schematic diagram of sampling points in a startup method of a two-stage isolated switching power supply with capacitor according to an embodiment of the present invention. DETAILED DESCRIPTION

[0017] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following is a brief introduction to the drawings required for the description of the embodiments. Obviously, the drawings described below are only some examples or embodiments of the present invention. For ordinary technicians in this field, the present invention can also be applied to other similar scenarios based on these drawings without creative work. Unless it is obvious from the language environment or otherwise explained, the same reference numerals in the figures represent the same structure or operation.

[0018] It should be understood that when a component is referred to as being "on another component," "connected to another component," "coupled to another component," or "contacting another component," it may be directly on, connected to, coupled to, or contacting the other component, or there may be intervening components. In contrast, when a component is referred to as being "directly on another component," "directly connected to," "directly coupled to," or "directly contacting" another component, there are no intervening components. Similarly, when a first component is referred to as being "electrically in contact with" or "electrically coupled to" a second component, there is an electrical path between the first component and the second component that allows current to flow. The electrical path may include capacitors, coupled inductors, and / or other components that allow current to flow, even without direct contact between conductive components.

[0019] like Figure 1 As shown, a two-stage isolated switching power supply with capacitor provided in this embodiment includes a primary circuit, a transformer T1, a secondary circuit, and a sampling control circuit. The primary circuit includes a power tube S1, a power tube S2, an inductor L1, and a rectifier bridge composed of a power tube S3, a power tube S4, a power tube S5, and a power tube S6.

[0020] The drain of the power tube S1 is connected to the positive pole of the input power supply, and the source of the power tube S1 is connected to one end of the inductor L1; the other end of the inductor L1 is connected to the positive input end of the rectifier bridge; the drain of the power tube S2 is connected to the source of the power tube S1, and the source of the power tube S12 is connected to the negative pole of the input power supply.

[0021] The secondary circuit includes a power tube S7 and a power tube S8, the drain of the power tube S7 is connected to the first positive output terminal of the transformer T1, the source of the power tube S7 is connected to the drain of the power tube S8 and the positive electrode of the load respectively; the source of the power tube S8 is connected to the negative output terminal of the transformer T1;

[0022] The transformer T1 further includes a second positive output terminal connected to the negative electrode of the load; the second positive input terminal is arranged at the middle position of the secondary coil of the transformer T1.

[0023] The sampling control circuit includes a primary capacitor C1, a voltage-dividing resistor R2 and a voltage-dividing resistor R3. One end of the primary capacitor C1 is connected to the positive input end of the rectifier bridge. The voltage-dividing resistor R2 and the voltage-dividing resistor R3 are connected in series and then connected in parallel with the primary capacitor C1. The node between the voltage-dividing resistor R2 and the voltage-dividing resistor R3 serves as a sampling end for the sampling voltage. The sampling control circuit also outputs a control signal to the gate of each power tube.

[0024] The secondary circuit also includes a secondary capacitor C2, one end of which is connected to the positive electrode of the load R1, and the other end is connected to the negative electrode of the load R1. The secondary capacitor C2 is used to collect energy in the secondary circuit after power failure to form a bias voltage, and transmit the bias voltage to the primary side.

[0025] During the operation of the switching power supply of this embodiment, if the working voltage is turned off, the output end is not completely discharged, so that there is residual voltage at the output end to form a bias voltage. The bias voltage on the secondary capacitor C2 is transmitted to the primary capacitor C1 through the transformer T1, and the voltage on the primary capacitor C1 is calculated by sampling the voltage. Then, the initial duty cycle of the control signal is calculated by the voltage on the primary capacitor C1 and the input voltage, so that the initial duty cycle of the control signal is matched with the working voltage of the power supply, thereby effectively reducing the backflow current when the switching power supply is restarted.

[0026] In one implementation, a filter capacitor C3 is connected in parallel to the voltage-dividing resistor R3 to ensure the accuracy of voltage collection.

[0027] Another embodiment of the present invention provides a startup method for the capacitor-equipped two-stage isolated switching power supply, comprising:

[0028] Set the working state of the switching power supply, disconnect the load and the power tube S1, control the power tube S7 and the power tube S8 to be turned on alternately with a fixed duty cycle, control one path of the rectifier bridge to be turned on when the power tube S7 is turned on, and control the other path of the rectifier bridge to be turned on when the power tube S8 is turned on, so that the bias voltage of the secondary circuit is transmitted from the secondary side of the transformer T1 to the primary circuit; obtain the sampling voltage; such as Figure 2 As shown, when obtaining the sampled voltage, the fixed duty cycle of the power tube S7 and the power tube S8 is 50%. When the power tube S7 is turned on, the power tube S3 and the power tube S6 are turned on. When the power tube S8 is turned on, the power tube S4 and the power tube S5 are turned on. The sampling point is generally in the positive half cycle when the voltage on the primary capacitor C1 is stable after multiple conduction cycles.

[0029] In this embodiment, the primary circuit output voltage is obtained by sampling the voltage; the initial duty cycle is calculated by the primary circuit output voltage and the primary circuit input voltage; and a control signal is generated according to the initial duty cycle to control the primary circuit and the secondary circuit to complete the startup of the switching power supply.

[0030] Furthermore, the initial duty cycle Dinitial is: Dinitial= Vc1 / Vin; wherein Vin is the primary circuit input voltage, and Vc1 is the voltage on the primary capacitor C1.

[0031] Furthermore, the primary circuit output voltage V_c1 is:

[0032]

[0033] Wherein, Vsingle is the sampling voltage.

[0034] In this embodiment, a control signal is generated by a sampling control circuit according to an initial duty cycle to complete the startup of a two-stage isolated switching power supply with a capacitor and a bias voltage, which can reduce the design of an anti-backflow circuit and the design of an isolated sampling circuit, thereby greatly reducing product cost and layout space.

[0035] For those skilled in the art, the above invention disclosure is only for example and does not constitute a limitation of the present invention. Although not explicitly stated herein, those skilled in the art may make various modifications, improvements and corrections to the present invention. Such modifications, improvements and corrections are suggested in the present invention, so such modifications, improvements and corrections still belong to the spirit and scope of the exemplary embodiments of the present invention.

[0036] Although the present invention has been described with reference to the current specific embodiments, those skilled in the art should recognize that the above embodiments are only used to illustrate the present invention, and various equivalent changes or substitutions may be made without departing from the spirit of the present invention. Therefore, any changes or modifications to the above embodiments within the spirit of the present invention will fall within the scope of the claims of the present invention.

Claims

1. A method for starting a two-stage isolated switching power supply with capacitor, characterized in that: Applied to a two-stage isolated switching power supply with capacitor, wherein the two-stage isolated switching power supply with capacitor includes a primary circuit, a transformer T1, a secondary circuit, and a sampling control circuit. The primary circuit includes: a power tube S1, a power tube S2, an inductor L1, and a rectifier bridge composed of a power tube S3, a power tube S4, a power tube S5, and a power tube S6; the drain of the power tube S1 is connected to the positive electrode of the input power supply, and the source of the power tube S1 is connected to one end of the inductor L1; the other end of the inductor L1 is connected to the positive input end of the rectifier bridge; the drain of the power tube S2 is connected to the source of the power tube S1, and the source of the power tube S2 is connected to the negative electrode of the input power supply; The secondary circuit includes a power tube S7 and a power tube S8, the drain of the power tube S7 is connected to the first positive output terminal of the transformer T1, the source of the power tube S7 is respectively connected to the drain of the power tube S8 and the positive electrode of the load R1; the source of the power tube S8 is connected to the negative output terminal of the transformer T1; The transformer T1 further includes a second positive output terminal, which is connected to the negative electrode of the load R1; the second positive input terminal is arranged at the middle position of the secondary coil of the transformer T1; The sampling control circuit comprises a primary capacitor C1, a voltage-dividing resistor R2 and a voltage-dividing resistor R3, one end of the primary capacitor C1 is connected to the positive input end of the rectifier bridge, the voltage-dividing resistor R2 and the voltage-dividing resistor R3 are connected in series and then connected in parallel with the primary capacitor C1, and the node between the voltage-dividing resistor R2 and the voltage-dividing resistor R3 serves as a sampling end for sampling voltage; the sampling control circuit also outputs a control signal to the gate of each power tube; The voltage dividing resistor R3 is connected in parallel with a filter capacitor C3; the secondary circuit further includes a secondary capacitor C2, one end of the secondary capacitor C2 is connected to the positive electrode of the load R1, and the other end is connected to the negative electrode of the load R1; The startup method comprises: Set the working state of the switching power supply, disconnect the load R1 and the power tube S1, control the power tube S7 and the power tube S8 to be turned on alternately with a fixed duty cycle, control one path of the rectifier bridge to be turned on when the power tube S7 is turned on, and control the other path of the rectifier bridge to be turned on when the power tube S8 is turned on, so that the bias voltage of the secondary circuit is transmitted from the secondary side of the transformer T1 to the primary circuit; Get the sample voltage; Obtaining the primary circuit output voltage through the sampled voltage; Calculating an initial duty cycle by using the primary circuit output voltage and the primary circuit input voltage; A control signal is generated according to the initial duty cycle, and the control signal controls the primary circuit and the secondary circuit to complete the startup of the switching power supply.

2. The method for starting a two-stage isolated switching power supply with capacitor according to claim 1, characterized in that: The initial duty cycle D initial for: D initial =V c1 / V in ; Among them, V in is the primary circuit input voltage, V c1 is the voltage on the primary capacitor C1.

3. The method for starting a two-stage isolated switching power supply with capacitor according to claim 2, characterized in that: The primary circuit output voltage V c1 for: Among them, V single is the sampling voltage.

4. The method for starting a two-stage isolated switching power supply with capacitor according to claim 1, characterized in that: The fixed duty cycle is 50%.

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