Soft switching auxiliary power supply

Abstract

The utility model relates to the technical field of auxiliary power supplies, in particular to a soft switching auxiliary power supply, which comprises a pulse width modulation (PWM) generator, a power supply voltage end of the PWM generator and one end of a primary winding of a transformer are connected with front-end power supply voltage, an output end of the PWM generator is connected with a grid electrode of a metal oxide semiconductor (MOS) tube Q1, a source electrode of the MOS tube Q1 is grounded, and a drain electrode of the MOS tube Q1 is connected with the other end of the primary winding of the transformer. Two ends of the primary winding of the transformer are connected in parallel with a capacitor C4, and a capacitor C3 is connected in parallel between one end, far away from the MOS tube Q1, of the capacitor C4 and the source electrode of the MOS tube Q1; one end of the secondary winding of the transformer is connected with the anode of the diode D2, the other end of the secondary winding of the transformer is grounded, the cathode of the diode D2 is connected with the anode of the filter capacitor C5, and the cathode of the filter capacitor C5 is grounded.

Description

Technical Field

[0001] This utility model relates to the field of auxiliary power supply technology, specifically to a soft-switching auxiliary power supply. Background Technology

[0002] In power electronic equipment, auxiliary power systems need to provide multiple isolated power supplies for functional units such as data acquisition modules, semiconductor switching device drive circuits, and communication modules. Due to limitations in equipment cost, space layout, and heat dissipation, traditional solutions generally employ a flyback topology based on multi-winding transformers to achieve multiple outputs. This topology simplifies the circuit structure through a single-stage transformation and utilizes the flexible configuration of transformer windings to meet multiple voltage level requirements, offering significant cost and size advantages in low-to-medium power applications. However, flyback auxiliary power supplies still have the following key drawbacks in practical applications:

[0003] Device stress issues: The switching transistors of the flyback topology must withstand the high voltage spike generated by the superposition of the transformer leakage inductance energy and the input voltage at the moment of turn-off, which leads to a significant increase in voltage stress on the power semiconductor devices, affecting system reliability and device lifespan.

[0004] Electromagnetic interference problem: In hard-switching operation mode, the resonant circuit formed by the transformer leakage inductance and the parasitic capacitance of the switching transistor will cause high-frequency oscillation and generate wideband electromagnetic noise. Such interference can easily couple to sensitive circuits through conduction and radiation, increasing the difficulty of equipment EMC design, and even causing communication errors or sampling distortion.

[0005] Therefore, how to provide an auxiliary power supply that is small in size, low in cost, and solves the problems of device stress and electromagnetic interference is an urgent problem to be solved in this field. Utility Model Content

[0006] The purpose of this invention is to provide a soft-switching auxiliary power supply that retains the cost and size advantages of flyback auxiliary power supplies while solving the problems of device stress and electromagnetic interference in flyback auxiliary power supplies.

[0007] To achieve the above objectives, this utility model provides the following technical solution:

[0008] In a first aspect, this utility model provides a soft-switching auxiliary power supply, including a PWM generator, a transformer T1, the power supply voltage terminal of the PWM generator and one end of the primary winding T1-A of the transformer are connected to the front-end power supply voltage, the output terminal of the PWM generator is connected to the gate of a MOSFET Q1, the source of the MOSFET Q1 is grounded, the drain of the MOSFET Q1 is connected to the other end of the primary winding T1-A of the transformer, a capacitor C4 is connected in parallel across the two ends of the primary winding T1-A of the transformer, and a capacitor C3 is connected in parallel between the end of the capacitor C4 away from the MOSFET Q1 and the source of the MOSFET Q1; one end of the secondary winding T1-B of the transformer is connected to the anode of a diode D2, the other end of the secondary winding T1-B of the transformer is grounded, the cathode of the diode D2 is connected to the anode of a filter capacitor C5, and the cathode of the filter capacitor C5 is grounded.

[0009] In conjunction with the first aspect, optionally, the PWM generator is model UC2843BD1R2G.

[0010] In conjunction with the first aspect, optionally, a frequency setting circuit is also included, the frequency setting circuit including a resistor R2 and a capacitor C2, the capacitor C2 is directly connected in series between the RT / CT pin and the CS pin of the PWM generator, the CS pin of the PWM generator is grounded, and a resistor R2 is connected in series between the VERF pin and the RT / CT pin of the PWM generator.

[0011] In conjunction with the first aspect, optionally, a soft-start circuit is also included, the soft-start circuit including a switching diode D1, a resistor R1 and a capacitor C1, the COM pin of the PWM generator is connected to the first pin of the switching diode D1, the third pin of the switching diode D1 is connected to ground after being connected in series with the capacitor C1, a resistor R1 is connected in parallel between the third pin and the second pin of the switching diode D1, and the second pin of the switching diode D1 is connected to the VERF pin of the PWM generator.

[0012] In conjunction with the first aspect, optionally, the switching diode D1 is a dual-diode device.

[0013] In conjunction with the first aspect, optionally, the switching diode D1 is model BAV99LT1G.

[0014] In conjunction with the first aspect, optionally, the front-end power supply voltage is a rectified DC 12V output voltage.

[0015] The beneficial effects of this invention are as follows: Using MOSFET Q1 as a switch, capacitor C3 as the primary-side power supply capacitor, capacitor C4 as a resonant capacitor, and capacitor C5 as a filter capacitor, the capacitance of capacitor C3 and the junction capacitance of MOSFET Q1 connected in series is the equivalent capacitance of the parallel circuit of capacitor C4. Therefore, when MOSFET Q1 is turned off, since the current flowing through transformer T1 cannot change abruptly, it will continue to charge capacitor C4 and its parallel circuit's equivalent capacitance, generating LC oscillation. The parallel equivalent capacitance is the capacitance of the junction capacitance of MOSFET Q1 and capacitor C3 connected in series. Since the capacitance of capacitor C3 is much larger than the junction capacitance of MOSFET Q1, the capacitance of capacitor C3 and... The series equivalent capacitance of the junction capacitance of MOSFET Q1 is approximately equal to the junction capacitance of MOSFET Q1. LC oscillation causes the DS voltage of MOSFET Q1 to change sinusoidally from 0 to 0V. When the DS voltage rises from low to high and then returns to 0V, MOSFET Q1 turns on again, thus achieving soft switching. Because MOSFET Q1 operates in a soft-switching state, there is no large voltage or current stress, improving the reliability of the device. Furthermore, soft switching does not produce the high-frequency oscillations generated by hard switching, thereby reducing electromagnetic radiation. At the same time, soft switching generates less heat, has no switching losses, and does not require a heat sink for the same power, thus reducing cost and size. Attached Figure Description

[0016] The accompanying drawings are provided to further illustrate the present invention and form part of the specification. They are used together with the embodiments of the present invention to explain the present invention, but do not constitute a limitation thereof. In the drawings:

[0017] Figure 1 This is the circuit diagram of this utility model;

[0018] Figure 2 This is a waveform diagram of the soft switch of this utility model. Detailed Implementation

[0019] The technical solution of this utility model will be described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the embodiments and specific features in the embodiments are detailed descriptions of the technical solution of this application, rather than limitations thereof.

[0020] In the description of this utility model, the terms "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of this utility model. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0021] like Figure 1 As shown, this utility model provides a soft-switching auxiliary power supply, including a PWM generator and a transformer T1. In some embodiments, the PWM generator is model UC2843BD1R2G. The power supply voltage terminal of the PWM generator and one end of the primary winding T1-A of the transformer are connected to the front-end power supply voltage, which is a DC 12V voltage output after rectification.

[0022] The output terminal of the PWM generator is connected to the gate of MOSFET Q1. The source of MOSFET Q1 is grounded. The drain of MOSFET Q1 is connected to the other end of the primary winding T1-A of the transformer. A capacitor C4 is connected in parallel across the two ends of the primary winding T1-A of the transformer. A capacitor C3 is connected in parallel between the end of capacitor C4 furthest from MOSFET Q1 and the source of MOSFET Q1. One end of the secondary winding T1-B of the transformer is connected to the anode of diode D2. The other end of the secondary winding T1-B of the transformer is grounded. The cathode of diode D2 is connected to the anode of filter capacitor C5. The cathode of filter capacitor C5 is grounded.

[0023] In some embodiments, the system also includes peripheral circuitry for the PWM generator, specifically a soft-start circuit and a frequency setting circuit.

[0024] The soft-start circuit includes a switching diode D1, a resistor R1, and a capacitor C1. The COM pin of the PWM generator is connected to the first pin of the switching diode D1. The third pin of the switching diode D1 is connected to ground after being connected in series with the capacitor C1. A resistor R1 is connected in parallel between the third pin and the second pin of the switching diode D1. The second pin of the switching diode D1 is connected to the VERF pin of the PWM generator.

[0025] The frequency setting circuit includes a resistor R2 and a capacitor C2. The capacitor C2 is directly connected in series between the RT / CT pin and the CS pin of the PWM generator. The CS pin of the PWM generator is grounded. The resistor R2 is connected in series between the VERF pin and the RT / CT pin of the PWM generator.

[0026] Both the FB pin and the GND pin of the PWM generator are grounded.

[0027] In some embodiments, the switching diode D1 is a dual-diode device, and in some specific examples, the switching diode D1 is model BAV99LT1G.

[0028] The working principle of this invention is as follows: When MOSFET Q1 is turned on, the input voltage is applied to the primary winding of transformer T1, and current flows through the primary winding of transformer T1. After coupling to the secondary side, the current is rectified by diode D2 and filtered by capacitor C5 to obtain the output voltage. Different output voltages can be obtained by adjusting the transformer turns ratio. When MOSFET Q1 is turned off, since the current flowing through transformer T1 cannot change abruptly, it will continue to charge capacitor C4 and its parallel circuit equivalent capacitance, generating LC oscillation. The parallel equivalent capacitance is the capacitance of the junction capacitance of MOSFET Q1 and capacitor C3 in series. Since the capacitance of capacitor C3 is much larger than the junction capacitance of MOSFET Q1, the equivalent capacitance of capacitor C3 and the junction capacitance of MOSFET Q1 in series is approximately equal to the junction capacitance of MOSFET Q1. The LC oscillation causes the DS voltage of MOSFET Q1 to change sinusoidally from 0 continuously. When the DS voltage rises from low to high and then returns to 0V, MOSFET Q1 is turned on again, thus achieving soft switching. The soft switching waveform is shown in the figure below. Figure 2 As shown.

[0029] The above description is merely a preferred embodiment of the present utility model and is not intended to limit the present utility model. Although the present utility model has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present utility model should be included within the protection scope of the present utility model.

Claims

1. A soft-switching auxiliary power supply, comprising a PWM generator and a transformer T1, characterized in that, The power supply voltage terminal of the PWM generator and one end of the primary winding T1-A of the transformer are connected to the front-end power supply voltage. The output terminal of the PWM generator is connected to the gate of the MOSFET Q1. The source of the MOSFET Q1 is grounded. The drain of the MOSFET Q1 is connected to the other end of the primary winding T1-A of the transformer. A capacitor C4 is connected in parallel across the two ends of the primary winding T1-A of the transformer. A capacitor C3 is connected in parallel between the end of the capacitor C4 away from the MOSFET Q1 and the source of the MOSFET Q1. One end of the secondary winding T1-B of the transformer is connected to the anode of the diode D2. The other end of the secondary winding T1-B of the transformer is grounded. The cathode of the diode D2 is connected to the anode of the filter capacitor C5. The cathode of the filter capacitor C5 is grounded.

2. The soft-switching auxiliary power supply according to claim 1, characterized in that: The PWM generator is model UC2843BD1R2G.

3. The soft-switching auxiliary power supply according to claim 2, characterized in that: It also includes a frequency setting circuit, which includes a resistor R2 and a capacitor C2. The RT / CT pin and CS pin of the PWM generator are directly connected in series with the capacitor C2. The CS pin of the PWM generator is grounded. The VERF pin and RT / CT pin of the PWM generator are connected in series with the resistor R2.

4. The soft-switching auxiliary power supply according to claim 2, characterized in that: It also includes a soft-start circuit, which includes a switching diode D1, a resistor R1 and a capacitor C1. The COM pin of the PWM generator is connected to the first pin of the switching diode D1. The third pin of the switching diode D1 is connected to ground after being connected in series with the capacitor C1. A resistor R1 is connected in parallel between the third pin and the second pin of the switching diode D1. The second pin of the switching diode D1 is connected to the VERF pin of the PWM generator.

5. The soft-switching auxiliary power supply according to claim 4, characterized in that: Switching diode D1 is a dual-diode device.

6. The soft-switching auxiliary power supply according to claim 4 or 5, characterized in that: The switching diode D1 is model BAV99LT1G.

7. The soft-switching auxiliary power supply according to claim 1, characterized in that: The front-end power supply voltage is 12V DC, which is rectified and output as 12V DC voltage.

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