Soft start circuit suitable for LLC topology

Abstract

The utility model provides a soft start circuit suitable for LLC topology, which is applied to an LLC main topology circuit and comprises an input current detection unit used for detecting input current as feedback quantity of closed-loop control, and the output of the input current detection unit is used as the input of a closed-loop control unit; the closed-loop control unit is used for performing closed-loop control on the input current and a set value, so that the input current is consistent with the set value, and the output of the closed-loop control unit serves as the input of the driving voltage control unit; and a driving voltage control unit. The soft start circuit has the beneficial effects that the soft start circuit suitable for the LLC topology is provided, the switch tube of the primary side is in a linear conduction interval in the soft start process, the start impact current can be effectively reduced, the circuit is simple and reliable, and the practical value is relatively high.

Description

TECHNICAL FIELD

[0001] The utility model relates to soft start circuit, especially a kind of soft start circuit suitable for LLC topology. BACKGROUND

[0002] In certain high power density LLC power supply, especially high voltage input, open loop control isolation output occasion, often use smaller transformer leakage inductance as resonance inductance, resulting in input high voltage start-up, conventional high-frequency soft start, regulation duty cycle soft start etc. SUMMARY

[0003] In order to solve the problems in the prior art, the utility model provides a kind of soft start circuit suitable for LLC topology.

[0004] The utility model provides a kind of soft start circuit suitable for LLC topology, be applied to LLC main topology circuit, comprising:

[0005] input current detection unit, for detecting input current, as the feedback of closed loop control, its output as the input of closed loop control unit;

[0006] closed loop control unit, for the closed loop control of input current and set value, so that input current and set value are consistent, its output as the input of drive voltage control unit;

[0007] drive voltage control unit, for controlling the drive voltage of LLC main topology circuit's primary side switch tube, LLC main topology circuit's primary side auxiliary power voltage VCC and the PWM signal of drive after this drive voltage control unit, the duty cycle of PWM signal is unchanged, but LLC main topology circuit's primary side auxiliary power voltage VCC becomes controlled linearly controlled voltage VD.

[0008] As the further improvement of the utility model, the drive voltage control unit includes triode Q1, triode Q2 and resistance R2, the base of triode Q2 is connected with the output of closed loop control unit, the emitter of triode Q2 is grounded, the collector of triode Q2 is connected with one end of resistance R2, the other end of resistance R2 is connected with the base of triode Q1, the emitter of triode Q1 is connected with LLC main topology circuit's primary side auxiliary power voltage VCC, and the collector of triode Q1 is output controlled linearly controlled voltage VD.

[0009] As the further improvement of the utility model, the drive voltage control unit can control linearly controlled voltage VD to realize 0~VCC output.

[0010] As a further improvement of the utility model, the closed loop control unit includes operational amplifier U1 and its compensation loop, the compensation loop is connected between the inverting input terminal and the output terminal of the operational amplifier U1, the inverting input terminal of the operational amplifier U1 is connected with the output sampling value Iin outputted by the input current detection unit, the noninverting input terminal of the operational amplifier U1 is connected with input current maximum setting value Iref, the input terminal of the operational amplifier U1 is connected with the base of the triode Q2.

[0011] As a further improvement of the utility model, the compensation loop of the operational amplifier U1 includes resistance R1, capacitor C1 and capacitor C2, one end of the capacitor C1 is connected with the inverting input terminal of the operational amplifier U1, the other end of the capacitor C1 is connected with the output terminal of the operational amplifier U1, one end of the resistance R1 is connected with the inverting input terminal of the operational amplifier U1, the other end of the resistance R1 is connected with one end of the capacitor C2, the other end of the capacitor C2 is connected with the output terminal of the operational amplifier U1.

[0012] As a further improvement of the utility model, the operational amplifier U1 is independent operational amplifier or operational amplifier integrated in analog chip.

[0013] As a further improvement of the utility model, the drive voltage control unit outputs the controlled linearly controllable voltage VD as the drive voltage of the primary side switch tube of the LLC main topology circuit.

[0014] The utility model discloses a kind of soft starting circuits suitable for LLC topology, so that the switch tube of primary side is in linear conduction interval during soft starting process, can effectively reduce starting impact current, circuit is simple and reliable, has higher practical value. BRIEF DESCRIPTION OF DRAWINGS

[0015] In order to more clearly illustrate the technical scheme of the embodiments of the utility model, the drawings needed to be used in the embodiment description will be simply introduced as follows, obviously, the drawings in the following description are only some embodiments of the utility model, and those skilled in the art can obtain other schemes according to these drawings without creating creative labor.

[0016] Fig. 1 It is the implementation block diagram of a kind of soft starting circuits suitable for LLC topology of the utility model.

[0017] Fig. 2 It is the implementation schematic diagram of a kind of soft starting circuits suitable for LLC topology of the utility model. CONCRETE EMBODIMENT

[0018] It should be noted that the embodiments in the utility model and the features in the embodiments can be combined with each other in the case of no conflict.

[0019] In the description of the utility model, it should be understood that the orientation or position relationship indicated by the terms "center", "longitudinal", "transverse", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer" and the like is the orientation or position relationship shown based on the drawings, and is only for the convenience of describing the utility model and simplifying the description, and therefore cannot be understood as indicating or implying that the devices or elements indicated must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the protection scope of the utility model. In addition, the terms "first", "second" and the like are only for the purpose of description, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the technical features indicated. Therefore, the features limited by "first", "second" and the like can explicitly or implicitly include one or more features. In the description of the utility model, the meaning of "a plurality of" is two or more, unless otherwise specified.

[0020] In the description of the utility model, it should be noted that, unless otherwise explicitly specified and limited, the terms "mounting", "connection", "connection" should be understood broadly, for example, it can be fixed connection, or detachable connection, or integrally connected, it can be directly connected, or indirectly connected through intermediate medium, it can be the communication inside two elements. For ordinary skilled in the art, the specific meaning of the above terms in the utility model can be understood through specific circumstances.

[0021] The utility model will be further described below in combination with the description and specific embodiments of the drawings.

[0022] As Figs. 1-2 The soft starting circuit suitable for LLC topology is applied to the LLC main topology circuit, and comprises:

[0023] The input current detection unit 101 is used for detecting input current as the feedback of closed-loop control, and the output thereof is input to the closed-loop control unit 102;

[0024] The closed-loop control unit 102 is used for performing closed-loop control on the input current and the set value, so that the input current is consistent with the set value, and the output thereof is input to the driving voltage control unit 103;

[0025] The drive voltage control unit 103 is used for controlling the drive voltage of the primary side switch tube of the LLC main topology circuit, and the PWM signal and the primary side auxiliary power supply voltage VCC of the LLC main topology circuit pass through the drive voltage control unit, so that the duty cycle of the PWM signal remains unchanged, and the primary side auxiliary power supply voltage VCC of the LLC main topology circuit becomes the linearly controllable voltage VD.

[0026] The linearly controllable voltage VD is less than or equal to VCC.

[0027] The drive voltage control unit 103 comprises a transistor Q1, a transistor Q2 and a resistor R2, the base of the transistor Q2 is connected with the output of the closed-loop control unit, the emitter of the transistor Q2 is grounded, the collector of the transistor Q2 is connected with one end of the resistor R2, the other end of the resistor R2 is connected with the base of the transistor Q1, the emitter of the transistor Q1 is connected with the primary side auxiliary power supply voltage VCC of the LLC main topology circuit, and the collector of the transistor Q1 outputs the linearly controllable voltage VD.

[0028] The drive voltage control unit 103 can control the linearly controllable voltage VD to realize the output of 0-VCC.

[0029] The closed-loop control unit 102 comprises an operational amplifier U1 and a compensation loop connected between the inverting input end and the output end of the operational amplifier U1, the inverting input end of the operational amplifier U1 is connected with the output sampling value Iin output by the input current detection unit, the non-inverting input end of the operational amplifier U1 is connected with the input current maximum setting value Iref, and the input end of the operational amplifier U1 is connected with the base of the transistor Q2.

[0030] The compensation loop of the operational amplifier U1 comprises a resistor R1, a capacitor C1 and a capacitor C2, one end of the capacitor C1 is connected with the inverting input end of the operational amplifier U1, the other end of the capacitor C1 is connected with the output end of the operational amplifier U1, one end of the resistor R1 is connected with the inverting input end of the operational amplifier U1, the other end of the resistor R1 is connected with one end of the capacitor C2, and the other end of the capacitor C2 is connected with the output end of the operational amplifier U1.

[0031] The drive voltage control unit outputs the linearly controllable voltage VD as the drive voltage of the four primary side switch tubes of the LLC main topology circuit, that is, the output ends of the drive voltage control unit are connected with the gates of the four primary side switch tubes of the LLC main topology circuit.

[0032] Preferably, the application range of the soft starting circuit suitable for the LLC topology provided by the utility model is a switching power supply LLC topology.

[0033] Preferably, the application range of the soft start circuit suitable for LLC topology provided by the utility model is the open-loop LLC topology soft start process with small leakage inductance.

[0034] The LLC topology is generally operated in high-frequency switching state above 100KHz due to its soft switching characteristic, and silicon MOSFET or silicon carbide MOSFET is generally used as switching device, the driving voltage threshold of the two devices is generally above 2V, and the full conduction voltage is generally above 8V. When the driving voltage is between the conduction threshold voltage and the full conduction voltage, the switch tube is in linear conduction state, and the conduction resistance is inversely proportional to the driving voltage. Therefore, by controlling the driving voltage, the MOSFET is operated in the linear region, and the equivalent adjustable resistance is connected in series with the switching link, and the input current value at the starting moment can be better controlled by adjusting the resistance value.

[0035] The soft start circuit suitable for LLC topology provided by the utility model is realized by setting the input current starting impact maximum value Iref, and the sampling value Iin of the input current is feedback controlled through the operational amplifier U1, the output of the operational amplifier is used for realizing real-time adjustment of VD through the linear conduction of the triode Q1 and the triode Q2, so that the primary side switch tube is in linear conduction state, and the purpose of controlling the input current to be always the set value is achieved.

[0036] Obviously, the application described herein can have many variations, such as the driving voltage unit can adopt MOSFET, optical coupling and the like, and such variations cannot be considered as departing from the spirit and scope of the application. Therefore, all changes obvious to those skilled in the art are included in the scope covered by the present claims.

Claims

1. A soft-start circuit suitable for LLC topology, applied to LLC main topology circuit, characterized in that, include: The input current detection unit is used to detect the input current as a feedback quantity for closed-loop control, and its output serves as the input to the closed-loop control unit. The closed-loop control unit is used to perform closed-loop control of the input current and the set value, so that the input current is consistent with the set value, and its output serves as the input of the drive voltage control unit. The drive voltage control unit is used to control the drive voltage of the primary-side switching transistor of the LLC main topology circuit. After the primary-side auxiliary power supply voltage VCC of the LLC main topology circuit and the drive PWM signal pass through the drive voltage control unit, the duty cycle of the PWM signal remains unchanged, but the primary-side auxiliary power supply voltage VCC of the LLC main topology circuit becomes a controlled linearly controllable voltage VD.

2. A soft-start circuit for an LLC topology as defined in claim 1, characterized in that: The drive voltage control unit includes transistors Q1 and Q2 and resistor R2. The base of transistor Q2 is connected to the output of the closed-loop control unit, the emitter of transistor Q2 is grounded, the collector of transistor Q2 is connected to one end of resistor R2, and the other end of resistor R2 is connected to the base of transistor Q1. The emitter of transistor Q1 is connected to the primary-side auxiliary power supply voltage VCC of the LLC main topology circuit, and the collector of transistor Q1 outputs a controlled, linearly controllable voltage VD.

3. A soft-start circuit for a LLC topology as defined in claim 2, characterized in that: The drive voltage control unit can control the linearly controllable voltage VD to achieve an output from 0 to VCC.

4. The soft-start circuit for a LLC topology of claim 2, wherein: The closed-loop control unit includes an operational amplifier U1 and its compensation loop. The compensation loop is connected between the inverting input terminal and the output terminal of the operational amplifier U1. The inverting input terminal of the operational amplifier U1 is connected to the output sampling value Iin output by the input current detection unit. The non-inverting input terminal of the operational amplifier U1 is connected to the maximum set value Iref of the input current. The input terminal of the operational amplifier U1 is connected to the base of the transistor Q2.

5. A soft-start circuit for a LLC topology as defined in claim 4, characterized in that: The compensation loop of the operational amplifier U1 includes a resistor R1, a capacitor C1, and a capacitor C2. One end of the capacitor C1 is connected to the inverting input terminal of the operational amplifier U1, and the other end of the capacitor C1 is connected to the output terminal of the operational amplifier U1. One end of the resistor R1 is connected to the inverting input terminal of the operational amplifier U1, and the other end of the resistor R1 is connected to one end of the capacitor C2. The other end of the capacitor C2 is connected to the output terminal of the operational amplifier U1.

6. The soft-start circuit for a LLC topology of claim 4, wherein: The operational amplifier U1 is either a standalone operational amplifier or an operational amplifier integrated within an analog chip.

7. The soft-start circuit for a LLC topology of claim 4, wherein: The drive voltage control unit outputs a controlled, linearly controllable voltage VD as the drive voltage for the primary-side switching transistors of the LLC main topology circuit.

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