CN112072906B

CN112072906B - Pre-bias starting circuit

Info

Publication number: CN112072906B
Application number: CN202010884397.0A
Authority: CN
Inventors: 李树佳; 蔚道刚; 王学睿
Original assignee: Mornsun Guangzhou Science and Technology Ltd
Current assignee: Mornsun Guangzhou Science and Technology Ltd
Priority date: 2020-08-28
Filing date: 2020-08-28
Publication date: 2022-04-15
Anticipated expiration: 2040-08-28
Also published as: CN112072906A

Abstract

The invention discloses a pre-bias starting circuit which comprises a voltage stabilizing diode D11, a voltage stabilizing diode D12, a resistor R11, a resistor R12, a resistor R15, an NPN triode Q11, a resistor R14 and a capacitor C12. The pre-bias starting circuit is externally arranged on the secondary side of the bridge power supply and is specifically connected between the reference voltage circuit and the voltage loop sampling control circuit, a control signal output by the bridge power supply in the starting process is taken as a first input end control signal, the voltage output by the reference voltage circuit is taken as a second input section control signal, and under the condition that a secondary side driving signal Gs2 of the bridge power supply lags behind a primary side driving signal Gs1 of the bridge power supply, no driving output of a primary side switching tube is ensured; and during the normal working period of the bridge power supply, the driving of the primary side switching tube is adjusted to realize the soft start of the power supply. The invention can ensure the synchronous start of the primary side drive and the secondary side drive of the half-bridge power supply and the full-bridge power supply with synchronous rectification function, effectively solves the problem of energy reverse filling caused by the advance of the primary side drive and improves the reliability of products.

Description

Pre-bias starting circuit

Technical Field

The invention relates to the field of bridge topology control ICs, in particular to a pre-bias starting circuit.

Background

With the development of miniaturization, greening and portability of modern electronic devices, people have higher requirements on the volume of a power supply necessary for the electronic devices, and the research on high-efficiency and high-power-density power supplies is more and more urgent. Meanwhile, the half-bridge topology and the full-bridge topology are increasingly applied to the field of high power density power modules.

Due to the requirement for high efficiency, most of the conventional half-bridge topology control IC or full-bridge topology control IC integrates the function of the driving control signal of the secondary synchronous rectifier tube, and the primary side driving signal and the secondary side driving signal of the bridge topology can be controlled by the master control IC. LM5036 is a half-bridge control IC, and is widely applied to the design of a half-bridge power supply and a full-bridge power supply; the LM5036 integrates the primary side driving control logic and the secondary side driving control logic of the bridge topology. In the application process of the LM5036, the situation that the secondary driving signal lags behind the primary driving signal occurs, so that in the process of designing a power supply using a bridge topology with a synchronous rectification function, the problem of backward flow of output energy occurs under the condition of outputting a light load, thereby affecting the reliability of the design of the bridge power supply.

In a traditional voltage loop sampling feedback circuit (as shown in fig. 1), in practical application, the voltage loop sampling feedback circuit as shown in the figure takes the output of a reference voltage circuit as an input source, and the non-inverting input end + Vin of the voltage loop sampling feedback circuit is connected with a reference voltage signal; the inverting input end-Vin is connected with the midpoint of a voltage dividing resistor in the reference voltage circuit, and the output voltage + Vo of the sampling bridge topology is a feedback signal; a reference voltage signal connected with the in-phase input end + Vin can be established in advance, the light emitting intensity of a secondary side light emitting diode U1A of the optocoupler U1 is controlled by comparing a sampling signal obtained by sampling the output voltage + Vo with the voltages of the positive and negative phase input ends, so that the conduction condition of a primary side photosensitive side U1B of the optocoupler U1 is controlled, the comp pin working current of the control IC is regulated, and the stability of the output voltage + Vo is finally realized; when the on-resistance of the primary side photosensitive side U1B is small and the operating current of the comp pin exceeds a certain value, the duty ratio is zero. The traditional voltage loop sampling feedback circuit can only stabilize the feedback performance of a product working loop under the condition that a power supply works stably, the stability of the output voltage of the bridge topology is guaranteed, and the bridge topology starting process cannot be adjusted. Meanwhile, the soft start of the traditional power supply product is integrated in the control IC, the monotonous rise of the output voltage is realized by controlling the duty ratio of the primary side switching tube to be slowly increased, and the soft start control on the driving signal cannot be carried out after the soft start time of the control IC is finished. Both working logics cannot meet the requirements of bridge topology using a synchronous rectification function, the output voltage is monotonously increased under all working conditions, the output energy flows backwards under the condition of light load easily, and the reliability of the design of a power supply product cannot be ensured.

Disclosure of Invention

Aiming at the problems in the prior art, the invention provides a pre-bias starting circuit which comprises a control signal V1, a pre-bias starting circuit, a reference voltage circuit and a voltage loop sampling feedback circuit. When the bridge topology with the synchronous rectification function is used for designing a power supply, the synchronous starting of the primary side driving control signal and the secondary side driving control signal is ensured, the synchronous starting of the primary side switching tube and the secondary side synchronous rectification tube is ensured, the problem of energy backflow caused by synchronous rectification driving delay is avoided, the monotonous rise of output voltage under all working conditions is ensured, and the reliability of the product is improved.

In order to achieve the purpose, the invention provides the following technical scheme:

a pre-bias start-up circuit for controlling a voltage loop sampling feedback circuit in a bridge topology, comprising: the device comprises a voltage-stabilizing diode D11, a voltage-stabilizing diode D12, a resistor R11, a resistor R12, a resistor R15, an NPN triode Q11, a resistor R14 and a capacitor C12;

the cathode of the zener diode D11 is used as a first input end of the pre-bias starting circuit and is used for inputting a control signal V1, the anode of the zener diode D11 is connected with one end of the resistor R11, one end of the resistor R12 and the anode of the zener diode D12, the other end of the resistor R12 is connected with the base of the NPN triode Q11, the collector of the NPN triode Q11 is connected with the connection point of one end of the resistor R14 and one end of the capacitor C12 and is used as a first output end of the pre-bias starting circuit and is used for connecting the non-inverting input end + Vin of the voltage loop sampling feedback circuit, the other end of the resistor R14 is used as a second input end of the pre-bias starting circuit and is used for inputting a reference voltage, the cathode of the zener diode D12 is connected with one end of the resistor R15, the other end of the resistor R15 is used as a second output end of the pre-bias starting circuit and is used for connecting the inverting input end-Vin of the voltage loop sampling feedback circuit, and the other end of the resistor R11 and the control circuit, The emitter of NPN transistor Q11 and the other end of capacitor C12 are commonly connected to ground.

Preferably, the control signal V1 is a control signal output by the bridge topology during the starting process, and covers two voltage intervals, namely a voltage V5 and a voltage V6, where V5 > V6; the control signal V1 is in a time interval T1, the control signal V1 outputs a voltage V5, the time interval T1 is the moment after the control signal V1 is started, and the time interval is adjustable; in the time interval T2, the control signal V1 outputs the voltage V6, and the time interval T2 is the time interval of the normal operation process of the bridge topology.

Preferably, the zener diode D11 has a zener value V7 satisfying V6 < V7 < V5.

Preferably, the pre-bias start-up circuit further includes a resistor R13 and a capacitor C11, and the resistor R13 and the capacitor C11 are connected in parallel between the base of the NPN transistor Q11 and the emitter of the NPN transistor Q11.

Preferably, the pre-bias start-up circuit and the voltage loop sampling feedback circuit are common ground.

Compared with the prior art, the invention has the following progressive effects:

1. the invention realizes the simultaneous output of the primary side driving control signal Gs1 and the secondary side driving control signal Gs2 of the bridge power supply, ensures the synchronous start of the primary side switching tube and the secondary side synchronous rectifier tube, avoids the problem of energy backflow caused by the synchronous rectifier driving delay, ensures the monotonous rise of the output voltage under all working conditions, and improves the reliability of the product.

2. According to the invention, through the external pre-bias starting circuit of the secondary side, the output voltage of the bridge power supply is ensured to be monotonically increased through the soft start arranged on the secondary side, and the debugging flexibility and the power supply reliability are improved.

Drawings

FIG. 1 is a schematic diagram of a voltage loop sampling feedback circuit;

FIG. 2 is a schematic diagram of a pre-bias start-up circuit coupled to a reference voltage circuit according to an embodiment of the present invention;

FIG. 3 is a timing logic diagram of the control signal V1, the output signals V3, V4 of the pre-biased start-up circuit, and the output voltage + Vo of the bridge power supply;

FIG. 4 is a timing logic diagram of the control signal V1, the primary side driving signal Gs1 of the bridge power supply, the secondary side driving signal Gs2 of the bridge power supply, and the output voltage + Vo of the bridge power supply.

Detailed Description

The technical scheme of the invention is more clearly and completely described below by combining the attached drawings in the embodiment of the invention. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

First embodiment

Fig. 2 is a schematic diagram of a pre-bias start-up circuit connected to a reference voltage circuit, including a pre-bias start-up circuit and a reference voltage circuit, according to an embodiment of the present invention, which is applied to a bridge power supply designed using a control IC LM 5036.

The pre-bias starting circuit comprises a voltage stabilizing diode D11, a voltage stabilizing diode D12, a resistor R11, a resistor R12, a resistor R15, an NPN triode Q11, a resistor R13, a resistor R14, a capacitor C11 and a capacitor C12. The cathode of the voltage-stabilizing diode D11 is used as the first input end of the pre-bias starting circuit, the anode of the voltage-stabilizing diode D11 is connected with one end of a resistor R11, one end of a resistor R12 and the anode of the voltage-stabilizing diode D12, the other end of the resistor R12 is connected with the base of an NPN triode Q11, a resistor R13 and a capacitor C11, a resistor R13 and a capacitor C11 are connected between the base of the NPN triode Q11 and the emitter of the NPN triode Q11 in parallel, the collector of the NPN triode Q11 is connected with the connection point of one end of the resistor R14 and one end of the capacitor C12, and as the first output end of the pre-bias starting circuit, the other end of the resistor R14 serves as the second input end of the pre-bias starting circuit, the cathode of the zener diode D12 is connected to one end of the resistor R15, the other end of the resistor R15 serves as the second output end of the pre-bias starting circuit, and the other end of the resistor R11, the emitter of the NPN triode Q11, and the other end of the capacitor C12 are grounded together.

The control signal V1 is a control signal output by the bridge topology in the starting process, and is used as a control signal input to the first input end of the pre-bias starting circuit, covering two voltage intervals, namely a voltage V5 and a voltage V6, wherein V5 is greater than V6, the control signal V1 is in a time interval T1, the control signal V1 outputs a voltage V5, and the time interval T1 is the moment after the control signal V1 is started, and the time interval is adjustable; in the time interval T2, the control signal V1 outputs the voltage V6, and the time interval T2 is the time interval during which the control signal V1 normally operates. The regulated voltage value V7 of the zener diode D11 satisfies V6 < V7 < V5.

The reference voltage circuit inputs a voltage V2 to a second input terminal of the pre-bias start-up circuit. The first output end of the pre-bias starting circuit is connected with the non-inverting input end + Vin of the voltage loop sampling feedback circuit, and a voltage signal V3 is input to the non-inverting input end + Vin; the second output terminal of the pre-bias starting circuit is connected with the inverting input terminal-Vin of the voltage loop sampling feedback circuit, and a voltage signal V4 is input to the inverting input terminal-Vin.

The reference voltage circuit comprises a resistor R16, a control IC TL431 and a capacitor C13. One end of the resistor R16 is connected with a power supply terminal Vcc, the other end of the resistor R16 is connected with the cathode of the control IC TL431, a reference voltage pin of the control IC TL431 is connected with one end of the capacitor C13, the connection point is connected with the other end of the resistor R14 in the pre-bias starting circuit, the regulated voltage V2 is output to the pre-bias starting circuit, and the anode of the control IC TL431 and the other end of the capacitor C13 are grounded together.

The pre-bias starting circuit, the reference voltage circuit and the voltage loop sampling feedback circuit are grounded in common.

The specific operation of the circuit after being connected to the circuit shown in fig. 1 is as follows:

in the time T1, since the situation that the secondary side driving signal Gs2 lags behind the primary side driving signal Gs1 occurs in the application process of the control IC LM5036, the problem that the output energy flows backwards occurs in the case that the output light load occurs in the power supply design process of the bridge topology using the synchronous rectification function, thereby affecting the reliability of the bridge power supply design. Therefore, in the starting process of the bridge topology designed by the control IC LM5036, a control signal V1 is firstly output, the control signal V1 outputs a voltage V5 within T1 time, because the voltage V5 is greater than a voltage stabilizing value V7 of a voltage stabilizing tube D11, the voltage stabilizing tube D11 breaks down, the pre-bias starting circuit works, and then the NPN triode Q11 is conducted. Since the reference voltage circuit output voltage V2 provides a reference voltage signal to the non-inverting input terminal + Vin of the voltage loop sampling feedback circuit through the resistor R14 and the capacitor C12, when the NPN transistor Q11 is turned on, the capacitor C12 discharges through the NPN transistor Q11, and thus the voltage signal V3 output by the first output terminal is at a low level. The voltage signal V3 controls the non-inverting input end + Vin of the voltage loop sampling feedback circuit, the voltage signal V4 output by the second output end is at a high level, and the signal controls the inverting input end-Vin of the voltage loop sampling feedback circuit, so that the output end of the operational amplifier U21 of the voltage loop sampling feedback circuit is at a low level, the luminous intensity of the luminous side U1A of the optocoupler U1 is increased, the conduction degree of the corresponding photosensitive side U1B is increased, the working current of the voltage loop feedback pin comp of the control IC LM5036 is increased, the voltage loop sampling feedback circuit is controlled to perform loop feedback, and finally the primary side driving signal Gs1 of the control IC 503LM 6 is not output.

Considering the selection and tolerance of the voltage-stabilizing value V7 of the voltage-stabilizing diode D11, under different working conditions, the situation that V7 does not satisfy V6 < V7 < V5 may occur, a resistor R13 may be selected by combining the selection of the voltage-stabilizing diode D11, and the base voltage of the NPN triode Q11 is controlled by the voltage division of the resistor R12 and the resistor R13, so that the purpose of more accurately controlling the conduction condition of the NPN triode Q11 is achieved.

Noise interference under different working conditions is considered, a low-capacitance capacitor C11 can be properly added for filtering, and the phenomenon of false triggering of the NPN triode Q11 is avoided.

When the bridge topology designed by the control IC LM5036 enters a T2 interval, the control signal V1 outputs a voltage V6, because the voltage V6 is smaller than a voltage stabilization value V7 of a voltage regulator D11, the voltage regulator D11 is turned off, the pre-bias starting circuit is turned off, the NPN triode Q11 is turned off, under the combined action of the resistor R14 and the capacitor C12, the circuit achieves soft start, the first output terminal gradually releases the voltage stabilization V2 output by the reference voltage circuit, and simultaneously, an output signal of the second output terminal of the pre-bias starting circuit is suspended, that is, the voltage signal V4 does not affect the voltage loop sampling feedback circuit, and the inverting input terminal-Vin of the voltage loop sampling feedback circuit performs loop feedback according to the sampling output voltage + Vo of the normal feedback circuit, so that the duty ratio of the primary side drive signal and the secondary side drive signal of the bridge topology designed by the control IC LM5036 is gradually released.

The T2 interval is the normal working time of the bridge topology, in the time interval, the delay release of the primary side driving signal of the bridge topology designed by the control IC LM5036 is controlled, and the situation that the secondary side driving signal Gs2 lags behind the primary side driving signal Gs1 does not occur in the application process; meanwhile, the in-phase input end + Vin of the voltage loop sampling feedback circuit inputs the gradually released voltage stabilization V2, so that the soft start of secondary side control is realized, and the monotonous rise of the output voltage of the bridge power supply is ensured.

The above are merely preferred embodiments of the present invention, and those skilled in the art to which the present invention pertains may make variations and modifications of the above-described embodiments. Therefore, the present invention is not limited to the specific control modes disclosed and described above, and modifications and variations of the present invention are also intended to fall within the scope of the claims of the present invention. Furthermore, although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

Claims

1. A pre-bias start-up circuit for controlling a voltage loop sampling feedback circuit in a bridge topology, comprising: the device comprises a voltage-stabilizing diode D11, a voltage-stabilizing diode D12, a resistor R11, a resistor R12, a resistor R15, an NPN triode Q11, a resistor R14 and a capacitor C12;

the cathode of the zener diode D11 is used as a first input end of the pre-bias starting circuit and is used for inputting a control signal V1, the anode of the zener diode D11 is connected with one end of the resistor R11, one end of the resistor R12 and the anode of the zener diode D12, the other end of the resistor R12 is connected with the base of the NPN triode Q11, the collector of the NPN triode Q11 is connected with the connection point of one end of the resistor R14 and one end of the capacitor C12 and is used as a first output end of the pre-bias starting circuit and is used for connecting the non-inverting input end + Vin of the voltage loop sampling feedback circuit, the other end of the resistor R14 is used as a second input end of the pre-bias starting circuit and is used for inputting a reference voltage, the cathode of the zener diode D12 is connected with one end of the resistor R15, the other end of the resistor R15 is used as a second output end of the pre-bias starting circuit and is used for connecting the inverting input end-Vin of the voltage loop sampling feedback circuit, and the other end of the resistor R11 and the control circuit, The emitter of the NPN triode Q11 and the other end of the capacitor C12 are grounded together;

the control signal V1 is set voltage value V5 in time interval T1, and time interval T1 is the moment after the bridge topology is started, and the time interval is adjustable; the control signal V1 is a set voltage value V6 in a time interval T2, and the time interval T2 is a time interval of the normal working process of the bridge topology; the voltage stabilizing value of the voltage stabilizing diode D11 is V7; and V6 < V7 < V5.

2. The pre-bias start-up circuit of claim 1, wherein: the circuit also comprises a resistor R13 and a capacitor C11, wherein the resistor R13 and the capacitor C11 are connected between the base of the NPN triode Q11 and the emitter of the NPN triode Q11 in parallel.

3. The pre-bias start-up circuit of claim 1 or 2, wherein: the pre-bias starting circuit and the voltage loop sampling feedback circuit are connected with the same ground.