CN114070104A

CN114070104A - Forward switching power supply, forward system control device, control method and chip

Info

Publication number: CN114070104A
Application number: CN202010778091.7A
Authority: CN
Inventors: 宗强; 方芳; 吴寿化; 刘准
Original assignee: Shenzhen Chip Hope Micro-Electronics Ltd
Current assignee: Shenzhen Chip Hope Micro-Electronics Ltd
Priority date: 2020-08-05
Filing date: 2020-08-05
Publication date: 2022-02-18

Abstract

The application discloses a forward switching power supply, a forward system control device, a control method and a chip. The forward system control device includes: a first terminal for obtaining a first sampled signal; the second terminal is used for being connected with the forward power circuit to obtain a second sampling signal reflecting the peak current of the forward power circuit; a third terminal for connecting the forward power circuit for obtaining a feedback signal reflecting load power supply; the forward system control device is used for controlling the turn-off time of the forward power circuit by using the second sampling signal and the feedback signal, and when the turn-on duration of the forward power circuit exceeds a duration threshold, the forward system control device controls the turn-off of the forward power circuit so that the power supply of a load does not exceed a maximum protection threshold, wherein the duration threshold is determined based on the first sampling signal, and the forward power circuit is in a continuous mode in an on-off period.

Description

Forward switching power supply, forward system control device, control method and chip

Technical Field

The present disclosure relates to the field of control circuits, and in particular, to a forward switching power supply, a forward system control device, a forward system control method, and a chip.

Background

In order to match the power supply of various loads such as electronic terminals, displays, servers, various instruments and meters, the ac power provided by the power grid is generally converted into the dc power suitable for various loads by the switching power supply. Due to different power requirements of loads, a flyback structure is generally adopted as a direct current circuit of the switching power supply to be suitable for a low-power occasion, for example, an occasion with an output power level of 100W or less. In a high-power situation, for example, where the output power level requirement is 100W-300W, the flyback structure is no longer applicable due to the limitation of the duty ratio and the conversion efficiency of the transformer, and at this time, the switching power supply adopts the forward structure as its direct current converter circuit to achieve high-power output.

However, when the control of the switching power supply with the forward structure is abnormal, the power supply output to the load is higher than the maximum range that the load can bear, so that the load is damaged.

Therefore, it is desirable to provide a control device of a forward excitation system to solve the above problems.

Disclosure of Invention

In view of the above-mentioned drawbacks of the related art, an object of the present application is to provide a forward switching power supply, a forward system control device, a control method, and a chip.

To achieve the above and other related objects, a first aspect of the present application discloses a forward system control apparatus for controlling a forward power circuit to perform energy conversion, comprising: the first terminal is used for connecting an external resistor to sample the rectified input signal so as to obtain a first sampling signal; the second terminal is used for being connected with the forward power circuit to obtain a second sampling signal reflecting the peak current of the forward power circuit; a third terminal for connecting the forward power circuit for obtaining a feedback signal reflecting load power supply; the forward system control device is used for controlling the turn-off time of the forward power circuit by using the second sampling signal and the feedback signal, and when the turn-on duration of the forward power circuit exceeds a duration threshold, the forward system control device controls the turn-off of the forward power circuit so that the power supply of a load does not exceed a maximum protection threshold, wherein the duration threshold is determined based on the first sampling signal, and the forward power circuit is in a continuous mode in an on-off period.

In certain embodiments of the first aspect of the present application, when the input signal is stable, the forward system control device adjusts the duration threshold by configuring external resistors with different impedances to change the maximum protection threshold.

In certain embodiments of the first aspect of the present application, the forward system control apparatus adjusts the duration threshold based on changes in the input signal to maintain stability of the maximum protection threshold.

In certain embodiments of the first aspect of the present application, the forward system control apparatus comprises: a drive control unit coupled to the second terminal and the third terminal for outputting a first turn-off signal based on the second sampling signal and the feedback signal; the duty ratio adjusting unit is coupled to the first terminal and used for outputting a second turn-off signal when the on duration of the forward power circuit is judged to exceed the duration threshold; and the driving unit is coupled to the driving control unit and the duty ratio adjusting unit and used for outputting a driving signal based on the first turn-off signal or the second turn-off signal so as to control the on and off of the forward power circuit.

In certain embodiments of the first aspect of the present application, the duty cycle adjusting unit comprises: a current conversion circuit coupled to the first terminal for converting the first sampling signal into an input current, the input current being associated with the duration threshold; and the second time delay circuit is coupled to the current conversion circuit and used for timing based on the input current so as to output the second turn-off signal when the on duration of the forward power circuit is judged to exceed the duration threshold.

In certain embodiments of the first aspect of the present application, the second delay circuit comprises: the second timing capacitor circuit comprises a timing capacitor and is used for receiving the input current to charge the timing capacitor; the second switch circuit is coupled to the second timing capacitor circuit, and configured to output the second turn-off signal when a voltage signal of an electrode side of the second timing capacitor reaches a threshold voltage of the switch circuit.

In certain embodiments of the first aspect of the present application, the drive control unit comprises: a constant voltage control unit for outputting a constant voltage control signal based on the feedback signal and the second sampling signal during a period when a load current is less than a preset constant current value; the constant current control unit is used for outputting a constant current control signal based on the second sampling signal when the load current reaches the preset constant current value; the constant current control signal or the constant voltage control signal is used as the first turn-off signal to be output to the driving unit so as to drive the forward power circuit to output constant voltage power supply to a load or output constant current power supply to the load.

In certain embodiments of the first aspect of the present application, the constant current control unit includes a first comparison circuit for comparing the second sampling signal with a first reference signal to output the constant current control signal; wherein the first reference signal corresponds to the preset constant current value.

In certain embodiments of the first aspect of the present application, the constant voltage control unit includes a second comparison circuit for comparing the second sampling signal and the feedback signal to output the constant voltage control signal during a period in which the feedback signal is smaller than the first reference signal.

In certain embodiments of the first aspect of the present application, the forward system control device further includes a short-circuit protection unit, coupled to the driving unit, for outputting a short-circuit protection signal to the driving unit during a period when the load voltage is lower than a short-circuit protection threshold value to control the forward power circuit to implement short-circuit protection during an output constant-current power supply phase.

In certain embodiments of the first aspect of the present application, the short-circuit protection unit is further configured to obtain the input signal to maintain the short-circuit protection threshold stable based on the input signal.

In certain embodiments of the first aspect of the present application, the short-circuit protection unit comprises: the first time delay circuit is coupled with the driving unit and the constant current control unit and used for forbidding the constant current control unit when the conduction duration of the forward power circuit is lower than the reference duration; wherein the reference duration is associated with the short-circuit protection threshold; and the third comparison circuit is coupled to the driving unit and used for comparing the second sampling signal with a second reference signal to output a comparison signal serving as the short-circuit protection signal to the driving unit.

In certain embodiments of the first aspect of the present application, the short-circuit protection unit further comprises: and the timing circuit is coupled with the third comparison circuit and the driving unit and used for timing based on the comparison signal and outputting the short-circuit protection signal to the driving unit to control the forward system control device to stop working after timing is finished.

In certain embodiments of the first aspect of the present application, the drive unit comprises: a PWM generating circuit for generating a PWM pulse signal; a logic circuit, coupled to the PWM generation circuit and at least one of the drive control unit, the short-circuit protection unit, and the duty ratio adjustment unit, for outputting a logic signal based on at least one of the PWM control signal, the first off signal, the second off signal, and the short-circuit protection signal; and the driving circuit is coupled to the logic circuit and used for outputting a driving signal based on the logic signal to control the forward power circuit to be switched on or switched off.

A second aspect of the present application discloses a control chip, which is packaged with a forward system control device as in any of the embodiments disclosed in the first aspect of the present application.

A third aspect of the present application discloses a forward switching power supply, including a rectifier circuit for receiving an external drive signal to output a rectified signal; the filter circuit is coupled to the rectifying circuit and used for filtering the rectifying signal to output a filtered signal; a forward system control apparatus as in any embodiment disclosed in the first aspect of the present application for outputting a drive signal; the control end of the switching device is coupled with the forward system control device and used for switching on or off based on the driving signal; and the forward power circuit is coupled with the switching device and used for carrying out energy conversion on the received input signal based on the on or off of the switching device.

The fourth aspect of the present application discloses a control method of a forward system, which is used for controlling a forward power circuit to perform energy conversion, and comprises the following steps: acquiring a first sampling signal, a second sampling signal and a feedback signal; the first sampling signal is obtained by sampling a rectified input signal through an external resistor, the second sampling signal reflects the peak current of the forward power circuit, and the feedback signal reflects the power supply of a load; controlling the turn-off time of the forward power circuit by using the second sampling signal and the feedback signal; and when the on-time of the forward power circuit exceeds a time threshold, controlling the forward power circuit to be switched off so that the power supply of a load does not exceed a maximum protection threshold, wherein the time threshold is determined based on the first sampling signal, and the forward power circuit is in a continuous mode in an on-off period.

In some embodiments disclosed in the fourth aspect of the present application, when the input signal is stable, the control method adjusts the duration threshold by configuring external resistors with different impedances to change the maximum protection threshold.

In some embodiments disclosed in the fourth aspect of the present application, the method further comprises the step of adjusting the duration threshold based on the change of the input signal to maintain the stability of the maximum protection threshold.

In summary, the forward switching power supply, the forward system control device, the forward system control method and the chip that are proposed in the present application limit the maximum value of the duty ratio of the driving signal output by the forward switching power supply through a duration threshold, so that the power supplied by the load output by the forward power circuit controlled by the driving signal does not exceed the maximum protection threshold of the load to protect the load. In addition, the duration threshold is associated with the first sampling signal acquired by the first terminal in a mode of additionally arranging the first terminal, so that the duration threshold can be adjusted based on the first sampling signal, namely the maximum value of the duty ratio of the driving signal can be adjusted, and the compatibility and the applicability of the forward system control device are further strong.

Drawings

The specific features of the invention to which this application relates are set forth in the appended claims. The features and advantages of the invention to which this application relates will be better understood by reference to the exemplary embodiments described in detail below and the accompanying drawings. The brief description of the drawings is as follows:

fig. 1 is a circuit block diagram of a switching power supply according to an embodiment of the present invention.

Fig. 2 is a schematic diagram showing an operating waveform of the forward control unit according to the present application.

Fig. 3 is a circuit block diagram of a forward system control apparatus according to an embodiment of the present invention.

Fig. 4 is a schematic diagram illustrating an operation waveform of the forward system control device according to an embodiment of the present invention.

Fig. 5 is a circuit block diagram of a forward system control device according to an embodiment of the present invention.

Fig. 6 is a circuit block diagram of a duty cycle adjusting unit according to an embodiment of the present application.

Fig. 7 is a schematic circuit diagram of a current converting circuit according to an embodiment of the present invention.

Fig. 8 is a circuit diagram of a second delay circuit according to an embodiment of the present invention.

Fig. 9 is a circuit block diagram of a driving control unit according to an embodiment of the present invention.

Fig. 10 is a circuit block diagram of the constant voltage control unit according to an embodiment of the present invention.

Fig. 11 is a circuit block diagram of a constant current control unit according to an embodiment of the present invention.

Fig. 12 is a circuit block diagram of a forward system control device according to another embodiment of the present application.

Fig. 13 is a waveform diagram illustrating a variation relationship between the energy storage and the load voltage of the forward power circuit according to an embodiment of the present invention.

Fig. 14 is a schematic diagram illustrating an output power waveform of a forward power circuit under the control of a forward system control device according to an embodiment of the present invention.

Fig. 15 is a circuit block diagram of the short-circuit protection unit according to an embodiment of the present invention.

Fig. 16 is a circuit structure diagram of a first delay circuit according to an embodiment of the present invention.

Fig. 17 is a circuit block diagram of the short-circuit protection unit according to another embodiment of the present application.

Fig. 18 is a schematic circuit diagram of a compensation circuit according to an embodiment of the present invention.

Fig. 19 is a circuit block diagram of a short-circuit protection unit according to another embodiment of the present application.

Fig. 20 is a circuit block diagram of a driving unit according to an embodiment of the present application.

Fig. 21 is a waveform diagram illustrating a driving unit outputting a driving signal based on each signal according to the present application.

Fig. 22 is a circuit block diagram of a forward switching power supply according to an embodiment of the present invention.

Detailed Description

The following description of the embodiments of the present application is provided for illustrative purposes, and other advantages and capabilities of the present application will become apparent to those skilled in the art from the present disclosure.

In the following description, reference is made to the accompanying drawings that describe several embodiments of the application. It is to be understood that other embodiments may be utilized and that mechanical, structural, electrical, and operational changes may be made without departing from the spirit and scope of the present disclosure. The following detailed description is not to be taken in a limiting sense, and the scope of embodiments of the present application is defined only by the claims of the issued patent. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. Spatially relative terms, such as "upper," "lower," "left," "right," "lower," "below," "lower," "above," "upper," and the like, may be used herein to facilitate describing one element or feature's relationship to another element or feature as illustrated in the figures.

Although the terms first, second, etc. may be used herein to describe various elements or parameters in some instances, these elements or parameters should not be limited by these terms. These terms are only used to distinguish one element or parameter from another element or parameter. For example, a first delay circuit may be referred to as a second delay circuit, and similarly, a second delay circuit may be referred to as a first delay circuit, without departing from the scope of the various described embodiments. The first delay circuit and the second delay circuit are both described as one delay circuit, but they are not the same delay circuit unless the context clearly indicates otherwise. The first comparison circuit and the second comparison circuit, or the first timing capacitor circuit and the second timing capacitor circuit, or the first switch circuit and the second switch circuit are also included in the similar situation.

Also, as used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context indicates otherwise. It will be further understood that the terms "comprises," "comprising," "includes" and/or "including," when used in this specification, specify the presence of stated features, steps, operations, elements, components, items, species, and/or groups, but do not preclude the presence, or addition of one or more other features, steps, operations, elements, components, species, and/or groups thereof. The terms "or" and/or "as used herein are to be construed as inclusive or meaning any one or any combination. Thus, "A, B or C" or "A, B and/or C" means "any of the following: a; b; c; a and B; a and C; b and C; A. b and C ". An exception to this definition will occur only when a combination of elements, functions, steps or operations are inherently mutually exclusive in some way.

In addition, it should be noted that the present disclosure is described below in terms of various embodiments in order to clearly illustrate various inventive features disclosed herein. But not to mean that the various embodiments can only be practiced individually. One skilled in the art may design the available embodiments according to the requirements, or only replaceable components/modules in different embodiments may be replaced according to the design requirements. In other words, the embodiments taught by the present disclosure are not limited to the aspects described in the following embodiments, but include substitutions and permutations and combinations of various embodiments/components/modules as may be made herein before.

The switch power supply is a device for converting electric energy, converts alternating current provided by a power grid into various direct current output voltages, and can be used for providing output voltages of 5V, 3.3V, 2.5V and the like required by a digital circuit and output voltages of +/-12V, +/-15V and the like required by an analog circuit in various electronic devices, industrial equipment and household appliances requiring power supply of multiple paths of different voltages.

Referring to fig. 1, which is a circuit block diagram of a switching power supply according to an embodiment of the present disclosure, as shown, the switching power supply 1 includes a rectifying unit 11, a driving control unit 12, a switching device 13, and a power conversion unit 14. The rectifying unit 11 is configured to receive an external driving signal to output a rectified signal as an input signal Vin of the power converting unit 14. The external driving signal may be, for example, an ac signal output by a utility grid, or may be a dc signal. The rectifier circuit 11 may be a full-wave rectifier circuit or a half-wave rectifier circuit including electronic components such as diodes, and rectifies the received external drive signal to output a rectified signal. The driving control unit 12 controls the power conversion circuit to convert the energy of the rectified signal to output the load power Vout by controlling the on and off of the switching device 13 coupled to the power conversion unit 14. In this application, drive control unit 12 controls when switching device 13 switches on, think control promptly power conversion unit 14 switches on, and it is also that power conversion unit 14 is in the excitation stage that also to say, drive control unit 12 controls when switching device 13 switches off, think control promptly power conversion unit 14 switches off, and it is also that power conversion unit 14 is in the demagnetization stage that also to say, switching device 13's on-off cycle is thought power conversion unit 14's on-off cycle promptly. The aforementioned and later mentioned controls for the switching on and off of the power conversion unit 14 are understood without particular reference.

In some embodiments, the switching device 13 may be a part of the power conversion unit 14, because the circuit modules are divided differently. In other embodiments, the switching device may be a part of the driving control unit 12, and the application is not limited thereto. In a specific embodiment, the switching device includes a controllable Transistor, which may be, for example, a Metal-oxide-semiconductor Field-effect Transistor (MOSFET) or a Bipolar Junction Transistor (BJT).

The power conversion unit 14 may select a flyback configuration or a forward configuration according to different applications, and configure a suitable driving control unit according to the selected configuration. For the sake of distinction, hereinafter, the power conversion unit 14 adopting the flyback structure is referred to as a flyback power circuit, the corresponding driving control unit 12 is referred to as a flyback control unit, the corresponding switching power supply is referred to as a flyback switching power supply, the power conversion unit 14 adopting the forward structure is referred to as a forward power circuit, the corresponding driving control unit 12 is referred to as a forward control unit, and the corresponding switching power supply is referred to as a forward switching power supply.

In practical applications, the flyback switching power supply is suitable for a small power situation with an output power level of less than 100W, on one hand, the duty ratio of the flyback switching power supply is generally limited to less than 0.5 in order to prevent the switching device in the flyback switching power supply from overvoltage breakdown, and the current flowing through the flyback switching power supply generally exhibits a Discontinuous Mode (DCM), and on the other hand, the conversion efficiency of the flyback switching power supply is low because the leakage inductance of the primary and secondary coils of the transformer is relatively large.

The energy storage inductor of the forward switching power supply provides output to the load during the period of controlling the switching device to be switched on and off, so that the load capacity of the forward switching power supply is relatively strong, the forward switching power supply is suitable for occasions with high power (such as 100W-300W), and under the condition of heavy load, the current flowing through the energy storage inductor of the forward switching power supply is in a Continuous Mode (CCM). The heavy load refers to a load factor of the switching power supply being too high, for example, the load factor is 80% to 95%, for a forward switching power supply, the forward switching power supply generally operates under the heavy load, but it should be noted that the load factor is only a relative comparative value between 80% and 95%, and is not understood as a strict definition of the heavy load, and a specific range of the load factor of the heavy load may be newly defined.

In the application, the forward control unit controls the forward power circuit to realize energy conversion in a Pulse Width Modulation (PWM) manner, that is, in the whole control process of the forward power circuit, the on-off period of the forward power circuit is not changed (that is, the on-off period is the period of the PWM Pulse signal output by the Pulse width modulation), and the control of the forward control unit to output load power supply of the forward power circuit is realized by changing the duty ratio of the forward power circuit. And because the current of the energy storage inductor of the forward power circuit is in a continuous mode under the heavy load condition, the forward control unit achieves the purpose of changing the duty ratio of the forward power circuit by changing the on-time or the off-time of the forward power circuit, and the adjustment of the on-time or the off-time of the forward power circuit mentioned later can be understood as the adjustment of the duty ratio.

Referring to fig. 2, a schematic diagram of a working waveform of the forward control unit according to the present application is shown, where as shown, the PWM is a PWM pulse signal generated inside the driving control unit, so that the logic signal Log generated by the forward control unit has a fixed period T, that is, the timing at which the logic signal Log changes to a high level is determined by the PWM pulse signal. The duration for which the high level of the logic signal Log can be maintained, that is, when the logic signal Log jumps from the high level to the low level, is determined by the Off signal Off generated by the forward control unit based on the load power supply and the peak current condition of the forward power circuit. The forward control unit outputs a driving signal Dri having the same frequency and duty ratio as the logic signal Log to control the forward power circuit to be turned on and off based on the logic signal Log, and specifically, for example, the forward control unit controls the forward power circuit to be in a turned-on state based on a high level of the driving signal Dri, and the forward control unit controls the forward power circuit to be in a turned-on state based on a low level of the driving signal Dri.

For the forward power circuit controlled by the forward control unit to work in a continuous mode, the relationship between the output load power supply Vout and the rectified input signal Vin is Vout to Ton/T Vin/N, where N is the primary-secondary side turn ratio of a transformer in the forward power circuit, Ton is the on-time of the forward power circuit controlled by the forward control unit, and T is an on-off period of the forward power circuit. As mentioned above, the forward control unit of the present application uses the period of the PWM pulse signal as the on-Off period for controlling the forward power circuit, and when the forward control unit is working normally, the forward control unit controls the on-time of the forward power circuit based on the Off signal Off to realize the output load power supply Vout. In this way, even if the input signal Vin acquired by the forward control unit is large, the load can be enabled to work within an acceptable power supply range.

However, when the forward control unit is abnormal, for example, an external electronic component of the forward control unit (for example, an optical coupler coupled between the forward power circuit and the forward control unit and used for obtaining power supply of a load) is damaged or fails, so that the received signal (for example, a signal for responding to power supply of the load corresponding to the optical coupler failure) is abnormal, and for example, an internal electronic component of the forward control unit is abnormal, so that the signal of the Off signal Off cannot be output or is output. The forward control unit cannot change the conduction duration (i.e. duty ratio) of the forward power circuit, and can only control the operation of the forward power circuit according to the inherent duty ratio of the PWM pulse signal. However, since the inherent duty ratio of the PWM pulse signal is generally set to be larger, in the case that the obtained input signal Vin is also higher, the load power supply Vout may be higher than the maximum value acceptable by the load, thereby damaging the load.

In view of the above, the present application provides a forward system control device for controlling a forward power circuit to perform energy conversion, wherein the forward system control device controls a range of a duty ratio of the forward power circuit so that a load power supply does not exceed an acceptable maximum value of the load power supply.

Referring to fig. 3, which is a circuit block diagram of the forward system control device in an embodiment of the present disclosure, as shown in the figure, the forward system control device 2 includes a first terminal P _21, a second terminal P _22, a third terminal P _23, and a fourth terminal P _24, where the first terminal P _21 is used for connecting an external resistor R2 to sample an input signal Vin to obtain a first sampling signal Vduty, the second terminal P _22 is used for connecting the forward power circuit to obtain a second sampling signal Cs reflecting a peak current of the forward power circuit, the third terminal P _23 is used for connecting the forward power circuit to obtain a feedback signal Fb reflecting a load power supply, and the fourth terminal P _24 is used for connecting a control terminal of a switching device to control the forward power circuit to be turned on and off. The forward system control device 2 is configured to control a turn-off timing of the forward power circuit by using the second sampling signal Cs and the feedback signal Fb, and when a turn-on duration of the forward power circuit exceeds a duration threshold, the forward system control device 2 controls the turn-off of the forward power circuit so that a load power supply does not exceed a maximum protection threshold Vmax, wherein the forward power circuit is in a continuous mode within an on-off period.

Specifically, referring to fig. 4, which is a schematic diagram illustrating an operating waveform of the forward system control device in an embodiment of the present invention, as shown in the figure, PWM is a PWM pulse signal generated inside the forward system control device 2, so that the driving signal Dri output by the forward system control device 2 has a fixed period T, that is, the timing of the driving signal Dri changing to the high level is determined by the PWM pulse signal. Based on the high level of the drive signal Dri, the forward system control device 2 controls the forward power circuit to be in the on state. When the forward system control device 2 can normally operate, as in the first three periods T in fig. 4, the time length for which the high level of the driving signal Dri can be maintained, that is, when the driving signal Dri jumps from the high level to the low level, is determined by the first Off signal Off1 generated by the forward system control device 2 based on the second sampling signal Cs and the feedback signal Fb, and the forward system control device 2 controls the forward power circuit to be in the Off state based on the low level of the driving signal Dri. When the forward system control device 2 is operating abnormally (for example, the feedback signal Fb is not normal), that is, the first Off signal Off1 of the forward system control device 2 cannot be output normally or is output abnormally, the forward system control device 2 outputs the second Off signal Off2 based on the first sampling signal Vduty (as in the last two periods T in fig. 4), and at this time, the timing at which the driving signal Dri changes from the high level to the low level is determined by the second Off signal Off2 so that the on-time of the forward power circuit does not exceed the time duration threshold, that is, the time duration threshold determines the maximum value of the duty ratio of the driving signal Dri output by the forward system control device 2.

Further, the duration threshold is determined based on the first sampling signal Vduty, that is, when the forward power circuit receives different input signals Vin or the forward system control device 2 configures the external resistor R2 with different impedances, the duration threshold is not the same fixed value, that is, the maximum value of the duty ratio of the driving signal Dri output by the forward system control device 2 is adjustable, so that the compatibility and the applicability of the forward system control device 2 of the present application are strong.

In one example, the forward system control device 2 adjusts the duration threshold based on changes in the input signal Vin to maintain the maximum protection threshold Vmax stable. In particular, since the maximum protection threshold Vmax of the forward power circuit follows the aforementioned formula

Wherein Tonmax is a time length threshold, and it can be known that the maximum protection threshold value Vmax of the forward power circuit is not only the same as the time length threshold Tonmax of the forward power circuit controlled by the forward system control device 2Off and with respect to the input signal Vin. When the input signal Vin changes, the forward system control device 2 adjusts the duration threshold Tonmax (i.e., adjusts the maximum value of the duty ratio) based on the change of the input signal Vin, so that the maximum protection threshold Vmax can be kept unchanged. Thus, under the condition of setting a fixed maximum value of the duty ratio, the forward system control device 2 avoids the situation that under the condition of setting a fixed maximum value of the duty ratio, the forward power circuit does not work under the control of the forward system control device 2 because the input signal Vin is increased to cause too-late protection, namely the load power supply already exceeds the maximum value which can be borne by the load, the forward system control device 2 does not trigger protection, and under the situation that under the condition that the input signal Vin is decreased to cause too-early protection, namely the load power supply does not reach the maximum value which can be borne by the load yet. Therefore, for the same load, even if the user accesses the forward power circuit to different input signals Vin or the input signals Vin are unstable, the forward system control device 2 of the present application can also ensure that the maximum protection threshold Vmax is unchanged, and the load can still be effectively protected.

In another example, the input signal Vin received by the forward power circuit is not changed, and the forward system control device 2 adjusts the duration threshold Tonmax to be suitable for different maximum protection thresholds Vmax by configuring external resistors R2 with different impedances. In particular, see also the formulae

Under the condition that the input signal Vin is not changed, if the time length threshold is not changed, the maximum protection threshold Vmax is not changed, so that the user can only apply the forward system control device 2 to the load with the bearing capacity above the maximum protection threshold Vmax, and the protection is invalid for the load with the bearing capacity below the maximum protection threshold Vmax, and the adaptability is poor. In this example, the user can configure the external resistor R2 with appropriate impedance for different loads, so that the forward system control device 2 has high compatibility and can be applied to loads with various requirements.

Referring to fig. 5, which is a circuit block diagram of the forward system control device of the present application in one embodiment, as shown in the figure, the forward system control device 2 includes a driving control unit 20, a duty ratio adjusting unit 25, and a driving unit 23. The drive control unit 20 is coupled to the second terminal P _22 and the third terminal P _23 for outputting a first Off signal Off1 on its output terminal P _201 based on the second sampling signal Cs and the feedback signal Fb. The duty ratio adjusting unit 25 is coupled to the first terminal P _21, and configured to output a second Off signal Off2 when the on-time of the forward power circuit is determined to exceed the time duration threshold. The driving unit 23 is coupled to the driving control unit 20 and the duty ratio adjusting unit 25, and is configured to output a driving signal Dri based on the first Off signal Off1 or the second Off signal Off2 to control the on and Off of the forward power circuit.

Referring to fig. 6, which is a circuit block diagram of an embodiment of the duty ratio adjusting unit of the present application, as shown in the figure, the duty ratio adjusting unit 25 includes a second delay circuit 251 and a current converting circuit 252. The input of the current converting circuit 252 is coupled to the first terminal P _21 to obtain a first sampling signal Vduty, and the output terminal P _253 of the current converting circuit 252 is coupled to the input of the second delay circuit 251 to convert the first sampling signal Vduty into an input current and output the input current to the second delay circuit 251. The output of the second delay circuit 251 is used as the output P _251 of the duty ratio adjusting unit 25, and is used for timing based on the input current to output a second Off signal Off2 when the on-time of the forward power circuit is judged to exceed the time duration threshold. Wherein the input current is associated with the duration threshold.

Referring to fig. 7, which is a schematic circuit diagram illustrating a current converting circuit according to an embodiment of the present invention, as shown in the figure, the current converting circuit 252 includes a resistor R3, a first pair of switching transistors (N4, N5), and a second pair of switching transistors (P5, P6). One end of the resistor R3 is coupled to the first terminal P _21, and the other end is coupled to the first ends of the first pair of switching tubes (N4, N5). The second end of the first pair of switching tubes (N4, N5) is grounded Gnd, and the third end is coupled with the first end of the second pair of switching tubes (P5, P6). The second end of the second pair of switching tubes (P5, P6) is coupled to the power supply Vcc, and the third end is coupled to the output end P _253 of the current converting circuit 252. The resistor R3 converts the first sampling signal Vduty into a current signal, and the first pair of switching transistors (N4, N5) and the second pair of switching transistors (P5, P6) are coupled to form a current mirror circuit, so that the current signal outputs an input current Ib4 at an output terminal P _253 of the current conversion circuit 252 to the second delay circuit 251. That is, the current value of the input current Ib4 has the same tendency of change as the first sampling signal Vduty, and the current value of the input current Ib4 increases as the first sampling signal Vduty becomes larger, and the current value of the input current Ib4 decreases as the first sampling signal Vduty becomes smaller. In practical applications, the input current Ib4 is output to the timing capacitor in the second delay circuit 251, so that the timing capacitor is charged with the input current Ib4, and when the first sampling signal Vduty changes, the threshold duration is changed by changing the charging speed of the timing capacitor, so as to achieve the purpose of adjusting the maximum value of the duty ratio, so that the forward system control device has strong applicability and can maintain the maximum protection threshold stable.

Referring to fig. 8, a circuit structure of the second delay circuit of the present application in an embodiment is shown, and as shown in the figure, the second delay circuit 251 includes a second timing capacitor circuit 2511 and a second switch circuit 2512. The second timing capacitor 2511 has an input terminal P _254 and an output terminal P _255, and the second timing capacitor 2511 includes an inverter Ng2, switching transistors N6 and P7, and a timing capacitor C2. The input of the not gate Ng2 is used as the input terminal P _254 of the second timing capacitor circuit 2511, the control terminals of the switch tubes N6 and P7 are coupled to the output of the not gate Ng2 after being connected, the first terminal of the switch tube P7 is coupled to the output terminal P _253 of the current converting circuit 252, the second terminal of the switch tube N6 is grounded Gnd, the second terminal of the switch tube P7 and the first terminal of the switch tube N6 are connected to one terminal of the timing capacitor C2, one terminal of the timing capacitor C2 is further connected to the output terminal P _255, and the other terminal of the timing capacitor C2 is grounded Gnd. The second switch circuit 2512 comprises a switch P8 and a not gate Ng3, wherein a control terminal of the switch P2 is connected to the output terminal P _255, a first terminal of the switch is coupled to the power supply Vcc, a second terminal of the switch is connected to the ground Gnd via the current source Ib5, the second terminal of the switch is further coupled to one terminal of the not gate Ng3, and the other terminal of the not gate Ng3 is connected to the output terminal P _251 of the duty ratio adjusting unit 25 to serve as the output of the duty ratio adjusting unit 25.

The input end P _254 of the second timing capacitor circuit 2511 is configured to be coupled to the driving unit to receive a logic signal Log output by the driving unit, so that the timing capacitor C2 performs timing operation based on the logic signal Log, where the logic signal Log can reflect on and off durations of the forward power circuit, when the logic signal Log is at a high level, it indicates that the forward power circuit is on, and when the logic signal Log is at a low level, it indicates that the forward power circuit is off, and a working principle of the driving unit outputting the logic signal Log is described in detail later, which is not expanded herein. When the voltage signal of one electrode side of the timing capacitor C2 reaches the threshold voltage, the second switch circuit 2512 indicates that the on-time of the forward power circuit reaches the maximum protection threshold Vmax, so as to output a second Off signal Off2 through the output terminal P _ 251.

It should be noted that the circuit structure of the second delay circuit 251 shown in fig. 8 is only an example, and in other embodiments, the types and connection modes of the switching tubes in the second timing capacitor circuit 2511 shown in fig. 8 can be flexibly selected according to actual situations and matched with additional electronic components according to requirements, the principle of which is similar to that shown in fig. 8, and the intended function of the second delay circuit 251 in the present application is not affected. The switch P8 in the second switch circuit 2512 in fig. 8 may also be replaced by other types or other devices and flexibly select logic devices to be collocated according to the replaced devices to achieve the above functions, for example, the second switch circuit 2512 may include a comparator, one input terminal of the comparator is coupled to one end of the timing capacitor C1, the other input terminal of the comparator is used to obtain a reference voltage (may be a voltage signal generated by the power supply Vcc, and the magnitude of the voltage signal may be, for example, equal to the threshold voltage of the switch P8, and may be specifically set according to practice), and the comparator outputs the second Off signal Off2 when it is determined by comparison that one end of the timing capacitor C1 reaches the reference voltage obtained by the comparator. The second delay circuit of the present application is not limited to the circuit structure shown in fig. 8, and it is within the scope covered by the second delay circuit of the present application as long as the timing of the on or Off duration of the forward power circuit based on the charging and discharging of the timing capacitor to output the second Off signal Off2 is completed.

The following description explains the working principle of the duty ratio adjusting unit in one embodiment to realize the load protection function, as shown in fig. 6 to 8. Taking the example that the switch transistor N6 is an N-type MOSFET and the switch transistors P7 and P8 are P-type MOSFETs in fig. 8, in one on-off period T of the forward power circuit, the current converting circuit 252 obtains the first sampling signal Vduty and converts it into the input current Ib 4. In the turn-off stage of the forward power circuit, the logic signal Log is at a low level, and changes to a high level after passing through the nor gate Ng2 in the second delay circuit 251, the switching tube P7 is turned off, the switching tube N6 is turned on, and the charging capacitor C2 discharges through the switching tube N6. In the conducting stage of the forward power circuit, the logic signal Log is at a high level and changes to a low level after passing through the nor gate Ng2, the switching tube P7 is turned on, the switching tube N6 is turned off, and the input current Ib4 converted by the current conversion circuit 252 flows into the switching tube P7 to charge the charging capacitor C2. If the voltage signal of one end of the charging capacitor C2, which is connected with the output end P _255, is at the threshold voltage corresponding to the turn-off point of the switching tube P8, it indicates that the on-time reaches the threshold time, the power supplied by the load reaches the maximum protection threshold Vmax, so that the switching tube P8 is in the off state, and the low level output by the second end of the switching tube P8 enables the nor gate Ng3 to output the high level as the Duty ratio adjustment signal Duty, so that the driving unit turns off the forward power circuit based on the signal. If the voltage signal of the end of the charging capacitor C2 connected to the output end P _255 does not exceed the threshold voltage corresponding to the turn-off point of the switch P8, the switch P8 is maintained at the on state, and the second end of the switch P8 is maintained at the high level, so that the not gate Ng3 outputs the low level. It should be noted that the current value of the input current Ib4 determines the charging speed of the charging capacitor C2, so that the threshold duration varies based on the variation of the input current Ib4, and the input current Ib4 is associated with the first sampling signal Vduty obtained by the current conversion circuit 252, so that when the first sampling signal Vduty varies, the input current Ib4 varies, and the threshold duration also varies. For the variation relationship between the threshold duration and the first sampling signal Vduty and how to make the forward system control device achieve the functions of strong adaptability and maintaining the maximum protection threshold stable, please refer to the description of fig. 3 and fig. 4, which is not described herein again.

As described above, when the forward system control device 2 is operating normally, the first Off signal Off1 is output by the drive control unit 20 based on the second sampling signal Cs and the feedback signal Fb to cause the drive unit 23 to output the drive signal Dri based on the first Off signal Off1 to drive the forward power circuit to turn on and Off, at which stage the duty ratio of the drive signal Dri is not greater than the above-described time length threshold (takes a waveform as in the first three periods T in fig. 4).

Referring to fig. 9, a circuit block diagram of a driving control unit according to an embodiment of the present invention is shown, as shown, the driving control unit 20 includes a constant voltage control unit 21 and a constant current control unit 22, the constant voltage control unit 21 having a first input terminal P _211, a second input terminal P _212, and an output terminal P _213, the first input terminal P _211 is coupled to the first terminal P _21 to obtain a second sampling signal Cs reflecting a peak current of the forward power circuit, the second input terminal P _212 is used for coupling the second terminal P _22 to obtain a feedback signal Fb reflecting the load power supply of the forward power circuit, the output terminal P _213 of the constant voltage control unit 21 is coupled to the output terminal P _201 of the driving control unit 20, and the constant voltage control unit 21 is configured to output the constant voltage control signal Cv through the output terminal P _213 based on the feedback signal Fb and the second sampling signal Cs during a period when the load current is smaller than the preset constant current value. The constant current control unit 22 has an input end P _221 and an output end P _222, the input end P _221 is coupled to the first terminal P _21 to receive the second sampling signal Cs, the output end P _222 of the constant current control unit 22 is coupled to the output end P _201 of the driving control unit 20, and the constant current control unit 22 is configured to output the constant current control signal Cc through the output end P _222 based on the second sampling signal Cs when the load current reaches a preset constant current value. The constant voltage control signal Cv or the constant current control signal Cc is output as a first Off signal Off1 to the driving unit through an output terminal P _201 of the driving control unit 20 to drive the forward power circuit to output constant voltage power supply to the load or output constant current power supply to the load. Therefore, the forward system control device can meet the high-power load which needs constant-current power supply.

The preset constant current value is reflected by a first reference signal arranged inside the forward system control device 2, the constant voltage control unit 21 works during the period that the feedback signal Fb does not reach the first reference signal (namely, the load current of the forward power circuit does not reach the preset constant current value), and the forward power circuit works in the constant voltage mode by comparing the second sampling signal Cs with the feedback signal Fb. The constant current control unit 22 operates in a constant current mode in which the forward power circuit operates by comparing the second sampling signal Cs with the first reference signal during a period in which the feedback signal Fb is greater than the first reference signal (i.e., the load current of the forward power circuit reaches a preset constant current value). In an embodiment, the first reference signal may be, for example, a reference voltage signal generated by a power supply of the forward system control device 2, and may also be, for example, a voltage signal provided by a constant voltage source, which is not limited in this application.

In an embodiment, please refer to fig. 10, which is a circuit block diagram of the constant voltage control unit in an embodiment of the present application, as shown in the figure, the constant voltage control unit 21 includes a second comparing circuit 211, one input terminal of the second comparing circuit 211 is used for connecting to the first input terminal P _211 to obtain the second sampling signal Cs, the other input terminal thereof is used for connecting to the second input terminal P _212 to obtain the feedback signal Fb, and the output terminal thereof is used as the output terminal P _213 of the constant voltage control unit 21 to output the constant voltage control signal Cv when the second comparing circuit 221 determines that the sampling signal Cs reaches the feedback signal Fb through comparison. In other words, in the present embodiment, the feedback signal Fb reflects the load power supply of the forward power circuit, and the heavier the load of the forward power circuit (i.e., the larger the load current), the larger the feedback signal Fb, and the feedback signal Fb determines the peak value to which the peak current of the steady forward power circuit should be reached in order to maintain the load voltage of the forward power circuit in each on-Off period during which the feedback signal Fb does not reach the first reference signal, so that the constant voltage control unit 21 outputs the constant voltage control signal Cv as the first Off signal Off1 so that the driving unit can control the turn-Off of the forward power circuit based on the first Off signal Off1 when it is determined by the second sampling signal Cs and the feedback signal Fb that the peak current of the forward power circuit reaches the peak value to which the constant maintaining voltage should be reached in one on-Off period.

In an embodiment, please refer to fig. 11, which is a circuit block diagram of the constant current control unit in an embodiment of the present application, as shown in the figure, the constant current control unit 22 includes a first comparison circuit 221, one input terminal of the first comparison circuit 221 is used for connecting to the input terminal P _221 of the constant current control unit 22 to obtain the second sampling signal Cs, the other input terminal thereof is used for obtaining the first reference signal Vref1, and the output terminal thereof is used as the output terminal P _222 of the constant voltage control unit 22 to output the constant current control signal Cc as the first Off signal Off1 when the first comparison circuit 221 determines, through comparison, that the second sampling signal Cs reaches the first reference signal Vref 1. In other words, in the present embodiment, the first reference signal Vref1 is set to a fixed value, it determines the peak value that the peak current of the forward power circuit should reach in order to maintain the load current of the forward power circuit stable at the preset constant current value, that is, during each on-off period during which the feedback signal Fb has reached said first reference signal Vref1, even if the load power supply of the forward power circuit is changed, in order to maintain the stability of the load current, the peak value which the peak current should reach is not changed, therefore, when the constant current control unit 22 judges that the peak current of the forward power circuit reaches a fixed value which should be reached for maintaining the load current to be constant through the second sampling signal Cs and the first reference signal Vref1 in an on-off period, the constant current control signal Cc is output as the first Off signal Off1 to enable the driving unit to control the forward power circuit to be turned Off based on the control signal Off1 as the first Off signal Off.

How the constant voltage control unit and the constant current control unit output the first Off signal Off1 in coordination with each other is described below with reference to fig. 10 and 11. Taking an on-off period of the forward power circuit as an example, during the on period of the forward power circuit, the peak current of the forward power circuit increases with time, that is, the second sampling signal Cs obtained by the constant voltage control unit 21 and the constant current control unit 22 increases. If the load current of the forward power circuit is smaller than the preset constant current value, that is, the feedback signal Fb is smaller than the first reference signal Vref1, at this time, once the second sampling signal Cs reaches the feedback signal Fb, the constant voltage control unit 21 outputs the constant voltage control signal Cv as the first Off signal Off1 first to enable the driving unit to control the forward power circuit to be turned Off, that is, during the period that the feedback signal Fb is smaller than the first reference signal Vref1, the second sampling signal Cs does not have a chance to reach the first reference signal Vref1, so that the constant current control unit 22 is at rest at this stage. If the load current of the forward power circuit increases to the preset constant current value, that is, the feedback signal Fb is greater than the first reference signal Vref1, at this time, once the second sampling signal Cs reaches the first reference signal Vref1, the constant current control unit 22 firstly outputs the constant current control signal Cc as the first Off signal Off1 to enable the driving unit to control the forward power circuit to be turned Off, that is, at this stage, the sampling signal Cs does not reach the opportunity of the feedback signal Fb, so that the constant voltage control unit 21 is stopped at this stage.

It should be noted that the circuit structure of the driving control unit 20 is not limited to that shown in fig. 9 to 11, for example, the driving control unit 20 may also only include the constant voltage control unit 21 or the constant current control unit 22, the principle of the independent operation of the constant voltage control unit 21 is similar to that described in fig. 10, and the principle of the independent operation of the constant current control unit 22 is similar to that described in fig. 11, which is not repeated herein. As another example, the drive control unit 20 includes a turn-Off detection unit configured to obtain the feedback signal Fb to set a reference value of a peak current of the forward power circuit based on the feedback signal Fb, and further configured to obtain the second sampling signal Cs to output a first turn-Off signal Off1 when the second sampling signal Cs reaches the reference value. As another example, the drive control unit 20 includes a peak current detection unit that acquires the second sampling signal Cs and compares the second sampling signal Cs with a reference signal to output a first Off signal Off 1. The drive control unit 20 is not limited in this application.

As can be seen from the foregoing, in the stage of outputting the constant current by the forward power circuit, the load current is stabilized at the preset constant current value, so that the load voltage changes with the change of the load resistance, and if the load voltage is too low and the load resistance is too small, the load still maintains the preset constant current value and exceeds the maximum value that the load can bear, thereby damaging the load.

In view of this, please refer to fig. 12, which is a circuit block diagram of the forward system control device in another embodiment of the present application, as shown in the figure, in this embodiment, the forward system control device 2 further includes a short-circuit protection unit 24, coupled to the driving unit 23 through an output end P _243 thereof, on the basis of the circuit architecture shown in fig. 5, for outputting a short-circuit protection signal Pro to the driving unit 23 during a period when the load voltage is lower than the short-circuit protection threshold value to control the forward power circuit to implement short-circuit protection in a stage of outputting a constant current.

In the present application, for a forward power circuit, the current of the energy storage inductor of the forward power circuit presents a continuous mode. Therefore, referring to fig. 13, a waveform diagram of a variation relationship between the energy storage and the load voltage of the forward power circuit according to an embodiment of the present invention is shown, as shown in the constant current stage, as the load voltage of the forward power circuit decreases, the peak value Ipkc that the peak current of the forward power circuit should reach is maintained (see the above description for fig. 11), but the initial current Ipk increases and the on-time Ton decreases when the forward power circuit is turned on (as shown in the curves V1 and V2 in fig. 13, the load voltage represented by the curve V1 is greater than the curve V2, and Ton2< Ton 1). Therefore, in view of the relationship between the load voltage and the on-time of the forward power circuit, the forward system control device 2 of the present application may determine the reference time length Tonleb corresponding to the short-circuit protection threshold in advance, so that the short-circuit protection unit 24 determines whether the load voltage is lower than the short-circuit protection threshold by determining whether the on-time length Ton is lower than the reference time length Tonleb. Meanwhile, in order to avoid that the forward system control device 2 controls the forward power circuit to work in the constant voltage power supply stage to generate error protection, so that the forward system control device 2 cannot control the forward power circuit to work normally, the short-circuit protection unit 24 in the present application makes the forward power circuit not to be maintained in the constant current stage when judging that the on-time Ton is lower than the reference time Ton, and at this time, the peak value Ipkc that the peak current of the forward power circuit should reach is not fixed any more and changes in an opposite relation with the on-time Ton (in the Ton stage as shown in fig. 13). Therefore, further, the short-circuit protection unit 24 outputs the short-circuit protection signal Pro by detecting the second sampling signal Cs reflecting the peak current of the forward power circuit and upon judging that the second sampling signal Cs reaches the second reference signal Vref 2. The second reference signal Vref2 reflects a peak value Ipkcmax corresponding to a time point selected in the Tonleb stage in fig. 13 (the selected time point should be close to the reference duration Tonleb), and the second reference signal Vref2 is greater than the first reference signal Vref 1.

Referring to fig. 14, a schematic diagram of a power supply waveform output by the forward power circuit under the control of the forward system control device according to an embodiment of the present invention is shown, as shown in the figure, when the load voltage of the forward power circuit drops to the short-circuit protection threshold Vpro in the constant current phase, under the control of the short-circuit protection unit 24 of the forward system control device 2, the forward power circuit is turned off after the load current thereof suddenly increases (corresponding to the control process of the short-circuit protection unit 24 outputting the short-circuit protection signal Pro when determining that the second sampling signal Cs reaches the second reference signal Vref 2). It should be noted that, since the constant current mode of the forward power circuit is affected by the load voltage, the maintained preset constant current value Io is not completely unchanged, and has a waveform as shown in the I-Io stage in fig. 14, the load current of the forward power circuit slightly increases with the decrease of the load voltage V, but since the maximum increment thereof can meet the current precision requirement of the constant current mode, the current slight change in the constant current stage is regarded as being maintained at the preset constant current value Io unless otherwise specified in the present application. In addition, under the control of the short-circuit protection unit, the forward power circuit is not turned off immediately after the load voltage drops to the short-circuit protection threshold Vpro, so the short-circuit protection point actually realized by the short-circuit protection unit 24 is slightly smaller than the short-circuit protection threshold Vmin, as shown in fig. 14, when the load voltage is Vpro. Since the difference between the two is small, the short-circuit protection threshold Vpro is described as a short-circuit protection point for the short-circuit protection unit 24 to implement short-circuit protection.

Referring to fig. 15, which is a circuit block diagram of the short-circuit protection unit according to an embodiment of the present invention, as shown, the short-circuit protection unit 24 includes a first delay circuit 241 and a third comparison circuit 242. The output end P _246 of the first delay circuit 241 is coupled to the constant current control unit (not shown in fig. 10) for disabling the constant current control unit when the on-time Ton of the forward power circuit is lower than the reference time Ton. One input terminal P _241 of the third comparing circuit 242 is configured to be coupled to the first terminal P _21 to obtain the second sampling signal Cs, the other input terminal P _242 is configured to obtain a second reference signal Vref2, and an output terminal thereof is configured to be an output terminal P _243 of the short-circuit protection unit 24 to be coupled to the driving unit, so as to output a comparison signal as a short-circuit protection signal Pro to the driving unit when the third comparing circuit 242 determines through comparison that the second sampling signal Cs reaches the second reference signal Vref2, so that the driving unit controls the forward constant current control device to stop operating based on the short-circuit protection signal Pro.

Referring to fig. 16, which is a schematic circuit diagram of a first delay circuit according to an embodiment of the present disclosure, as shown in the figure, the first delay circuit 241 includes a first timing capacitor circuit 2411 and a first switch circuit 2412. The first timing capacitor circuit 2411 includes an input terminal P _244 and an output terminal P _245, and includes a not gate Ng1, switching transistors N1 and P1, and a timing capacitor C1. The input of the not gate Ng1 is used as the input terminal P _244 of the first timing capacitor circuit, the control terminals of the switch tube N1 and the switch tube P1 are coupled to the output of the not gate Ng1 after being connected, the first terminal of the switch tube P1 is coupled to the power supply Vcc via the current source Ib1, the second terminal of the switch tube N1 is grounded Gnd, the second terminal of the switch tube P1 and the first terminal of the switch tube N1 are connected to one terminal of the timing capacitor C1, one terminal of the timing capacitor C1 is further connected to the output terminal P _245, and the other terminal of the timing capacitor C1 is grounded Gnd. The first switch circuit 2412 includes a switch tube P2 and a latch D1, the control terminal of the switch tube P2 is connected to the output terminal P _245, the first terminal thereof is coupled to the power supply Vcc, the second terminal thereof is connected to the ground Gnd via the current source Ib2, the second terminal thereof is further coupled to one terminal of the latch D1, and the other terminal of the latch D1 is connected to the output terminal P _246 of the first delay circuit 241 for serving as the output of the first delay circuit 241.

The input end P _244 of the first timing capacitor circuit 2411 is configured to be coupled to the driving unit to receive a logic signal Log output by the driving unit, so that the timing capacitor C1 performs a timing operation based on the logic signal Log, where the logic signal Log can reflect the on and off durations of the forward power circuit, and the working principle of the driving unit outputting the logic signal Log is described in detail later, and is not expanded here. The first switch circuit 2412 outputs an disable signal Uable through the output terminal P _246 to disable the constant current control unit when the voltage signal of one electrode side of the timing capacitor C1 reaches its threshold voltage.

The operation of the first delay circuit in the embodiment shown in fig. 16 is explained below. Taking the example that the switch tube N1 in fig. 11 is an N-type MOSFET, and the switch tubes P1 and P2 are P-type MOSFETs, in an on-off period T of the forward power circuit, at the off stage of the forward power circuit, the logic signal Log is at a low level, and becomes a high level after passing through the nor gate Ng2, the switch tube P1 is turned off, the switch tube N1 is turned on, and the charging capacitor C1 is discharged through the switch tube N1. In the conducting stage of the forward power circuit, the logic signal Log is at a high level and changes to a low level after passing through the nor gate Ng1, the switch tube P1 is turned on, the switch tube N1 is turned off, and the power supply Vcc takes the current value of the current source Ib1 as a charging current to charge the charging capacitor C1 through the switch tube P1. If the on-time of the forward power circuit exceeds the reference time Tonleb (i.e. the load voltage is higher than the short-circuit protection threshold), the voltage signal of the end of the charging capacitor C1 connected to the output end P _245 is at a threshold voltage higher than that corresponding to the off point of the switching tube P2, so that the switching tube P2 is in an off state, and the low level output by the second end of the switching tube P2 can trigger the latch D1 to output the disable signal Uable. If the on-time of the forward power circuit does not exceed the reference time Tonleb (i.e. the load voltage is lower than the short-circuit protection threshold), the voltage signal at the end of the charging capacitor C1 connected to the output end P _245 does not exceed the threshold voltage corresponding to the off-point of the switch tube P2, so that the switch tube P2 is turned on, the second end of the switch tube P2 becomes high level, and the latch D1 latches the high level to output the disable signal Uable. The current value of the current source Ib1 determines the charging speed C1 of the charging capacitor, and under the condition that the threshold voltage of the switching tube P2 is not changed, a person skilled in the art can set the reference time length Tonleb by selecting an appropriate current source Ib1 according to requirements.

It should be noted that the circuit structure of the first delay circuit 241 shown in fig. 16 is only an example, and in other embodiments, the types and connection modes of the switch tubes in the first timing capacitor circuit 2411 shown in fig. 16 can be flexibly selected according to actual situations and matched with additional electronic components according to requirements, the principle of which is similar to that shown in fig. 16, and the intended function of fig. 16 is not affected. The switch P2 in the first switch circuit 2422 in fig. 16 can be replaced by other types or other devices and flexibly select logic devices to be collocated according to the replaced devices to achieve the above functions, for example, the first switch circuit 2422 can include a comparator and a latch, one input terminal of the comparator is coupled to one end of the timing capacitor C1, the other input terminal is used for obtaining a reference voltage (which can be a voltage signal generated by the power supply Vcc and whose magnitude can be, for example, equal to the threshold voltage of the switch P2, and can be specifically set according to practice), when one end of the timing capacitor C1 is determined to be dropped to the reference voltage obtained by the comparator through comparison, the comparator outputs a high level to the latch, so that the latch latches the high level to output the disable signal Uable. The first delay circuit of the present application is not limited to the circuit structure shown in fig. 16, and it is within the scope covered by the first delay circuit of the present application as long as the timing of the on or off duration of the forward power circuit based on the charging and discharging of the timing capacitor can be completed to output the disable signal.

The working principle of the first delay circuit described in fig. 16 is described below with reference to fig. 15, fig. 10, fig. 11, and fig. 12, in which the working principle of the short-circuit protection unit 24 in an embodiment of the present application is described, and in the constant-voltage phase, the load current is small, that is, the feedback signal Fb is smaller than the first reference signal Vref1 and the second reference signal Vref2, when once the second sampling signal Cs reaches the feedback signal Fb, the constant-voltage control unit 21 outputs the constant-voltage control signal Cv as the first Off signal Off1 to make the driving unit control the forward power circuit to be turned Off, that is, the sampling signal Cs does not reach the first reference signal Vref1 or the second reference signal Vref2 in the constant-voltage phase, so that the constant-current control unit 22 and the short-circuit protection unit 24 are at the stop in this phase, even if the first delay circuit 241 in the short-circuit protection unit 24 detects that the on-time of the forward power circuit is lower than the reference time Tonleb, the third comparison circuit 242 in the short-circuit protection unit 24 cannot be caused to output the short-circuit protection signal Pro. In the constant current stage, since the load current is large, the feedback signal Fb is greater than the first reference signal Vref1 and the second reference signal Vref2, the constant voltage control unit 21 is inactive, when the first delay circuit 241 of the short-circuit protection unit 24 determines that the on-time of the forward power circuit is lower than the reference time Tonleb (the load voltage is lower than the short-circuit protection threshold), the disable signal Uable is output, the constant current control unit 22 disables based on the disable signal Uable, the magnitudes of the second sampling signal Cs and the first reference signal Vref1 are not compared, and the magnitudes of the second sampled signal Cs and the second reference signal Vref2 are compared by the third comparison circuit 242 of the short-circuit protection unit 24, when the second sampling signal Cs reaches the second reference signal Vref2, the comparison signal is output as a short-circuit protection signal Pro, the drive unit 23 turns off the forward power circuit based on the short-circuit protection signal Pro, therefore, short-circuit protection is realized in the constant current stage, and the control device of the forward system can not be influenced to control the forward power circuit to work in the constant voltage stage.

As can be seen from the description of fig. 1 and fig. 2, for the forward power circuit, which performs energy conversion on the input signal Vin under the control of the forward system control device 2, the power supply of the load output by the forward power circuit is not only related to the turn-off timing (i.e. duty ratio) of the forward power circuit controlled by the forward system control device 2, but also related to the input signal Vin. When the input signal Vin changes, if the short-circuit protection unit 24 still compares the on-time of the forward power circuit with the set fixed reference time Tonleb to output the short-circuit protection signal, the short-circuit protection signal is output according to the formula

Wherein Vpro is the short-circuit protection threshold and N is the origin of the transformer in the forward power circuitThe secondary winding ratio indicates that the actual short-circuit protection point is not the expected short-circuit protection threshold. For example, in a case where the input signal Vin is not considered to be changed (for example, Vin is 230V), the set reference time duration Tonleb is 0.3ms, and the short-circuit protection point reached by the short-circuit protection unit 24 is the expected short-circuit protection threshold 2.5V, that is, the load voltage is actually lower than 2.5V, and the short-circuit protection is triggered. However, once the input signal Vin fluctuates or changes (for example, Vin is 250V), the short-circuit protection unit 24 still uses the reference time length Tonleb is 0.3ms as a criterion for determining whether the load voltage is lower than 2.5V, the short-circuit protection point reached by the short-circuit protection unit 24 is actually 3V, that is, the load voltage triggers short-circuit protection already when lower than 3V, or the input signal Vin becomes smaller (for example, Vin is 210V), the short-circuit protection point reached by the short-circuit protection unit 24 is actually 2V, that is, the load voltage starts to trigger short-circuit protection only when lower than 2V, and it is not favorable for the load whether to trigger the short-circuit protection early or too late.

In view of the above, in another embodiment, the short-circuit protection unit 24 is further configured to obtain the input signal Vin to maintain the stability of the short-circuit protection threshold value based on the input signal Vin. As shown in fig. 17, fig. 17 is a circuit block diagram of the short-circuit protection unit in another embodiment of the present application, and as shown in the figure, the short-circuit protection unit 24 further includes a compensation circuit 243 based on the circuit architecture shown in fig. 15, the compensation circuit 243 obtains the input signal Vin through an input end P _247 thereof, and is coupled to the first delay circuit (not shown in fig. 12) through an output end P _248 thereof, and the compensation circuit 243 compensates the reference time length based on a change of the input signal Vin to maintain a stable short-circuit protection threshold. In particular, also according to the conversion formula of the forward power circuit

When the input signal Vin changes, the reference time duration Tonleb may be changed according to an inverse transformation rule, and when the input signal Vin increases, the reference time duration Tonleb is decreased, and when the input signal Vin decreases, the reference time duration Tonleb is increased.

Referring to fig. 18, which is a schematic circuit diagram of the compensation circuit of the present application in an embodiment, as shown in the figure, the compensation circuit 243 includes a resistor R1, a first pair of switching transistors (N2, N3), and a second pair of switching transistors (P3, P4). One end of the resistor R1 is coupled to the input terminal P _247 of the compensation circuit 243, and the other end is coupled to the first end of the first pair of switching tubes (N2, N3). The second end of the first pair of switching tubes (N2, N3) is grounded Gnd, and the third end is coupled with the first end of the second pair of switching tubes (P3, P4). The second end of the second pair of switching tubes (P3, P4) is coupled to the power supply Vcc, and the third end is coupled to the output end P _248 of the compensation circuit 243. The resistor R1 is used for sampling the input signal Vin, and the first pair of switching transistors (N2, N3) and the second pair of switching transistors (P3, P4) are coupled to form a current mirror circuit so as to output a charging current Ib3 to the first delay circuit at the output terminal P _248 of the compensation circuit 243 based on the sampling of the resistor R1. That is, the current value of charge current Ib3 has the same trend of change as input signal Vin, and as input signal Vin becomes larger, the current value of charge current Ib3 increases, and as input signal Vin becomes smaller, the current value of charge current Ib3 decreases. In practical applications, the charging current Ib3 is output to the timing capacitor in the first delay circuit 241, so that the timing capacitor is charged with the charging current Ib3, and when the input signal Vin changes, the reference time duration is changed by changing the charging speed of the timing capacitor, so as to achieve the purpose of maintaining the stability of the short-circuit protection threshold of the short-circuit protection unit 24.

Further, when the first delay circuit 241 adopts the circuit structure shown in fig. 16, the output terminal P _248 of the compensation circuit 243 shown in fig. 18 is coupled to the first terminal of the switch tube P2 shown in fig. 16. However, it should be noted that, in order to simplify the circuit connection and facilitate the adjustment, when the first delay circuit 241 shown in fig. 16 is coupled to the compensation circuit 243 shown in fig. 18, the first terminal of the switch tube P2 in fig. 16 is not necessarily coupled to the power supply Vcc via the current source Ib 1.

With reference to fig. 16 and 18, it is described how the short-circuit protection unit 24 changes the reference time length Tonleb to maintain the stability of the short-circuit protection threshold, the current value of the charging current Ib3 output by the compensation circuit 243 follows the change of the input signal Vin, when the input signal Vin becomes larger, the charging current Ib3 also increases, the first timing capacitor circuit 2411 charges the timing capacitor C1 with the charging current Ib3 during the turn-off period of the forward power circuit, and as the charging speed increases, the time length for the voltage signal at one end of the timing capacitor C1 to become the threshold voltage corresponding to the turn-off point of the switching tube P2 decreases, and then the reference time length Tonleb decreases, so that Vin in the above formula is unchanged, and the short-circuit protection threshold is still the corresponding short-circuit protection threshold before the input signal Vin does not increase; when the input signal Vin is decreased, the charging current Ib3 is also decreased, the first timing capacitor circuit 2411 charges the timing capacitor C1 with the charging current Ib3 during the turn-off period of the forward power circuit, and as the charging speed is decreased, the duration that the voltage signal at one end of the timing capacitor C1 becomes the threshold voltage corresponding to the turn-off point of the switching tube P2 is increased, and the reference duration Tonleb is increased, so that Vin × Tonleb in the above formula is not changed, and the short-circuit protection threshold is still the corresponding short-circuit protection threshold before the input signal Vin is not decreased.

It should be noted that, when an interference test such as EFT (Electrical Fast Transient/burst), a lightning stroke, etc. is performed, a peak current flowing through the forward power circuit may be instantaneously increased to the second reference signal Vref2, so that the third comparison circuit 242 outputs a comparison signal, and if the comparison signal is used as the short-circuit protection signal Pro to the driving unit, the driving unit controls the forward system control device to stop working, so that the short-circuit protection function is triggered by mistake. In order to avoid the false triggering of the short-circuit protection unit caused by these disturbances, as shown in fig. 19, it is shown as a circuit block diagram of the short-circuit protection unit in a further embodiment of the present application, as shown in fig. 19, the short-circuit protection unit 24 further includes a timing circuit 244 (shown in fig. 19 based on the circuit architecture of fig. 17) on the basis of the circuit architecture shown in fig. 17 or fig. 15, where the third comparison circuit 242 is coupled to the driving unit via a path P _249 for outputting a comparison signal according to the aforementioned principle, the driving unit controls the forward power circuit to be turned off based on the comparison signal in one period, one end of the timing circuit 244 is coupled to the output of the third comparison circuit 242, and the other end is coupled to an output terminal P _243 of the short-circuit protection unit 24 for timing based on the comparison signal output by the third comparison circuit 242, and outputting the short-circuit protection signal Pro to the driving unit at the end of timing to control the forward system control device to stop the forward system control device And (6) working. In one example, the timing circuit includes a pulse counter for counting based on the comparison signal output by the third comparison circuit 242 and outputting the short-circuit protection signal Pro when the comparison signal reaches a preset number. In another example, the timing circuit includes a timer for counting a preset fixed time period based on the comparison signal output by the third comparison circuit 242, and outputting the short-circuit protection signal Pro when it is determined that the preset fixed time period is reached. Therefore, only if the comparison signals are output in continuous periods, the driving unit can control the forward system control device to stop working, and therefore the anti-interference capability of the forward system control device can be effectively enhanced. As shown in fig. 5 and 12, the first Off signal Off1 output by the driving control unit 20, the short-circuit protection signal Pro output by the short-circuit protection unit 24, and the second Off signal Off2 output by the duty ratio adjustment unit 25 are all output to the driving unit 23, and the driving unit 23 outputs a logic signal Log based on at least one of the signals to output a driving signal Dri based on the logic signal Log to control the forward power circuit to be turned on or Off for energy conversion.

Referring to fig. 20, which is a circuit block diagram of a driving unit according to an embodiment of the present invention, as shown, the driving unit 23 includes a PWM generating circuit 231, a logic circuit 232, and a driving circuit 233. The output terminal of the PWM generating circuit 231 is coupled to the logic circuit 232 to generate a PWM pulse signal to be output to the logic circuit 232, the logic circuit 232 is coupled to the output terminal P _201 of the driving control unit 20, the output terminal P _243 of the short-circuit protection unit 24, and the output terminal P _251 of the duty ratio adjusting unit 25, so as to output a logic signal Log based on at least one of the first Off signal Off1, the short-circuit protection signal Pro, and the second Off signal Off2, and the PWM pulse signal, and the driving circuit 233 is connected to the output of the logic circuit 232 to output a driving signal Dri based on the logic signal Log to control the forward power circuit to be turned on or Off to achieve the above function. The logic circuit 232 includes, but is not limited to, a flip-flop, a timer, a selector, an and gate, a nor, etc. according to the control logic, which is not limited in this application.

Fig. 21 is a schematic diagram showing waveforms of driving signals output by the driving unit based on various signals according to the present application, where PWM is the PWM pulse signal, and the logic signal Log output by the driving unit has a fixed period T, that is, the timing of the logic signal Log changing to the high level is determined by the PWM pulse signal. Based on the high level of the logic signal Log, the driving unit controls the forward power circuit to be in a conducting state. The duration of time that the high level of the logic signal Log can be maintained, that is, when the logic signal Log transitions from the high level to the low level, is determined by at least one of the first Off signal Off1, the short-circuit protection signal Pro, and the second Off signal Off 2. Based on the low level of the logic signal Log, the driving unit controls the forward power circuit to be in a turn-off state. During normal operation of the forward system control device, the drive unit can only receive the first Off signal Off1 and thereby determine the timing at which the logic signal Log becomes low. As soon as the load supply is greater than the maximum protection threshold Vmax (i.e. the maximum value that the load can withstand), the duty cycle adjustment unit 25 outputs a second Off signal Off2, and the drive unit determines the timing at which the logic signal Log becomes low based on the second Off signal Off 2. In addition, during the operation in which the load current I is greater than the preset constant current value Io, when the load voltage is lower than the short-circuit protection threshold Vpro (i.e., when the load voltage is low and the current is large), the short-circuit protection signal Pro output from the short-circuit protection unit 24 is generated, and the driving unit determines the timing at which the logic signal Log becomes the low level based on the short-circuit protection signal Pro. The output logic signal Log is used for controlling the driving circuit 233 to output a driving signal Dri to control the forward power circuit to be turned on or off for energy conversion to realize the above function. Wherein the driving signal Dri has the same duty ratio as the logic signal Log. In addition, when the short-circuit protection signal Pro or the second Off signal Off2 occurs, it is described that the forward system control device operates in an abnormal state, the logic signal Log and the driving signal Dri output by the driving unit may continue at a low level for a preset time period (for example, 100T) or at a low level, and fig. 21 does not show the logic signal Log and the driving signal Dri in this state for explaining the control timing of each signal, and a person skilled in the art should not limit what is shown in the figure.

In summary, the forward system control device provided in the present application limits the maximum value of the duty ratio of the driving signal output by the forward system control device through a duration threshold, so that the power supplied by the load output by the forward power circuit controlled by the driving signal does not exceed the maximum protection threshold of the load to protect the load. In addition, the duration threshold is associated with the first sampling signal acquired by the first terminal in a mode of additionally arranging the first terminal, so that the duration threshold can be adjusted based on the first sampling signal, namely the maximum value of the duty ratio of the driving signal can be adjusted, and the compatibility and the applicability of the forward system control device are further strong.

The application also discloses a control chip, the control chip encapsulation is as above any embodiment just swashing system control device. The control chip further comprises a plurality of pins, in an embodiment, the chip is packaged with the drive control unit, the duty ratio adjusting unit and the drive unit as described above, and the plurality of pins comprise a first pin for acquiring a first sampling signal obtained by sampling the rectified input signal, a second pin for acquiring a sampling signal reflecting a peak current of the forward power circuit, a third pin for acquiring a feedback signal, a fourth pin for outputting the drive signal, a fifth pin for acquiring a power supply of the chip, and a sixth pin for grounding. In another embodiment, the chip package includes the driving control unit, the duty ratio adjusting unit, the short-circuit protection unit, and the driving unit as described above, and the plurality of pins include a first pin for acquiring a first sampling signal obtained by sampling the rectified input signal, a second pin for acquiring a sampling signal reflecting a peak current of the forward power circuit, a third pin for acquiring a feedback signal, a fourth pin for outputting the driving signal, a fifth pin for acquiring the rectified input signal, a sixth pin for acquiring a power supply of the chip, and a seventh pin for grounding. The modules and circuits in the embodiments refer to the foregoing description of fig. 1 to 21, which are not repeated herein.

Referring to fig. 22, a circuit block diagram of the forward switching power supply in an embodiment of the present invention is shown, and as shown in the figure, the forward switching power supply 30 includes a rectifying circuit 31, a filter circuit 32, a forward system control device 33, a switching device 34, and a forward power circuit 35.

The rectifying circuit 31 is configured to receive an external driving signal to output a rectified signal. The external driving signal may be, for example, an ac signal output by a utility grid, or may be a dc signal. The rectifier circuit 31 may be a full-wave rectifier circuit or a half-wave rectifier circuit including electronic components such as diodes for rectifying the received external drive signal and outputting a rectified signal.

The filter circuit 32 is coupled to the rectifier circuit 31, and is configured to filter the rectified signal output by the rectifier circuit 31 to output a filtered signal to the forward power circuit 35. In an embodiment, the filter circuit 32 may be a pi filter circuit, an LC filter circuit, an RC filter circuit, an LC pi filter circuit, an RC pi filter circuit, or the like, which is not limited in this application.

The forward system control device 33 is configured to output a driving signal, and the forward system control device 33 may adopt the forward system control device disclosed in the present application, and the structure and the working principle thereof please refer to the description of fig. 1 to 21, which is not described herein again.

A control terminal of the switching device 34 is coupled to the forward system control device 33 for turning on or off based on the driving signal. In an embodiment, the switching device is a three-terminal controllable device that can be controlled to be turned on and off by a control signal, and the three-terminal controllable device includes a control terminal, a first terminal, and a second terminal, and the control terminal controls the turn-on or turn-off between the first terminal and the second terminal based on a received driving signal. The three-terminal controllable device includes a controllable Transistor, such as a Metal-oxide-semiconductor Field-effect Transistor (MOSFET) or a Bipolar Junction Transistor (BJT).

The forward power circuit 35 is coupled between the filter circuit 32 and the switching device 34, and is configured to perform energy conversion on the received input signal based on the on or off of the switching device 34; wherein the input signal is the filtered signal. It should be noted that, in some embodiments, the filter circuit 32 may not be included, in which case the forward power circuit 35 is coupled between the rectifying circuit 31 and the switching device 34, and the input signal received by the forward power circuit 35 is a rectified signal.

The application also discloses a control method of the forward system, and the control method is applied to a forward system control device adopting pulse width modulation. The control method of the forward system includes steps S20, S21, and S22 (not shown).

In step S20, the forward system control device acquires the first sampling signal, the second sampling signal, and the feedback signal.

Please refer to the description of fig. 3, the forward system control device 2 includes a first terminal P _21, a second terminal P _22, and a third terminal P _23, wherein the first terminal P _21 is used for connecting an external resistor R2 to sample an input signal Vin to obtain a first sampling signal Vduty, the second terminal P _22 is used for connecting the forward power circuit to obtain a second sampling signal Cs reflecting a peak current of the forward power circuit, and the third terminal P _23 is used for connecting the forward power circuit to obtain a feedback signal Fb reflecting a load power supply. Specifically, please refer to the description of fig. 3 for the forward system control device 2 to obtain the first sampling signal, the second sampling signal, and the feedback signal, which is not described herein again.

In step S21, the forward system control device controls the turn-off timing of the forward power circuit using the second sampling signal and the feedback signal.

As described with reference to fig. 5, the forward system control device 2 includes a driving control unit 20, a duty ratio adjusting unit 25, and a driving unit 23. The drive control unit 20 is configured to output a first Off signal Off1 based on the second sampling signal Cs and the feedback signal Fb, so that the drive unit 23 controls the turn-Off timing of the forward power circuit based on a first Off signal Off 1. The circuit structure and the operation principle of the driving control unit 20 refer to the descriptions of fig. 5 and fig. 9 to fig. 11, which are not repeated herein.

It should be noted that, when the driving control unit 20 includes the constant current control unit, in the stage of outputting the constant current by the forward power circuit, the load current is stabilized at the preset constant current value, so that the load voltage may change with the change of the load resistance, and if the load voltage is too low and the load resistance is too small, the load still maintains at the preset constant current value and may exceed the maximum value that the load can bear, thereby damaging the load.

In view of this, the control method further includes the step that the forward system control device outputs a short-circuit protection signal to the driving unit during the period that the load voltage is lower than the short-circuit protection threshold value so as to control the forward power circuit to achieve short-circuit protection in the stage of outputting the constant current. Referring to fig. 12, in an embodiment, the forward system control device 2 further includes a short-circuit protection unit 24, and the short-circuit protection unit 24 executes step S23, and the circuit structure and the working principle of the short-circuit protection unit 23 are described with reference to fig. 12 to 19, which are not repeated herein.

In step S22, the forward system control device controls the forward power circuit to turn off when the on-time of the forward power circuit exceeds a time threshold, where the time threshold is determined based on the first sampling signal, so that the load power supply does not exceed a maximum protection threshold, and the forward power circuit is in a continuous mode during an on-off period.

Referring to the description of fig. 3 to 8, please refer to the description of fig. 3 to 8 for the circuit structure and the operation principle of the step S22 executed by the forward system control device and the duty ratio adjustment unit, which are not described herein again.

In summary, the flyback switching power supply, the forward system control device, the control method and the chip provided in the present application limit the maximum value of the duty ratio of the driving signal output by the flyback switching power supply through a duration threshold, so that the power supplied by the load output by the forward power circuit controlled by the driving signal does not exceed the maximum protection threshold of the load to protect the load. In addition, the duration threshold is associated with the first sampling signal acquired by the first terminal in a mode of additionally arranging the first terminal, so that the duration threshold can be adjusted based on the first sampling signal, namely the maximum value of the duty ratio of the driving signal can be adjusted, and the compatibility and the applicability of the forward system control device are further strong.

The above embodiments are merely illustrative of the principles and utilities of the present application and are not intended to limit the application. Any person skilled in the art can modify or change the above-described embodiments without departing from the spirit and scope of the present application. Accordingly, it is intended that all equivalent modifications or changes which can be made by those skilled in the art without departing from the spirit and technical concepts disclosed in the present application shall be covered by the claims of the present application.

Claims

1. A forward system control apparatus for controlling a forward power circuit for energy conversion, comprising:

the first terminal is used for connecting an external resistor to sample the rectified input signal so as to obtain a first sampling signal;

the second terminal is used for being connected with the forward power circuit to obtain a second sampling signal reflecting the peak current of the forward power circuit;

a third terminal for connecting the forward power circuit for obtaining a feedback signal reflecting load power supply;

the forward system control device is used for controlling the turn-off time of the forward power circuit by using the second sampling signal and the feedback signal, and when the turn-on duration of the forward power circuit exceeds a duration threshold, the forward system control device controls the turn-off of the forward power circuit so that the power supply of a load does not exceed a maximum protection threshold, wherein the duration threshold is determined based on the first sampling signal, and the forward power circuit is in a continuous mode in an on-off period.

2. The forward system control device according to claim 1, wherein when the input signal is stable, the forward system control device adjusts the duration threshold by configuring external resistors with different impedances to change the maximum protection threshold.

3. A forward system control as claimed in claim 1 wherein said forward system control adjusts said duration threshold based on changes in said input signal to maintain stability of a maximum protection threshold.

4. A forward system control as claimed in claim 1, wherein said forward system control comprises:

a drive control unit coupled to the second terminal and the third terminal for outputting a first turn-off signal based on the second sampling signal and the feedback signal;

the duty ratio adjusting unit is coupled to the first terminal and used for outputting a second turn-off signal when the on duration of the forward power circuit is judged to exceed the duration threshold;

and the driving unit is coupled to the driving control unit and the duty ratio adjusting unit and used for outputting a driving signal based on the first turn-off signal or the second turn-off signal so as to control the on and off of the forward power circuit.

5. The forward system control device of claim 4, wherein the duty cycle adjusting unit comprises:

a current conversion circuit coupled to the first terminal for converting the first sampling signal into an input current, the input current being associated with the duration threshold;

and the second time delay circuit is coupled to the current conversion circuit and used for timing based on the input current so as to output the second turn-off signal when the on duration of the forward power circuit is judged to exceed the duration threshold.

6. The forward system control device of claim 5, wherein the second delay circuit comprises:

the second timing capacitor circuit comprises a timing capacitor and is used for receiving the input current to charge the timing capacitor;

the second switch circuit is coupled to the second timing capacitor circuit, and configured to output the second turn-off signal when a voltage signal of an electrode side of the second timing capacitor reaches a threshold voltage of the switch circuit.

7. The forward system control device according to claim 4, wherein the drive control unit includes:

a constant voltage control unit for outputting a constant voltage control signal based on the feedback signal and the second sampling signal during a period when a load current is less than a preset constant current value;

the constant current control unit is used for outputting a constant current control signal based on the second sampling signal when the load current reaches the preset constant current value; the constant current control signal or the constant voltage control signal is used as the first turn-off signal to be output to the driving unit so as to drive the forward power circuit to output constant voltage power supply to a load or output constant current power supply to the load.

8. The forward system control device according to claim 7, wherein the constant current control unit includes a first comparison circuit for comparing the second sampling signal with a first reference signal to output the constant current control signal; wherein the first reference signal corresponds to the preset constant current value.

9. The forward system control device according to claim 8, wherein the constant voltage control unit includes a second comparison circuit for comparing the second sampling signal and the feedback signal to output the constant voltage control signal during a period in which the feedback signal is smaller than the first reference signal.

10. The forward system control device according to claim 7, further comprising a short-circuit protection unit, coupled to the driving unit, for outputting a short-circuit protection signal to the driving unit during a period when the load voltage is lower than a short-circuit protection threshold value to control the forward power circuit to implement short-circuit protection during the output constant-current power supply phase.

11. The forward system control device of claim 10 wherein the short-circuit protection unit is further configured to obtain the input signal to maintain the short-circuit protection threshold stable based on the input signal.

12. The forward system control device of claim 10, wherein the short-circuit protection unit comprises:

the first time delay circuit is coupled with the driving unit and the constant current control unit and used for forbidding the constant current control unit when the conduction duration of the forward power circuit is lower than the reference duration; wherein the reference duration is associated with the short-circuit protection threshold;

and the third comparison circuit is coupled to the driving unit and used for comparing the second sampling signal with a second reference signal to output a comparison signal serving as the short-circuit protection signal to the driving unit.

13. The forward system control device of claim 12, wherein the short-circuit protection unit further comprises: and the timing circuit is coupled with the third comparison circuit and the driving unit and used for timing based on the comparison signal and outputting the short-circuit protection signal to the driving unit to control the forward system control device to stop working after timing is finished.

14. A forward system control apparatus as claimed in any one of claims 4 to 13 wherein said drive unit includes:

a PWM generating circuit for generating a PWM pulse signal;

a logic circuit, coupled to the PWM generation circuit and at least one of the drive control unit, the short-circuit protection unit, and the duty ratio adjustment unit, for outputting a logic signal based on at least one of the PWM control signal, the first off signal, the second off signal, and the short-circuit protection signal;

and the driving circuit is coupled to the logic circuit and used for outputting a driving signal based on the logic signal to control the forward power circuit to be switched on or switched off.

15. A control chip, wherein the chip is packaged with the forward system control device as claimed in any one of claims 1 to 14.

16. A forward switching power supply, comprising:

a rectifying circuit for receiving an external driving signal to output a rectified signal;

the filter circuit is coupled to the rectifying circuit and used for filtering the rectifying signal to output a filtered signal;

a forward system control apparatus as claimed in any one of claims 1 to 14 for outputting a drive signal;

the control end of the switching device is coupled with the forward system control device and used for switching on or off based on the driving signal;

and the forward power circuit is coupled with the switching device and used for carrying out energy conversion on the received input signal based on the on or off of the switching device.

17. A control method of a forward system is used for controlling a forward power circuit to perform energy conversion, and comprises the following steps:

acquiring a first sampling signal, a second sampling signal and a feedback signal; the first sampling signal is obtained by sampling a rectified input signal through an external resistor, the second sampling signal reflects the peak current of the forward power circuit, and the feedback signal reflects the power supply of a load;

controlling the turn-off time of the forward power circuit by using the second sampling signal and the feedback signal;

and when the on-time of the forward power circuit exceeds a time threshold, controlling the forward power circuit to be switched off so that the power supply of a load does not exceed a maximum protection threshold, wherein the time threshold is determined based on the first sampling signal, and the forward power circuit is in a continuous mode in an on-off period.

18. The control method of claim 17, wherein the control method adjusts the duration threshold by configuring external resistors with different impedances to change the maximum protection threshold when the input signal is stable.

19. The control method of claim 17, further comprising the step of adjusting the duration threshold based on changes in the input signal to maintain a stable maximum protection threshold.