Forward constant current control device, switching power supply, control method and chip

Abstract

The present application discloses a forward constant current control device, system, control method and chip. The forward constant current control device is used to control a forward power circuit to perform energy conversion, including: a constant voltage control unit, which is used to output a constant voltage control signal based on the obtained feedback signal and sampling signal during the period when the load current is less than a preset constant current value; wherein the feedback signal reflects the load current of the forward power circuit, and the sampling signal reflects the peak current of the forward power circuit; a constant current control unit, which is used to output a constant current control signal based on the sampling signal when the load current reaches the preset constant current value; a driving unit, coupled to the constant voltage control unit and the constant current control unit, which is used to drive the forward power circuit to output a constant voltage power supply to the load or output a constant current power supply to the load based on the constant voltage control signal or the constant current control signal. The present application can be applied to high-power loads with constant current power supply requirements.

Description

Technical Field

[0001] The present application relates to the field of control circuit technology, and in particular to a forward constant current control device, a switching power supply, a control method, and a chip. Background Art

[0002] To power various loads such as electronic terminals, displays, servers, and various instruments and meters, a switching power supply typically converts the AC power provided by the grid into a DC output suitable for these loads. Due to the varying power requirements of these loads, switching power supplies typically employ a flyback structure as their indirect DC conversion circuit for low-power applications, such as those with output power levels below 100W. However, in high-power applications, such as those with output power levels between 100W and 300W, the flyback structure is no longer suitable due to limitations in duty cycle and transformer conversion efficiency. In these cases, switching power supplies employ a forward structure as their indirect DC conversion circuit to achieve high-power output.

[0003] Although forward switching power supplies are widely used in high-power applications due to their high conversion efficiency, simple topology, synchronous rectification and other advantages, existing forward switching power supplies can only achieve constant output voltage. As such, they are not suitable for loads that require constant current power supply, such as high-power LED screens.

[0004] Therefore, it is urgent to propose a forward constant current control device to enable a forward switching power supply to achieve output constant current. Summary of the Invention

[0005] In view of the shortcomings of the related technologies described above, the purpose of the present application is to provide a forward constant current control device, a switching power supply, a control method and a chip.

[0006] To achieve the above-mentioned purpose and other related purposes, the first aspect of the present application discloses a forward constant current control device for controlling a forward power circuit to perform energy conversion, including: a constant voltage control unit for outputting a constant voltage control signal based on an acquired feedback signal and a sampling signal during a period when the load current is less than a preset constant current value; wherein the feedback signal reflects the load current of the forward power circuit, and the sampling signal reflects the peak current of the forward power circuit; a constant current control unit for outputting a constant current control signal based on the sampling signal when the load current reaches the preset constant current value; a driving unit coupled to the constant voltage control unit and the constant current control unit, for driving the forward power circuit to output a constant voltage power supply to the load or to output a constant current power supply to the load based on the constant voltage control signal or the constant current control signal.

[0007] In certain embodiments of the first aspect of the present application, the constant current control unit includes a first comparison circuit for comparing the sampling signal and a first reference signal to output the constant current control signal; wherein the first reference signal reflects the preset constant current value.

[0008] In certain embodiments of the first aspect of the present application, the constant voltage control unit includes a second comparison circuit for comparing the sampling signal and the feedback signal to output the constant voltage control signal during a period when the feedback signal is less than the first reference signal.

[0009] In certain embodiments of the first aspect of the present application, a short-circuit protection unit is further included, coupled to the drive unit, for outputting a short-circuit protection signal to the drive unit during a period when the load voltage is lower than a short-circuit protection threshold to control the forward power circuit to achieve short-circuit protection during the stage of outputting constant current power supply to the load.

[0010] In certain embodiments of the first aspect of the present application, the short-circuit protection unit is further configured to maintain the stability of the short-circuit protection threshold based on the acquired rectified input signal.

[0011] In certain embodiments of the first aspect of the present application, the short-circuit protection unit includes: a first delay circuit, coupled to the constant current control unit, for disabling the constant current control unit when the conduction time of the forward power circuit is lower than a reference time; wherein the reference time is associated with the short-circuit protection threshold; a third comparison circuit, coupled to the drive unit, for comparing the sampling signal and a second reference signal to output a comparison signal as the short-circuit protection signal to the drive unit.

[0012] In certain embodiments of the first aspect of the present application, the first delay circuit includes: a first timing capacitor circuit, including a timing capacitor, for performing a timing operation; a first switch circuit, coupled to the first timing capacitor circuit, for disabling the constant current control unit when the voltage signal on an electrode side of the timing capacitor reaches a threshold voltage of the switch circuit.

[0013] In certain embodiments of the first aspect of the present application, the short-circuit protection unit further includes a compensation circuit coupled to the first delay circuit, for compensating the reference duration based on changes in the acquired rectified input signal to maintain the stability of the short-circuit protection threshold.

[0014] In certain embodiments of the first aspect of the present application, the compensation circuit changes the reference time by changing a charging speed of a timing capacitor.

[0015] In certain embodiments of the first aspect of the present application, the short-circuit protection unit further includes: a timing circuit, coupled to the third comparison circuit and the driving unit, for timing based on the comparison signal, and outputting the short-circuit protection signal to the driving unit at the end of the timing to control the forward constant current control device to stop working.

[0016] In certain embodiments of the first aspect of the present application, it further includes: a duty cycle adjustment unit, coupled to the driving unit, for outputting a duty cycle adjustment signal to the driving unit to control the forward power circuit to shut down when the conduction time of the forward power circuit exceeds a time threshold.

[0017] In certain embodiments of the first aspect of the present application, the driving unit includes: a PWM generating circuit for generating a PWM pulse signal; a logic circuit coupled to at least one of the constant voltage control unit, the constant current control unit, the short-circuit protection unit, and the duty cycle adjustment unit and the PWM generating circuit, for outputting a logic signal based on at least one of the PWM pulse, the constant voltage control signal, the constant current control signal, the short-circuit protection signal, and the duty cycle adjustment signal; and a driving circuit coupled to the logic circuit for controlling the forward power circuit to be turned on or off based on the logic signal for energy conversion.

[0018] The second aspect of the present application discloses a control chip, wherein the chip is packaged with the forward constant current control device as described in any embodiment disclosed in the first aspect of the present application.

[0019] The third aspect of the present application discloses a forward constant current switching power supply, comprising: in certain embodiments of the second aspect of the present application, a rectifier circuit, for receiving an external drive signal to output a rectified signal; a filter circuit, coupled to the rectifier circuit, for filtering the rectified signal to output a filtered signal; a forward constant current control device as described in any embodiment disclosed in the first aspect of the present application, for outputting a drive signal; a switching device, whose control end is coupled to the forward constant current control device, for turning on or off based on the drive signal; a forward power circuit, coupled to the switching device, for performing energy conversion on a received input signal based on the turning on or off of the switching device to switch from outputting a constant voltage to outputting a constant current when the load current reaches a preset constant current value; wherein, the input signal is the filtered signal.

[0020] The third aspect of the present application discloses a forward constant current control method for controlling a forward power circuit to perform energy conversion, comprising the following steps: obtaining a feedback signal and a sampling signal; outputting a constant voltage control signal based on the feedback signal and the sampling signal during a period when the load current is less than a preset constant current value; wherein the feedback signal reflects the load current of the forward power circuit, and the sampling signal reflects the peak current of the forward power circuit; outputting a constant current control signal based on the sampling signal when the load current reaches the preset constant current value; and driving the forward power circuit to output a constant voltage power supply to the load or a constant current power supply to the load based on the constant voltage control signal or the constant current control signal.

[0021] In certain embodiments of the third aspect of the present application, the step is further included: outputting a short-circuit protection signal during a period when the load voltage is lower than the short-circuit protection threshold to control the forward power circuit to achieve short-circuit protection in the constant current stage.

[0022] In certain embodiments of the third aspect of the present application, the further step is included: when the conduction time of the forward power circuit exceeds a preset time threshold, a duty cycle adjustment signal is output to control the forward power circuit to be turned off.

[0023] To sum up, the forward constant current control device, system, control method and chip proposed in this application can control the forward power circuit to switch from output constant voltage to output constant current when the load current exceeds the preset constant current value. It can be suitable for high-power loads with constant current power supply requirements. In addition, by setting a short-circuit protection unit, short-circuit protection can be achieved in the constant current stage to avoid the load voltage being too low and the current being too large to burn the load. By setting a duty cycle adjustment unit, the forward constant current control device can provide protection when the load power supply exceeds the maximum value that the load can withstand, and it has strong applicability. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The specific features of the invention involved in this application are shown in the appended claims. The features and advantages of the invention involved in this application can be better understood by referring to the exemplary embodiments described in detail below and the accompanying drawings. A brief description of the drawings is as follows:

[0025] Figure 1 Shown is the block diagram of a constant current control circuit for a high-power LED load.

[0026] Figure 2 Shown is a schematic diagram of the output power supply waveform of the forward power circuit under the control of the forward constant current control device in one embodiment of the present application.

[0027] Figure 3 Shown is a block diagram of an external circuit of the forward constant current control device of the present application in one embodiment.

[0028] Figure 4Shown is a circuit block diagram of a forward constant current control device in one embodiment of the present application.

[0029] Figure 5 Shown is a circuit block diagram of a constant voltage control unit in one embodiment of the present application.

[0030] Figure 6 Shown is a circuit block diagram of a constant current control unit in one embodiment of the present application.

[0031] Figure 7 Shown is a circuit block diagram of another embodiment of the forward constant current control device of the present application.

[0032] Figure 8 A waveform diagram showing the relationship between the energy storage and load voltage changes of the forward power circuit of the present application in one embodiment is shown.

[0033] Figure 9 Shown is a schematic diagram of the power supply waveform output by a forward power circuit under the control of a forward constant current control device in another embodiment of the present application.

[0034] Figure 10 Shown is a circuit block diagram of a short-circuit protection unit in one embodiment of the present application.

[0035] Figure 11 FIG. 1 is a schematic diagram showing the circuit structure of the first delay circuit of the present application in one embodiment.

[0036] Figure 12 Shown is a circuit block diagram of another embodiment of the short-circuit protection unit of the present application.

[0037] Figure 13 FIG. 1 is a schematic diagram showing the circuit structure of the compensation circuit of the present application in one embodiment.

[0038] Figure 14 Shown is a circuit block diagram of a short-circuit protection unit in yet another embodiment of the present application.

[0039] Figure 15 Shown is a circuit block diagram of yet another embodiment of the present application.

[0040] Figure 16 FIG. 1 is a circuit block diagram of a duty cycle adjustment unit in one embodiment of the present application.

[0041] Figure 17 FIG. 1 is a schematic diagram showing the circuit structure of the current conversion circuit of the present application in one embodiment.

[0042] Figure 18 FIG. 1 is a schematic diagram showing the circuit structure of the second delay circuit of the present application in one embodiment.

[0043] Figure 19Shown is a waveform diagram of the logic signal output by the driving unit of the present application based on various signals.

[0044] Figure 20 Shown is a circuit block diagram of a driving unit in one embodiment of the present application.

[0045] Figure 21 Shown is a circuit block diagram of a forward constant current switching power supply in one embodiment of the present application. DETAILED DESCRIPTION

[0046] The following describes the implementation of the present application through specific embodiments. People familiar with this technology can easily understand other advantages and effects of the present application from the contents disclosed in this specification.

[0047] In the following description, reference is made to the accompanying drawings, which describe several embodiments of the present application. It should be understood that other embodiments may also be used, 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 should not be considered restrictive, and the scope of the embodiments of the present application is limited only by the claims of the published patents. The terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the present application. Spatially related terms, such as "upper", "lower", "left", "right", "below", "below", "lower", "above", "upper", etc., may be used in the text to illustrate the relationship between one element or feature shown in the figure and another element or feature.

[0048] Although in some instances the terms first, second, etc. are used in this document to describe various elements or parameters, 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 can be referred to as a second delay circuit, and similarly, a second delay circuit can 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 describing a delay circuit, but unless the context clearly indicates otherwise, they are not the same delay circuit. Similar situations also include a first comparison circuit and a second comparison circuit, or a first timing capacitor circuit and a second timing capacitor circuit, or a first switching circuit and a second switching circuit.

[0049] Furthermore, 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 should be further understood that the terms "comprise", "include" indicate the presence of the described features, steps, operations, elements, components, items, kinds, and / or groups, but do not exclude the presence, occurrence, or addition of one or more other features, steps, operations, elements, components, items, kinds, and / or groups. The terms "or" and "and / or" used herein are interpreted as inclusive, or mean 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". Exceptions to this definition occur only when the combination of elements, functions, steps, or operations is inherently mutually exclusive in some way.

[0050] In addition, it should be noted that in order to clearly illustrate the various inventive features disclosed in this application, this document describes each embodiment in the form of multiple embodiments as follows. However, this does not mean that each embodiment can only be implemented alone. Those skilled in the art can design feasible implementation examples together according to their needs, or simply replace the replaceable components / modules in different embodiments according to design requirements. In other words, the implementation methods taught in this case are not limited to the aspects described in the following embodiments, but also include the replacement and permutation and combination of each embodiment / component / module when feasible, which are described here first.

[0051] Flyback switching power supplies are suitable for low-power applications with an output power level below 100W. On the one hand, to prevent overvoltage breakdown of the switching devices in the flyback switching power supply, its duty cycle is generally limited to less than 0.5, and the current flowing through the flyback switching power supply generally exhibits discontinuous conduction mode (DCM). On the other hand, the leakage inductance of the primary and secondary windings of the flyback switching power supply's transformer is relatively large, resulting in low conversion efficiency.

[0052] Since the forward switching power supply's energy storage inductor provides output to the load both during the on and off periods of the controlled switching device, its load capacity is relatively strong and suitable for high-power applications (e.g., 100W-300W). Under heavy load conditions, the current flowing through the forward switching power supply's energy storage inductor exhibits a continuous conduction mode (CCM). Heavy load refers to excessively high load factors of the switching power supply, such as a load factor of 80% to 95%. Forward switching power supplies generally operate under heavy loads. However, it should be noted that the load factor of 80% to 95% here is only a relative comparison value and is not to be understood as a strict definition of heavy load. The specific range of heavy load factors can also be redefined.

[0053] However, in practical applications, forward switching power supplies typically use a constant voltage output to power the load. This load current varies with the load's impedance, making it unsuitable for loads requiring constant current. For example, high-power LED loads are expensive to operate at a constant voltage. On the one hand, the current flowing through the high-power LED load increases with temperature rise. On the other hand, according to the LED load's volt-ampere characteristic curve, a small change in voltage can cause a sharp change in current. This can easily lead to overcurrent in the high-power LED load, shortening its lifespan or even causing it to burn out.

[0054] In order to prevent the current flowing through the high-power LED load from exceeding the maximum value and causing damage, it is expected that the LED load can operate in constant current mode. Figure 1 , shown as a block diagram of the constant current control circuit for high-power LED loads, as Figure 1 As shown, a forward switching power supply 10 with a constant voltage output is usually used as a constant voltage power supply, and a constant current module 11 is externally installed to achieve constant current power supply to the LED load, wherein the forward switching power supply 10 is used to convert an external AC signal AC into a DC constant voltage output to the constant current module 11 to convert it into a constant current output to power the LED load.

[0055] but, Figure 1 The constant current control circuit structure is complicated. For users, professionals are required to match the corresponding constant current module 11 for the forward switching power supply 10 that outputs constant voltage power and complete the circuit construction. Figure 1 As for the circuit structure shown, on the one hand, it needs to perform secondary conversion of electric energy, and the conversion efficiency and working stability are not good enough. On the other hand, it can only work in one output constant current mode, and cannot adapt to the changes in load and switch between output constant voltage power supply and output constant current power supply.

[0056] In view of the above situation, the present application proposes a forward constant current control device for controlling a forward power circuit to perform energy conversion, so that when the load current reaches a preset constant current value, the forward power circuit switches from an output constant voltage power supply mode to an output constant current power supply mode. Figure 2 , which is a schematic diagram of the output power supply waveform of the forward power circuit under the control of the forward constant current control device in one embodiment of the present application. As shown in the figure, the preset constant current value Io is the load current value when the forward power circuit enters the output constant current stage. When the load current I of the forward power circuit is less than the preset constant current value Io, the external high-power LED load will not be damaged due to the increase in the load current. The forward constant current control device can control the forward power circuit to operate in the output constant voltage power supply mode (as shown in FIG. Figure 2The V = Vo waveform corresponding to the I < Io stage); after the load current I of the forward power circuit reaches the preset constant current value Io, if the load current I of the forward power circuit continues to increase, it will cause damage to the high-power LED load. Therefore, once the load current I of the forward power circuit reaches the preset constant current value Io, the forward constant current control device controls the forward power circuit to operate in the output constant current power supply mode (such as Figure 2 the waveform in the I > Io stage) so that the load current I of the forward power circuit remains basically unchanged. It should be noted that due to the influence of the load voltage on the constant current mode of the forward power circuit, the preset constant current value Io maintained by it does not change completely, such as Figure 2 the waveform in the I > Io stage in. The load current of the forward power circuit will increase slightly as the load voltage V decreases, but since its maximum increment can meet the current accuracy requirements of the constant current mode, in this application, if there is no special explanation later, the slight change in current during the constant current stage is regarded as being maintained at the preset constant current value Io.

[0057] It should be noted that the forward constant current control device proposed in this application controls the forward power circuit to output constant voltage power supply or constant current power supply to the load by means of pulse width modulation (PWM). That is, during the entire control process of the forward power circuit in this application, the on-off cycle of the forward power circuit remains unchanged (that is, constant frequency, and the on-off cycle is the cycle of the PWM pulse signal output by pulse width modulation). The forward constant current control device controls the forward power circuit to output constant voltage power supply or constant current power supply by changing the duty cycle of the forward power circuit. Also, since this application is applied to the forward power circuit, the current of its energy storage inductor shows a continuous mode under heavy load conditions. Therefore, the forward constant current control device changes the on-time or off-time of the forward power circuit to achieve the purpose of changing the duty cycle of the forward power circuit. The subsequent mention of adjusting the on-time or off-time of the forward power circuit can be understood as an adjustment of the duty cycle.

[0058] In addition, the forward constant current control device of this application realizes the above functions of controlling the forward power circuit by controlling the on and off of a switching device coupled to the forward power circuit, as Figure 3 shown, Figure 3Shown is an external circuit block diagram of the forward constant current control device of the present application in one embodiment, the switching device 50 is a three-terminal controllable device, and the three-terminal controllable device includes a control terminal, a first terminal, and a second terminal, the first terminal is coupled to the forward power circuit 40, and the second terminal is grounded GND, and the control terminal is based on the control of the forward constant current control device 20 to make the first terminal and the second terminal conductive or disconnected, so that the forward power circuit 40 converts the received input signal Vin into energy to output load power Vout to the load, wherein the load power supply Vout is a constant voltage power supply or a constant current power supply, and the input signal Vin is an electrical signal output after rectifying the external AC signal. In this application, when the forward constant current control device controls the switching device to turn on, it is considered to control the forward power circuit to turn on, that is, the forward power circuit is in the excitation stage. When the forward constant current control device controls the switching device to turn off, it is considered to control the forward power circuit to turn off, that is, the forward power circuit is in the demagnetization stage. The on-off cycle of the switching device is considered to be the on-off cycle of the forward power circuit. Unless otherwise specified, the control of the on and off of the forward power circuit mentioned above and below shall be understood in this manner.

[0059] In which, due to the different ways of dividing the circuit modules, in some embodiments, the switching device can be used as part of the forward power circuit. In other embodiments, the switching device can be used as part of a forward constant current control device, and the present application is not limited to this. In a specific embodiment, the switching device includes a controllable transistor, and the controllable transistor can be exemplified by a metal-oxide-semiconductor field-effect transistor (MOSFET) or a bipolar junction transistor (BJT).

[0060] See also Figure 4, which is a circuit block diagram of a forward constant current control device according to an embodiment of the present application. As shown in the figure, the forward constant current control device 20 includes a constant voltage control unit 21, a constant current control unit 22, and a driving unit 23. The constant voltage control unit 21 has 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 used to couple with the forward power circuit to obtain a sampling signal Cs reflecting the peak current of the forward power circuit. The second input terminal P_212 is used to couple with the forward power circuit to obtain a feedback signal Fb reflecting the load current of the forward power circuit. When the load current is less than a preset constant current value, the constant voltage control unit 21 outputs a constant voltage control signal Cv via the output terminal P_213 based on the feedback signal Fb and the sampling signal Cs. The constant current control unit 22 has an input terminal P_221 and an output terminal P_222. The input terminal P_221 obtains the sampling signal Cs. When the load current reaches a preset constant current value, the constant current control unit 22 outputs a constant current control signal Cc via the output terminal P_222 based on the sampling signal Cs. The driving unit is coupled to the first input terminal P_211 and the input terminal P_221, and is configured to drive the forward power circuit to output a constant voltage power supply or a constant current power supply to the load based on the constant voltage control signal Cv or the constant current control signal Cc.

[0061] Wherein, the preset constant current value is reflected by a first reference signal set inside the forward constant current control device 20, and the constant voltage control unit 21 operates during the period when the feedback signal Fb does not reach the first reference signal (that is, the load current of the forward power circuit does not reach the preset constant current value), and compares the sampling signal Cs with the feedback signal Fb to make the forward power circuit operate in the output constant voltage power supply mode. The constant current control unit 22 operates during the period when the feedback signal Fb is greater than the first reference signal (that is, the load current of the forward power circuit reaches the preset constant current value), and compares the sampling signal Cs with the first reference signal to make the forward power circuit operate in the output constant current power supply mode. In an embodiment, the first reference signal can be, for example, a reference voltage signal generated by the power supply of the forward constant current control device 20, and can also be, for example, a voltage signal provided by a constant voltage source, but the present application is not limited thereto.

[0062] In one embodiment, see Figure 5, which is a circuit block diagram of a constant voltage control unit in one embodiment of the present application. As shown in the figure, the constant voltage control unit 21 includes a second comparison circuit 211, one of the input terminals of the second comparison circuit 211 is used to connect to the first input terminal P_211 to obtain the sampling signal Cs, and the other input terminal is used to connect to the second input terminal P_212 to obtain the feedback signal Fb. The output terminal serves as the output terminal P_213 of the constant voltage control unit 21 to output the constant voltage control signal Cv when the second comparison circuit 221 determines through comparison that the sampling signal Cs reaches the feedback signal Fb. In other words, in this embodiment, the feedback signal Fb reflects the load current of the forward power circuit. The larger the load current of the forward power circuit, the larger the feedback signal Fb. In each on-off cycle during which the feedback signal Fb does not reach the first reference signal, the feedback signal Fb determines the peak value of the peak current of the forward power circuit in order to maintain the stability of the load voltage of the forward power circuit. Therefore, when the constant voltage control unit 21 determines that the peak current of the forward power circuit has reached the peak value that should be reached to maintain the voltage constant through the sampling signal Cs and the feedback signal Fb within one on-off cycle, it outputs the constant voltage control signal Cv so that the drive unit can control the forward power circuit to be turned off based on the constant voltage control signal Cv.

[0063] In one embodiment, see Figure 6 , which is a circuit block diagram of a constant current control unit in one embodiment of the present application. As shown in the figure, the constant current control unit 22 includes a first comparison circuit 221, one of the input terminals of the first comparison circuit 221 is used to connect to the input terminal P_221 of the constant current control unit 22 to obtain the sampling signal Cs, and the other input terminal thereof is used to obtain the first reference signal Vref1, and the output terminal thereof serves as the output terminal P_222 of the constant current control unit 22 to output the constant current control signal Cc when the first comparison circuit 221 determines through comparison that the sampling signal Cs reaches the first reference signal Vref1. In other words, in this embodiment, the first reference signal Vref1 is set to a fixed value, which determines the peak value of the peak current of the forward power circuit in order to maintain the load current of the forward power circuit stable at a preset constant current value. That is to say, in each on-off cycle during which the feedback signal Fb is greater than the first reference signal Vref1, in order to maintain the stability of the load current, the peak value of the peak current is fixed. Therefore, when the constant current control unit 22 determines that the peak current of the forward power circuit has reached the fixed value that should be reached to maintain the load current constant through the sampling signal Cs and the first reference signal Vref1 within one on-off cycle, it outputs the constant current control signal Cc so that the drive unit can control the forward power circuit to be turned off based on the constant current control signal Cc.

[0064] The following combination Figure 5 and Figure 6To illustrate how the constant voltage control unit and the constant current control unit work in coordination. Taking an on-off cycle of the forward power circuit as an example, during the on-time of the forward power circuit, the peak current of the forward power circuit continues to increase with time, that is, the sampling signal Cs obtained by the constant voltage control unit 21 and the constant current control unit 22 continues to increase. If the load current of the forward power circuit is less than the preset constant current value, that is, the feedback signal Fb is less than the first reference signal Vref1, at this time, once the sampling signal Cs reaches the feedback signal Fb, the constant voltage control unit 21 will first output the constant voltage control signal Cv to enable the drive unit to control the forward power circuit to turn off, that is, during the period when the feedback signal Fb is less than the first reference signal Vref1, the sampling signal Cs has no chance of reaching the first reference signal Vref1, so that the constant current control unit 22 is dormant at this stage. If the load current of the forward power circuit increases to a preset constant current value, that is, the feedback signal Fb is greater than the first reference signal Vref1, then once the sampling signal Cs reaches the first reference signal Vref1, the constant current control unit 22 first outputs the constant current control signal Cc to cause the drive unit to control the forward power circuit to shut down. That is, at this stage, the sampling signal Cs has no chance of reaching the feedback signal Fb, and the constant voltage control unit 21 is thus suspended at this stage.

[0065] As can be seen from the foregoing, during the forward power circuit's constant current output phase, the load current is stabilized at a preset constant current value. Consequently, the load voltage varies with changes in the load resistance. If the load voltage is too low and the load resistance is too small, the load will still maintain the preset constant current value, exceeding the maximum current the load can withstand, thereby damaging the load.

[0066] For this reason, see Figure 7 , which is a circuit block diagram of another embodiment of the forward constant current control device of the present application. As shown in the figure, in this embodiment, the forward constant current control device is Figure 4 The circuit architecture shown also includes a short-circuit protection unit 24, which is coupled to the drive unit 23 through its output terminal P_243, and is used to output a short-circuit protection signal Pro to the drive unit 23 during the period when the load voltage is lower than the short-circuit protection threshold to control the forward power circuit to achieve short-circuit protection in the output constant current stage.

[0067] In this application, for the forward power circuit, the current of its energy storage inductor is in continuous mode. Therefore, please refer to Figure 8 , which is a waveform diagram showing the relationship between the energy storage and the load voltage of the forward power circuit of the present application in one embodiment. As shown in the figure, 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 remains unchanged (for details, please refer to the aforementioned Figure 6Introduction), but when the forward power circuit is turned on, the initial current Ipk is increasing and the conduction duration Ton is decreasing (as shown by curves V1 and V2 in Figure 8 . The load voltage represented by curve V1 is greater than that of curve V2, and Ton2 < Ton1). Therefore, in view of the relationship between the load voltage and the conduction duration of the forward power circuit as described above, the forward constant current control device of the present application can pre-determine the reference duration Tonleb corresponding to the short-circuit protection threshold, so that the short-circuit protection unit 24 determines whether the load voltage is lower than the short-circuit protection threshold by judging whether the conduction duration Ton is lower than the reference duration Tonleb. At the same time, in order to prevent the forward constant current control device from mis-protecting when controlling the forward power circuit to operate in the constant voltage stage, resulting in the forward constant current control device being unable to control the forward power circuit to operate normally, the short-circuit protection unit 24 of the present application makes the forward power circuit not maintain in the constant current stage when judging that the conduction duration Ton is lower than the reference duration Tonleb. At this time, the peak current Ipkc that the forward power circuit should reach is no longer fixed and changes in the opposite relationship with the conduction duration Ton (as shown in the Tonleb stage in Figure 8 ). Therefore, further, the short-circuit protection unit 24 outputs a short-circuit protection signal Pro by detecting the sampling signal Cs reflecting the peak current of the forward power circuit and judging that the sampling signal Cs reaches the second reference signal Vref2. The second reference signal Vref2 reflects Figure 8 the peak Ipkcmax corresponding to a time point selected in the Tonleb stage (the selected time point should be close to the reference duration Tonleb), and the second reference signal Vref2 is greater than the aforementioned first reference signal Vref1.

[0068] Please refer to Figure 9 , which shows a schematic diagram of the power supply waveform output by the forward power circuit under the control of the forward constant current control device in another embodiment of the present application. As shown in the figure, based on the waveform shown in Figure 2 , in the constant current stage, when the load voltage of the forward power circuit drops to the short-circuit protection threshold Vpro, under the above control of the short-circuit protection unit of the forward constant current control device, the forward power circuit will turn off after the load current suddenly increases (corresponding to the control process where the short-circuit protection unit judges that the sampling signal Cs reaches the second reference signal Vref2 and outputs the short-circuit protection signal Pro). It should be noted that since the forward power circuit does not immediately turn off after the load voltage drops to the short-circuit protection threshold Vpro under the control of the short-circuit protection unit, the actual short-circuit protection point realized by the short-circuit protection unit is slightly smaller than the short-circuit protection threshold Vmin. As shown in Figure 9 , the actual short-circuit protection point realized is when the load voltage is Vpro. Since the difference between the two is small, in the present application, the short-circuit protection threshold Vpro is used as the short-circuit protection point for the short-circuit protection unit 24 to realize short-circuit protection for description.

[0069] See also Figure 10 , which is a circuit block diagram of a short-circuit protection unit in one embodiment of the present application. As shown in the figure, the short-circuit protection unit 24 includes a first delay circuit 241 and a third comparison circuit 242. The output terminal P_246 of the first delay circuit 241 is coupled to the constant current control unit (not shown). Figure 10 ), is used to disable the constant current control unit when the conduction duration Ton of the forward power circuit is lower than the reference duration Tonleb. One of the input terminals P_241 of the third comparison circuit 242 is used to obtain the sampling signal Cs, and the other input terminal P_242 is used to obtain the second reference signal Vref2. The output terminal of the third comparison circuit 242 serves as the output terminal P_243 of the short-circuit protection unit 24 to be coupled to the drive unit, and is used to output the comparison signal as the short-circuit protection signal Pro to the drive unit when the third comparison circuit 242 determines through comparison that the sampling signal Cs reaches the second reference signal Vref2, so that the drive unit controls the forward constant current control device to stop working based on the short-circuit protection signal Pro.

[0070] See also Figure 11 , which is a schematic diagram of the circuit structure of the first delay circuit of the present application in one embodiment. 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 has an input terminal P_244 and an output terminal P_245. The first timing capacitor circuit 2411 includes a NOT gate Ng1, switches N1 and P1, and a timing capacitor C1. The input of the NOT gate Ng1 serves as the input terminal P_244 of the first timing capacitor circuit. The control terminals of the switches N1 and P1 are connected and then coupled to the output of the NOT gate Ng1. The first terminal of the switch P1 is coupled to the power supply Vcc via the current source Ib1. The second terminal of the switch N1 is grounded to Gnd. The second terminal of the switch P1 and the first terminal of the switch N1 are connected to one terminal of the timing capacitor C1. One terminal of the timing capacitor C1 is also connected to the output terminal P_245. The other terminal of the timing capacitor C1 is grounded to Gnd. The first switching circuit 2412 includes a switch tube P2 and a latch D1. The control end of the switch tube P2 is connected to the output end P_245. Its first end is coupled to the power supply Vcc, and its second end is connected to the ground Gnd via the current source Ib2. The second end is also coupled to one end of the latch D1. The other end of the latch D1 is connected to the output end P_246 of the first delay circuit 241 to serve as the output of the first delay circuit 241.

[0071] The input terminal P_244 of the first timing capacitor circuit 2411 is coupled to the driver unit to receive the logic signal Log output by the driver unit, so that the timing capacitor C1 performs a timing operation based on the logic signal Log. The logic signal Log can reflect the on and off durations of the forward power circuit. The operating principle of the driver unit outputting the logic signal Log will be described in detail later and will not be elaborated here. The first switch circuit 2412 outputs a disable signal Uable via the output terminal P_246 to disable the constant current control unit when the voltage signal on one electrode side of the timing capacitor C1 reaches its threshold voltage.

[0072] The following instructions Figure 11 The working principle of the first delay circuit 241 in the embodiment shown is shown in FIG. Figure 11 For example, if switch N1 is an N-type MOSFET and switches P1 and P2 are P-type MOSFETs, during an on-off cycle T of a forward power circuit, during the off-phase of the forward power circuit, the logic signal Log is low and becomes high after passing through the inverter Ng2, turning switch P1 off and switch N1 on, discharging charging capacitor C1 through switch N1. During the on-phase of the forward power circuit, the logic signal Log is high and becomes low after passing through the inverter Ng1, turning switch P1 on and switch N1 off. Power supply Vcc uses the current value of current source Ib1 as the charging current to charge capacitor C1 through switch P1. If the forward power circuit's on-time exceeds the reference time Tonleb (i.e., the load voltage is higher than the short-circuit protection threshold), the voltage signal at the end of the charging capacitor C1 connected to the output terminal P_245 is higher than the threshold voltage corresponding to the turn-off point of the switch P2, thereby turning the switch P2 off. The low level output from the second end of the switch P2 triggers the latch D1 to output the disable signal Uable. If the forward power circuit's on-time 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 terminal P_245 does not exceed the threshold voltage corresponding to the turn-off point of the switch P2, thereby turning the switch P2 on. The second end of the switch P2 becomes high, and the latch D1 latches the high level to output the disable signal Uable. Among them, the current value of the current source Ib1 determines the charging speed C1 of the charging capacitor. When the threshold voltage of the switch tube P2 remains unchanged, those skilled in the art can set the reference time Tonleb by selecting an appropriate current source Ib1 according to needs.

[0073] It should be noted that Figure 11 The circuit structure of the first delay circuit 241 shown in FIG is only an example. In other embodiments, Figure 11The type and connection mode of each switch tube in the first timing capacitor circuit 2411 shown in FIG can be flexibly selected according to actual conditions and additional electronic components can be matched according to needs. Figure 11 Similar to the one shown, it does not affect Figure 11 The function you want to achieve. Figure 11 The switch tube P2 in the first switch circuit 2422 can also be replaced with other types or other devices and the logic devices required to be matched can be flexibly selected according to the replaced components to achieve the above functions. For example, the first switch circuit 2422 may include a comparator and a latch. One input end of the comparator is coupled to one end of the timing capacitor C1, and the other input end is used to obtain a reference voltage (which can be a voltage signal generated by the power supply Vcc, and its size can be, for example, equal to the threshold voltage of the switch tube P2, which can be set according to actual conditions). When the comparator determines through comparison that one end of the timing capacitor C1 drops to the reference voltage obtained by the comparator, it 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 based on Figure 11 The circuit structure shown is limited to this. As long as the timing of the on or off time of the forward power circuit can be completed based on the charging and discharging of the timing capacitor to output a disable signal, it falls within the scope of the first delay circuit of this application.

[0074] The following is based on Figure 11 The working principle of the first delay circuit 241 is combined with Figure 10 、 Figure 5 、 Figure 6 ,as well as Figure 7To illustrate the working principle of the short-circuit protection unit 24 in one embodiment of the present application, in the constant voltage stage, 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. At this time, once the sampling signal Cs reaches the feedback signal Fb, the constant voltage control unit 21 first outputs the constant voltage control signal Cv to enable the drive unit to control the forward power circuit to turn off. That is, in the constant voltage stage, the sampling signal Cs does not reach the first reference signal Vref1 or the second reference signal Vref2, so that the constant current control unit 22 and the short-circuit protection unit 24 are suspended at this stage. Even if the first delay circuit 241 in the short-circuit protection unit 24 detects that the conduction time of the forward power circuit is shorter than the reference time Tonleb, the third comparison circuit 242 in the short-circuit protection unit 24 cannot output the short-circuit protection signal Pro. In the constant current stage, due to the large load current, the feedback signal Fb is greater than the first reference signal Vref1 and the second reference signal Vref2, and the constant voltage control unit 21 is dormant. When the first delay circuit 241 of the short-circuit protection unit 24 determines that the conduction time of the forward power circuit is less 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 is disabled based on the disable signal Uable, and no longer compares the size of the sampling signal Cs and the first reference signal Vref1. Instead, the third comparison circuit 242 of the short-circuit protection unit 24 compares the size of the sampling signal Cs and the second reference signal Vref2. When the sampling signal Cs reaches the second reference signal Vref2, the comparison signal is output as the short-circuit protection signal Pro. The driving unit 23 disconnects the forward power circuit based on the short-circuit protection signal Pro, thereby realizing short-circuit protection in the constant current stage and will not affect the operation of the forward constant current control device in controlling the forward power circuit in the constant voltage stage.

[0075] According to Figure 3 As can be seen from the description, for the forward power circuit, it converts the input signal Vin into energy under the control of the forward constant current control device to realize the output load power supply. The load power supply output by the forward power circuit is not only related to the shutdown timing (i.e., duty cycle) of the forward constant current control device controlling the forward power circuit, 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, then according to the formula Where Vpro is the short-circuit protection threshold, and N is the primary-to-secondary turns ratio of the transformer in the forward power circuit. It can be seen that the actual short-circuit protection point reached is not the expected short-circuit protection threshold. For example, without considering the possibility of changes in the input signal Vin (e.g., Vin = 230V), and setting the reference duration Tonleb = 0.3ms, the short-circuit protection point reached by the short-circuit protection unit 24 is the expected short-circuit protection threshold of 2.5V, that is, the short-circuit protection is triggered when the load voltage is indeed lower than 2.5V. However, once the input signal Vin fluctuates or changes (for example, Vin = 250V), the short-circuit protection unit 24 still uses the reference time length Tonleb = 0.3ms as the basis 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 short-circuit protection is triggered when the load voltage is lower than 3V. Alternatively, when the input signal Vin decreases (for example, Vin = 210V), the short-circuit protection point reached by the short-circuit protection unit 24 is actually 2V, that is, the short-circuit protection is triggered only when the load voltage is lower than 2V. Whether the short-circuit protection is triggered too early or too late is disadvantageous to the load.

[0076] In view of the above situation, 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 based on the input signal Vin. Figure 12 As shown, Figure 12 The circuit block diagram of another embodiment of the short circuit protection unit of the present application is shown in the figure. As shown in the figure, the short circuit protection unit 24 is Figure 10 The circuit structure shown in FIG. 1 further includes a compensation circuit 243. The compensation circuit 243 obtains the input signal Vin through its input terminal P_247 and couples the first delay circuit ( Figure 12 The compensation circuit 243 compensates the reference time based on the change of the input signal Vin to maintain the stability of the short-circuit protection threshold. When the input signal Vin changes, this can be achieved by changing the reference time length Tonleb according to the opposite change rule. When the input signal Vin increases, the reference time length Tonleb is reduced, and when the input signal Vin decreases, the reference time length Tonleb is increased.

[0077] See also Figure 13, shows a schematic diagram of the circuit structure of the compensation circuit of the present application in one 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 transistors (N2, N3). The second end of the first pair of switching transistors (N2, N3) is grounded Gnd, and the third end is coupled to the first end of the second pair of switching transistors (P3, P4). The second end of the second pair of switching transistors (P3, P4) is coupled to the power supply Vcc, and the third end is coupled to the output terminal P_248 of the compensation circuit 243. The resistor R1 is used to sample the input signal Vin. 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 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. In other words, the current value of charging current Ib3 follows the same changing trend as the input signal Vin: as the input signal Vin increases, the current value of charging current Ib3 increases, and as the input signal Vin decreases, the current value of charging current Ib3 decreases. In practical applications, the charging current Ib3 is output to the timing capacitor in the first delay circuit 241, causing the timing capacitor to charge with the charging current Ib3. As the input signal Vin changes, the charging speed of the timing capacitor changes, thereby changing the reference time duration, thereby maintaining a stable short-circuit protection threshold of the short-circuit protection unit 24.

[0078] Furthermore, the first delay circuit 241 adopts the following Figure 11 When the circuit structure shown is Figure 13 The output terminal P_248 of the compensation circuit 243 is coupled to Figure 11 However, it should be noted that in order to simplify the circuit connection and facilitate adjustment, Figure 11 The first delay circuit 241 shown in FIG. Figure 13 The compensation circuit 243 is shown coupled to Figure 11 The first terminal of the switch tube P2 does not need to be coupled to the power supply Vcc via the current source Ib1.

[0079] The following combination Figure 13 and Figure 11The following describes how the short-circuit protection unit 24 changes the reference time 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 increases, the charging current Ib3 also increases. The first timing capacitor circuit 2411 charges the timing capacitor C1 with the charging current Ib3 during the shutdown period of the forward power circuit. As the charging speed increases, the time it takes 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 switch tube P2 is shortened, and the reference time Tonleb becomes smaller, so that Vin*To in the above formula can be reduced. nleb remains unchanged, and the short-circuit protection threshold remains the short-circuit protection threshold corresponding to before the input signal Vin increases. When the input signal Vin decreases, the charging current Ib3 also decreases. The first timing capacitor circuit 2411 charges the timing capacitor C1 with the charging current Ib3 during the shutdown period of the forward power circuit. Due to the reduced charging speed, the time it takes for the voltage signal at one end of the timing capacitor C1 to reach the threshold voltage corresponding to the turn-off point of the switch tube P2 increases, and the reference time Tonleb increases, so that Vin*Tonleb in the above formula remains unchanged, and the short-circuit protection threshold remains the short-circuit protection threshold corresponding to before the input signal Vin decreases.

[0080] It should also be noted that, when conducting interference tests such as EFT (Electrical Fast Transient / burst), lightning strikes, etc., the peak current flowing through the forward power circuit may instantly increase to the second reference signal Vref2, so that the aforementioned third comparison circuit 242 will output a comparison signal. At this time, if the comparison signal is given to the drive unit as a short-circuit protection signal Pro, the drive unit will control the forward constant current control device to stop working, thereby falsely triggering the short-circuit protection function. In order to avoid false triggering of the short-circuit protection unit due to these interferences, as shown in FIG. Figure 14 As shown in the figure, it is a circuit block diagram of the short circuit protection unit in another embodiment of the present application. As shown in the figure, the short circuit protection unit 24 is Figure 12 or Figure 10 The circuit structure block diagram shown in FIG. 1 also includes a timing circuit 244 ( Figure 14 China-Israel Figure 12(shown as a basis for the circuit architecture of ), here, the third comparison circuit 242 is coupled to the drive unit via path P_249, and is used to output a comparison signal according to the principle described above. Within one cycle, the drive unit controls the forward power circuit to be turned off based on the comparison signal. 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 the output end P_243 of the short-circuit protection unit 24, and is used to count based on the comparison signal output by the third comparison circuit 242, and output the short-circuit protection signal to the drive unit at the end of the timing to control the forward constant current control device to stop 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 has been reached. In this way, only when the comparison signal is outputted in several consecutive cycles, the driving unit will control the forward constant current control device to stop working, thereby effectively enhancing the anti-interference capability of the forward constant current control device.

[0081] Furthermore, for the forward power circuit controlled by the forward constant current control device and operating in the continuous mode, the relationship between the output load power supply Vout and the input signal Vin is: Wherein N is the primary-to-secondary turns ratio of the transformer in the forward power circuit, Ton is the on-time of the forward constant current control device controlling the forward power circuit, and T is an on-off cycle of the forward power circuit. As mentioned above, the forward constant current control device proposed in this application uses the period of the PWM pulse signal as the on-off cycle for controlling the forward power circuit. When the forward constant current control device is working normally, the forward constant current control device controls the on-time of the forward power circuit based on the constant voltage control signal or the constant current control signal to achieve output constant voltage or output constant current. At this stage, the duty cycle of the forward power circuit does not exceed the duty cycle of the PWM pulse signal. In this way, even when the input signal Vin obtained by the forward constant current control device is large, the load can operate within an acceptable power supply range.

[0082] However, when the forward constant current control device is unable to control the conduction time of the forward power circuit (i.e., no constant voltage control signal or constant current control signal appears during the high level period of the PWM pulse signal), for example, due to damage or failure of the external electronic components of the forward constant current control device (such as the optocoupler coupled between the forward power circuit and the forward constant current control device for obtaining load power supply), the received signal (such as the feedback signal corresponding to the failure of the optocoupler) is abnormal, or the constant voltage control unit or constant current control unit is abnormal and cannot output or outputs an abnormal constant voltage control signal or constant current control signal. Then the forward constant current control device cannot change the conduction time (i.e., duty cycle) of the forward power circuit, and can only control the operation of the forward power circuit according to the inherent duty cycle of the PWM pulse signal. However, since the inherent duty cycle of the PWM pulse signal is generally set to be large, when the input signal Vin obtained is also high, the load power supply Vout will be higher than the maximum value that the load can accept, thereby damaging the load.

[0083] In view of this, in another embodiment, the forward constant current control device is Figure 4 or Figure 7 The circuit architecture shown in the figure also includes a duty cycle adjustment unit to adjust the duty cycle of the Figure 7 The circuit architecture shown also includes a duty cycle adjustment unit, for example, see Figure 15 , shown as a circuit block diagram of another embodiment of the present application, the duty cycle adjustment unit 25 has an input terminal P_252 and an output terminal P_251, the input terminal P_252 is used to connect an external resistor R2 to sample the input signal Vin and obtain a sampling signal Vduty (in order to distinguish it from the aforementioned sampling signal Cs reflecting the peak current, the sampling signal Vduty mentioned here will be referred to as the first sampling signal in the future), the output terminal P_251 is coupled to the driving unit 23, and is used to output the duty cycle adjustment signal Duty to the driving unit 23 to control the forward power circuit to shut down when the conduction time of the forward power circuit exceeds the duration threshold, so that the load power supply of the forward power circuit does not exceed the maximum protection threshold Vmax (which corresponds to the maximum power supply that the load can accept). In other words, the duration threshold determines the maximum value that the conduction time of the forward power circuit can reach, that is, it determines the maximum value of the duty cycle. It should be noted that, Figure 15 Just an example, Figure 4 Based on the circuit architecture shown in FIG, the connection mode and working principle of the duty cycle adjustment unit 25 are similar to those of FIG. Figure 15 The same is not shown here again.

[0084] Among them, 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 when the duty cycle adjustment unit 25 is configured with an external resistor R2 of different impedance, the duration threshold is not the same fixed value. In this way, the forward constant current control device has strong applicability.

[0085] In one example, the duty cycle adjustment unit 25 adjusts the duration threshold based on the change of the input signal Vin to maintain the stability of the maximum protection threshold Vmax. Specifically, since the maximum protection threshold Vmax of the forward power circuit follows the aforementioned formula Where Tonmax is the duration threshold. It can be seen that the maximum protection threshold Vmax of the forward power circuit is not only related to the duration threshold of the forward constant current control device controlling the forward power circuit, but also to the input signal Vin. When the input signal Vin changes, the duty cycle adjustment unit 25 adjusts the duration threshold (i.e., adjusts the maximum duty cycle value) based on the change in the input signal Vin, thereby maintaining the maximum protection threshold Vmax. This avoids the situation where, when a fixed maximum duty cycle is set, the input signal Vin increases, leading to late protection (i.e., the load power supply exceeds the maximum load capacity before the forward constant current control device triggers protection), and premature protection (i.e., the load power supply has not yet reached the maximum load capacity before the forward constant current control device has already controlled the forward power circuit to stop operating) due to a decrease in the input signal Vin. Therefore, for the same load, even if the user connects the forward power circuit to a different input signal Vin or the input signal Vin is unstable, the forward constant current control device of the present application can ensure that the maximum protection threshold Vmax remains unchanged, and the load can still be effectively protected.

[0086] In another example, the input signal Vin received by the forward power circuit remains unchanged, and the duty cycle adjustment unit 25 adjusts the duration threshold to be suitable for different maximum protection thresholds Vmax by configuring the external resistor R2 with different impedances. When the input signal Vin remains unchanged, if the duration threshold remains unchanged, the maximum protection threshold Vmax remains unchanged. Therefore, the user can only apply the forward constant current control device to loads with a tolerance above the maximum protection threshold Vmax. For loads with a tolerance below the maximum protection threshold Vmax, the protection is ineffective, resulting in poor adaptability. In this example, the user can configure an external resistor R2 with an appropriate impedance for different loads, thereby making the forward constant current control device highly compatible and applicable to loads with various requirements.

[0087] See also Figure 16, which is a circuit block diagram of the duty cycle adjustment unit of the present application in one embodiment. As shown in the figure, the duty cycle adjustment unit 25 includes a second delay circuit 251 and a current conversion circuit 252. The input of the current conversion circuit 252 serves as the input terminal P_252 of the duty cycle adjustment unit 25 to obtain the first sampling signal Vduty. The current conversion circuit 252 is coupled to the input of the second delay circuit 251 via its output terminal P_253 to convert the first sampling signal Vduty into an input current and output it to the second delay circuit 251. The output of the second delay circuit 251 serves as the output terminal P_251 of the duty cycle adjustment unit 25, and is used to output the duty cycle adjustment signal Duty when it is determined that the conduction time of the forward power circuit exceeds the time threshold based on the input current. The input current is associated with the time threshold.

[0088] See also Figure 17 , shows a schematic diagram of the circuit structure of the current conversion circuit of the present application in one embodiment. As shown in the figure, the current conversion 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 input terminal P_252 of the duty cycle adjustment unit 25, and the other end is coupled to the first end of the first pair of switching transistors (N4, N5). The second end of the first pair of switching transistors (N4, N5) is grounded Gnd, and the third end is coupled to the first end of the second pair of switching transistors (P5, P6). The second end of the second pair of switching transistors (P5, P6) is coupled to the power supply Vcc, and the third end is coupled to the output terminal P_253 of the current conversion circuit 252. The resistor R3 converts the first sampling signal Vduty into a current signal. 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, which outputs the input current Ib4 to the second delay circuit 251 at the output terminal P_253 of the current conversion circuit 252 using the current signal. In other words, the current value of input current Ib4 follows the same changing trend as the first sampling signal Vduty: when the first sampling signal Vduty increases, the current value of input current Ib4 increases, and when the first sampling signal Vduty decreases, the current value of input current Ib4 decreases. In practical applications, input current Ib4 is output to the timing capacitor in the second delay circuit 251, causing the timing capacitor to charge with input current Ib4. As the first sampling signal Vduty changes, the threshold duration is changed by varying the charging speed of the timing capacitor. This achieves the purpose of adjusting the maximum duty cycle, enhancing the applicability of the forward constant current control device and maintaining a stable maximum protection threshold.

[0089] See also Figure 18, which is a schematic diagram of the circuit structure of a second delay circuit in one embodiment of the present application. 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 circuit 2511 has an input terminal P_254 and an output terminal P_255. The second timing capacitor circuit 2511 includes a NOT gate Ng2, switches N6 and P7, and a timing capacitor C2. The input of the NOT gate Ng2 serves as the input terminal P_254 of the second timing capacitor circuit 2511. The control terminals of the switches N6 and P7 are connected and then coupled to the output of the NOT gate Ng2. The first terminal of the switch P7 is coupled to the output terminal P_253 of the current conversion circuit 252. The second terminal of the switch N6 is grounded to Gnd. The second terminal of the switch P7 and the first terminal of the switch N6 are connected to one end of the timing capacitor C2. One end of the timing capacitor C2 is also connected to the output terminal P_255. The other end of the timing capacitor C2 is grounded to Gnd. The second switch circuit 2512 includes a switch tube P8 and a NOT gate Ng3. The control end of the switch tube P2 is connected to the output end P_255. Its first end is coupled to the power supply Vcc, and its second end is connected to the ground Gnd via the current source Ib5. The second end is also coupled to one end of the NOT gate Ng3. The other end of the NOT gate Ng3 is connected to the output end P_251 of the duty cycle adjustment unit 25 to serve as the output of the duty cycle adjustment unit 25.

[0090] The input terminal P_254 of the second timing capacitor circuit 2511 is coupled to the driver unit to receive the logic signal Log output by the driver unit, causing the timing capacitor C2 to perform a timing operation based on the logic signal Log. The logic signal Log can reflect the on- and off-times of the forward power circuit. The operating principle of the driver unit outputting the logic signal Log will be described in detail later and will not be elaborated here. When the voltage signal on one electrode side of the timing capacitor C2 reaches its threshold voltage, it indicates that the on-time of the forward power circuit has reached the maximum protection threshold Vmax, and the second switch circuit 2512 outputs the duty cycle adjustment signal Duty via the output terminal P_251.

[0091] It should be noted that Figure 18 The circuit structure of the second delay circuit 251 shown in FIG is only an example. In other embodiments, Figure 18 The type and connection mode of each switch tube in the second timing capacitor circuit 2511 shown in FIG can be flexibly selected according to actual conditions and additional electronic components can be matched according to needs. Figure 18 The same is shown, and does not affect the function to be achieved by the second delay circuit 251 of the present application. Figure 18The switch tube P8 in the second switch circuit 2512 can also be replaced with other types or other devices and the logic devices required to be matched can be flexibly selected according to the replaced components to achieve the above functions. For example, the second switch circuit 2512 may include a comparator, one input end of the comparator is coupled to one end of the timing capacitor C1, and the other input end is used to obtain a reference voltage (which can be a voltage signal generated by the power supply Vcc, and its size can be, for example, equal to the threshold voltage of the switch tube P8, which can be set according to actual conditions). When the comparator determines through comparison that one end of the timing capacitor C1 reaches the reference voltage obtained by the comparator, it outputs the duty cycle adjustment signal Duty. The second delay circuit of the present application is not based on Figure 18 The circuit structure shown is limited to this. As long as the timing of the on or off time of the forward power circuit can be completed based on the charging and discharging of the timing capacitor to output the duty cycle adjustment signal Duty, it falls within the scope covered by the second delay circuit of this application.

[0092] The following instructions Figures 16 to 18 The figure shows the working principle of the duty cycle adjustment circuit in one embodiment to realize the load protection function. Figure 18For example, if switch N6 is an N-type MOSFET and switches P7 and P8 are P-type MOSFETs, during an on-off cycle T of the forward power circuit, the current conversion circuit 252 acquires the first sampling signal Vduty and converts it into an input current Ib4. During the off-phase of the forward power circuit, the logic signal Log is low and becomes high after passing through the NOT gate Ng2 in the second delay circuit 251. Switch P7 is turned off, switch N6 is turned on, and charging capacitor C2 is discharged through switch N6. During the on-phase of the forward power circuit, the logic signal Log is high and becomes low after passing through the NOT gate Ng2. Switch P7 is turned on, switch N6 is turned off, and input current Ib4 converted by the current conversion circuit 252 flows into switch P7 to charge charging capacitor C2. If the voltage signal at the end of the charging capacitor C2 connected to the output terminal P_255 reaches the threshold voltage corresponding to the turn-off point of the switch P8, it indicates that the on-time has reached the threshold time and the load power supply has reached the maximum protection threshold Vmax, thus turning off the switch P8. The second end of the switch P8 outputs a low level, causing the inverter Ng3 to output a high level as the duty cycle adjustment signal Duty, causing the drive unit to shut down the forward power circuit based on this signal. If the voltage signal at the end of the charging capacitor C2 connected to the output terminal P_255 does not exceed the threshold voltage corresponding to the turn-off point of the switch P8, the switch P8 remains on, and the second end of the switch P8 remains high, causing the inverter Ng3 to output a low level. It should be noted that the current value of input current Ib4 determines the charging speed of charging capacitor C2, and thus the threshold duration varies based on changes in input current Ib4. Input current Ib4 is associated with the first sampling signal Vduty obtained by current conversion circuit 252. Therefore, when the first sampling signal Vduty changes, input current Ib4 changes, and the threshold duration also changes. For the relationship between the threshold duration and the first sampling signal Vduty, and how to make the forward constant current control device achieve strong adaptability and maintain the maximum protection threshold stability, please refer to the following. Figures 15 to 17 The description will not be repeated here.

[0093] like Figure 4 、 Figure 7 、 Figure 15 As shown, the constant voltage control signal Cv output by the constant voltage control unit 21, the constant current control signal Cc output by the constant current control unit 22, the short circuit protection signal Pro output by the short circuit protection unit 24, and the duty cycle adjustment signal Duty output by the duty cycle adjustment unit 25 are all output to the driving unit 23. The driving unit 23 outputs a logic signal Log based on at least one of the signals to control the forward power circuit to be turned on or off based on the logic signal Log to perform energy conversion to achieve the above functions.

[0094] See also Figure 19, shows a waveform diagram of the logic signal output by the drive unit of the present application based on various signals, as shown in the figure, where PWM is a PWM pulse signal generated internally by the drive unit, which makes the logic signal Log output by the drive unit have a fixed period T, that is, the timing when the logic signal Log becomes high is determined by the PWM pulse signal. Based on the high level of the logic signal Log, the drive unit controls the forward power circuit to be in the on state. The length of time that 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 at least one of the constant voltage control signal Cv, the constant current control signal Cc, the short-circuit protection signal Pro, and the duty cycle adjustment signal Duty. Based on the low level of the logic signal Log, the drive unit controls the forward power circuit to be in the off state. When the load current I is less than the preset constant current value Io during normal operation, the constant voltage control unit 21 outputs the constant voltage control signal Cv, and the drive unit determines the timing when the logic signal Log becomes low based on the constant voltage control signal Cv. During normal operation when the load current I is greater than the preset constant current value Io, the constant current control unit 22 outputs the constant current control signal Cc, and the driving unit determines the timing when the logic signal Log becomes low based on the constant current control signal Cc. During this period, once the load power supply is lower than the short-circuit protection threshold Vpro (i.e., the load voltage is low and the current is large), the short-circuit protection signal Pro output by the short-circuit protection unit 24, the driving unit determines the timing when the logic signal Log becomes low based on the short-circuit protection signal Pro. During the output constant voltage or output constant current period, once the load power 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 the duty cycle adjustment signal Duty, and the driving unit determines the timing when the logic signal Log becomes low based on the duty cycle adjustment signal Duty. It should be noted that Figure 19 The occurrence of the duty cycle adjustment signal Duty during the period when the load current is less than the preset constant current value is only an example and does not limit the timing of the occurrence of the duty cycle adjustment signal Duty. In fact, if the load power supply is greater than the maximum protection threshold Vmax during the period when the load current is greater than the preset constant current value, the duty cycle adjustment signal Duty may also appear during the period when the load current is greater than the preset constant current value. In addition, when the short-circuit protection signal Pro or the duty cycle adjustment signal Duty appears, it indicates that the forward constant current control device is operating in an abnormal state, and the logic signal output by the drive unit remains at a low level for a preset period of time (for example, 100T) or remains at a low level. Figure 19 In order to illustrate the control timing of each signal, the logic signal Log is not shown in this state, and those skilled in the art should not be limited to the diagram.

[0095] See also Figure 20, which is a circuit block diagram of a driving unit in one embodiment of the present application. As shown in the figure, the driving unit 23 includes a PWM generating circuit 231, a logic circuit 232, and a driving circuit 233. The output end of the PWM generating circuit 231 is coupled to the logic circuit 232 to output the PWM pulse signal to the logic circuit 232. The logic circuit 232 is coupled to the output end P_213 of the constant voltage control unit 21, the output end P_222 of the constant current control unit 22, the output end P_243 of the short-circuit protection unit 24, and the output end P_251 of the duty cycle adjustment unit 25, thereby outputting a logic signal Log based on at least one of the constant voltage control signal Cv, the constant current control signal Cc, the short-circuit protection signal Pro, and the duty cycle adjustment signal Duty and the PWM pulse signal. The driving circuit 233 is connected to the output of the logic circuit 232 to control the forward power circuit to be turned on or off based on the logic signal Log to achieve the above functions. For its specific implementation method and the relationship between each signal, please refer to the embodiment of the present invention. Figure 19 The description of the waveform diagram is omitted here. Wherein, the logic circuit 232 includes but is not limited to a trigger, a timer, a selector, an AND gate, or a NOT, etc. according to the control logic, and this application does not limit this.

[0096] To sum up, the forward constant current control device proposed in this application can control the forward power circuit to switch from output constant voltage to output constant current when the load current exceeds the preset constant current value. It can be suitable for high-power loads with constant current power supply requirements. In addition, by setting a short-circuit protection unit, short-circuit protection can be achieved in the constant current stage to avoid the load voltage being too low and the current being too large to burn the load. By setting a duty cycle adjustment unit, the forward constant current control device can provide protection when the load power supply exceeds the maximum value that the load can withstand, and it has strong applicability.

[0097] The present application also discloses a control chip, which is packaged with a forward constant current control device as described in any of the above embodiments. The control chip also includes a plurality of pins. In one embodiment, the chip is packaged with the above-mentioned constant current control unit, constant voltage control unit, and drive unit, and the plurality of pins include a first pin for obtaining a sampling signal reflecting the peak current of the forward power circuit, a second pin for obtaining a feedback signal reflecting the load current, a third pin for outputting a drive signal, a fourth pin for obtaining a chip power supply, and a fifth pin for grounding. In another embodiment, the chip is packaged with the above-mentioned constant current control unit, constant voltage control unit, short-circuit protection unit, and drive unit, and the plurality of pins include a first pin for obtaining a sampling signal reflecting the peak current of the forward power circuit, a second pin for obtaining a feedback signal reflecting the load current, a third pin for obtaining an input signal of the forward power circuit, a fourth pin for obtaining a chip power supply, and a fifth pin for grounding. In another embodiment, the chip package includes the above-mentioned constant current control unit, constant voltage control unit, short circuit protection unit, duty cycle adjustment unit, and drive unit, and the plurality of pins include a first pin for obtaining a first sampling signal obtained by sampling a rectified input signal, a second pin for obtaining a sampling signal reflecting the peak current of the forward power circuit, a third pin for obtaining a feedback signal, a fourth pin for outputting a drive signal, a fifth pin for obtaining a rectified input signal, a sixth pin for obtaining a chip power supply, and a seventh pin for grounding. For the modules and circuits in each embodiment, please refer to the aforementioned description of the modules and circuits. Figures 4 to 20 The description will not be repeated here.

[0098] This application also discloses a forward constant current switching power supply, see Figure 21 , which is a circuit block diagram of the forward constant current switching power supply of the present application in one embodiment. As shown in the figure, the forward constant current switching power supply 30 includes a rectifier circuit 31, a filter circuit 32, a forward constant current control device 33, a switching device 34, and a forward power circuit 35.

[0099] The rectifier circuit 31 is configured to receive an external drive signal and output a rectified signal. The external drive signal may be, for example, an AC signal output from a mains power grid, or a DC signal. The rectifier circuit 31 may employ a full-wave rectifier circuit or a half-wave rectifier circuit composed of electronic components such as diodes to rectify the received external drive signal and output a rectified signal.

[0100] 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 and output the filtered signal to the forward power circuit 35. In an embodiment, the filter circuit 32 may be a π-type filter circuit, an LC-type filter circuit, an RC-type filter circuit, an LCπ-type filter circuit, an RCπ-type filter circuit, etc., and this application does not impose any limitation thereto.

[0101] The forward constant current control device 33 is used to output a driving signal. The forward constant current control device 33 can adopt the forward constant current control device disclosed in the present application. For its structure and working principle, please refer to the embodiment of the present invention. Figures 4 to 20 The description will not be repeated here.

[0102] The control terminal of the switching device 34 is coupled to the forward constant current control device 33, and is used to turn on or off based on the drive signal. In an embodiment, the switching device refers to 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 conduction or shutoff between the first terminal and the second terminal based on the received drive signal. The three-terminal controllable device includes a controllable transistor, and the controllable transistor can be exemplified by a metal-oxide-semiconductor field-effect transistor (MOSFET) or a bipolar junction transistor (BJT).

[0103] The forward power circuit 35 is coupled between the filter circuit 32 and the switch device 34 and is configured to convert energy from a received input signal based on the on / off state of the switch device 34, thereby switching from outputting a constant voltage to outputting a constant current when the load current reaches a preset constant current value. The input signal is the filtered signal. It should be noted that in some embodiments, the filter circuit 32 may not be included. In this case, the forward power circuit 35 is coupled between the rectifier circuit 31 and the switch device 34, and the input signal received by the forward power circuit 35 is the rectified signal.

[0104] The present application also discloses a forward constant current control method, which is applied to a forward constant current control device using pulse width modulation. The forward constant current control method includes steps S20, S21, S22, and S23 (not shown).

[0105] In step S20 , the forward constant current control device obtains a feedback signal and a sampling signal.

[0106] See the Figure 4 、 Figure 7 ,as well as Figure 15 The forward constant current control device includes a constant voltage control unit, a constant current control unit, and a drive unit. The constant voltage control unit obtains a feedback signal and a sampling signal, and the constant current control unit obtains the sampling signal. The feedback signal reflects the load current of the forward power circuit controlled by the forward constant current control device, and the sampling signal reflects the peak current of the forward power circuit.

[0107] In step S21, the constant voltage control unit outputs a constant voltage control signal based on the feedback signal and the sampling signal during the period when the load current is less than the preset constant current value. Under the control of the constant voltage control signal, the forward power circuit outputs constant voltage power to the load.

[0108] In some embodiments, the constant voltage control unit compares the sampling signal and the feedback signal to output the constant voltage control signal during the period when the feedback signal is less than the first reference signal, wherein the first reference signal reflects the preset constant current value. Figure 4 and Figure 5 The description is not repeated here.

[0109] In step S22, when the load current reaches the preset constant current value, a constant current control signal is output based on the sampling signal, and under the control of the constant current control signal, the forward power circuit outputs constant current power to the load.

[0110] In some embodiments, when the feedback signal is less than the first reference signal, the constant current control unit compares the sampling signal with the first reference signal to output the constant current control signal, wherein the first reference signal reflects the preset constant current value. Figure 4 and Figure 6 The description is not repeated here.

[0111] During the constant current output phase of the forward power circuit, the load current is stabilized at a preset constant current value. Therefore, the load voltage will change with changes in the load resistance. If the load voltage is too low and the load resistance is too small, the load will still maintain the preset constant current value, which will exceed the maximum value that the load can withstand, thereby damaging the load.

[0112] For this reason, please refer to Figure 7 The forward constant current control device further includes a short circuit protection unit. The short circuit protection unit outputs a short circuit protection signal during the period when the load voltage is lower than the short circuit protection threshold to control the forward power circuit to achieve short circuit protection in the constant current stage. The circuit structure and working principle of the short circuit protection unit can be found in the Figures 7 to 14 The description will not be repeated here.

[0113] In step S23 , the driving unit drives the forward power circuit to switch from outputting constant voltage to outputting constant current when the load current reaches a preset constant current value based on the constant voltage control signal or the constant current control signal.

[0114] See the Figure 4 、 Figure 7 、 Figure 15 As can be seen from the description, the drive unit is connected to the constant voltage control unit, the constant current control unit, the short circuit protection unit, and the duty cycle adjustment unit, so that the drive unit outputs a logic signal based on at least one of the signals output by each unit to control the forward power circuit to turn on or off based on the logic signal so as to switch from outputting constant voltage to outputting constant current when the load current reaches a preset constant current value, and can achieve protection when the load power supply exceeds the maximum value that the load can withstand during the constant voltage period and achieve short circuit protection during the constant current period. The circuit structure and working principle of the drive unit can be referred to the circuit structure and working principle of the drive unit. Figure 19 and Figure 20 The description will not be repeated here.

[0115] From steps S20 to S23, it can be seen that the forward constant current control device proposed in this application uses the period of the PWM pulse signal output by pulse width modulation as the on-off period of the forward power circuit. When the forward constant current control device is working normally, the forward constant current control device controls the on-time of the forward power circuit based on the constant voltage control signal or the constant current control signal to achieve output constant voltage or output constant current. At this stage, the duty cycle of the forward power circuit does not exceed the duty cycle of the PWM pulse signal. In this way, even when the input signal obtained by the forward constant current control device is large, the load can operate within an acceptable power supply range.

[0116] However, when the forward constant current control device is unable to control the conduction time of the forward power circuit (i.e., no constant voltage control signal or constant current control signal appears during the high level period of the PWM pulse signal), for example, due to damage or failure of the external electronic components of the forward constant current control device (such as the optocoupler coupled between the forward power circuit and the forward constant current control device for obtaining load power supply), the received signal (such as the feedback signal corresponding to the failure of the optocoupler) is abnormal, or the constant voltage control unit or constant current control unit is abnormal and cannot output or outputs an abnormal constant voltage control signal or constant current control signal. Then the forward constant current control device cannot change the conduction time (i.e., duty cycle) of the forward power circuit, and can only control the operation of the forward power circuit according to the inherent duty cycle of the PWM pulse signal. However, since the inherent duty cycle of the PWM pulse signal is generally set to be large, when the input signal obtained is also high, the load power supply will be higher than the maximum value that the load can accept, thereby damaging the load.

[0117] In view of this, the forward constant current control method also includes step S24 (not shown in the figure). In step S24, when the forward constant current control device determines that the conduction time of the forward power circuit exceeds the preset time threshold (that is, when the load power supply exceeds the maximum protection threshold), it outputs a duty cycle adjustment signal to control the forward power circuit to shut down.

[0118] In one embodiment, see Figure 15 The forward constant current control device further includes a duty cycle adjustment unit. When the duty cycle adjustment unit determines that the conduction time of the forward power circuit exceeds the preset time threshold (i.e., when the load power supply exceeds the maximum protection threshold), the forward constant current control device outputs a duty cycle adjustment signal to control the forward power circuit to shut down. For the circuit structure and working principle of the duty cycle adjustment unit, please refer to the Figures 15 to 18 The description will not be repeated here.

[0119] To sum up, the forward constant current control device, system, control method and chip proposed in this application can control the forward power circuit to switch from output constant voltage to output constant current when the load current exceeds the preset constant current value. It can be suitable for high-power loads with constant current power supply requirements. In addition, by setting a short-circuit protection unit, short-circuit protection can be achieved in the constant current stage to avoid the load voltage being too low and the current being too large to burn the load. By setting a duty cycle adjustment unit, the forward constant current control device can provide protection when the load power supply exceeds the maximum value that the load can withstand, and it has strong applicability.

[0120] The above embodiments are merely illustrative of the principles and effects of this application and are not intended to limit this application. Anyone skilled in the art may modify or alter the above embodiments without departing from the spirit and scope of this application. Therefore, all equivalent modifications or alterations made by one of ordinary skill in the art without departing from the spirit and technical concepts disclosed in this application shall be covered by the claims of this application.

Claims

1. A forward constant current control device, characterized in that: Used to control a forward power circuit to perform energy conversion, including: A constant voltage control unit, configured to output a constant voltage control signal based on an acquired feedback signal and a sampling signal during a period when the load current is less than a preset constant current value; wherein the feedback signal reflects the load current of the forward power circuit, and the sampling signal reflects the peak current of the forward power circuit; A constant current control unit, configured to output a constant current control signal based on the sampling signal when the load current reaches the preset constant current value; a driving unit, coupled to the constant voltage control unit and the constant current control unit, for driving the forward power circuit to output constant voltage power supply to the load or constant current power supply to the load based on the constant voltage control signal or the constant current control signal; A short-circuit protection unit is coupled to the drive unit and is used to output a short-circuit protection signal to the drive unit during a period when the load voltage is lower than a short-circuit protection threshold to control the forward power circuit to achieve short-circuit protection during the constant current power supply stage to the load; the short-circuit protection unit includes a first delay circuit coupled to the constant current control unit and a third comparison circuit coupled to the drive unit, the first delay circuit is used to disable the constant current control unit when the conduction time of the forward power circuit is lower than a reference time associated with the short-circuit protection threshold, and the third comparison circuit is used to compare the sampling signal and the second reference signal to output a comparison signal as the short-circuit protection signal to the drive unit.

2. The forward constant current control device according to claim 1, characterized in that: The constant current control unit includes a first comparison circuit for comparing the sampling signal with a first reference signal to output the constant current control signal; wherein the first reference signal reflects the preset constant current value.

3. The forward constant current control device according to claim 2, characterized in that: The constant voltage control unit includes a second comparison circuit, configured to compare the sampling signal and the feedback signal to output the constant voltage control signal during a period when the feedback signal is less than the first reference signal.

4. The forward constant current control device according to claim 1, characterized in that: The short-circuit protection unit is further configured to maintain the stability of the short-circuit protection threshold based on the acquired rectified input signal.

5. The forward constant current control device according to claim 1, characterized in that: The first delay circuit includes: A first timing capacitor circuit includes a timing capacitor for performing a timing operation; The first switch circuit is coupled to the first timing capacitor circuit and is configured to disable the constant current control unit when a voltage signal at an electrode side of the timing capacitor reaches a threshold voltage of the switch circuit.

6. The forward constant current control device according to claim 1, characterized in that: The short-circuit protection unit further includes a compensation circuit coupled to the first delay circuit, configured to compensate the reference duration based on a change in the acquired rectified input signal to maintain the stability of the short-circuit protection threshold.

7. The forward constant current control device according to claim 6, characterized in that: The compensation circuit changes the reference time by changing the charging speed of a timing capacitor.

8. The forward constant current control device according to claim 1, characterized in that: The short-circuit protection unit further includes: a timing circuit coupled to the third comparison circuit and the driving unit, for timing based on the comparison signal, and outputting the short-circuit protection signal to the driving unit when the timing ends to control the forward constant current control device to stop working.

9. The forward constant current control device according to claim 1, characterized in that: Also includes: The duty cycle adjustment unit is coupled to the driving unit and is used to output a duty cycle adjustment signal to the driving unit to control the forward power circuit to be turned off when the on-time of the forward power circuit exceeds a time threshold.

10. The forward constant current control device according to claim 9, characterized in that: The driving unit includes: A PWM generating circuit, used for generating a PWM pulse signal; a logic circuit coupled to at least one of the constant voltage control unit, the constant current control unit, the short circuit protection unit, and the duty cycle adjustment unit, and the PWM generation circuit, and configured to output a logic signal based on at least one of the PWM pulse, the constant voltage control signal, the constant current control signal, the short circuit protection signal, and the duty cycle adjustment signal; The driving circuit is coupled to the logic circuit and is used to output a driving signal based on the logic signal to control the forward power circuit to be turned on or off to perform energy conversion.

11. A control chip, characterized in that: The chip package is provided with the forward constant current control device according to any one of claims 1 to 10.

12. A forward constant current switching power supply, characterized in that: include: a rectifier circuit, configured to receive an external driving signal and output a rectified signal; a filter circuit, coupled to the rectifier circuit, for filtering the rectified signal to output a filtered signal; The forward constant current control device according to any one of claims 1 to 10, configured to output a drive signal; a switch device, a control terminal of which is coupled to the forward constant current control device, and is configured to be turned on or off based on the drive signal; A forward power circuit is coupled to the switching device and is used to convert energy of a received input signal based on the on or off state of the switching device so as to switch from outputting a constant voltage to outputting a constant current when the load current reaches a preset constant current value; wherein the input signal is the filtered signal.

13. A forward constant current control method, characterized in that: The forward constant current control device according to any one of claims 1 to 10 is used to control a forward power circuit to perform energy conversion, comprising the following steps: Obtain feedback signals and sampling signals; Outputting a constant voltage control signal based on the feedback signal and the sampling signal during a period when the load current is less than a preset constant current value; wherein the feedback signal reflects the load current of the forward power circuit, and the sampling signal reflects the peak current of the forward power circuit; outputting a constant current control signal based on the sampling signal when the load current reaches the preset constant current value; Based on the constant voltage control signal or the constant current control signal, the forward power circuit is driven to output constant voltage power supply to the load or constant current power supply to the load; wherein a short-circuit protection signal is output during the period when the load voltage is lower than the short-circuit protection threshold to control the forward power circuit to achieve short-circuit protection in the constant current stage.

14. The forward constant current control method according to claim 13, characterized in that: The method further includes the step of outputting a duty cycle adjustment signal to control the forward power circuit to be turned off when the conduction time of the forward power circuit exceeds a preset time threshold.

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