Isolated switching power supply and control method of secondary side controller thereof

Abstract

The invention relates to an isolated switching power supply and a control method of a secondary side controller thereof, the power supply comprises a transformer, a power level circuit, a primary side controller, a secondary side controller and a coupling element, the transformer comprises a primary side winding and a secondary side winding; the power level circuit comprises a primary side switching device; the secondary side controller is used for determining a pulse width modulation frequency for the primary side switching device based on the output power of the secondary side winding when the power supply is in a continuous current working mode, and generating a first pulse width modulation control signal based on the pulse width modulation frequency; the coupling element is used for transmitting the first pulse width modulation control signal to the primary side controller; and the primary side controller is used for controlling on and off of the primary side switching device based on the first pulse width modulation control signal. According to the isolation type switching power supply, a power supply framework of secondary side sampling and secondary side control is realized, and PWM frequency control of full load and full frequency, medium load and underclocking and light load and low frequency can be realized.

Description

Technical Field

[0001] The present application relates to the technical field of isolated switching power supplies, and more specifically to a control method of an isolated switching power supply and a secondary side controller thereof. Background Art

[0002] For the power supply architecture of isolated switching power supply, according to the respective functions of primary side and secondary side, there are traditionally two types of architectures: the first type of architecture is primary side sampling and primary side control, and the second type of architecture is secondary side sampling and primary side control.

[0003] Among them, for the power supply architecture with primary side sampling and primary side control, the main power switch is on the primary side, and the pulse width modulation (PWM) control chip (IC) of the primary side indirectly samples the output voltage and / or output current to control the opening and closing of the main switch of the primary side, so as to achieve the purpose of stabilizing the output. For the power supply architecture with secondary side sampling and primary side control, the main power switch is on the primary side, and the error amplifier directly samples the output voltage and / or output current on the secondary side, and transmits the sampling result (called the error signal output by the error amplifier) ​​to the PWM control IC of the primary side through the isolation device, and then uses this error signal to control the opening and closing of the main switch of the primary side, so as to achieve the purpose of stabilizing the output.

[0004] Since the output voltage and output current are measured indirectly, the output voltage control accuracy of the first architecture (primary sampling, primary control) is lower than that of the second architecture (secondary sampling, primary control), and it is even more difficult to achieve accurate output current control; at the same time, indirect measurement is more prone to failure in short-circuit testing, resulting in system control failure. The second architecture (secondary sampling, primary control) usually uses an optocoupler to transmit error information from the secondary side to the primary side. The aging of the optocoupler causes voltage drift and loop gain changes, which deteriorates the stability of the system. At the same time, the optocoupler requires a static bias current, which increases the difficulty of further reducing the standby power consumption of the system. Summary of the invention

[0005] The present application is proposed to solve the above problems. According to one aspect of the present application, an isolated switching power supply is provided, the power supply comprising a transformer, a power stage circuit, a primary controller, a secondary controller and a coupling element, wherein: the transformer comprises a primary winding and a secondary winding; the power stage circuit comprises a primary switching device; the secondary controller is used to determine a pulse width modulation frequency for the primary switching device based on the output power of the secondary winding when the power supply is in a continuous current working mode, and to generate a first pulse width modulation control signal based on the pulse width modulation frequency; the coupling element is used to transmit the first pulse width modulation control signal to the primary controller; the primary controller is used to control the on and off of the primary switching device based on the first pulse width modulation control signal.

[0006] In one embodiment of the present application, the secondary controller determines the pulse width modulation frequency for the primary switching device based on the output power of the secondary winding, including: the secondary controller determines the pulse width modulation frequency for the primary switching device based on the output power of the secondary winding according to a first corresponding relationship, wherein the first corresponding relationship refers to the corresponding relationship between the output power and the pulse width modulation frequency.

[0007] In one embodiment of the present application, the first corresponding relationship is preset or configurable.

[0008] In one embodiment of the present application, the first corresponding relationship includes a linear corresponding relationship.

[0009] In one embodiment of the present application, the secondary side controller generates a first pulse width modulation control signal based on the pulse width modulation frequency, including: the secondary side controller calculates the on-time of the primary side switching device based on the pulse width modulation frequency and the duty cycle, and generates the first pulse width modulation control signal based on the on-time.

[0010] In one embodiment of the present application, the secondary controller is also used to determine the peak current for the primary switching device based on the output power of the secondary winding when the power supply is in the discontinuous current operating mode, and generate a second pulse width modulation control signal based on the peak current; the coupling element is also used to transmit the second pulse width modulation control signal to the primary controller; the primary controller is also used to control the conduction and shutdown of the primary switching device based on the second pulse width modulation control signal.

[0011] In one embodiment of the present application, the secondary controller determines the peak current for the primary switching device based on the output power of the secondary winding, including: the secondary controller determines the peak current for the primary switching device based on the output power of the secondary winding according to a second corresponding relationship, wherein the second corresponding relationship refers to the corresponding relationship between output power and peak current.

[0012] In one embodiment of the present application, the second corresponding relationship is preset or configurable.

[0013] In one embodiment of the present application, the second corresponding relationship includes a linear corresponding relationship.

[0014] In one embodiment of the present application, the secondary controller generates a second pulse width modulation control signal based on the peak current, including: the secondary controller calculates the on-time of the primary switching device based on the inductance of the primary winding, the peak current and the input voltage of the primary winding, and generates the second pulse width modulation control signal based on the on-time.

[0015] In one embodiment of the present application, the secondary-side controller is further configured to determine the working mode of the power supply based on a pulse width modulation control signal of the primary-side switching device.

[0016] In one embodiment of the present application, the secondary controller determines the operating mode of the power supply based on the pulse width modulation control signal of the primary switching device, including: when the pulse width modulation control signal changes from a high level to a low level, it is determined that the power supply is in the discontinuous current operating mode; when the pulse width modulation control signal changes from a low level to a high level and the output current of the secondary winding is greater than zero, it is determined that the power supply is in the continuous current operating mode.

[0017] In one embodiment of the present application, the secondary side controller is further used to set the pulse width modulation frequency used for the primary side switching device to be greater than or equal to a preset frequency value when the output power is greater than or equal to a preset threshold value to eliminate audio noise.

[0018] In one embodiment of the present application, the power supply further includes a secondary side switch device for synchronous rectification, and the secondary side controller is further used to generate a control instruction for controlling the switching on and off of the secondary side switch device.

[0019] In one embodiment of the present application, the power supply is applicable to any one of the following topologies: forward converter topology, flyback converter topology, half-bridge topology, and full-bridge topology.

[0020] According to another aspect of the present application, a control method for a secondary controller of an isolated switching power supply is provided, the control method comprising: collecting the output voltage and output current of the secondary winding of the transformer of the isolated switching power supply, and obtaining the output power based on the output voltage and the output current; when the power supply is in a continuous current working mode, determining the pulse width modulation frequency of the primary switching device of the power supply based on the output power, and generating a first pulse width modulation control signal based on the pulse width modulation frequency, so as to transmit the signal to the primary controller of the power supply to control the on and off of the primary switching device.

[0021] In one embodiment of the present application, determining the pulse width modulation frequency of the primary switching device used for the power supply based on the output power includes: determining the pulse width modulation frequency of the primary switching device used for the power supply based on the output power according to a first corresponding relationship, wherein the first corresponding relationship refers to the corresponding relationship between the output power and the pulse width modulation frequency.

[0022] In one embodiment of the present application, the first corresponding relationship is preset or configurable.

[0023] In one embodiment of the present application, the first corresponding relationship includes a linear corresponding relationship.

[0024] In one embodiment of the present application, generating the first pulse width modulation control signal based on the pulse width modulation frequency includes: calculating the on-time of the primary switching device based on the pulse width modulation frequency and the duty cycle, and generating the first pulse width modulation control signal based on the on-time.

[0025] In one embodiment of the present application, the method also includes: when the power supply is in a discontinuous current operating mode, determining a peak current for the primary switching device based on the output power, and generating a second pulse width modulation control signal based on the peak current to be transmitted to the primary controller to control the conduction and shutdown of the primary switching device.

[0026] In one embodiment of the present application, determining the peak current for the primary switching device based on the output power includes: determining the peak current for the primary switching device based on the output power according to a second corresponding relationship, wherein the second corresponding relationship refers to the corresponding relationship between the output power and the peak current.

[0027] In one embodiment of the present application, the second corresponding relationship is preset or configurable.

[0028] In one embodiment of the present application, the second corresponding relationship includes a linear corresponding relationship.

[0029] In one embodiment of the present application, generating a second pulse width modulation control signal based on the peak current includes: calculating the on-time of the primary switching device based on the inductance of the primary winding of the transformer, the peak current and the input voltage of the primary winding, and generating a second pulse width modulation control signal based on the on-time.

[0030] In one embodiment of the present application, the method further includes: determining the working mode of the power supply based on a pulse width modulation control signal of the primary switching device.

[0031] In one embodiment of the present application, the operating mode of the power supply is determined based on the pulse width modulation control signal of the primary switching device, including: when the pulse width modulation control signal changes from a high level to a low level, it is determined that the power supply is in the discontinuous current operating mode; when the pulse width modulation control signal changes from a low level to a high level and the output current of the secondary winding is greater than zero, it is determined that the power supply is in the continuous current operating mode.

[0032] In one embodiment of the present application, the method further includes: when the output power is greater than or equal to a preset threshold, setting the pulse width modulation frequency used for the primary switching device to be greater than or equal to a preset frequency value to eliminate audio noise.

[0033] The isolated switching power supply of the present application realizes a power supply architecture of secondary side sampling and secondary side control, can realize accurate output voltage / output current control, and sends the PWM control instruction of the primary side switching device to the primary side controller, which can avoid the problems caused by the transmission of analog signals by the optocoupler, and the system is more reliable and has lower standby power consumption. In addition, when the power supply is in the continuous current working mode, the secondary side controller can determine the PWM frequency for the primary side switching device based on the output power of the secondary side winding, and generate a PWM control signal for controlling the conduction and shutdown of the primary side switching device based on the PWM frequency, which can realize PWM frequency control of full load and full frequency, medium load and reduced frequency, and light load and low frequency, greatly improving the system efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] By describing the embodiments of the present application in more detail in conjunction with the accompanying drawings, the above and other purposes, features and advantages of the present application will become more apparent. The accompanying drawings are used to provide a further understanding of the embodiments of the present application and constitute a part of the specification. Together with the embodiments of the present application, they are used to explain the present application and do not constitute a limitation of the present application. In the accompanying drawings, the same reference numerals generally represent the same components or steps.

[0035] Figure 1 A schematic diagram of the architecture of an isolated switching power supply according to an embodiment of the present application is shown.

[0036] Figure 2 A schematic flow chart showing a method for a secondary side controller of an isolated switching power supply according to an embodiment of the present application to determine a pulse width modulation frequency based on output power.

[0037] Figure 3 A schematic flow chart of adaptive constant on-time (COT) control performed by a secondary-side controller of an isolated switching power supply according to an embodiment of the present application is shown.

[0038] Figure 4 A schematic flow chart showing a method for determining a peak current based on output power by a secondary side controller of an isolated switching power supply according to an embodiment of the present application.

[0039] Figure 5 A schematic flow chart showing a secondary side controller of an isolated switching power supply according to an embodiment of the present application determining a working mode of the power supply.

[0040] Figure 6 A schematic diagram showing a secondary-side controller of an isolated switching power supply according to an embodiment of the present application simultaneously controlling a primary-side switching device and a secondary-side switching device.

[0041] Figure 7 A schematic flow chart of a control method of a secondary side controller of an isolated switching power supply according to an embodiment of the present application is shown. DETAILED DESCRIPTION

[0042] In order to make the purpose, technical solutions and advantages of the present application more obvious, the example embodiments according to the present application will be described in detail with reference to the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application, and it should be understood that the present application is not limited to the example embodiments described herein. Based on the embodiments of the present application described in the present application, all other embodiments obtained by those skilled in the art without creative work should fall within the scope of protection of the present application.

[0043] As mentioned above, the two traditional architectures of the power supply architecture of the isolated switching power supply (primary sampling, primary control architecture and secondary sampling, primary control structure) have their own shortcomings. Based on this, the present application provides a new power supply architecture of an isolated switching power supply, in which the main power switch is on the primary side, the output voltage is sampled on the secondary side, and the primary main switch control instruction is generated on the secondary side, and the control instruction is transmitted to the primary side through the isolation device, so as to control the opening and closing of the primary main switch, thereby achieving the purpose of stabilizing the output. The following is described in conjunction with the accompanying drawings.

[0044] Figure 1 FIG. 1 shows a schematic diagram of the architecture of an isolated switching power supply 100 according to an embodiment of the present application. Figure 1As shown, the isolated switching power supply 100 includes a transformer 110, a power stage circuit 120, a primary controller 130, a secondary controller 140 and a coupling element 150. Among them: the transformer 110 includes a primary winding and a secondary winding; the power stage circuit 120 includes a primary switch device (the number of the primary switch devices may be N, where N is a natural number greater than or equal to 1); the secondary controller 140 is used to determine the pulse width modulation frequency for the primary switch device based on the output power of the secondary winding when the power supply 100 is in a continuous current working mode, and generate a first pulse width modulation control signal based on the pulse width modulation frequency; the coupling element 150 is used to transmit the first pulse width modulation control signal to the primary controller 130; the primary controller 130 is used to control the conduction and disconnection of the primary switch device based on the first pulse width modulation control signal.

[0045] In an embodiment of the present application, a power supply 100 architecture with secondary side sampling and secondary side control is implemented. Among them, the primary side controller 130 is a controller set on the primary side, and the secondary side controller 140 is a controller set on the secondary side. On the one hand, the secondary side controller 140 obtains the output power of the secondary winding of the acquisition transformer 110, that is, it directly measures the output voltage and output current on the secondary side. Compared with the first architecture (primary side sampling, primary side control) described above, accurate output voltage / output current control can be achieved. In addition, in the short-circuit test, compared with the indirect measurement that is prone to failure, the direct measurement method on the secondary side allows the sampling circuit (not shown) to work stably and reliably, ensuring the normal and reliable operation of the controller and the protection circuit (not shown).

[0046] On the other hand, compared with the second architecture described above (secondary side sampling, primary side control), the power supply 100 architecture of the present application sends the PWM control instructions of the primary side switching device to the primary side controller 130 through digital isolation (magnetic isolation, capacitive isolation, optical isolation, etc.). Since the digital control instruction signal is sent directly instead of sending the output voltage / current acquisition result in the form of an analog error signal, the problems caused by the optocoupler transmitting analog signals (aging of the optocoupler and the existence of static working current) can be avoided, and the system is more reliable and has lower standby power consumption.

[0047] On the other hand, the secondary controller 140 of the present application includes an output power and PWM frequency setting circuit. Specifically, the secondary controller 140 can determine the PWM frequency for the primary switching device based on the output power of the secondary winding, and generate a first PWM control signal (named so as to distinguish it from the second PWM control signal described later) for controlling the on and off of the primary switching device based on the PWM frequency, and can achieve full-load full-frequency, medium-load reduced-frequency, and light-load low-frequency PWM frequency control, which greatly improves system efficiency.

[0048] In an embodiment of the present application, the secondary controller 140 determines the PWM frequency for the primary switching device based on the output power of the secondary winding, which may include: the secondary controller 140 determines the PWM frequency for the primary switching device based on the output power of the secondary winding according to a first corresponding relationship (named so as to distinguish it from the second corresponding relationship described later), wherein the first corresponding relationship refers to the corresponding relationship between the output power and the PWM frequency. Figure 2 The flow of the secondary controller 140 determining the PWM frequency for the primary switching device based on the output power of the secondary winding is described.

[0049] like Figure 2 As shown, the secondary side controller 140 can control the acquisition circuit to measure the output voltage Vo and the output current Io, and calculate the output power Po (where Po = Vo*Io); then, according to the corresponding relationship between the output power Po and the PWM frequency Fs (referred to as the first corresponding relationship), determine Fs. Here, the corresponding relationship between the output power Po and the PWM frequency Fs can be preset or configurable. In one example, the corresponding relationship between the output power Po and the PWM frequency Fs can be a linear relationship. For example, the larger the output power Po, the linear increase of the PWM frequency Fs; the smaller the output power Po, the linear decrease of the PWM frequency Fs; the peak value Pmax of the output power Po can correspond to the peak value Fmax of the PWM frequency Fs. In one example, both the peak power Pmax and the peak frequency Fmax can be customized by the user. This makes the isolated switching power supply 100 more suitable for different user needs.

[0050] In an embodiment of the present application, the secondary side controller 140 generates a first PWM control signal based on the PWM frequency, which may include: the secondary side controller 140 calculates the on-time of the primary side switch device based on the PWM frequency and the duty cycle, and generates the first PWM control signal based on the on-time. Figure 3 The process of the secondary-side controller 140 generating the first PWM control signal based on the PWM frequency is described.

[0051] like Figure 3As shown, the secondary controller 140 can determine whether the instruction has changed, that is, whether it has changed from OFF to ON, when the PWM instruction of the primary switch device (i.e., the primary switch tube) is OFF: if the instruction has not changed from OFF to ON, re-determine whether the instruction has changed; if it is determined that the instruction has changed from OFF to ON, the on-time Ton of the primary switch device can be calculated according to the current PWM frequency Fs and the duty cycle D, where Ton=D*1 / Fs. The duty cycle Ton is related to the input voltage Vin of the transformer 110, the output voltage Vo and the turns ratio N of the transformer 110. Specifically, D=Vo / (Vin / N+Vo). After determining the on-time Ton, a first PWM control signal can be generated based on this and sent to the primary controller 130 to control the primary switch device to turn on. Then, it can be determined whether the Ton time has been turned on: if the Ton time has not been turned on and no instruction to turn off the primary switching device has been received, it is re-determined whether the Ton time has been turned on; if the Ton time has been turned on or an instruction to turn off the primary switching device has been received, the PWM instruction of the primary switching device is set to OFF.

[0052] Combined with the previous article Figure 2 and Figure 3 In the example shown, the control strategy of the secondary controller 140 when the isolated switching power supply 100 operates in the continuous current working mode (Continuous Current Mode, referred to as CCM) is described. In the embodiment of the present application, the isolated switching power supply 100 can also support the discontinuous current working mode (Discontinuous Current Mode, referred to as DCM), and the control strategy of the secondary controller 140 in the discontinuous current working mode is described below.

[0053] In DCM mode, the input power and the peak current of the primary switching device satisfy the following formula (1):

[0054]

[0055] Among them, Pin is the input power, L PRI is the primary winding, Fs is the primary switch PWM frequency, and Ip is the primary switch peak current. From the formula, it can be seen that if the output power is to be increased, it can be achieved by: (1) increasing Ip; and / or, (2) increasing Fs. Considering the improvement of system efficiency, an effective method is to adjust the optimized PWM frequency according to the output power. PWM frequency control is achieved with full load and full frequency, medium load and reduced frequency, and light load and low frequency. According to formula (1), the control of PWM frequency can be achieved by setting the corresponding peak current Ip.

[0056] In DCM mode, the peak current Ip of the primary switching device can be expressed by the following formula (2):

[0057]

[0058] Where, Vin is the input voltage of the switching power supply 100, and Ton is the conduction time of the primary switch device. Therefore, if you want to control Ip to be equal to a given value, you need to control Ton, as shown in formula (3):

[0059]

[0060] Therefore, in a further embodiment of the present application, the secondary controller 140 may also include a peak current setting and control method in the DCM mode, specifically, when the power supply 100 is in DCM, the peak current for the primary switching device is determined based on the output power of the secondary winding, and a second PWM control signal is generated based on the peak current; the coupling element 150 is also used to transmit the second PWM control signal to the primary controller 130; the primary controller 130 is also used to control the on and off of the primary switching device based on the second PWM control signal, and can achieve PWM frequency control of full load and full frequency, medium load and reduced frequency, and light load and low frequency, thereby greatly improving system efficiency.

[0061] In an embodiment of the present application, the secondary controller 140 determines the peak current for the primary switch device based on the output power of the secondary winding, which may include: the secondary controller 140 determines the peak current for the primary switch device based on the output power of the secondary winding according to the second corresponding relationship, wherein the second corresponding relationship refers to the corresponding relationship between the output power and the peak current. Figure 4 The flow of the secondary controller 140 determining the peak current for the primary switching device based on the output power of the secondary winding is described.

[0062] like Figure 4As shown, the secondary side controller 140 can control the acquisition circuit to measure the output voltage Vo and the output current Io, and calculate the output power Po (where Po = Vo*Io); then, according to the corresponding relationship between the output power Po and the peak current Ip (referred to as the second corresponding relationship in order to distinguish it from the first corresponding relationship described above), determine Ip. Here, the corresponding relationship between the output power Po and the peak current Ip can be preset or configurable. In one example, the corresponding relationship between the output power Po and the peak current Ip can be a linear relationship. For example, the larger the output power Po, the linear increase of the peak current Ip; the smaller the output power Po, the linear decrease of the peak current Ip; the peak value Pmax of the output power Po can correspond to the peak value Imax of the peak current Ip. In one example, both the peak power Pmax and the peak current Imax can be customized by the user. This makes the isolated switching power supply 100 more suitable for different user needs.

[0063] Continue to refer Figure 4 After the peak current Ip of the primary switch device is determined based on the corresponding relationship between the output power Po and the peak current Ip, the conduction time Ton of the primary switch device can be determined based on it. Wherein, Ton=(Ip*Lpri) / Vin, that is, the secondary controller 140 is based on the inductance L of the primary winding. PRI , peak current Ip and input voltage Vin of the primary winding calculate the on-time Ton of the primary switching device, and generate a second PWM control signal (named so to distinguish it from the first PWM control signal mentioned above) based on the on-time Ton for controlling the primary switching device.

[0064] As described above, the isolated switching power supply 100 of the present application can support both CCM mode and DCM mode. Regardless of which mode, the control based on the secondary side controller 140 can achieve PWM frequency control of full load and full frequency, medium load frequency reduction, and light load and low frequency, which greatly improves the system efficiency. Specifically, for the CCM mode, the secondary side controller 140 controls the PWM frequency based on the output power, so that it can achieve PWM frequency control of full load and full frequency, medium load frequency reduction, and light load and low frequency; for the DCM mode, the secondary side controller 140 controls the peak current of the primary side switching device based on the output power, so that it can achieve peak current control, and then achieve PWM frequency control, and finally achieve PWM frequency control of full load and full frequency, medium load frequency reduction, and light load and low frequency.

[0065] Since the isolated switching power supply 100 can support both CCM mode and DCM mode, different controls can be performed in different modes. Therefore, the secondary side controller 140 of the present application can also judge the DCM mode and the CCM mode. Specifically, the secondary side controller 140 judges the working mode of the power supply 100 based on the PWM control signal of the primary side switching device, which may include: when the PWM control signal changes from a high level to a low level, it is judged that the power supply 100 is in the DCM working mode; when the PWM control signal changes from a low level to a high level and the output current of the secondary winding is greater than zero, it is judged that the power supply 100 is in the CCM working mode. The following is combined with Figure 5 To describe the judgment process.

[0066] like Figure 5 As shown, the secondary controller 140 can determine whether the instruction has changed when the PWM instruction of the primary switch device (i.e., the primary switch tube) is ON, that is, whether it changes from ON to OFF (i.e., the PWM control signal changes from a high level to a low level): if the instruction does not change from ON to OFF, the current working mode is the CCM mode and remains unchanged; if it is determined that the instruction changes from ON to OFF, CCM=0 (i.e., the DCM mode is at this time). After this, it can be determined whether the PWM instruction has changed, that is, whether it changes from OFF to ON (i.e., the PWM control signal changes from a low level to a high level): if the instruction does not change from OFF to ON, the current working mode is the DCM mode and remains unchanged; if it is determined that the instruction changes from OFF to ON, it is determined whether the current of the secondary winding is greater than 0; if it is not greater than 0, the current working mode is the DCM mode and remains unchanged; if it is greater than 0, CCM=1 (i.e., the CCM mode is at this time).

[0067] In an embodiment of the present application, when the secondary controller 140 mentioned above determines the PWM frequency for the primary switching device based on the output power of the secondary winding, when the output power is greater than or equal to a preset threshold, the PWM frequency for the primary switching device can be set to be greater than or equal to a preset frequency value to eliminate audio noise. For example, the output power preset threshold can be set to 0W, and the PWM preset frequency value for the primary side switching device can be set to 20kHz or a higher frequency. When the power supply 100 is in the CCM working mode, since the PWM frequency is always greater than or equal to the preset frequency value 20KHz, there is no audio noise; when the power supply 100 is in the DCM working mode, the secondary side controller 140 controls the peak current of the primary side switching device based on the output power, so that it realizes peak current control, and then realizes PWM frequency control, so that under light load to full load conditions, the PWM frequency is always greater than or equal to 20KHz, so there is no audio noise; under no-load and deep light load conditions, considering that the audio noise volume is small, in order to maximize efficiency, there is no need to control the PWM frequency to be greater than 20kHz; in summary, therefore, from no-load to full load conditions, the secondary side controller 140 of the present application can eliminate audio noise by controlling the PWM frequency.

[0068] In order to improve the efficiency of the isolated switching power supply 100, a switch tube is usually used to replace the diode (synchronous rectification) on the secondary side. The switch tube on the primary side and the switch tube on the secondary side are not allowed to be turned on at the same time, otherwise the power supply 100 system will be short-circuited. However, in the first architecture (primary side sampling, primary side control) and the second architecture (secondary side sampling, primary side control) described above, the primary side switch tube is controlled by the primary side PWM control IC, while the secondary side switch tube is controlled by the secondary side synchronous rectification control IC. The primary side PWM control IC and the secondary side synchronous rectification control IC are electrically isolated. Unless isolated communication is used (increasing system complexity and cost), the switching command interlocking logic of the primary side switch tube and the secondary side switch tube cannot be realized between the two. This problem can also be solved in the present application.

[0069] Specifically, in the embodiment of the present application, the isolated switching power supply 100 may further include a rectifier filter circuit 160, which includes a secondary side switch device for synchronous rectification (for example, including M secondary side switches, where M is a natural number greater than or equal to 1), and the secondary side controller 140 may also be used to generate a control instruction for controlling the conduction and shutdown of the secondary side switch device. Therefore, the secondary side controller 140 of the present application may be as follows: Figure 6 As shown, the primary and secondary switch tubes are controlled simultaneously ( Figure 6 The first controller is the primary side controller, and the second controller is the secondary side controller), which naturally avoids the direct-through problem of the primary and secondary side switches, greatly improves the safety and reliability of the system, and also reduces the complexity of the secondary side synchronous rectification control.

[0070] The above exemplary shows the isolated switching power supply 100 according to the embodiment of the present application. The isolated switching power supply 100 can be applied to various topologies, such as a forward converter topology, a flyback converter topology, a half-bridge topology, and a full-bridge topology.

[0071] Based on the above description, the isolated switching power supply according to the embodiment of the present application is a PWM control IC (secondary controller) on the secondary side that senses the secondary side output voltage and output current in real time, thereby generating PWM control signals for the primary side switch tube and the secondary side synchronous rectification switch tube, and using a coupling element to transmit the primary side switch tube PWM control signal to the primary side to control the primary side switch tube to be turned off or turned on, which can solve the problems of the two traditional architectures. In addition, the isolated switching power supply according to the embodiment of the present application adopts PWM frequency open-loop control adaptive timing switch technology, which is simple and reliable, and reduces IC cost (saving frequency comparator, counter and other circuits); at the same time, the secondary side controller can perform output power and PWM frequency planning, and realize PWM frequency control of full load and full frequency, medium load and reduced frequency, and light load and low frequency. In addition, the secondary controller can perform audio noise elimination control. For example, the output power preset threshold can be set to 0W, and the PWM preset frequency value for the primary switch device can be set to 20kHz or higher. When the power supply 100 is in the CCM working mode, since the PWM frequency is always greater than or equal to the preset frequency value 20KHz, there is no audio noise; when the power supply 100 is in the DCM working mode, the secondary controller 140 controls the peak current of the primary switch device based on the output power, so that it can achieve peak current control, and then achieve PWM frequency control, so that the PWM frequency is always greater than or equal to 20KHz from light load to full load conditions, so there is no audio noise; under no-load and deep light load conditions, considering that the audio noise volume is small, in order to maximize efficiency, it is not necessary to control the PWM frequency to be greater than 20KHz; in summary, therefore, from no-load to full load conditions, the secondary controller 140 of the present application can eliminate audio noise by controlling the PWM frequency. In addition, the secondary controller also realizes the setting and control of the peak current of the primary switch tube in the DCM mode.

[0072] Combine the following Figure 7 A control method 700 of a secondary side controller of an isolated switching power supply according to another aspect of the present application is described. Figure 7 As shown, the control method 700 of the secondary side controller of the isolated switching power supply may include the following steps:

[0073] In step S710, the output voltage and output current of the secondary winding of the transformer of the isolated switching power supply are collected, and the output power is obtained based on the output voltage and the output current.

[0074] In step S720, when the power supply is in the continuous current operation mode, the pulse width modulation frequency of the primary switching device of the power supply is determined based on the output power, and a first pulse width modulation control signal is generated based on the pulse width modulation frequency to be transmitted to the primary controller of the power supply to control the conduction and shutdown of the primary switching device.

[0075] The control method 700 of the secondary side controller of the isolated switching power supply according to the embodiment of the present application is the operation performed by the secondary side controller 140 in the isolated switching power supply 100 described above. Since the operations performed by the secondary side controller have been described in detail above, the details will not be repeated here for the sake of brevity, and only some main operations will be described.

[0076] In one embodiment of the present application, determining the pulse width modulation frequency of the primary switching device used for the power supply based on the output power as described in step S720 may include: determining the pulse width modulation frequency of the primary switching device used for the power supply based on the output power according to a first corresponding relationship, wherein the first corresponding relationship refers to the corresponding relationship between the output power and the pulse width modulation frequency.

[0077] In one embodiment of the present application, the first corresponding relationship is preset or configurable.

[0078] In one embodiment of the present application, the first corresponding relationship includes a linear corresponding relationship.

[0079] In one embodiment of the present application, generating the first pulse width modulation control signal based on the pulse width modulation frequency in step S720 includes: calculating the on-time of the primary switching device based on the pulse width modulation frequency and the duty cycle, and generating the first pulse width modulation control signal based on the on-time.

[0080] In one embodiment of the present application, method 700 may further include the following steps: when the power supply is in the discontinuous current operating mode, determining the peak current for the primary switching device based on the output power, and generating a second pulse width modulation control signal based on the peak current to be transmitted to the primary controller to control the conduction and shutdown of the primary switching device.

[0081] In one embodiment of the present application, determining a peak current for a primary switching device based on output power includes: determining a peak current for a primary switching device based on output power according to a second corresponding relationship, wherein the second corresponding relationship refers to a corresponding relationship between output power and peak current.

[0082] In one embodiment of the present application, the second corresponding relationship is preset or configurable.

[0083] In one embodiment of the present application, the second corresponding relationship includes a linear corresponding relationship.

[0084] In one embodiment of the present application, a second pulse width modulation control signal is generated based on the peak current, including: calculating the on-time of the primary switching device based on the inductance of the primary winding of the transformer, the peak current and the input voltage of the primary winding, and generating the second pulse width modulation control signal based on the on-time.

[0085] In one embodiment of the present application, the method 700 may further include: determining the working mode of the power supply based on the pulse width modulation control signal of the primary switching device.

[0086] In one embodiment of the present application, the operating mode of the power supply is determined based on the pulse width modulation control signal of the primary switching device, including: when the pulse width modulation control signal changes from a high level to a low level, it is determined that the power supply is in a discontinuous current operating mode; when the pulse width modulation control signal changes from a low level to a high level and the output current of the secondary winding is greater than zero, it is determined that the power supply is in a continuous current operating mode.

[0087] In one embodiment of the present application, the method 700 may further include: when the output power is greater than or equal to a preset threshold, setting the pulse width modulation frequency for the primary switching device to be greater than or equal to a preset frequency value to eliminate audio noise.

[0088] Based on the above description, the control method 700 of the secondary side controller of the isolated switching power supply according to the embodiment of the present application senses the secondary side output voltage and output current in real time, and then generates PWM control signals of the primary side switch tube and the secondary side synchronous rectification switch tube, and uses a coupling element to transmit the primary side switch tube PWM control signal to the primary side to control the switch tube of the primary side to turn off or turn on, which can solve the problems of the two traditional architectures. In addition, the control method 700 of the secondary side controller of the isolated switching power supply according to the embodiment of the present application adopts PWM frequency open-loop control adaptive timing switch technology, which is simple and reliable, and reduces IC cost (saving frequency comparator, counter and other circuits); at the same time, the secondary side controller can perform output power and PWM frequency planning, and realize PWM frequency control of full load and full frequency, medium load and reduced frequency, and light load and low frequency. In addition, the secondary controller can perform audio noise elimination control. For example, the output power preset threshold can be set to 0W, and the PWM preset frequency value for the primary switch device can be set to 20kHz or higher. When the power supply 100 is in the CCM working mode, since the PWM frequency is always greater than or equal to the preset frequency value 20KHz, there is no audio noise; when the power supply 100 is in the DCM working mode, the secondary controller 140 controls the peak current of the primary switch device based on the output power, so that it can achieve peak current control, and then achieve PWM frequency control, so that the PWM frequency is always greater than or equal to 20KHz from light load to full load conditions, so there is no audio noise; under no-load and deep light load conditions, considering that the audio noise volume is small, in order to maximize efficiency, it is not necessary to control the PWM frequency to be greater than 20KHz; in summary, therefore, from no-load to full load conditions, the secondary controller 140 of the present application can eliminate audio noise by controlling the PWM frequency. In addition, the secondary controller also realizes the setting and control of the peak current of the primary switch tube in the DCM mode.

[0089] Although example embodiments have been described herein with reference to the accompanying drawings, it should be understood that the above example embodiments are merely exemplary and are not intended to limit the scope of the present application to this. Those of ordinary skill in the art may make various changes and modifications therein without departing from the scope and spirit of the present application. All these changes and modifications are intended to be included within the scope of the present application as required by the appended claims.

[0090] Those of ordinary skill in the art will appreciate that the units and algorithm steps of each example described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professional and technical personnel can use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of this application.

[0091] In the several embodiments provided in this application, it should be understood that the disclosed devices and methods can be implemented in other ways. For example, the device embodiments described above are only schematic, for example, the division of the units is only a logical function division, and there may be other division methods in actual implementation, such as multiple units or components can be combined or integrated into another device, or some features can be ignored or not executed.

[0092] In the description provided herein, a large number of specific details are described. However, it is understood that the embodiments of the present application can be practiced without these specific details. In some instances, well-known methods, structures and techniques are not shown in detail so as not to obscure the understanding of this description.

[0093] Similarly, it should be understood that in order to streamline the present application and help understand one or more of the various inventive aspects, in the description of the exemplary embodiments of the present application, the various features of the present application are sometimes grouped together into a single embodiment, figure, or description thereof. However, the method of the present application should not be interpreted as reflecting the following intention: the claimed application requires more features than the features clearly stated in each claim. More specifically, as reflected in the corresponding claims, the inventive point is that the corresponding technical problem can be solved with features less than all the features of a single disclosed embodiment. Therefore, the claims following the specific embodiment are hereby explicitly incorporated into the specific embodiment, wherein each claim itself serves as a separate embodiment of the present application.

[0094] It will be understood by those skilled in the art that, except for mutually exclusive features, all features disclosed in this specification (including the accompanying claims, abstracts and drawings) and all processes or units of any method or device disclosed in this specification may be combined in any combination. Unless otherwise expressly stated, each feature disclosed in this specification (including the accompanying claims, abstracts and drawings) may be replaced by an alternative feature that provides the same, equivalent or similar purpose.

[0095] In addition, those skilled in the art will appreciate that, although some embodiments described herein include certain features included in other embodiments but not other features, the combination of features of different embodiments is meant to be within the scope of the present application and form different embodiments. For example, in the claims, any one of the claimed embodiments can be used in any combination.

[0096] The various component embodiments of the present application can be implemented in hardware, or in software modules running on one or more processors, or in a combination thereof. It should be understood by those skilled in the art that a microprocessor or a digital signal processor (DSP) can be used in practice to implement some or all of the functions of some modules according to the embodiments of the present application. The present application can also be implemented as a plug-in program (e.g., a computer program and a computer program product) for executing part or all of the methods described herein. Such a program implementing the present application can be stored on a computer-readable medium, or can have the form of one or more signals. Such a signal can be downloaded from an Internet website, or provided on a carrier signal, or provided in any other form.

[0097] It should be noted that the above embodiments illustrate rather than limit the present application, and that those skilled in the art may design alternative embodiments without departing from the scope of the appended claims. In the claims, any reference symbol between brackets shall not be construed as a limitation on the claims. The word "comprising" does not exclude the presence of elements or steps not listed in the claims. The word "one" or "an" preceding an element does not exclude the presence of a plurality of such elements. The present application may be implemented with the aid of hardware comprising a number of different elements and with the aid of a suitably programmed computer. In a unit claim listing a number of strips, several of these strips may be embodied by the same hardware item. The use of the words first, second, and third, etc. does not indicate any order. These words may be interpreted as names.

[0098] The above is only a specific implementation or description of a specific implementation of the present application, and the protection scope of the present application is not limited thereto. Any technician familiar with the technical field can easily think of changes or substitutions within the technical scope disclosed in the present application, which should be included in the protection scope of the present application. The protection scope of the present application shall be based on the protection scope of the claims.

Claims

1. An isolated switching power supply, characterized in that: The power supply includes a transformer, a power stage circuit, a primary side controller, a secondary side controller and a coupling element, wherein: The transformer comprises a primary winding and a secondary winding; The power stage circuit includes a primary side switching device; The secondary controller is used to determine a pulse width modulation frequency for the primary switching device based on the output power of the secondary winding when the power supply is in a continuous current operation mode, and generate a first pulse width modulation control signal based on the pulse width modulation frequency; The coupling element is used to transmit the first pulse width modulation control signal to the primary side controller; The primary-side controller is used to control the on and off of the primary-side switching device based on the first pulse width modulation control signal.

2. The power supply according to claim 1, characterized in that: The secondary controller determines a pulse width modulation frequency for the primary switching device based on the output power of the secondary winding, comprising: The secondary controller determines the pulse width modulation frequency for the primary switching device based on the output power of the secondary winding according to a first corresponding relationship, wherein the first corresponding relationship refers to the corresponding relationship between the output power and the pulse width modulation frequency.

3. The power supply according to claim 2, characterized in that: The first corresponding relationship is preset or configurable.

4. The power supply according to claim 2, characterized in that: The first corresponding relationship includes a linear corresponding relationship.

5. The power supply according to claim 1, characterized in that: The secondary side controller generates a first pulse width modulation control signal based on the pulse width modulation frequency, comprising: The secondary-side controller calculates the on-time of the primary-side switching device based on the pulse width modulation frequency and the duty cycle, and generates a first pulse width modulation control signal based on the on-time.

6. The power supply according to claim 1, characterized in that: The secondary controller is further configured to determine a peak current for the primary switching device based on the output power of the secondary winding when the power supply is in the discontinuous current operation mode, and to generate a second pulse width modulation control signal based on the peak current; The coupling element is also used to transmit the second pulse width modulation control signal to the primary side controller; The primary side controller is further used to control the on and off of the primary side switch device based on the second pulse width modulation control signal.

7. The power supply according to claim 6, characterized in that: The secondary controller determines a peak current for the primary switching device based on the output power of the secondary winding, including: The secondary controller determines the peak current for the primary switching device based on the output power of the secondary winding according to a second corresponding relationship, wherein the second corresponding relationship refers to the corresponding relationship between the output power and the peak current.

8. The power supply according to claim 7, characterized in that: The second corresponding relationship is preset or configurable.

9. The power supply according to claim 7, characterized in that The second corresponding relationship includes a linear corresponding relationship.

10. The power supply according to claim 6, characterized in that: The secondary-side controller generates a second pulse width modulation control signal based on the peak current, comprising: The secondary controller calculates the on-time of the primary switching device based on the inductance of the primary winding, the peak current and the input voltage of the primary winding, and generates a second pulse width modulation control signal based on the on-time.

11. The power supply according to claim 6, characterized in that: The secondary side controller is further used to determine the working mode of the power supply based on the pulse width modulation control signal of the primary side switch device.

12. The power supply according to claim 11, characterized in that The secondary side controller determines the working mode of the power supply based on the pulse width modulation control signal of the primary side switch device, including: When the pulse width modulation control signal changes from a high level to a low level, it is determined that the power supply is in the discontinuous current working mode; When the pulse width modulation control signal changes from a low level to a high level and the output current of the secondary winding is greater than zero, it is determined that the power supply is in the continuous current operation mode.

13. The power supply according to any one of claims 1 to 12, characterized in that: The secondary side controller is further configured to set the pulse width modulation frequency for the primary side switching device to be greater than or equal to a preset frequency value when the output power is greater than or equal to a preset threshold value, so as to eliminate audio noise.

14. The power supply according to any one of claims 1 to 12, characterized in that: The power supply further includes a secondary side switch device for synchronous rectification, and the secondary side controller is further used to generate a control instruction for controlling the switching on and off of the secondary side switch device.

15. The power supply according to any one of claims 1 to 12, characterized in that: The power supply is applicable to any one of the following topologies: forward converter topology, flyback converter topology, half-bridge topology, and full-bridge topology.

16. A control method for a secondary side controller of an isolated switching power supply, characterized in that: The control method comprises: Collecting the output voltage and output current of the secondary winding of the transformer of the isolated switching power supply, and obtaining the output power based on the output voltage and the output current; When the power supply is in the continuous current operation mode, the pulse width modulation frequency of the primary switching device of the power supply is determined based on the output power, and a first pulse width modulation control signal is generated based on the pulse width modulation frequency to be transmitted to the primary controller of the power supply to control the conduction and shutdown of the primary switching device.

17. The method according to claim 16, characterized in that The step of determining a pulse width modulation frequency of a primary switching device of the power supply based on the output power comprises: According to a first corresponding relationship, a pulse width modulation frequency of a primary switching device of the power supply is determined based on the output power, wherein the first corresponding relationship refers to a corresponding relationship between output power and pulse width modulation frequency.

18. The method according to claim 17, characterized in that The first corresponding relationship is preset or configurable.

19. The method according to claim 17, characterized in that The first corresponding relationship includes a linear corresponding relationship.

20. The method according to claim 16, characterized in that The step of generating a first pulse width modulation control signal based on the pulse width modulation frequency comprises: The on-time of the primary switching device is calculated based on the pulse width modulation frequency and the duty cycle, and a first pulse width modulation control signal is generated based on the on-time.

21. The method according to claim 16, characterized in that The method further comprises: When the power supply is in the discontinuous current operation mode, the peak current for the primary switching device is determined based on the output power, and a second pulse width modulation control signal is generated based on the peak current to be transmitted to the primary controller to control the conduction and shutdown of the primary switching device.

22. The method according to claim 21, characterized in that The determining of a peak current for the primary switching device based on the output power comprises: According to a second corresponding relationship, a peak current for the primary switching device is determined based on the output power, wherein the second corresponding relationship refers to a corresponding relationship between output power and peak current.

23. The method according to claim 22, characterized in that The second corresponding relationship is preset or configurable.

24. The method according to claim 22, characterized in that The second corresponding relationship includes a linear corresponding relationship.

25. The method according to claim 21, characterized in that The generating a second pulse width modulation control signal based on the peak current comprises: The on-time of the primary switching device is calculated based on the inductance of the primary winding of the transformer, the peak current and the input voltage of the primary winding, and a second pulse width modulation control signal is generated based on the on-time.

26. The method according to claim 21, characterized in that The method further comprises: The working mode of the power supply is determined based on the pulse width modulation control signal of the primary switching device.

27. The method according to claim 26, characterized in that The determining the working mode of the power supply based on the pulse width modulation control signal of the primary switching device includes: When the pulse width modulation control signal changes from a high level to a low level, it is determined that the power supply is in the discontinuous current working mode; When the pulse width modulation control signal changes from a low level to a high level and the output current of the secondary winding is greater than zero, it is determined that the power supply is in the continuous current operation mode.

28. The method according to any one of claims 16 to 27, characterized in that The method further comprises: When the output power is greater than or equal to a preset threshold, the pulse width modulation frequency for the primary switching device is set to be greater than or equal to a preset frequency value to eliminate audio noise.

Images