Powered Devices and Power over Ethernet Systems

Abstract

The present invention discloses a powered device and an Ethernet power supply system. The power receiving device and the Ethernet power supply system include: a powered device controller connected between a DC input voltage and a first reference ground for communicating with a power supply device; and a switching power converter for converting a DC input voltage into a DC output voltage to provide an output current to a subsequent load, wherein the switching power converter includes a power switch tube and a switching power controller for controlling the on or off of the power switch tube, the switching power controller is connected to a second reference ground, and the first reference ground is different from the second reference ground. The present invention sets the powered device controller and the switching power controller to be non-commonly grounded, thereby sampling the output voltage through the primary winding, without the need to use an auxiliary winding in the circuit, thereby greatly reducing the production cost and difficulty of the circuit.

Description

Technical Field

[0001] The present invention relates to the field of electronic technology, and more particularly to a powered device and an Ethernet power supply system. Background Art

[0002] Power over Ethernet (PoE), also known as PoE, is a technology that can transmit power and data to devices through twisted pair cables in Ethernet. This technology is compatible with existing Ethernet cabling infrastructure and allows devices to be powered through their network ports, thus eliminating the need for power cables and saving cabling and hardware costs. Ethernet power technology has been widely used in video phones, security, IoT devices and other fields.

[0003] The Ethernet power supply system generally includes power sourcing equipment (PSE), powered devices (PD), and Ethernet cables that transmit power and data between the two.

[0004] In a PoE power supply system, the powered device usually needs to convert the high-voltage AC power received from the Ethernet cable into a low-voltage DC power suitable for the internal circuit. The flyback converter is a commonly used power conversion topology, which is widely used in the power management of powered devices due to its simplicity, low cost and high efficiency.

[0005] The flyback converter usually includes a primary side circuit and a secondary side circuit, and controls the on and off of the power switch in the primary side circuit to output a constant voltage in the secondary side circuit. In the PoE system, the subsequent switching power converter must start working only after the surge current limiting of the previous powered device controller ends, otherwise it may not start normally. Therefore, the powered device controller is usually required to output an enable signal to control the working state of the subsequent switching power converter. If the subsequent switching power converter and the previous powered device controller are in the same ground, the enable signal output by the powered device controller can be directly used to control the subsequent switching power converter. However, if the powered device controller and the subsequent switching power converter are not in the same ground, it is often necessary to perform level conversion on the enable signal output by the powered device controller before controlling the subsequent switching power converter, which not only increases the complexity of the control circuit, but also often requires a high-voltage BCD process to design the controller, resulting in increased costs.

[0006] Figure 1 A system structure block diagram of a power receiving device according to the prior art is shown. Figure 2 FIG. 2 shows a circuit diagram of a switching power converter according to the prior art. Figure 1and Figure 2 As shown, the existing powered device 100 includes a rectifier bridge 110, a powered device controller 120 and a switching power converter 130, wherein the switching power converter 130 is implemented by a flyback converter, including a start-up circuit 131, a switch control circuit 132, a power switch tube Q1, a primary winding L1, a secondary winding L2, a diode D2 and an output capacitor Co. In the prior art powered device, by connecting the output ground of the powered device controller 120 to the ground terminal of the switching power converter 130, the powered device controller 120 can directly control the subsequent switching power converter 130 through the PG terminal, without setting a level conversion circuit between the two, thereby reducing the complexity of the control circuit. However, this solution requires adding an auxiliary winding L3 and a diode D1 to the switching power converter 130 to obtain the output voltage feedback parameter, and the voltage at both ends of the auxiliary winding L3 is divided by the resistor R1 and the resistor R2 to obtain the output voltage feedback signal. Since the winding process of the auxiliary winding is relatively complicated, the solution of the prior art will increase the production cost and manufacturing difficulty of the powered device, and the introduction of the auxiliary winding may also cause electromagnetic interference inside the circuit. Summary of the invention

[0007] In view of this, the object of the present invention is to provide a powered device and an Ethernet power supply system, in which the powered device controller and the switching power supply controller are set to a non-common ground mode, so that the output voltage can be sampled through the primary winding, and there is no need to use an auxiliary winding in the circuit, which greatly reduces the production cost and manufacturing difficulty of the circuit.

[0008] According to one aspect of the present invention, there is provided a powered device, comprising: a powered device controller, connected between a DC input voltage and a first reference ground, for communicating with a power supply device; and a switching power converter, for converting the DC input voltage into a DC output voltage to provide an output current to a subsequent load, wherein the switching power converter comprises a power switch tube and a switching power controller for controlling the on or off of the power switch tube, the switching power controller is connected to a second reference ground, and the first reference ground is different from the second reference ground.

[0009] Optionally, the switching power supply controller is used to sample the DC input voltage to obtain a first sampling voltage based on the second reference ground, convert the first sampling voltage into a second sampling voltage based on the first reference ground, compare the second sampling voltage with a set threshold voltage, and control the switching power supply converter to enter a working state after the second sampling voltage is greater than the threshold voltage.

[0010] Optionally, the switching power supply controller is further configured to control the switching power supply converter to enter a working state after a preset time when the second sampling voltage is greater than the threshold voltage.

[0011] Optionally, the powered device further includes: a first capacitor arranged between the powered device controller and the switching power supply controller, the first end of the first capacitor being connected to the DC input voltage, and the second end of the first capacitor being connected to the first reference ground, wherein the preset time is set according to the time required for the first capacitor to charge to the platform voltage.

[0012] Optionally, the switching power supply controller includes: a switching control circuit, which generates a switching control signal according to a current sampling signal and a feedback signal of the DC output voltage; a driving circuit, which receives the switching control signal and generates a switching driving signal to drive the power switch tube to be turned on or off; a starting control circuit, which is connected between the DC input voltage and the second reference ground, and is used to sample the DC input voltage to obtain the first sampling voltage based on the second reference ground, and convert the first sampling voltage into the second sampling voltage based on the first reference ground, and generate a valid starting indication signal when the second sampling voltage is greater than the threshold voltage; and a delay circuit, which is connected to the starting control circuit, and is used to delay the preset time to output a valid enable control signal to the switching control circuit after receiving the valid start indication signal, so as to control the switching control circuit to be enabled and turned on.

[0013] Optionally, the startup control circuit includes: an N-order filtering module, connected between the DC input voltage and the second reference ground, for converting the first sampling voltage into the second sampling voltage, where N is an integer greater than or equal to 1; a voltage divider module, for dividing the second sampling voltage to obtain a voltage divider signal of the second sampling voltage; and a first comparator, whose non-phase input terminal is used to receive the voltage divider signal of the second sampling voltage, the inverting input terminal is used to receive the first reference voltage representing the threshold voltage, and the output terminal is used to output the startup indication signal.

[0014] Optionally, the switch control circuit includes: a sampling and holding module, used to sample and hold the feedback signal according to the switch control signal to obtain a sampled and held voltage; an error amplifier, whose non-phase input terminal is used to receive a second reference voltage, whose inverting input terminal is used to receive the sampled and held voltage, and whose output terminal is used to output an error signal; a second comparator, whose non-phase input terminal is used to receive the current sampling signal, whose inverting input terminal is used to receive the error signal, and whose output terminal is used to output a comparison signal; and an RS trigger, whose set terminal is used to receive a clock signal, whose reset terminal is used to receive the comparison signal, and whose output terminal is used to provide the switch control signal.

[0015] Optionally, the switching power supply controller further includes: a power supply circuit, configured to provide a power supply voltage to the switching control circuit according to the DC input voltage.

[0016] Optionally, the switch control circuit further includes: a switch frequency control module, configured to generate the clock signal according to the error signal, wherein the switch frequency of the switch control signal is set by the clock frequency of the clock signal.

[0017] Optionally, the switching power converter also includes: the power switch tube, a first end of which is connected to the DC input voltage, and a second end of which is connected to a second reference ground; a transformer, including a primary winding and a secondary winding, the first end of the primary winding is connected to the second reference ground, and the second end of the primary winding is connected to the first reference ground; a diode and an output capacitor, connected in series between the two ends of the secondary winding, for rectifying and filtering the voltage across the secondary winding to generate a DC output voltage; and a feedback circuit, connected between the second reference ground and the first reference ground, for sampling the DC output voltage to obtain the feedback signal.

[0018] Optionally, the switching power converter further includes: a current sampling resistor connected between the second end of the power switch tube and the second reference ground, and the current sampling resistor is used to provide the current sampling signal to the switching power controller.

[0019] Optionally, the switching power supply controller further includes: a current sampling circuit connected to the first end of the power switch tube and configured to generate the current sampling signal.

[0020] Optionally, an anode of the diode is connected to a first end of the secondary winding, a cathode of the diode is connected to a first end of the output capacitor, and a second end of the output capacitor is connected to a second end of the secondary winding and a third reference ground.

[0021] Optionally, it also includes: a rectifier bridge, used to convert the AC input voltage into the DC input voltage.

[0022] Optionally, the first reference ground is a fixed ground, and the second reference ground is a floating ground.

[0023] According to another aspect of the present invention, there is provided an Ethernet power supply system, comprising: a power supply device; and the above-mentioned powered device.

[0024] In summary, the present application proposes a low-cost powered device for a PoE system, in which the powered device controller and the switching power supply controller are set to be non-shared ground. Compared with the traditional powered device including a flyback converter, the output voltage sampling can be realized through the primary winding, and there is no need to use an auxiliary winding in the circuit, which can greatly reduce the production cost and manufacturing difficulty of the flyback converter. In addition, since there is no introduction of an auxiliary winding, the electromagnetic interference inside the circuit is reduced.

[0025] In addition, the switching power converter of the present application sets the power switch tube and the switching power supply controller on the high side and the primary winding on the low side, so that the switching power supply controller and the power switch tube both use the floating ground as the reference ground, thereby reducing the difficulty of the drive design and the cost of the chip.

[0026] In addition, the switching power supply controller of the present application is also provided with a startup control circuit, through which the DC input voltage is sampled to obtain a first sampling voltage based on the floating ground, and the first sampling voltage is converted into a second sampling voltage based on the fixed ground of the powered device controller, so that the second sampling voltage based on the fixed ground can be compared with the threshold voltage based on the fixed ground, so as to control the subsequent switching power supply converter to start working after the surge current limiting of the powered device controller ends. Through this design, it is ensured that the switching power supply converter starts working only after the surge current limiting of the powered device controller ends, avoiding the problem that the switching power supply converter cannot start normally.

[0027] Furthermore, the switching power supply controller of the present application is also used to delay the setting time before turning on after the second sampling voltage is greater than the threshold voltage, thereby avoiding the problem that the output voltage of the powered device is insufficient due to the need to charge the capacitor at the powered device controller end, and the switching power converter cannot output the target output voltage. Therefore, the solution of the present application not only reduces the cost of the powered device, but also improves the reliability and stability of the powered device, ensuring the normal startup and operation of the switching power converter. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The above and other objects, features and advantages of the present invention will become more apparent through the following description of the embodiments of the present invention with reference to the accompanying drawings.

[0029] Figure 1A system structure block diagram of a powered device according to the prior art is shown.

[0030] Figure 2 FIG. 1 is a circuit diagram of a switching power converter according to the prior art.

[0031] Figure 3 A system block diagram of a powered device according to a first embodiment of the present invention is shown.

[0032] Figure 4 Show Figure 3 Schematic diagram of the structure of the switching power supply controller.

[0033] Figure 5 Show Figure 4 Schematic diagram of the structure of the startup control circuit.

[0034] Figure 6 Show Figure 4 Schematic diagram of the switch control circuit in FIG.

[0035] Figure 7 Show Figure 5 Input and output waveforms of the startup control circuit in .

[0036] Figure 8 Show Figure 4 The waveform diagram of the start indication signal and enable control signal in .

[0037] Fig. 9 Show Figure 6 Working waveform diagram of the switch control circuit in .

[0038] Fig.10 A system block diagram of a powered device according to a second embodiment of the present invention is shown.

[0039] Fig.11 Show Fig.10 Schematic diagram of the structure of the switching power supply controller.

[0040] Fig.12 A structural block diagram of an Ethernet power supply system according to a third embodiment of the present invention is shown. DETAILED DESCRIPTION

[0041] Various embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. In each of the accompanying drawings, the same elements are represented by the same or similar reference numerals. For the sake of clarity, the various parts in the accompanying drawings are not drawn to scale.

[0042] The present invention may be embodied in various forms, some examples of which will be described below.

[0043] Figure 3FIG. 2 shows a system structure block diagram of a powered device according to a first embodiment of the present invention. Figure 3 As shown, the powered device 200 of this embodiment includes a rectifier bridge 210 , a powered device controller 220 , a capacitor Cp and a switching power converter 230 .

[0044] The rectifier bridge 210 is used to rectify the AC input voltage obtained from the Ethernet cable to obtain a DC input voltage Vin.

[0045] The powered device controller 220 is connected between the DC input voltage Vin and the reference ground GND1, and is used to perform a handshake protocol with the power supply equipment (PSE device) in the PoE system, and obtain the required energy and output it to the subsequent switching power converter 230. For example, when the powered device 200 is connected to the Ethernet cable, the powered device controller 220 communicates with the PSE device to confirm the existence of the device and determine its power requirements, thereby ensuring that the PSE device can provide appropriate power without overloading or damaging the network. In addition, the powered device controller also has a protection function, which can monitor various parameters during power transmission, such as current, voltage, and temperature. Once an abnormal situation is detected, the powered device controller will quickly take measures, such as disconnecting the power supply or adjusting the power output, to protect the safety of the powered device and the entire PoE system. Further, the powered device controller 220 also supports various PoE standards and protocols, such as IEEE 802.3af, IEEE 802.3at, and IEEE802.3bt. These standards specify different power levels and communication methods, and the powered device controller needs to be compatible with these standards to ensure interoperability with various PSE devices.

[0046] The capacitor Cp is arranged between the powered device controller 220 and the switching power converter 230, and is connected between the DC input voltage Vin and the reference ground GND1. The capacitor Cp is used to smooth the DC input voltage Vin and absorb the surge current during the startup of the powered device controller 220. For example, the capacitor Cp may be an electrolytic capacitor or a ceramic capacitor.

[0047] The switching power converter 230 is used to perform power conversion and regulation functions, converting the DC input voltage Vin into a DC output voltage Vout suitable for the powered device, so as to minimize energy loss and ensure stable operation of the device.

[0048] By way of example, a first embodiment of the present invention provides a switching power converter 230 of a flyback topology without an auxiliary winding, including a switching power controller 231, a power switch tube Q1, a transformer T1 (including a primary winding L1 and a secondary winding L2), a current sampling resistor Rcs, a freewheeling diode D1, an output capacitor Co and a feedback circuit 233.

[0049] Among them, the first end of the power switch tube Q1 (such as a transistor, a field effect tube, a thyristor, etc.) is connected to the DC input voltage Vin, the second end of the power switch tube Q1 is connected to the first end of the current sampling resistor Rcs and the current detection end CS of the switch power controller 231, the second end of the current sampling resistor Rcs is connected to the reference ground VS (for example, the reference ground VS is a floating ground), the control end of the power switch tube Q1 is connected to the driving end DRV of the switch power controller 231 to receive the switch drive signal DRV, and the power switch tube Q1 is used to control the transmission of power from the input end to the output end according to the switch drive signal DRV. In an exemplary embodiment, the power switch tube Q1 is an NMOS (N-Metal-Oxide-Semiconductor) transistor, and its first end, second end and control end are respectively a drain, a source and a gate. Of course, the present invention is not limited to this. In some other embodiments, the power switch tube Q1 can be a PMOS (P-Metal-Oxide-Semiconductor) transistor, and its first end, second end and control end are the source, drain and gate respectively.

[0050] A first end of the primary winding L1 is connected to a reference ground VS, and a second end is connected to a reference ground GND1. An anode of the diode D1 is connected to a first end of the secondary winding L2, and a cathode of the diode D1 is connected to a first end of the output capacitor Co and a load Ro. Second ends of the output capacitor Co and the load Ro are connected to a second end of the secondary winding L2 and the reference ground GND2.

[0051] The feedback circuit 233 is connected between the reference ground VS and the reference ground GND1, and is used to divide the DC output voltage Vout to obtain the feedback signal FB. For example, the feedback circuit 233 includes a resistor R1 and a resistor R2 connected in series between the reference ground VS and the reference ground GND1, and the middle node of the resistor R1 and the resistor R2 is used to provide the feedback signal FB.

[0052] The current sampling resistor Rcs is used to sample the current flowing through the power switch tube Q1 to obtain a current sampling signal CS, and the intermediate node between the power switch tube Q1 and the current sampling resistor Rcs is used to output the current sampling signal CS. Of course, the present invention is not limited to this, and those skilled in the art can also select other current sampling methods to obtain the current in the power switch tube Q1 according to actual circumstances.

[0053] The switching power supply controller 231 is connected to the DC input voltage Vin, the feedback signal FB, the current sampling signal CS and the reference ground VS, and is used to generate a switch drive signal DRV according to the feedback signal FB and the current sampling signal CS, and provide it to the control end of the power switch tube Q1.

[0054] exist Figure 3 In the embodiment, the ground terminal of the powered device controller 220 is connected to the reference ground GND1, and the ground terminal of the switching power supply controller 231 is connected to the reference ground VS. The two controllers are not grounded together, so the powered device controller 220 cannot be used to directly control the subsequent switching power supply converter. Therefore, the switching power supply controller 231 of this embodiment is also used to sample the DC input voltage Vin to obtain a first sampling voltage based on the reference ground VS, and convert the first sampling voltage into a second sampling voltage based on the reference ground GND1, and compare the second sampling voltage with a set threshold voltage, and then enable the switching power supply converter 230 to start working after the second sampling voltage is greater than the threshold voltage, thereby avoiding the problem that the switching power supply converter 230 starts working when the powered device controller 220 is still in the surge current limiting stage, which causes the entire PoE system to fail to start normally, thereby improving the reliability of the circuit.

[0055] Furthermore, since a capacitor Cp connected between the input voltage Vin and the reference ground GND1 is also provided between the powered device controller 220 and the switching power supply controller 231, the switching power supply controller 231 is also used to enable the switching power supply converter 230 after a preset time from the time when the second sampling voltage is greater than the threshold voltage, thereby avoiding the problem of insufficient PoE power due to the need to charge the capacitor Cp at the powered device controller end during startup, which in turn causes the switching power supply converter to be unable to provide the target output voltage, and further improves the reliability of the circuit. For example, the preset time can be set according to the time required for the capacitor Cp to charge to the platform voltage.

[0056] Figure 4 Show Figure 3 The schematic diagram of the switching power supply controller in FIG. Figure 4 As shown, the switching power supply controller 231 includes: a switching control circuit 301 , a start-up control circuit 302 , a delay circuit 303 , a power supply circuit 304 and a drive circuit 305 .

[0057] The switch control circuit 301 is used to generate a switch control signal PWM for controlling the switch action of the power switch tube Q1 according to the current sampling signal CS and the feedback signal FB, so as to stabilize the DC output voltage Vout at a set value. In an exemplary embodiment, for a switching power supply controller in a constant off-time control (COT, Constant Off-Time Control) mode, the switch control circuit 301 controls the turn-on moment of the power switch tube Q1 according to a set clock signal, and controls the turn-off moment of the power switch tube Q1 according to the feedback signal FB and the current sampling signal CS.

[0058] The startup control circuit 302 is connected between the DC input voltage Vin and the reference ground VS, and is used to sample the DC input voltage Vin to obtain the first sampling voltage, convert the first sampling voltage into the second sampling voltage, and generate a valid (for example, high level) startup indication signal POR when the second sampling voltage is greater than the threshold voltage.

[0059] The delay circuit 303 is connected to the start control circuit 302, and is used to start timing when receiving the valid start indication signal POR, and provide a valid (for example, high level) enable control signal EN to the switch control circuit 301 after the timing reaches the preset time, so as to control the switch control circuit 301 to enable operation.

[0060] The power supply circuit 304 is connected to the DC input voltage Vin and is used to provide a power supply voltage Vcc to the switch control circuit 301 according to the DC input voltage Vin. In addition, the switch power supply controller 231 also includes an input capacitor Cin connected between the power supply terminal of the switch control circuit 301 and the reference ground VS.

[0061] The input end of the driving circuit 305 is connected to the output of the switch control circuit 301, and the output end of the driving circuit 305 is connected to the control end of the power switch tube Q1. The driving circuit 305 is used to enhance and amplify the switch control signal PWM to generate a switch drive signal DRV applied to the control end of the power switch tube Q1 to control the conduction and shutdown of the power switch tube Q1.

[0062] Figure 5 Show Figure 4 The schematic diagram of the startup control circuit in FIG. Figure 5 As shown, the startup control circuit 302 includes an N-order filtering module 3021 , a voltage dividing module 3022 , a comparator CMP and a reference module 3023 .

[0063] Wherein, the N-order filter module 3021 is connected between the DC input voltage Vin and the reference ground VS, and is used to convert the first sampling voltage Va1 into the second sampling voltage Va2, where N is an integer greater than or equal to 1. For example, the N-order filter module 3021 includes N RC filter units cascaded in sequence, the first RC filter unit includes a resistor R11 and a capacitor C11, the resistor R11 and the capacitor C11 are connected in series between the DC input voltage Vin and the reference ground VS, the second RC filter unit includes a resistor R12 and a capacitor C12, the resistor R12 and the capacitor C12 are connected in series between the middle node of the resistor R11 and the capacitor C11 and the reference ground VS, and so on, the last RC filter unit includes a resistor R1N and a capacitor C1N, and the middle node of the resistor R1N and the capacitor C1N is used to output the second sampling voltage Va2.

[0064] The voltage dividing module 3022 is used to divide the second sampling voltage Va2 to obtain a voltage dividing signal Vb1 of the second sampling voltage Va2. The reference module 3023 is used to provide a first reference voltage Vref1 that represents the threshold voltage. The positive input terminal of the comparator CMP is used to receive the voltage dividing signal Vb1, and the negative input terminal of the comparator CMP is used to receive the first reference voltage Vref1. The comparator CMP is used to compare the voltage dividing signal Vb1 with the first reference voltage Vref1 to provide a start indication signal POR at the output terminal. When the voltage dividing signal Vb1 is greater than the first reference voltage Vref1, it indicates that the second sampling voltage Va2 is greater than the threshold voltage (for example, 36V), and the comparator CMP outputs a valid (for example, high level) start indication signal POR.

[0065] In this embodiment, the N-order filtering module 3021 is used to integrate and average the first sampling voltage Va1 (Va1=Vin-VS, when the voltage difference of the current sampling circuit is ignored, the first sampling voltage can also be referred to as the voltage difference between the drain and source of the power switch tube Q1) over time, so as to obtain the second sampling voltage Va2.

[0066] Assume that the voltages at the two input terminals of the N-order filter module 3021 are the first sampling voltage Va1=Vin-VS, the voltage across the capacitor Cp connected between the DC input voltage Vin and the reference ground GND1 is Vp, and the terminal voltage of the primary winding is VOR when the power switch tube Q1 is turned off.

[0067] According to Figure 4 It can be obtained that when the power switch tube Q1 is turned off:

[0068] Vin-GND1=Vp (1)

[0069] GND1-VS=VOR (2)

[0070] By adding formula (1) and (2), we can get:

[0071] Vin-VS=Vp+VOR (3)

[0072] When the power tube Q1 is turned on, the voltage on the current sampling resistor Rcs is very small and can be ignored, so Vin-VS=0.

[0073] Figure 7 Show Figure 5 The input and output waveforms of the startup control circuit in Figure 7 2 and 3 respectively show the waveforms of the input voltage Vin-VS of the startup control circuit 302 and the switch drive signal DRV. Figure 7 As shown in FIG. 1 , when the switch drive signal DRV is at a high level, the power switch tube Q1 is turned on; when the switch drive signal DRV is at a low level, the power switch tube Q1 is turned off. Among them, the ratio of the conduction time to the switching cycle time (i.e., the duty cycle) is D. Therefore, according to the above content and Figure 7 It can be seen that when the switch driving signal DRV is at a high level, Vin-VS=0; when the switch driving signal DRV is at a low level, Vin-VS=Vp+VOR.

[0074] The N-order filter module 3021 integrates Vin-VS over time and averages it (which can also be understood as filtering), and the output voltage obtained is:

[0075] Va2=(Vp+VOR)*(1-D) (4)

[0076] Because, when the power switch tube Q1 is turned on, the voltage across the primary winding L1 of the transformer T1 is Vin-GND1; when the power switch tube Q1 is turned off, the voltage across the primary winding L1 of the transformer T1 is VOR. According to the volt-second balance principle, we can get:

[0077] (Vin-GND1)*D=VOR*(1-D) (5)

[0078] Substituting formula (1) into formula (5), we can obtain:

[0079] Vp*D=VOR*(1-D) (6)

[0080] From formula (6), we can get:

[0081] VOR=Vp*D / (1-D) (7)

[0082] Substituting formula (7) into formula (4), we can obtain:

[0083] Va2=Vp=Vin-GND1.

[0084] It can be seen that the N-th order filter module 3021 realizes the conversion of the input voltage (Vin-VS) based on the reference ground VS into the output voltage (Vin-GND1) based on the reference ground GND1.

[0085] Figure 6 Show Figure 4 The schematic diagram of the switch control circuit in FIG. Figure 6 As shown, the switch control circuit 301 includes a sampling and holding module 3011 , an error amplifier P1 , a comparator P2 , a switching frequency control module 3012 and an RS trigger 3013 .

[0086] The sampling and holding module 3011 is used to sample and hold the feedback signal FB according to the switch control signal PWM to obtain the third sampled voltage Va3. For example, the sampling and holding module 3011 is used to sample the feedback signal FB when the switch control signal PWM is at a low level, and hold the sampled voltage when the switch control signal PWM is at a high level, so as to obtain the third sampled voltage Va3.

[0087] The non-inverting input terminal of the error amplifier P1 is used to receive the second reference voltage Vref2, and the inverting input terminal is used to receive the third sampling voltage Va3. The error amplifier P1 is used to amplify the difference between the second reference voltage Vref2 and the third sampling voltage Va3 to obtain an error signal Comp.

[0088] The positive input terminal of the comparator P2 is used to receive the current sampling signal CS, and the negative input terminal is used to receive the error signal Comp. The comparator P2 is used to compare the current sampling signal CS with the error signal Comp to obtain a comparison signal. For example, the comparison signal is a square wave signal with high and low levels switched.

[0089] The switching frequency control module 3012 is used to control the internal oscillator to generate the clock signal CLK according to the level amplitude of the error signal Comp, and provide the clock signal CLK with a certain clock frequency to the RS trigger 3013.

[0090] The set terminal S of the RS trigger 3013 is used to receive the clock signal CLK, the reset terminal R is connected to the output terminal of the comparator P2 to receive the comparison signal, and the output terminal Q is used to output the switch control signal PWM. For example, the RS trigger 3013 is used to set the switch control signal PWM to a high level when the rising edge of the clock signal CLK at the set terminal S arrives, thereby turning on the power switch tube Q1; and when the current sampling signal CS is greater than the error signal Comp, the comparator P2 outputs a high level, and the RS trigger 3013 sets the switch control signal PWM to a low level according to the high level of the reset terminal R, thereby turning off the power switch tube Q1. When the next rising edge of the clock signal CLK arrives, the RS trigger 3013 sets the switch control signal PWM to a high level again, and so on. It can be seen that the switching frequency of the switch control signal PWM of this embodiment can be set by the clock frequency of the clock signal CLK.

[0091] Figure 8 Show Figure 4 The waveform diagram of the start indication signal and enable control signal in Figure 8 , respectively, show the waveforms of the second sampling voltage Va2, the start indication signal POR, and the enable control signal EN. Figure 8 As shown, before time t1, the PoE system has not been turned on, and the second sampling voltage Va2 is 0 at this time, so the start indication signal POR and the enable control signal EN are both low levels. The period between time t1-t3 is the surge current limiting stage, when the PoE system is turned on, the output voltage of the rectifier bridge charges the capacitor Cp, the voltage on the capacitor Cp rises linearly, and the second sampling voltage Va2 rises linearly at the same time. At time t2, the second sampling voltage Va2 rises to the set threshold voltage, and the start indication signal POR flips to a high level. At time t3, the voltage on the capacitor Cp rises to the platform voltage (for example, 48V), and the surge current limiting ends. Time t2-t4 is the delay time set by the delay circuit. After the preset delay time, the enable control signal EN flips to a valid level (for example, a high level), and the control switch control circuit 301 starts working.

[0092] Fig. 9 Show Figure 6 The working waveform of the switch control circuit in FIG. Fig. 9As shown, during the on-time Ton, the switch drive signal DRV is at a high level, the power switch tube Q1 is turned on, and the voltage across the current sampling resistor Rcs rises. At this time, the current sampling signal CS is still very small, and the voltage sampled by the feedback circuit 233 on the primary winding L1 is negative. Since there is a reverse diode clamp inside the switching power supply controller, the negative voltage is clamped at -0.7V to prevent the negative voltage from damaging the chip. During the off-time Toff, the switch drive signal DRV is at a low level, so the power switch tube Q1 is turned off, the primary winding L1 is positive at the bottom and negative at the top, so the voltage sampled by the feedback circuit 233 is positive. In addition, it should be noted that Fig. 9 FIG. 4 shows a voltage waveform when the switch control circuit is in the DCM mode, so there is a voltage fluctuation in the feedback signal FB after the off time Toff.

[0093] Fig.10 A system block diagram of a powered device according to a second embodiment of the present invention is shown. Fig.10 The embodiment shown provides an example of a flyback topology switching power converter without an auxiliary winding and without a current sampling resistor Rcs for a powered device. Specifically, the powered device 300 includes a rectifier bridge 310, a powered device controller 320, a capacitor Cp, and a switching power converter 330. The rectifier bridge 310 and the powered device controller 320 of this embodiment are exactly the same as the rectifier bridge 210 and the powered device controller 220 of the first embodiment, and are not described in detail here.

[0094] The difference between the switching power converter 330 of this embodiment and the switching power converter 230 of the first embodiment is that the current sampling resistor Rcs is not provided in the switching power converter 330, that is, the second end of the power switch tube Q1 is directly connected to the first end of the primary winding L1 and the floating reference ground terminal VS of the switching power controller 331, and the current detection terminal CS is not provided in the switching power controller 331.

[0095] Fig.11 Show Fig.10 The schematic diagram of the switching power supply controller in FIG. Fig.11 As shown, the switching power supply controller 331 of this embodiment is Figure 4 The difference between the switching power supply controller 231 shown in FIG3 is that the switching power supply controller 331 further includes a current sampling circuit 306, wherein the current sampling circuit 306 is connected to the first end of the power switch tube Q1, and is used to obtain a current sampling signal CS representing the peak value of the inductor current according to the drain-source voltage difference of the power switch tube Q1, and provide it to the switch control circuit 301. Specifically, the current sampling circuit 306 synchronously samples the drain-source voltage difference of the power switch tube Q1 according to the on and off actions of the power switch tube Q1 to obtain the current sampling signal CS.

[0096] Fig.12 FIG. 4 is a block diagram showing a structure of an Ethernet power supply system according to a third embodiment of the present invention. Fig.12 As shown, the Ethernet power supply system 400 includes a power supply device (PSE device) 410 and a powered device (PD device) 420. The power supply device 410 can be a network device such as a switch, a router, a firewall or a hub. The powered device 420 can be an Internet Protocol (IP) phone, a wireless LAN access point, a micro base station or a network camera.

[0097] refer to Fig.12 , the power supply device 410 and the powered device 420 may be provided with multiple Ethernet interfaces, and each Ethernet interface of the power supply device 410 may be connected to an Ethernet interface of the powered device 420 via an Ethernet twisted pair cable. The power supply device 410 may transmit a data signal to the powered device 420 via the Ethernet twisted pair cable, and may also transmit a power signal to the powered device 420, thereby supplying power to the powered device 420. The powered device 420 may be implemented by the powered device 200 and the powered device 300 of the above-mentioned embodiment.

[0098] The working mode of the power supply device 410 can be controlled by a control circuit, such as an MCU controller or a power supply controller. The working mode of the power supply device 410 includes, for example, supplying normal power to the powered device 420, providing MPS current to the powered device 420, or stopping supplying power to the powered device 420.

[0099] For convenience, Fig.12 Some structures in the Ethernet power supply system are omitted. It should be understood that the omitted parts have been described in other parts of the embodiments of the present disclosure or can be inferred by those skilled in the art under the enlightenment of the contents of the present disclosure, and will not be described in detail.

[0100] In summary, the present application proposes a low-cost powered device for a PoE system, in which the powered device controller and the switching power supply controller are set to be non-shared ground. Compared with the traditional powered device including a flyback converter, the output voltage sampling can be realized through the primary winding, and there is no need to use an auxiliary winding in the circuit, which can greatly reduce the production cost and manufacturing difficulty of the flyback converter. In addition, since there is no introduction of an auxiliary winding, the electromagnetic interference inside the circuit is reduced.

[0101] In addition, the switching power converter of the present application sets the power switch tube and the switching power supply controller on the high side and the primary winding on the low side, so that the switching power supply controller and the power switch tube both use the floating ground as the reference ground, thereby reducing the difficulty of the drive design and the cost of the chip.

[0102] In addition, the switching power supply controller of the present application is also provided with a startup control circuit, through which the DC input voltage is sampled to obtain a first sampling voltage based on the floating ground, and the first sampling voltage is converted into a second sampling voltage based on the fixed ground of the powered device controller, so that the DC input voltage can be compared with the threshold voltage based on the fixed ground, so as to control the subsequent switching power supply converter to start working after the surge current limiting of the powered device controller ends. Through this design, it is ensured that the switching power supply converter starts working only after the surge current limiting of the powered device controller ends, avoiding the problem that the switching power supply converter cannot start normally.

[0103] Furthermore, the switching power supply controller of the present application is also used to delay the setting time before turning on after the second sampling voltage is greater than the threshold voltage, thereby avoiding the problem that the output voltage of the powered device is insufficient due to the need to charge the capacitor at the powered device controller end, and the switching power converter cannot output the target output voltage. Therefore, the solution of the present application not only reduces the cost of the powered device, but also improves the reliability and stability of the powered device, ensuring the normal startup and operation of the switching power converter.

[0104] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply that there is any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that the process, method, article or equipment including a series of elements includes not only those elements, but also includes other elements not explicitly listed, or also includes elements inherent to such process, method, article or equipment. In the absence of more restrictions, the elements defined by the sentence "comprise one..." do not exclude the existence of other identical elements in the process, method, article or equipment including the elements.

[0105] According to the embodiments of the present invention as described above, these embodiments do not describe all the details in detail, nor do they limit the invention to the specific embodiments described. Obviously, according to the above description, many modifications and changes can be made. This specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present invention, so that those skilled in the art can make good use of the present invention and the modified use based on the present invention. The present invention is only limited by the claims and their full scope and equivalents.

Claims

1. A power receiving device, characterized in that: include: A powered device controller, connected between the DC input voltage and the first reference ground, and used for communicating with the power supply device; as well as A switching power converter is used to convert the DC input voltage into a DC output voltage to provide an output current to a subsequent load. The switching power converter includes a power switch tube and a switching power controller for controlling the on or off of the power switch tube. The switching power controller is connected to a second reference ground, and the first reference ground is different from the second reference ground.

2. The power receiving device according to claim 1, characterized in that: The switching power supply controller is used to sample the DC input voltage to obtain a first sampling voltage based on the second reference ground, convert the first sampling voltage into a second sampling voltage based on the first reference ground, compare the second sampling voltage with a set threshold voltage, and control the switching power supply converter to enter a working state after the second sampling voltage is greater than the threshold voltage.

3. The power receiving device according to claim 2, characterized in that: The switching power supply controller is further configured to control the switching power supply converter to enter a working state after a preset time when the second sampling voltage is greater than the threshold voltage.

4. The power receiving device according to claim 3, characterized in that: Also includes: A first capacitor is provided between the powered device controller and the switching power supply controller, wherein a first end of the first capacitor is connected to the DC input voltage, and a second end of the first capacitor is connected to the first reference ground. The preset time is set according to the time required for the first capacitor to charge to the platform voltage.

5. The power receiving device according to claim 3, characterized in that: The switching power supply controller comprises: A switch control circuit generates a switch control signal according to the current sampling signal and the feedback signal of the DC output voltage; A driving circuit receives the switch control signal and generates a switch driving signal to drive the power switch tube to be turned on or off; a startup control circuit, connected between the DC input voltage and the second reference ground, configured to sample the DC input voltage to obtain the first sampled voltage based on the second reference ground, convert the first sampled voltage into the second sampled voltage based on the first reference ground, and generate a valid startup indication signal when the second sampled voltage is greater than the threshold voltage; and The delay circuit is connected to the start control circuit and is used to delay the preset time to output a valid enable control signal to the switch control circuit after receiving a valid start indication signal, so as to control the switch control circuit to be enabled and turned on.

6. The power receiving device according to claim 5, characterized in that: The startup control circuit comprises: An N-order filtering module, connected between the DC input voltage and the second reference ground, and configured to convert the first sampled voltage into the second sampled voltage, wherein N is an integer greater than or equal to 1; a voltage dividing module, configured to divide the second sampled voltage to obtain a voltage dividing signal of the second sampled voltage; and The first comparator has a non-phase input terminal for receiving the voltage division signal of the second sampling voltage, an inverting input terminal for receiving a first reference voltage representing the threshold voltage, and an output terminal for outputting the start indication signal.

7. The power receiving device according to claim 5, characterized in that: The switch control circuit comprises: A sampling and holding module, used for sampling and holding the feedback signal according to the switch control signal to obtain a sampled and held voltage; An error amplifier, whose non-phase input terminal is used to receive the second reference voltage, whose inverting input terminal is used to receive the sample-and-hold voltage, and whose output terminal is used to output an error signal; A second comparator, whose non-phase input terminal is used to receive the current sampling signal, whose inverting input terminal is used to receive the error signal, and whose output terminal is used to output a comparison signal; and The RS trigger has a set end for receiving a clock signal, a reset end for receiving the comparison signal, and an output end for providing the switch control signal.

8. The power receiving device according to claim 5, characterized in that: The switching power supply controller also includes: A power supply circuit is used to provide a power supply voltage to the switch control circuit according to the DC input voltage.

9. The power receiving device according to claim 7, characterized in that: The switch control circuit further includes: A switching frequency control module is used to generate the clock signal according to the error signal, wherein the switching frequency of the switching control signal is set by the clock frequency of the clock signal.

10. The power receiving device according to claim 5, characterized in that: The switching power converter further comprises: The power switch tube has a first end connected to the DC input voltage and a second end connected to a second reference ground; A transformer, comprising a primary winding and a secondary winding, wherein a first end of the primary winding is connected to the second reference ground, and a second end of the primary winding is connected to the first reference ground; A diode and an output capacitor are connected in series between the two ends of the secondary winding, and are used to rectify and filter the voltage across the two ends of the secondary winding to generate a DC output voltage; and A feedback circuit is connected between the second reference ground and the first reference ground, and is used for sampling the DC output voltage to obtain the feedback signal.

11. The power receiving device according to claim 10, characterized in that: The switching power converter further comprises: A current sampling resistor connected between the second end of the power switch tube and the second reference ground, the current sampling resistor is used to provide the current sampling signal to the switching power supply controller.

12. The power receiving device according to claim 10, characterized in that: The switching power supply controller also includes: The current sampling circuit is connected to the first end of the power switch tube and is used to generate the current sampling signal.

13. The power receiving device according to claim 10, characterized in that: The anode of the diode is connected to the first end of the secondary winding, the cathode of the diode is connected to the first end of the output capacitor, and the second end of the output capacitor is connected to the second end of the secondary winding and a third reference ground.

14. The power receiving device according to claim 1, characterized in that: Also includes: The rectifier bridge is used to convert the AC input voltage into the DC input voltage.

15. The power receiving device according to any one of claims 1 to 14, characterized in that: The first reference ground is a fixed ground, and the second reference ground is a floating ground.

16. An Ethernet power supply system, characterized in that: include: Power supply equipment; as well as The power receiving device according to any one of claims 1 to 15.

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