Powered device and power over ethernet system

Abstract

Disclosed in the present invention are a powered device and a power over Ethernet system. The power over Ethernet system comprises: a powered device controller, which is connected between a direct-current input voltage and a first reference ground, and is used for communicating with power sourcing equipment; and a switch power supply converter, which is used for converting the direct-current input voltage into a direct-current output voltage, and providing an output current to a post-stage load, wherein the switch power supply converter comprises a power switch tube and a switch power supply controller for controlling the turn-on or turn-off of the power switch tube, the switch power supply controller is connected to a second reference ground, and the first reference ground is different from the second reference ground. In the present invention, a powered device controller and a switch power supply controller are configured to be not commonly grounded, such that the sampling of an output voltage can be realized by means of a primary winding without the need to use an auxiliary winding in a circuit, thereby greatly reducing the production cost and manufacturing difficulty of the circuit.

Description

Powered device and power over Ethernet system

[0001] The present application claims priority to the Chinese Invention Application No. 202411154369.8, filed on August 21, 2024, entitled “Powered device and power over Ethernet system”, and incorporates by reference the entire specification, claims, drawings, and abstract of the aforementioned Chinese Invention Application. TECHNICAL FIELD

[0002] The present application relates to the field of electronic technology, and more particularly, to a powered device and a power over Ethernet system. BACKGROUND

[0003] Power over Ethernet (PoE) is a technology that can transmit power and data to a device through a twisted pair cable in Ethernet. This technology is compatible with the existing Ethernet cabling infrastructure and allows devices to be powered through their network ports, thus eliminating the need for power cables and saving on wiring and hardware costs. Power over Ethernet technology has been widely used in video telephones, security, IoT devices and other fields.

[0004] A power over Ethernet system generally includes a power sourcing equipment (PSE), a powered device (PD), and an Ethernet cable that transmits power and data between the two.

[0005] In a PoE power supply system, the powered device usually needs to convert the high-voltage alternating current received from the Ethernet cable into low-voltage direct current suitable for internal circuit use. Flyback converter is a commonly used power conversion topology, which is widely used in power management of powered devices due to its simplicity, low cost, high efficiency and other advantages.

[0006] The flyback converter usually comprises a primary side circuit and a secondary side circuit, and a constant voltage is outputted in the secondary side circuit by controlling the on-off of the power switch in the primary side circuit. In the PoE system, the post-stage switch power converter must start to work after the surge current limiting of the pre-stage powered device controller ends, otherwise it may cause the failure of normal start, so the powered device controller usually outputs an enable signal to control the working state of the post-stage switch power converter. If the post-stage switch power converter and the pre-stage powered device controller are common ground, the enable signal outputted by the powered device controller can be directly used to control the post-stage switch power converter. However, if the powered device controller and the post-stage switch power converter are not common ground, the enable signal outputted by the powered device controller usually needs to be level-converted before being used to control the post-stage switch power converter, which not only increases the complexity of the control circuit, but also requires high-voltage BCD process to design the controller, resulting in cost increase.

[0007] FIG. 1 shows a system structure block diagram of a powered device according to the prior art, and FIG. 2 shows a circuit schematic diagram of a switch power converter according to the prior art. As shown in FIG. 1 and FIG. 2, the existing powered device 100 comprises a rectifier bridge 110, a powered device controller 120 and a switch power converter 130, wherein the switch power converter 130 is realized by a flyback converter, comprising a starting circuit 131, a switch control circuit 132, a power switch Q1, a primary winding L1, a secondary winding L2, a diode D2 and an output capacitor Co. In the existing powered device, the output ground of the powered device controller 120 is connected with the ground terminal of the switch power converter 130, so that the powered device controller 120 can directly control the post-stage switch power converter 130 through the PG terminal, without the need of setting a level conversion circuit between them, thereby reducing the complexity of the control circuit. However, this scheme needs to increase an auxiliary winding L3 and a diode D1 in the switch power converter 130 to obtain the output voltage feedback parameter, and the feedback signal of the output voltage is obtained by dividing the voltage across the auxiliary winding L3 through resistors R1 and R2. Since the winding process of the auxiliary winding is relatively complex, the existing scheme increases the production cost and manufacturing difficulty of the powered device, and the introduction of the auxiliary winding may also cause electromagnetic interference in the circuit. SUMMARY

[0008] Therefore, the purpose of the present application is to provide a powered device and a PoE system, in which the powered device controller and the switch power controller are set to be not common ground, so that the output voltage can be sampled through the primary winding, without the need of using an auxiliary winding in the circuit, thereby greatly reducing the production cost and manufacturing difficulty of the circuit.

[0009] According to an aspect of the present application, a power receiving device is provided, comprising: a power receiving 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 load, wherein the switching power converter comprises a power switch and a switching power controller for controlling the power switch to turn on or turn off, the switching power controller being connected to a second reference ground, and the first reference ground being different from the second reference ground.

[0010] Optionally, the switching power controller is configured to sample the DC input voltage to obtain a first sampling voltage referenced to the second reference ground, convert the first sampling voltage into a second sampling voltage referenced to the first reference ground, compare the second sampling voltage with a threshold voltage, and control the switching power converter to enter an operating state after the second sampling voltage is greater than the threshold voltage.

[0011] Optionally, the switching power controller is further configured to control the switching power converter to enter the operating state after a preset time when the second sampling voltage is greater than the threshold voltage.

[0012] Optionally, the power receiving device further comprises a first capacitor disposed between the power receiving device controller and the switching power controller, a first end of the first capacitor being connected to the DC input voltage, and a second end of the first capacitor being connected to the first reference ground, wherein the preset time is set according to a time required for charging the first capacitor to a plateau voltage.

[0013] Optionally, the switching power controller comprises: a switching control circuit configured to generate a switching control signal according to a current sampling signal and a feedback signal of the DC output voltage; a driving circuit configured to receive the switching control signal and generate a switching driving signal to drive the power switch to turn on or turn off; a start control circuit connected between the DC input voltage and the second reference ground, configured to sample the DC input voltage to obtain the first sampling voltage referenced to the second reference ground, convert the first sampling voltage into the second sampling voltage referenced to the first reference ground, and generate an effective start indication signal when the second sampling voltage is greater than the threshold voltage; and a delay circuit connected to the start control circuit, configured to output an effective enable control signal to the switching control circuit after a delay of the preset time when the effective start indication signal is received, to control the switching control circuit to enable the switching control circuit to start.

[0014] Optionally, the start control circuit comprises: an N-order filter module connected between the DC input voltage and the second reference ground, configured to convert the first sampling voltage into the second sampling voltage, where N is an integer greater than or equal to 1; a voltage dividing module configured to divide the second sampling voltage to obtain a voltage dividing signal of the second sampling voltage; and a first comparator having a positive input end configured to receive the voltage dividing signal of the second sampling voltage, a negative input end configured to receive a first reference voltage representing the threshold voltage, and an output end configured to output the start indication signal.

[0015] Optionally, the switch control circuit comprises: a sample-and-hold module configured to sample and hold the feedback signal according to the switch control signal to obtain a sample-and-hold voltage; an error amplifier having a positive input end configured to receive a second reference voltage, a negative input end configured to receive the sample-and-hold voltage, and an output end configured to output an error signal; a second comparator having a positive input end configured to receive the current sampling signal, a negative input end configured to receive the error signal, and an output end configured to output a comparison signal; and an RS flip-flop having a set end configured to receive a clock signal, a reset end configured to receive the comparison signal, and an output end configured to provide the switch control signal.

[0016] Optionally, the switch power supply controller further comprises: a power supply circuit configured to provide a power voltage to the switch control circuit according to the DC input voltage.

[0017] Optionally, the switch control circuit further comprises: a switch frequency control module configured to generate the clock signal according to the error signal, where a switch frequency of the switch control signal is set by a clock frequency of the clock signal.

[0018] Optionally, the switch power supply converter further comprises: the power switch tube having 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, the primary winding having a first end connected to the second reference ground and a second end connected to the first reference ground; a diode and an output capacitor connected in series between two ends of the secondary winding, configured to rectify and filter a 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, configured to sample the DC output voltage to obtain the feedback signal.

[0019] Optionally, the switch power supply converter further comprises: a current sampling resistor connected between the second end of the power switch tube and the second reference ground, configured to provide the current sampling signal to the switch power supply controller.

[0020] Optionally, the switching power supply controller further comprises a current sampling circuit connected to the first end of the power switch tube, for generating the current sampling signal.

[0021] Optionally, 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 the third reference ground.

[0022] Optionally, the switching power supply converter further comprises a rectifier bridge for converting an alternating input voltage into the direct input voltage.

[0023] Optionally, the first reference ground is a fixed ground, and the second reference ground is a floating ground.

[0024] According to another aspect of the present application, there is provided a power over Ethernet system, comprising a power sourcing equipment and the above-mentioned powered device.

[0025] In summary, the present application provides a low-cost powered device for a PoE system, in which the powered device controller and the switching power supply controller are arranged in a non-common ground manner. Compared with the conventional powered device containing a flyback converter, the output voltage can be sampled through the primary winding, and an auxiliary winding is not needed in the circuit, which can greatly reduce the production cost and manufacturing difficulty of the flyback converter. Moreover, the introduction of the auxiliary winding reduces the electromagnetic interference inside the circuit.

[0026] In addition, the switching power supply converter of the present application arranges the power switch tube and the switching power supply controller on the high side and arranges the primary winding on the low side, so that the switching power supply controller and the power switch tube are both referenced to the floating ground, thereby reducing the difficulty of driving design and the cost of the chip.

[0027] In addition, the switching power supply controller of the present application further comprises a start control circuit, which samples the direct input voltage to obtain a first sampling voltage referenced to the floating ground, and converts the first sampling voltage into a second sampling voltage referenced to the fixed ground of the powered device controller, so that the second sampling voltage referenced to the fixed ground can be compared with a threshold voltage referenced to the fixed ground, to control the start of the subsequent switching power supply converter after the surge current limiting of the powered device controller is completed. Through this design, it is ensured that the switching power supply converter starts to work only after the surge current limiting of the powered device controller is completed, thereby avoiding the problem that the switching power supply converter cannot start normally.

[0028] Further, the switch power supply controller of the present application is further used to delay the starting for a set time after the second sampling voltage is greater than the threshold voltage, so as to avoid the problem that the output voltage of the powered device is insufficient due to the charging of the capacitor at the powered device controller end, and thus the switch power supply converter cannot output the target output voltage. Therefore, the scheme of the present application not only reduces the cost of the powered device, but also improves the reliability and stability of the powered device, and ensures the normal starting and operation of the switch power supply converter. BRIEF DESCRIPTION OF DRAWINGS

[0029] The above and other objects, features and advantages of the present application will become more apparent from the following description when taken in conjunction with the accompanying drawings, in which:

[0030] Fig. 1 shows a system structure block diagram of a powered device according to the prior art.

[0031] Fig. 2 shows a circuit schematic diagram of a switch power supply converter according to the prior art.

[0032] Fig. 3 shows a system structure block diagram of a powered device according to a first embodiment of the present application.

[0033] Fig. 4 shows a structure schematic diagram of a switch power supply controller in Fig. 3.

[0034] Fig. 5 shows a structure schematic diagram of a starting control circuit in Fig. 4.

[0035] Fig. 6 shows a structure schematic diagram of a switch control circuit in Fig. 4.

[0036] Fig. 7 shows an input and output waveform diagram of the starting control circuit in Fig. 5.

[0037] Fig. 8 shows a waveform diagram of a starting indication signal and an enable control signal in Fig. 4.

[0038] Fig. 9 shows a working waveform diagram of the switch control circuit in Fig. 6.

[0039] Fig. 10 shows a system structure block diagram of a powered device according to a second embodiment of the present application.

[0040] Fig. 11 shows a structure schematic diagram of a switch power supply controller in Fig. 10.

[0041] Fig. 12 shows a structure block diagram of a power over Ethernet system according to a third embodiment of the present application. DETAILED DESCRIPTION

[0042] Various embodiments of the present application will be described in more detail with reference to the drawings. In the various drawings, the same elements are denoted by the same or similar reference numerals. For the sake of clarity, each part in the drawings is not drawn to scale.

[0043] The present application can be presented in various forms, some examples of which will be described below.

[0044] Fig. 3 shows a system structure block diagram of the powered device according to the first embodiment of the present application. As shown in Fig. 3, the powered device 200 of the present embodiment includes a rectifier bridge 210, a powered device controller 220, a capacitor Cp and a switching power converter 230.

[0045] The rectifier bridge 210 is configured to rectify the AC input voltage obtained from the Ethernet cable to obtain a DC input voltage Vin.

[0046] The powered device controller 220 is connected between the DC input voltage Vin and the reference ground GND1, and is configured to perform a handshake protocol with a power sourcing equipment (PSE device) in the PoE system, and output the required energy to the switching power converter 230 in the rear stage after obtaining the required energy. 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 presence 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 such as current, voltage and temperature during power transmission. Once an abnormal situation is detected, the powered device controller will take prompt 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 IEEE 802.3bt, etc. 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.

[0047] 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 configured to perform a smoothing filtering on the DC input voltage Vin, and to absorb the inrush current during the startup of the powered device controller 220. For example, the capacitor Cp can be an electrolytic capacitor or a ceramic capacitor.

[0048] The switching power converter 230 is configured to perform power conversion and regulation functions, and converts the DC input voltage Vin into a DC output voltage Vout suitable for use by the powered device, so as to minimize energy loss and ensure stable operation of the device.

[0049] In an example, the first embodiment of the present application provides a switching power converter 230 with an auxiliary winding-free flyback topology, which includes a switching power controller 231, a power switch 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.

[0050] In an example, the first end of the power switch Q1 (e.g., a transistor, a field effect transistor, a thyristor, etc.) is connected to the DC input voltage Vin, the second end of the power switch Q1 is connected to the first end of the current sampling resistor Rcs and the current sensing terminal CS of the switching power controller 231, the second end of the current sampling resistor Rcs is connected to the reference ground VS (e.g., a floating ground), the control terminal of the power switch Q1 is connected to the driving terminal DRV of the switching power controller 231 to receive a switching driving signal DRV, and the power switch Q1 is configured to control the power transmission from the input terminal to the output terminal according to the switching driving signal DRV. In an example, the power switch Q1 is an NMOS (N-Metal-Oxide-Semiconductor) transistor, and the first end, the second end, and the control terminal of the power switch Q1 are the drain, the source, and the gate, respectively. Of course, the present application is not limited thereto, and in other examples, the power switch Q1 can be a PMOS (P-Metal-Oxide-Semiconductor) transistor, and the first end, the second end, and the control terminal of the power switch Q1 are the source, the drain, and the gate, respectively.

[0051] The first end of the primary winding L1 is connected to the reference ground VS, the second end of the primary winding L1 is connected to the reference ground GND1, the anode of the diode D1 is connected to the first end of the secondary winding L2, the cathode of the diode D1 is connected to the first end of the output capacitor Co and the load Ro, and the second end of the output capacitor Co and the load Ro is connected to the second end of the secondary winding L2 and the reference ground GND2.

[0052] The feedback circuit 233 is connected between the reference ground VS and the reference ground GND1, and is configured to divide the DC output voltage Vout to obtain a feedback signal FB. In an 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 intermediate node of the resistor R1 and the resistor R2 is configured to provide the feedback signal FB.

[0053] The current sampling resistor Rcs is used to sample the current flowing through the power switch Q1 to obtain a current sampling signal CS, and the middle node of the power switch Q1 and the current sampling resistor Rcs is used to output the current sampling signal CS. Of course, the present application does not limit this, and those skilled in the art can also select other current sampling methods to obtain the current in the power switch Q1 according to the actual situation.

[0054] The switching power supply controller 231 is connected with 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 switching 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 Q1.

[0055] In FIG. 3, the ground end of the powered device controller 220 is connected to the reference ground GND1, and the ground end of the switching power supply controller 231 is connected to the reference ground VS, and the two controllers are not common ground, so the powered device controller 220 cannot be used to directly control the switching power supply converter in the rear stage. Therefore, the switching power supply controller 231 of the present embodiment is also used to sample the DC input voltage Vin to obtain a first sampling voltage with the reference ground VS as the reference, and convert the first sampling voltage to a second sampling voltage with the reference ground GND1 as the reference, and compare the second sampling voltage with a set threshold voltage, and make the switching power supply converter 230 start to work after the second sampling voltage is greater than the threshold voltage, so as to avoid the problem that the switching power supply converter 230 starts to work when the powered device controller 220 is still in the surge current limiting stage, causing the entire PoE system to fail to start normally, and improve the reliability of the circuit.

[0056] Further, since the 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 to start after a preset time after the second sampling voltage is greater than the threshold voltage, so as to avoid the problem that the PoE power is insufficient due to the charging of the capacitor Cp at the powered device controller end during startup, and then causing the switching power supply converter to fail to provide the target output voltage, and further improve the reliability of the circuit. For example, the preset time can be set according to the time required for charging the capacitor Cp to the platform voltage.

[0057] FIG. 4 shows a structural schematic diagram of the switching power supply controller in FIG. 3. As shown in FIG. 4, the switching power supply controller 231 includes a switching control circuit 301, a start control circuit 302, a delay circuit 303, a power supply circuit 304 and a drive circuit 305.

[0058] The switch control circuit 301 is configured to generate a switch control signal PWM for controlling the switch operation of the power switch 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 switch power supply controller in a constant off-time control (COT) mode, the switch control circuit 301 controls the turn-on time of the power switch Q1 according to a set clock signal, and controls the turn-off time of the power switch Q1 according to the feedback signal FB and the current sampling signal CS.

[0059] The start control circuit 302 is connected between the DC input voltage Vin and the reference ground VS, configured 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 an effective (e.g., high level) start indication signal POR when the second sampling voltage is greater than the threshold voltage.

[0060] The delay circuit 303 is connected with the start control circuit 302, configured to start timing when the effective start indication signal POR is received, and provide an effective (e.g., 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.

[0061] The power supply circuit 304 is connected with the DC input voltage Vin, configured 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 further comprises an input capacitor Cin connected between the power supply end of the switch control circuit 301 and the reference ground VS.

[0062] The input end of the drive circuit 305 is connected with the output of the switch control circuit 301, and the output of the drive circuit 305 is connected with the control end of the power switch Q1. The drive circuit 305 is configured to enhance and amplify the switch control signal PWM, so as to generate a switch drive signal DRV applied to the control end of the power switch Q1, and control the turn-on and turn-off of the power switch Q1.

[0063] FIG. 5 shows a structure diagram of the start control circuit in FIG. 4. As shown in FIG. 5, the start control circuit 302 comprises an N-order filter module 3021, a voltage division module 3022, a comparator CMP, and a reference module 3023.

[0064] The N-order filtering module 3021 is connected between the direct current input voltage Vin and the reference ground VS, and is configured to convert the first sampling voltage Va1 into a second sampling voltage Va2, where N is an integer greater than or equal to 1. In an example, the N-order filtering module 3021 includes N RC filtering units connected in cascade. The first RC filtering unit includes a resistor R11 and a capacitor C11 connected in series between the direct current input voltage Vin and the reference ground VS. The second RC filtering unit includes a resistor R12 and a capacitor C12 connected in series between the intermediate node of the resistor R11 and the capacitor C11 and the reference ground VS. The last RC filtering unit includes a resistor R1N and a capacitor C1N, and the intermediate node of the resistor R1N and the capacitor C1N is configured to output the second sampling voltage Va2.

[0065] The voltage dividing module 3022 is configured 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 configured to provide a first reference voltage Vref1 representing the threshold voltage. The positive input terminal of the comparator CMP is configured to receive the voltage dividing signal Vb1, and the inverting input terminal of the comparator CMP is configured to receive the first reference voltage Vref1. The comparator CMP is configured 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, which represents that the second sampling voltage Va2 is greater than the threshold voltage (for example, 36V), the comparator CMP outputs the valid (for example, high level) start indication signal POR.

[0066] In this embodiment, the N-order filtering module 3021 is configured to integrate and average the first sampling voltage Va1 (Va1=Vin-VS, which can also be referred to as the voltage difference between the source and the drain of the power switch Q1 in the case of ignoring the voltage difference of the current sampling circuit) with respect to time, thereby obtaining the second sampling voltage Va2.

[0067] Suppose that the voltages at the two input terminals of the N-order filtering module 3021 are the first sampling voltage Va1=Vin-VS, and the voltage across the capacitor Cp connected between the direct current input voltage Vin and the reference ground GND1 is Vp. When the power switch Q1 is off, the voltage at the terminal of the primary winding is VOR.

[0068] According to FIG. 4, when the power switch Q1 is off, the following equation can be obtained:

[0069] (1)

[0070] (2)

[0071] Adding formula (1) and (2) can obtain:

[0072] (3)

[0073] When the power tube Q1 is turned on, the voltage on the current sampling resistor Rcs is very small and can be ignored, so .

[0074] Figure 7 shows the input and output waveform diagram of the start-up control circuit in Figure 5, and Figure 7 shows the waveform diagram of the input voltage Vin-VS and the switch driving signal DRV of the start-up control circuit 302. As shown in Figure 7, when the switch driving signal DRV is high, the power switch tube Q1 is turned on; when the switch driving signal DRV is low, the power switch tube Q1 is turned off. The ratio of the on-time to the switching cycle time (i.e. the duty cycle) is D. Therefore, according to the above content and Figure 7, when the switch driving signal DRV is high, Vin-VS=0; when the switch driving signal DRV is low, Vin-VS=Vp+VOR.

[0075] The N-order filter module 3021 integrates and averages (which can also be understood as filtering) Vin-VS with respect to time, and the output voltage obtained is:

[0076] (4)

[0077] Because, when the power switch tube Q1 is turned on, the voltage of the primary winding L1 of the transformer T1 is Vin-GND1; when the power switch tube Q1 is turned off, the voltage of the primary winding L1 of the transformer T1 is VOR, according to the volt-second balance principle, the following can be obtained:

[0078] (5)

[0079] Substituting formula (1) into formula (5), the following can be obtained:

[0080] (6)

[0081] According to formula (6), the following can be obtained:

[0082] (7)

[0083] Substituting formula (7) into formula (4), the following can be obtained:

[0084] 。

[0085] Therefore, the N-order filter module 3021 realizes the conversion of the input voltage (Vin-VS) with the reference ground VS as the reference to the output voltage (Vin-GND1) with the reference ground GND1 as the reference.

[0086] FIG. 6 shows a structure diagram of the switch control circuit in FIG. 4. As shown in FIG. 6, the switch control circuit 301 includes a sample-and-hold module 3011, an error amplifier P1, a comparator P2, a switch frequency control module 3012, and an RS flip-flop 3013.

[0087] The sample-and-hold module 3011 is configured to sample and hold the feedback signal FB according to the switch control signal PWM to obtain a third sampling voltage Va3. For example, the sample-and-hold module 3011 is configured 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 sampling voltage Va3.

[0088] The non-inverting input terminal of the error amplifier P1 is configured to receive the second reference voltage Vref2, and the inverting input terminal is configured to receive the third sampling voltage Va3. The error amplifier P1 is configured to amplify the difference between the second reference voltage Vref2 and the third sampling voltage Va3 to obtain an error signal Comp.

[0089] The non-inverting input terminal of the comparator P2 is configured to receive the current sampling signal CS, and the inverting input terminal is configured to receive the error signal Comp. The comparator P2 is configured 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.

[0090] The switch frequency control module 3012 is configured to control the internal oscillator to generate a clock signal CLK according to the amplitude of the error signal Comp, and provide the clock signal CLK with a certain clock frequency to the RS flip-flop 3013.

[0091] The set terminal S of the RS flip-flop 3013 is configured 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 configured to output the switch control signal PWM. For example, the RS flip-flop 3013 is configured to set the switch control signal PWM to high level when the rising edge of the clock signal CLK of the set terminal S arrives, so as to turn on the power switch Q1. When the current sampling signal CS is greater than the error signal Comp, the comparator P2 outputs high level, and the RS flip-flop 3013 sets the switch control signal PWM to low level according to the high level of the reset terminal R, so as to turn off the power switch Q1. When the next rising edge of the clock signal CLK arrives, the RS flip-flop 3013 sets the switch control signal PWM to high level again, and the process is repeated. Therefore, the switching frequency of the switch control signal PWM in the embodiment can be set by the clock frequency of the clock signal CLK.

[0092] Fig. 8 shows the waveforms of the start-up indication signal and the enable control signal in Fig. 4, and Fig. 8 shows the waveforms of the second sampling voltage Va2, the start-up indication signal POR and the enable control signal EN, respectively. As shown in Fig. 8, before time t1, the PoE system has not been started up, at this time, the second sampling voltage Va2 is 0, thus the start-up indication signal POR and the enable control signal EN are both low. Between time t1 and t3, it is the inrush current limiting stage, at this time, the PoE system has been started up, the output voltage of the rectifier bridge charges the capacitor Cp, the voltage on the capacitor Cp linearly rises, and the second sampling voltage Va2 linearly rises. At time t2, the second sampling voltage Va2 rises to the set threshold voltage, the start-up indication signal POR flips to high. At time t3, the voltage on the capacitor Cp rises to the platform voltage (for example, 48V), the inrush current limiting ends, the delay time set by the delay circuit is between time t2 and t4, after the preset time, the enable control signal EN flips to the active level (for example, high), and the switch control circuit 301 starts to work.

[0093] Fig. 9 shows the working waveforms of the switch control circuit in Fig. 6. As shown in Fig. 9, during the on time Ton, the switch drive signal DRV is high, the power switch Q1 is on, and the voltage across the current sampling resistor Rcs rises, at this time, the current sampling signal CS is still small, the feedback circuit 233 samples the voltage of the primary winding L1 as negative voltage, and the negative voltage is clamped at -0.7V by the reverse diode in the switch power supply controller, so as to prevent the negative voltage from damaging the chip. During the off time Toff, the switch drive signal DRV is low, thus the power switch Q1 is off, and the voltage of the primary winding L1 is positive. In addition, it should be noted that the voltage waveforms shown in Fig. 9 are in the DCM mode of the switch control circuit, thus there is a voltage fluctuation in the feedback signal FB after the off time Toff.

[0094] Fig. 10 shows the system structure block diagram of the powered device according to the second embodiment of the present application. The embodiment shown in Fig. 10 gives an example of the switch power supply converter of the flyback topology without auxiliary winding and without current sampling resistor Rcs for the powered device. Specifically, the powered device 300 includes a rectifier bridge 310, a powered device controller 320, a capacitor Cp and a switch power supply converter 330. The rectifier bridge 310 and the powered device controller 320 of the present embodiment are completely the same as the rectifier bridge 210 and the powered device controller 220 of the first embodiment, and will not be described here again.

[0095] In the switching power supply converter 330, a current sampling resistor Rcs is not arranged, i.e., the second terminal of the power switch Q1 is directly connected to the first terminal of the primary winding L1 and the floating reference ground terminal VS of the switching power supply controller 331, and the current detection terminal CS is not arranged in the switching power supply controller 331.

[0096] FIG. 11 shows a structure diagram of the switching power supply controller in FIG. 10. As shown in FIG. 11, the switching power supply controller 331 in the embodiment further includes a current sampling circuit 306, which is connected to the first terminal of the power switch Q1, for obtaining a current sampling signal CS representing the peak value of the inductor current according to the drain-source voltage difference of the power switch Q1 and providing the current sampling signal CS to the switching control circuit 301. Specifically, the current sampling circuit 306 samples the drain-source voltage difference of the power switch Q1 synchronously according to the on and off actions of the power switch Q1 to obtain the current sampling signal CS.

[0097] FIG. 12 shows a structure block diagram of a power over Ethernet system according to a third embodiment of the present application. As shown in FIG. 12, the power over Ethernet system 400 includes a power supplying device (PSE device) 410 and a power receiving device (PD device) 420. The PSE device 410 can be a network device such as a switch, a router, a firewall or a hub. The PD device 420 can be an Internet Protocol (IP) telephone, a wireless local area network access point, a micro base station or a network camera.

[0098] Referring to FIG. 12, the PSE device 410 and the PD device 420 can each be provided with a plurality of Ethernet interfaces, and each Ethernet interface of the PSE device 410 can be connected to one Ethernet interface of the PD device 420 through one Ethernet twisted pair. The PSE device 410 can transmit data signals to the PD device 420 through the Ethernet twisted pair and can also transmit power signals to the PD device 420 to supply power to the PD device 420. The PD device 420 can be implemented by the PD device 200 and the PD device 300 in the above embodiments.

[0099] The working mode of the PSE device 410 can be controlled by a control circuit, for example, an MCU controller or a power supply controller, and the working mode of the PSE device 410 can include, for example, normally supplying power to the PD device 420, providing an MPS current to the PD device 420, or stopping supplying power to the PD device 420.

[0100] For the convenience of illustration, some structures in the power over Ethernet system are omitted in FIG. 12. 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 inspiration of the present disclosure, and will not be described here again.

[0101] In summary, the power receiving device for the PoE system provided by the present application has low cost, the power receiving device controller and the switching power supply controller are arranged in a non-common ground manner, compared with the traditional power receiving device containing a flyback converter, the output voltage can be sampled through the primary winding, and an auxiliary winding does not need to be used in the circuit, so that the production cost and manufacturing difficulty of the flyback converter can be greatly reduced. Moreover, since the auxiliary winding is not introduced, the electromagnetic interference in the circuit is reduced.

[0102] In addition, the switching power supply converter of the present application arranges the power switch tube and the switching power supply controller on the high side and arranges the primary winding on the low side, so that the switching power supply controller and the power switch tube are both referenced to the floating ground, thereby reducing the difficulty of driving design and the cost of the chip.

[0103] In addition, the switching power supply controller of the present application further comprises a starting control circuit, the starting control circuit samples the direct current input voltage to obtain a first sampling voltage referenced to the floating ground, and converts the first sampling voltage into a second sampling voltage referenced to the fixed ground of the power receiving device controller, so that the direct current input voltage can be compared with a threshold voltage referenced to the fixed ground, to control the starting of the switching power supply converter after the surge current limiting of the power receiving device controller is completed. Through this design, it is ensured that the switching power supply converter starts to work only after the surge current limiting of the power receiving device controller is completed, and the problem that the switching power supply converter cannot start normally is avoided.

[0104] Further, the switching power supply controller of the present application is further used to delay for a set time before being started again after the second sampling voltage is greater than the threshold voltage, so as to avoid the problem that the output voltage of the power receiving device is insufficient due to the need to charge the capacitor at the power receiving device controller end, and the problem that the switching power supply converter cannot output the target output voltage. Therefore, the scheme of the present application not only reduces the cost of the power receiving device, but also improves the reliability and stability of the power receiving device, and ensures the normal starting and running of the switching power supply converter.

[0105] It is to be understood that the phrases such as first and second, and the like, can refer to various inanimate entities or actions that are to be distinguished from, but not necessarily implicitly related to, or ordered in time, one another. Moreover, the terms "comprises", "comprising", or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but can include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element proceeded by "comprises... a" does not, without more constraints, exclude the existence of additional identical elements in the process, method, article, or apparatus that comprises the recited element.

[0106] In accordance with the practices of the present application, these embodiments have been described in relation to the above-described embodiments, which are merely illustrative of the many possible modifications and variations that come within the scope of the present application. It is therefore apparent that claims are intended to cover all modifications and variations of this application unless claimed otherwise, including full use of equivalents.

Claims

1. A power receiving device characterized by comprising: The application relates to a power supply system, comprising: a power receiving device controller connected between a direct current input voltage and a first reference ground for communicating with a power supply device; a switching power converter for converting the direct current input voltage into a direct current output voltage to provide an output current to a load, wherein the switching power converter comprises a power switch and a switching power controller for controlling the on or off of the power switch, the switching power controller being connected to a second reference ground, and the first reference ground being different from the second reference ground. The switching power controller is configured to sample the direct current input voltage to obtain a first sampling voltage referenced to the second reference ground, convert the first sampling voltage into a second sampling voltage referenced to the first reference ground, compare the second sampling voltage with a set threshold voltage, and control the switching power converter to enter an operating state after the second sampling voltage is greater than the threshold voltage.

2. The power receiving apparatus according to claim 1, characterized by, The switching power controller is further configured to control the switching power converter to enter the operating state after a preset time when the second sampling voltage is greater than the threshold voltage.

3. The power receiving apparatus according to claim 2, characterized in that, The application further comprises:

4. The power-receiving apparatus according to claim 3, wherein a first capacitor arranged between the power receiving device controller and the switching power controller, a first end of the first capacitor being connected to the direct current input voltage, and a second end of the first capacitor being connected to the first reference ground, wherein the preset time is set according to a time required for charging the first capacitor to a platform voltage. The switching power controller comprises:

5. The power-receiving apparatus according to claim 3, wherein a switching control circuit configured to generate a switching control signal according to a current sampling signal and a feedback signal of the direct current output voltage; a driving circuit configured to receive the switching control signal and generate a switching driving signal to drive the on or off of the power switch; a start control circuit connected between the direct current input voltage and the second reference ground, configured to sample the direct current input voltage to obtain the first sampling voltage referenced to the second reference ground, convert the first sampling voltage into the second sampling voltage referenced to the first reference ground, and generate a valid start indication signal when the second sampling voltage is greater than the threshold voltage; and a delay circuit connected to the start control circuit, configured to output a valid enable control signal to the switching control circuit after a delay of the preset time when the valid start indication signal is received, to control the switching control circuit to enable the on. The start control circuit comprises:

6. The power-receiving apparatus according to claim 5, wherein an N-order filtering module connected between the direct current input voltage and the second reference ground, configured to convert the first sampling voltage into the second sampling voltage, wherein N is an integer greater than or equal to 1; a voltage dividing module configured to divide the second sampling voltage to obtain a voltage dividing signal of the second sampling voltage; and a first comparator having a positive input end configured to receive the voltage dividing signal of the second sampling voltage, a negative input end configured to receive a first reference voltage representing the threshold voltage, and an output end configured to output the start indication signal. The switching control circuit comprises:

7. The power-receiving apparatus according to claim 5, wherein ​ a sample-and-hold module configured to sample and hold the feedback signal according to the switch control signal to obtain a sample-and-hold voltage; an error amplifier having a non-inverting input configured to receive a second reference voltage, an inverting input configured to receive the sample-and-hold voltage, and an output configured to output an error signal; a second comparator having a non-inverting input configured to receive the current sampling signal, an inverting input configured to receive the error signal, and an output configured to output a comparison signal; and an RS flip-flop having a set input configured to receive a clock signal, a reset input configured to receive the comparison signal, and an output configured to provide the switch control signal.

8. The power-receiving apparatus according to claim 5, wherein The switch power supply controller further comprises: a power supply circuit configured to provide a power voltage to the switch control circuit according to the direct current input voltage.

9. The power receiving apparatus according to claim 7, wherein The switch control circuit further comprises: a switch frequency control module configured to generate the clock signal according to the error signal, wherein a switch frequency of the switch control signal is set by a clock frequency of the clock signal.

10. The power-receiving apparatus according to claim 5, wherein The switch power supply converter further comprises: the power switch tube, a first end of which is connected with the direct current input voltage, and a second end of which is connected with a second reference ground; a transformer including a primary winding and a secondary winding, a first end of the primary winding being connected with the second reference ground, and a second end of the primary winding being connected with the first reference ground; a diode and an output capacitor connected in series between two ends of the secondary winding, configured to rectify and filter a voltage across the secondary winding to generate a direct current output voltage; and a feedback circuit connected between the second reference ground and the first reference ground, configured to sample the direct current output voltage to obtain the feedback signal.

11. The power receiving apparatus according to claim 10, wherein The switch power supply 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 being configured to provide the current sampling signal to the switch power supply controller.

12. The power receiving apparatus according to claim 10, wherein The switch power supply controller further comprises: a current sampling circuit connected with the first end of the power switch tube, configured to generate the current sampling signal.

13. The power-receiving apparatus according to claim 10, wherein an anode of the diode being connected with a first end of the secondary winding, a cathode of the diode being connected with a first end of the output capacitor, and a second end of the output capacitor being connected with a second end of the secondary winding and a third reference ground.

14. The power-receiving apparatus according to claim 1, wherein The switch power supply converter further comprises: a rectifier bridge configured to convert an alternating current input voltage into the direct current input voltage.

15. The powered device of any one of claims 1-14, wherein, The first reference ground is a fixed ground, and the second reference ground is a floating ground.

16. A Power over Ethernet system, characterized by The switch power supply converter comprises: a power supply device; and a powered device according to any one of claims 1 to 15. The switch power supply converter comprises: a power supply device; and a powered device according to any one of claims 1 to 15.

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