Power conversion circuit and power supply system

Abstract

The present application discloses a power conversion circuit and a power supply system. The power conversion circuit comprises: a transformer comprising a primary winding and a secondary winding; a primary interface configured to receive an excitation current, wherein the transformer is configured such that when the primary winding receives an excitation current, the secondary winding generates an initial induced current; a secondary interface configured to output an induced current; a control circuit connected to the primary winding and the primary interface, wherein the control circuit is configured to control, on the basis of a first control signal, the primary winding to receive the excitation current from the primary interface; and an output circuit connected to the secondary winding and the secondary interface, wherein the output circuit is configured to output an induced current to the secondary interface on the basis of the initial induced current, and the induced current is a continuous current.

Description

Power conversion circuits and power supply systems

[0001]

[0002] This application claims priority to Chinese Patent Application No. 202411633121.X, filed on November 14, 2024, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application relates to the field of electronic power technology, specifically to a power conversion circuit and a power supply system. Background Technology

[0004] In related technologies, regulations impose high requirements on the input harmonics of high-power charging equipment. In order to suppress current harmonics, a power factor correction (PFC) circuit is usually added to the charging circuit for power factor correction. Invention Overview

[0005] However, most charging devices on the market use Boost converters for power factor correction, but Boost converters can only boost voltage, and their output voltage is limited by the input voltage. Therefore, a DC / DC converter is usually added after the Boost converter for voltage regulation. This two-stage architecture requires more components, is more expensive, has lower energy efficiency, and wastes more energy.

[0006] With the development of new energy vehicles, high-power charging piles are becoming more and more common, and people's requirements for the performance of charging piles are also increasing.

[0007] This application provides a power conversion circuit, including a transformer, a primary-side interface, a secondary-side interface, a control circuit, and an output circuit. The transformer includes a primary-side coil and a secondary-side coil. The primary-side interface is configured to receive an excitation current. The transformer is configured such that when an excitation current is received in the primary-side coil, the secondary-side coil generates an initial induced current. The secondary-side interface is configured to output the induced current. The control circuit is connected to the primary-side coil and the primary-side interface. The control circuit is configured to control the primary-side coil to receive the excitation current from the primary-side interface based on a first control signal. The output circuit is connected to the secondary-side coil and the secondary-side interface. The output circuit is configured to output an induced current to the secondary-side interface based on the initial induced current, wherein the induced current is a continuous current.

[0008] This application also provides a power supply system for supplying power from a power source to a load. The power supply system includes the power conversion circuit as described above. The primary side interface of the power conversion circuit is connected to the power source. The secondary side interface is connected to the load. Beneficial effects

[0009] The power conversion circuit provided in this application includes an output circuit in the secondary circuit of the transformer, so that when the primary side of the transformer receives an intermittent input signal, the secondary side of the transformer can output a continuous output signal, thereby reducing the ripple of the secondary circuit of the transformer. Attached Figure Description

[0010] Figure 1 is a schematic diagram of the power conversion circuit provided in an embodiment of this application.

[0011] Figure 2 is a schematic diagram of the specific structure of a power conversion circuit provided in an embodiment of this application.

[0012] Figure 3 is a schematic diagram of another power conversion circuit provided in an embodiment of this application.

[0013] Figure 4 is a schematic diagram of the working timing of the power conversion circuit provided in the embodiment of this application.

[0014] Figure 5 is a schematic diagram of the power conversion circuit of a feedback loop provided in an embodiment of this application.

[0015] Figure 6 is a schematic diagram of the power conversion circuit of another feedback loop provided in an embodiment of this application.

[0016] Figure 7 is a schematic diagram of the working timing of the power conversion circuit provided in the embodiment of this application in the critical conduction mode.

[0017] Figure 8 is a schematic diagram of the power supply system provided in an embodiment of this application.

[0018] Explanation of reference numerals in the attached figures:

[0019] 100. Power conversion circuit; 200. Control circuit; 300. Output circuit; 400. Feedback loop; 401. Comparison circuit; 402. Second detection circuit.

[0020] Implementation methods of this application

[0021] Specifically, please refer to Figures 1 to 8. This application provides a power conversion circuit to reduce the ripple of the output current of a power factor correction circuit (PFC). The power conversion circuit provided in this embodiment will be described in detail below with reference to the accompanying drawings.

[0022] Referring to Figure 1, which is a schematic diagram of the power conversion circuit provided in this embodiment, the power conversion circuit 100 includes: a transformer, a control circuit 200, and an output circuit 300.

[0023] The transformer includes a primary coil W1 and a secondary coil W2, which are coupled to each other.

[0024] It should be noted that in the example diagram shown in Figure 1, the primary coil W1 and the secondary coil W2 are coupled with the same name, which does not constitute a limitation on this embodiment. Those skilled in the art can adjust the specific connection structure of the corresponding circuit based on the difference between same-name coupling and dissimilar-name coupling in a transformer to obtain an embodiment suitable for dissimilar-name coupling of the primary coil W1 and the secondary coil W2.

[0025] The primary side interface A of the power conversion circuit 100 is configured to receive an excitation current, the transformer is configured such that when the primary side coil W1 receives an excitation current, the secondary side coil W2 generates an initial induced current, and the secondary side interface B of the power conversion circuit 100 is configured to output the induced current.

[0026] Specifically, when the excitation current connected to the primary side interface A passes through the primary side coil W1 of the transformer, it generates a magnetic field. The secondary side coil W2 generates an initial induced current based on the magnetic field generated by the primary side coil W1. The output circuit 300 adjusts the initial induced current and outputs the induced current, which is output at the secondary side interface B.

[0027] The control circuit 200 connects the primary coil W1 and the primary interface A; the control circuit 200 is configured to control the primary coil W1 to receive excitation current from the primary interface A based on a first control signal.

[0028] As can be seen from the description of the control circuit 200, the function of the control circuit 200 can be regarded as a "switch". When the "switch" is activated, the excitation current can flow through the primary coil W1 of the transformer; when the "switch" is not activated, the excitation current cannot flow through the primary coil W1 of the transformer.

[0029] The output circuit 300 is connected to the secondary coil W2 and the secondary interface B; the output circuit 300 is configured to output an induced current to the secondary interface B based on the initial induced current, and the induced current is a continuous current.

[0030] Specifically, when the primary coil W1 is subjected to an intermittent excitation current, the magnetic field generated by the primary coil W1 is also intermittent, and the secondary coil W2 generates an intermittent initial induced current based on the intermittent magnetic field; the purpose of setting up the output circuit 300 is to make the initial induced current continuous, so that the secondary coil outputs a continuous induced current.

[0031] For the power conversion circuit 100 provided in this embodiment, an output circuit is provided in the secondary circuit of the transformer so that the secondary circuit of the transformer can output a continuous output signal when the primary circuit of the transformer is subjected to an intermittent input signal, thereby reducing the ripple of the secondary circuit of the transformer.

[0032] Referring to Figure 1 and Figures 2 and 3, which are schematic diagrams of the specific structure of the power conversion circuit provided in this embodiment, in some embodiments, the primary-side interface A is configured to connect to a power supply. In one example, the power supply includes an AC power supply Vin and a rectifier circuit, with the primary-side interface A connected to the output terminal of the rectifier circuit; wherein, the rectifier circuit is configured to rectify the AC power output from the AC power supply Vin to output DC power, and the DC power output by the rectifier circuit is the excitation current required to be connected to the primary-side interface A. Specifically, the rectifier circuit can be implemented based on a rectifier bridge; wherein, the rectifier bridge includes, but is not limited to, a full-bridge circuit or a half-bridge circuit. In another example, the power supply can be based on a DC power supply, with the primary-side interface A connected to the output terminal of the DC power supply, and the DC power of the DC power supply being the excitation current required to be connected to the primary-side interface A.

[0033] In some embodiments, the power conversion circuit 100 further includes an input energy storage capacitor Cin; wherein, if the power supply is based on a DC power supply, the input energy storage capacitor Cin is connected to the primary side interface A and is arranged in parallel with the DC power supply; if the power supply is based on an AC power supply and a rectifier circuit, the input energy storage capacitor Cin is located at the output terminal of the rectifier circuit. The input energy storage capacitor Cin is configured as an input filter to reduce the voltage ripple of the input voltage.

[0034] In some embodiments, the control circuit 200 includes a control switch, which is connected in series at a first end and / or a second end of the primary coil W1; the control switch is configured to turn on the branch where the primary coil W1 is located based on a first control signal. It should be noted that, for the first control signal described in this example, the first control signal is controlled and sent by the controller of the device containing the power conversion circuit 100.

[0035] Specifically, when the control switch is turned on, the power supply, primary coil W1, and control switch form a circuit, and the excitation current flows through the primary coil W1, thereby generating a magnetic field in the primary coil W1. When the control switch is turned off, the power supply, primary coil W1, and control switch cannot form a circuit, and the excitation current cannot flow through the primary coil W1.

[0036] Specifically, when the control switch is off, the power supply and the primary coil W1 form a circuit, and the excitation current flows through the primary coil W1, thereby generating a magnetic field in the primary coil W1. When the control switch is on, the power supply and the control switch form a circuit, and the excitation current cannot flow through the primary coil W1.

[0037] In some embodiments, the control switch is based on a first MOSFET Q1, wherein the gate of the first MOSFET Q1 is configured to receive a first control signal. It should be noted that Figures 2 and 3 illustrate the control switch using the first MOSFET Q1 interface, but this does not constitute a limitation of this embodiment. In other embodiments, the control switch may also be based on a switch, or a relay or other switching structure.

[0038] In some embodiments, the output circuit 300 includes a conversion capacitor C1, a conversion inductor L1, and a current-cutting circuit. The first terminal of the conversion capacitor C1 is connected to the first terminal of the secondary coil W2; the first terminal of the conversion inductor L1 is connected to the second terminal of the conversion capacitor C1; the input terminal of the current-cutting circuit is connected to the second terminal of the secondary coil W2 and forms a secondary interface B with the second terminal of the conversion inductor L1, and its output terminal is connected to the second terminal of the conversion capacitor C1; the current-cutting circuit is configured to conduct the branch containing the current-cutting circuit based on a preset conduction direction.

[0039] Specifically, the purpose of setting up the current-cutting circuit is to ensure unidirectional current flow from the input terminal to the output terminal. In some embodiments, specifically referring to FIG2, the current-cutting circuit can be based on diode D1, which can ensure unidirectional current flow from the input terminal to the output terminal. In other embodiments, specifically referring to FIG3, the current-cutting circuit can be based on a second MOSFET Q2, the gate of which is configured to receive a second control signal, ensuring unidirectional current flow by switching the circuit branch on and off. Specifically, when the current-cutting circuit needs to carry current in a preset conduction direction, the second MOSFET Q2 is turned on by the second control signal; when the current-cutting circuit does not need to carry current in a preset conduction direction, the second MOSFET Q2 is turned off by the second control signal. It should be noted that the second control signal described in this embodiment is controlled and sent by the controller of the device containing the power conversion circuit 100.

[0040] In some embodiments, the secondary interface B of the power conversion circuit 100 is configured to connect to the load Ro, and the power supplied by the power source is supplied to the load Ro through the power conversion circuit 100 to complete the power supply of the power source to the load Ro.

[0041] In some embodiments, the power conversion circuit 100 further includes an output energy storage capacitor Co, which is connected to the secondary interface B and in parallel with the load Ro. The output energy storage capacitor Co is configured as an output filter to reduce the voltage ripple of the output voltage.

[0042] The working principle of the power conversion circuit shown in Figure 2 is illustrated in Figure 4, which is a timing diagram of the power conversion circuit provided in this embodiment. In the figure, i_L1 represents the current flowing through the conversion inductor L1, i_CO represents the current flowing through the output energy storage capacitor Co, i_Q1 represents the current flowing through the first MOSFET Q1, VDS_Q1 represents the source-drain voltage of the first MOSFET Q1, and PWM_Q1 represents the waveform of the first control signal corresponding to the first MOSFET Q1.

[0043] For the primary circuit of the transformer, when the first MOSFET Q1 is turned on (PWM_Q1 is high), the magnetizing current flows through the primary coil W1 and the first MOSFET Q1, thus generating a current i_Q1 flowing through the first MOSFET Q1. i_Q1 increases instantaneously, but due to the presence of the primary coil W1, the loop current cannot jump to its maximum instantaneously; instead, it increases slowly. That is, the current flowing through the primary coil W1 and the first MOSFET Q1 gradually increases, and i_Q1 gradually increases while PWM_Q1 is high. When the first MOSFET Q1 is turned off, the magnetizing current can no longer flow through the primary coil W1 and the first MOSFET Q1, and i_Q1 instantly returns to zero.

[0044] Furthermore, when the first MOSFET Q1 is turned on, its impedance is close to 0, and it can be considered as a wire. Therefore, the source-drain power supply VDS_Q1 of the first MOSFET Q1 is 0. When the first MOSFET Q1 is turned off, its impedance is very large, so the source-drain power supply VDS_Q1 of the first MOSFET Q1 is close to the power supply voltage. As the primary coil W1 discharges, the voltage drop across the primary coil W1 gradually decreases, and the source-drain power supply VDS_Q1 of the first MOSFET Q1 slowly increases to the power supply voltage.

[0045] For the secondary circuit of the transformer, when the primary coil W1 generates a magnetic field based on the excitation current, and the secondary coil W2 generates an initial induced current based on the magnetic field, diode D1 is cut off, capacitor C1 discharges, and inductor L1 charges. The current i_L1 flowing through inductor L1 increases, naturally increasing the current flowing through the load Ro and the output capacitor Co. When the primary coil W1 no longer generates a magnetic field and the secondary coil W2 no longer generates an induced current, diode D1 turns on, capacitor C1 charges, and inductor L1 enters freewheeling mode. The current i_L1 flowing through inductor L1 decreases, naturally decreasing the current flowing through the load Ro and the output capacitor Co.

[0046] In short, the function of the output circuit 300 can be regarded as the function of the boost circuit, which is configured to perform boost discharge. However, the output circuit 300 provided in this embodiment splits the components in the original boost circuit and partially sets them in the secondary output circuit of the transformer to reduce the ripple of the secondary output current.

[0047] In some embodiments, the output energy storage capacitor Co is based on an electrolytic capacitor. The capacitance of an electrolytic capacitor can be set to a higher value than that of a regular capacitor, but as the capacitance increases, the circuit area and device cost it occupies will increase significantly. In the power conversion circuit 100 provided in this embodiment, since the ripple of the secondary circuit is reduced, the capacitance value of the required output energy storage capacitor Co is reduced. The output energy storage capacitor Co, which is based on an electrolytic capacitor, no longer needs to be set to a large capacitance value, which greatly reduces the circuit area occupied by the output energy storage capacitor Co and greatly reduces the circuit cost.

[0048] As mentioned above, when the control circuit 200 controls the primary coil W1 to receive the excitation current, the output parameters of the secondary interface B increase; when the control circuit 200 controls the primary coil W1 to not receive the excitation current, the output parameters of the secondary interface B decrease.

[0049] In some embodiments, the power conversion circuit 100 further includes a feedback loop 400. The feedback loop 400 is configured to adjust the duty cycle of the first control signal based on a comparison between the output parameters of the secondary interface B and preset parameters. The output parameters of the secondary interface B may include output current, output voltage, etc., and the preset parameters may also be preset current, preset voltage, etc.

[0050] The feedback loop 400 outputs the duty cycle of the first control signal based on the comparison result between the output current of the secondary interface B and the preset current, or the comparison result between the output voltage of the secondary interface B and the preset voltage. The duty cycle of the first control signal determines the conduction time of the control circuit 200, thereby adjusting the output parameter of the secondary interface B.

[0051] In this embodiment, the power conversion circuit 100 is configured with a feedback loop 400 to stabilize the output of the power conversion circuit 100, and the output parameters of the power conversion circuit 100 are close to the preset parameters.

[0052] Referring specifically to Figure 5, in some embodiments, the feedback loop 400 includes a first detection circuit, a comparison circuit 401, and a processing circuit. The first detection circuit is configured to acquire the output parameters of the secondary interface B; the comparison circuit 401 is configured to generate a parameter adjustment value based on the comparison result between the output parameters of the secondary interface B and preset parameters; and the processing circuit is configured to adjust the duty cycle of the first control signal based on the parameter adjustment value.

[0053] In one example, the first detection circuit can read the output parameters of the secondary interface B using a voltmeter or ammeter; in another example, the first detection circuit can obtain the output parameters of the secondary interface B using a probe or similar means.

[0054] For the comparator circuit 401, in some embodiments, after the first detection circuit obtains the output voltage Vo of the secondary interface B, the difference between the output voltage Vo and the reference voltage Vref is adjusted by the compensation network to generate a first compensation voltage VEA. The first compensation voltage VEA is adjusted by the input voltage Vin to generate a compensation current Iref. The difference between the compensation current Iref and the input current Iin is adjusted by the compensation network to generate a parameter adjustment value VFB.

[0055] It should be noted that the specific structure of the comparison circuit 401 and processing circuit shown in Figure 5 does not constitute a limitation on this embodiment. Those skilled in the art can set the structure of the specific feedback loop 400 according to the textual description of the comparison circuit 401 and processing circuit and the required functions of the feedback loop 400.

[0056] In one example, the processing circuit generates a first control signal based on a parameter adjustment value VFB and an initial control pulse, wherein the parameter adjustment value VFB is configured to adjust the duty cycle of the generated first control signal.

[0057] Referring to Figure 6, in some embodiments, the feedback loop 400 further includes: a second detection circuit 402 and a judgment circuit. The second detection circuit 402 is configured to acquire the output parameters of the secondary coil W2; the judgment circuit is configured to determine whether the output parameters of the secondary coil W2 are at a valley value, and if the output parameters are at a valley value, to provide a trigger signal; the processing circuit is configured to provide a first control signal based on the trigger signal.

[0058] Specifically, the second detection circuit 402 detects whether the output parameter of the secondary coil W2 is at its lowest value, thereby triggering the critical conduction mode (CRM) of the power conversion circuit 100 based on the embodiment of this application.

[0059] It should be noted that the valley detection circuit in Figure 6, which is composed of a coil and a resistor connected in parallel, is configured to implement the functions of the second detection circuit 402 and the judgment circuit. This does not constitute a limitation on this embodiment. Those skilled in the art can select other detection and judgment methods based on the description of the second detection circuit 402 and the judgment circuit. For example, the output parameters of the secondary coil W2 can be read by means of a voltmeter or an ammeter, or the output parameters of the secondary coil W2 can be obtained by means of a probe.

[0060] For the critical conduction mode, its working principle is shown in Figure 7. Combined with Figure 4, the relevant descriptions in Figure 4 will not be repeated in this embodiment. The difference between Figure 7 and Figure 4 is that in the critical conduction mode, the turn-on time and turn-off time of the control circuit 200 are just enough to make the output parameters of the secondary coil W2 reach the peak / valley value. When the output parameters of the secondary coil W2 reach the peak / valley value, the input parameters of the primary coil W1 also reach the peak / valley value accordingly. Therefore, after the current i_Q1 flowing through the first MOS transistor Q1 gradually increases to the peak value, the first MOS transistor Q1 is turned off, and PWM_Q1 jumps to the low level.

[0061] For the power conversion circuit 100 provided in this embodiment, an output circuit is provided in the secondary circuit of the transformer so that the secondary circuit of the transformer can output a continuous output signal when the primary circuit of the transformer is subjected to an intermittent input signal, thereby reducing the ripple of the secondary circuit of the transformer.

[0062] It should be noted that the ripple mentioned in the above description in this embodiment, if configured to characterize voltage ripple, represents the difference between the maximum and minimum voltage values; if configured to characterize current ripple, represents the difference between the maximum and minimum current values.

[0063] It should be noted that, without conflict, the features applied for in the power conversion circuit provided in the above embodiments can be randomly combined to obtain new power conversion circuit embodiments.

[0064] Another embodiment of this application provides a power supply system for supplying power from a power source to a load. The power supply system includes a power conversion circuit as provided in the above embodiments. The primary side interface of the power conversion circuit is connected to the power source, and the secondary side interface of the power conversion circuit is connected to the load.

[0065] The power conversion circuits in the embodiments of this application can refer to the descriptions in any of the above embodiments of this application, and will not be repeated here.

[0066] In some embodiments, the power supply system includes multiple power conversion circuits, the primary interfaces of the multiple power conversion circuits are connected in parallel and connected to a power source, and the secondary interfaces of the multiple power conversion circuits are connected in parallel and connected to a load.

[0067] As shown in Figure 8, there are N power conversion circuits, where N ≥ 2 and N is an integer.

[0068] Referring specifically to Figure 8, which is a schematic diagram of the power supply system in this embodiment, the primary interfaces of multiple power conversion circuits are connected to the same power source, and the secondary interfaces are connected to the same load, thereby realizing the interleaved parallel connection of multiple power conversion circuits to further improve the power supply parameters such as power supply voltage and power supply power of the power supply system.

[0069] It should be noted that in the example of this application shown in Figure 8, the primary-side interfaces of multiple power conversion circuits are connected to the same power supply. In other embodiments, the primary-side interfaces of multiple power conversion circuits can be connected to different power supplies.

[0070] In the power supply system provided in this embodiment, an output circuit is set in the secondary circuit of the transformer so that the secondary circuit of the transformer can output a continuous output signal when the primary circuit of the transformer is subjected to an intermittent input signal, thereby reducing the ripple of the secondary circuit of the transformer.

[0071] In addition, the power supply system provided in this embodiment can be applied to vehicle power supply systems, and the vehicle can be a fuel vehicle, a plug-in hybrid electric vehicle, or a new energy vehicle, etc. This application does not make any specific limitations in this regard.

Claims

1. A power conversion circuit, comprising: A transformer consists of a primary winding and a secondary winding; The primary side interface is configured to receive the excitation current. The transformer is configured such that when the primary winding is connected to an excitation current, the secondary winding generates an initial induced current. The secondary interface is configured to output induced current; The control circuit connects the primary coil and the primary interface; The control circuit is configured to control the primary coil to receive the excitation current from the primary interface based on a first control signal. An output circuit is connected to the secondary coil and the secondary interface; the output circuit is configured to output the induced current to the secondary interface according to the initial induced current, the induced current being a continuous current.

2. The power conversion circuit of claim 1, wherein, The output circuit includes: A switching capacitor, wherein the first end of the switching capacitor is connected to the first end of the secondary coil; A switching inductor, wherein the first end of the switching inductor is connected to the second end of the switching capacitor; A current-cutting circuit is provided, wherein the input terminal of the current-cutting circuit is connected to the second terminal of the secondary coil, and the input terminal of the current-cutting circuit and the second terminal of the conversion inductor form the secondary interface; and the output terminal of the current-cutting circuit is connected to the second terminal of the conversion capacitor. The current-cutting circuit is configured to conduct the branch where the current-cutting circuit is located based on a preset conduction direction.

3. The power conversion circuit of claim 1 or 2, wherein, The control circuit includes a control switch, which is connected in series at the first end and / or the second end of the primary coil; the control switch is configured to turn on the branch where the primary coil is located based on the first control signal.

4. The power conversion circuit of any one of claims 1 to 3, wherein, The primary-side interface is configured to connect to a power source, the secondary-side interface is configured to connect to a load, and the power conversion circuit further includes: An input energy storage capacitor is connected to the primary-side interface and is configured in parallel with the power supply. An output energy storage capacitor is connected to the secondary interface and is configured in parallel with the load.

5. The power conversion circuit of claim 4, wherein, The output energy storage capacitor is based on an electrolytic capacitor.

6. The power conversion circuit of any one of claims 1 to 5, wherein, The power conversion circuit further includes a feedback loop configured to adjust the duty cycle of the first control signal based on a comparison between the output parameters of the secondary interface and preset parameters.

7. The power conversion circuit of claim 6, wherein, The feedback loop includes: The first detection circuit is configured to acquire the output parameters of the secondary interface. The comparator circuit is configured to generate a parameter adjustment value based on the comparison result between the output parameter of the secondary interface and the preset parameter; The processing circuit is configured to adjust the duty cycle of the first control signal based on the parameter adjustment value.

8. The power conversion circuit of claim 7, wherein, The feedback loop also includes: The second detection circuit is configured to acquire the output parameters of the secondary coil. The judgment circuit is configured to determine whether the output parameter of the secondary coil is a valley value, and if the output parameter is the valley value, then provide a trigger signal; The processing circuit is configured to provide the first control signal based on the trigger signal.

9. A power supply system for supplying power from a power source to a load, the power supply system comprising a power conversion circuit as described in any one of claims 1 to 8, wherein the primary side interface of the power conversion circuit is connected to the power source, and the secondary side interface of the power conversion circuit is connected to the load.

10. The power supply system of claim 9, wherein, The power conversion circuit comprises a primary side interface and a secondary side interface. The power conversion circuit comprises a primary side interface and a secondary side interface.

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