Isolation power supply of Buck structure

Abstract

An isolation power supply of a Buck structure belongs to the field of power supply circuit structures, and is characterized in that in an isolation power supply converter using a transformer primary winding as a Buck structure power supply converter inductor, an MOS switch tube Q2 is used for replacing a freewheel diode of the Buck structure power supply, and the Buck structure power supply works in an FCCM mode; according to the utility model, a non-isolated Buck-structure power supply output and an isolated power supply output can be output at the same time, the device has the characteristics of high forward power density and high transient response, and also has the capability of flyback multi-path output, and when a converter of a Buck structure and a secondary side of a transformer are controlled to work in an FCCM (Forced Continuous Current Modulation) mode, the output voltage of the converter and the secondary side of the transformer are reduced. Energy bidirectional transmission among secondary side output, primary side output and input ends can be realized, so that a better cross adjustment index is achieved, and compared with a conventional power supply structure, each path of output can drive a larger honor load and an inductive load.

Description

Technical Field

[0001] The present invention belongs to the field of power supply circuit structures, and particularly relates to an isolated power supply with a Buck structure. Background Art

[0002] Isolated power supplies are required in many application scenarios. Common isolated power supplies have various topological structures such as flyback, forward, LLC, etc. Their basic conversion methods are all isolated through transformers, and the voltage is regulated by using the primary or secondary feedback method.

[0003] The flyback isolated power supply has the characteristics of simple structure and multiple outputs. However, the power density of the flyback is smaller than that of the forward, not suitable for high power, and the cross-regulation rate is poor when there are multiple outputs. The forward power supply has a complex structure and is not suitable for multiple outputs, but its power density is larger than that of the flyback. That is, under the same power condition, the volume of the transformer can be smaller. Compared with the flyback, it has a higher transient response ability and is often used in high-power power conversion. The LLC conversion circuit has a complex structure and cumbersome parameter design, and is more suitable for occasions with relatively large power and high efficiency requirements.

[0004] Improvements to existing power converters based on the standard Buck structure, such as a switching buck converter disclosed in the document with publication number CN205566087U, are composed of a MOS switching tube, an inductor, a freewheeling diode, an input capacitor, an output capacitor, etc. As Figure 1 shown, its basic composition is to use the primary winding of the transformer as the inductor of the Buck structure power converter on the basis of the Buck structure, use the same-name end of the secondary side of the transformer and the primary output terminal as the isolated power supply output, and the secondary winding is rectified by a rectifier diode to obtain the isolated output voltage; the primary winding is grounded through a freewheeling diode. The MOS switching tube Q1 is periodically turned on and off by PWM control. When the input power is turned on by Q1, it flows into the input end of the inductor through Q1 and flows to the output end through the inductor. The output capacitor is used for filtering. When Q1 is turned off, the input end of the inductor continues to flow through the freewheeling diode from the ground loop to continue charging the output capacitor until the current on the inductor drops to zero or PWM controls Q1 to be turned on again. If the current on the inductor has dropped to zero during the period when PWM controls Q1 to be turned off and Q1 still remains off, the current on the inductor remains zero until PWM controls Q1 to be turned on again. This mode is called DCM (discontinuous current mode); if the current on the inductor has not dropped to zero during the period when PWM controls Q1 to be turned off and PWM controls the MOS switching tube to be turned on again, the current on the inductor will resume growth. This mode is called CCM (continuous current mode); if the inductor current drops to zero and PWM controls Q1 to be turned on again, it is called the critical mode.

[0005] A switching buck converter disclosed by the prior art can only provide auxiliary power supply with relatively small power on the secondary side, and the isolation function ability of the secondary side is affected by the primary input voltage and the primary output power, and cannot provide an isolated power supply with relatively stable output power and large output power. Summary of the Invention

[0006] The present invention aims to solve the above problems and provides an isolated power supply with a Buck structure that can simultaneously output a non-isolated power supply output of a Buck structure and an isolated power supply output after isolation.

[0007] In the isolated power supply with a Buck structure of the present invention, in an isolated power converter that uses the primary winding of a transformer as the inductor of a Buck structure power converter, a MOS switch tube Q2 is used to replace the freewheeling diode of the Buck structure power supply, and the Buck structure power supply operates in the FCCM mode; during the PWM off period, Q2 is turned on by a drive complementary to the PWM. When driven, at this time, the magnetic energy in the transformer winding forms a standard freewheeling process of the Buck power converter on the primary side, and a flyback power converter is formed on the secondary side of the transformer. The magnetic energy of the transformer is simultaneously converted into energy for both the primary winding and the secondary winding. VOBuck and IVOut are proportional to the number of turns of the primary and secondary windings of the transformer; when the magnetic energy in the transformer winding is completely converted into electrical energy, if Q2 is still in the on state, at this time, the voltage on the output capacitor COut of the output terminal VObuck of the Buck structure power supply passes through the loop formed by the transformer and Q2, generating a reverse current on the primary side of the transformer. At this time, the reverse currents of the secondary winding and the primary winding form a forward converter. The induced voltage generated by the forward conversion on the secondary side and the drive voltage on the primary side are proportional to the number of turns of the primary and secondary sides of the transformer. Therefore, under the drive of VOBuck on the primary side, the induced voltage generated on the secondary side is IVOut and has the same polarity as that during flyback, and the energy is transmitted from the primary output VOBuck to the secondary output IVOut. The energy on out is transferred to CIOut through the transformer. Therefore, in the FCCM mode, a higher power output can be obtained on the secondary side, and in an ideal state, only through the feedback regulation of the Buck structure power supply on the primary side, a stable voltage can be output on the secondary side.

[0008] Furthermore, for the isolated power supply with the Buck structure of the present invention, the rectifying diode of the secondary winding of the transformer is replaced by the MOS switch tube Q3, and Q3 operates in the FCCM mode, maintaining simultaneous on and off with Q2. Among the three ports of Vin, IVOut, and VObuck, three independent bidirectional DCDC conversion circuits are formed by pairwise combination; thus, the energy between the isolated output terminal IVOut and the output terminal VObuck of the Buck structure power supply can be transferred to each other, and the energy transfer direction depends on the magnitudes of the loads of their respective loops; meanwhile, the energy at the IVOut and VObuck terminals can also be transferred to the power input terminal Vin to achieve energy feedback.

[0009] Furthermore, for the isolated power supply with the Buck structure of the present invention, the voltages of the three ports of Vin, IVOut, and VObuck depend on the duty cycle of the PWM and the turns ratio of the primary and secondary windings of the transformer; when the load of a certain port is large, the energy flowing out of it increases; when there is net energy inflow into a certain port, the bidirectional DCDC conversion mechanism causes the energy to flow to other ports. When there is energy inflow into both the IVOut and VObuck ports, the bidirectional DCDC conversion mechanism causes the energy to flow to the Vin input terminal, enabling the isolated power supply with the Buck structure of the present invention to drive capacitive loads and inductive loads larger than those of conventional power supplies.

[0010] Furthermore, for the isolated power supply with the Buck structure of the present invention, the transformer includes multiple secondary windings, and each secondary winding uses a MOS switch tube to replace the rectifying diode, and the MOS switch tubes used to replace the rectifying diodes all operate in the FCCM mode, maintaining simultaneous on and off with Q2. Among each port of the secondary output, VObuck, and Vin, multiple DCDC bidirectional conversion circuits are formed by pairwise combination; thus, the energy between each secondary output port IVout2 and more output ports and IVOut can also be transferred to each other, that is, for the isolated power supply with the Buck structure composed of multiple secondary windings, its secondary output ports can output energy and can also input energy, can drive capacitive loads and inductive loads larger than those of conventional power supplies, and can provide a better cross-regulation rate than conventional isolated power supplies.

[0011] The present invention provides an isolated power supply based on the Buck structure, which can simultaneously output the power output of the non-isolated Buck structure and the isolated power output, and has the characteristics of high forward power density and high transient response, and also has the ability of flyback multi-output. When controlling the Buck structure converter and the secondary side of the transformer to operate in the FCCM, that is, the forced continuous current mode, the bidirectional energy transfer between the secondary output, the primary output, and the input terminal can be realized, thereby having better cross-regulation rate indicators, and compared with the conventional power supply structure for each output, it can drive larger capacitive loads and inductive loads. Description of the Drawings

[0012] Figure 1 Schematic diagram of the circuit structure of the Buck - type power converter described in the background art of the present invention; Figure 2 Schematic diagram of the isolated power supply circuit structure of the Buck - type described in the embodiment of the present invention; Figure 3 Schematic diagram of the circuit structure in which both the primary and secondary sides operate in the FCCM mode in the embodiment of the present invention; Figure 4 Schematic diagram of the circuit structure with dual - output on the secondary side and using the FCCM mode in the embodiment of the present invention; Figure 5 Schematic diagram of the circuit structure described in the embodiment of the present invention. Detailed implementation manners

[0013] The isolated power supply based on the Buck - type structure of the present invention will be described in detail below with reference to the accompanying drawings and embodiments.

[0014] As Figure 1 shown, the primary winding of the transformer is used as the inductor of the Buck - type structure, a standard Buck - type power converter is formed on the primary side of the transformer, the port of the secondary winding that is of the same name as the output end of the primary winding is used as the isolated power supply output, and the isolated output voltage is obtained through diode rectification. In an ideal state, the ratio of the output voltage to the voltage output by the Buck - type power supply is equal to the ratio of the number of turns of the primary and secondary windings of the transformer. It should be noted that in actual engineering, the forward conduction voltage drop of the diode, the DC resistance of the transformer winding, and the voltage loss caused by the leakage inductance of the transformer due to process and other factors need to be considered.

[0015] For the Buck - type power converter, a free - wheeling diode is used to free - wheel the inductor, and there is no reverse current flowing through the inductor. When the primary winding of the transformer is used as the inductor of the Buck - type structure, when the PWM controls Q1 to turn off, the magnetic energy in the inductor can either free - wheel through the diode to continue charging COut or charge CIOut through the rectifier diode on the secondary side, which depends on the magnitudes of the loads at the VObuck terminal and the IVout terminal. At this time, the operation of the secondary winding is similar to that of a fly - back power supply, that is, its energy comes from the magnetic energy stored in the inductor. Therefore, in this structure, the power obtained by the secondary IVout is restricted by the magnitude of the input voltage and the load at the VObuck terminal. Those skilled in the art can easily prove that the maximum power that can be output at the IVout terminal is: Where is the power output by the secondary isolated power supply, is the actual power output by the Buck - type power supply formed by the primary winding. The above formula shows that as Figure 1The converter with the basic Buck structure shown can only provide an isolated power supply output with limited power. As an isolated power supply for small-signal transmission or when the VObuck load is large enough, or when the input voltage Vin is high enough, as long as the above requirements are met, it can work properly and output the required isolated voltage.

[0016] Embodiment 1 To increase the output power of the secondary isolated power supply, this embodiment discloses an isolated power supply with a Buck structure, as Figure 2 shown. In an isolated power supply converter that uses the primary winding of the transformer as the inductor of the Buck structure power converter, an MOS switch tube Q2 is used to replace the freewheeling diode, and the power supply with the Buck structure operates in the FCCM mode. During the PWM off period, Q2 is driven by a drive complementary to the PWM to conduct. At this time, the magnetic energy in the transformer winding forms a standard freewheeling process of the Buck power converter on the primary side, and a flyback power converter is formed on the secondary side of the transformer. The magnetic energy of the transformer converts energy to both the primary winding and the secondary winding at the same time. VOBuck and IVOut are proportional to the number of turns of the primary and secondary windings of the transformer. After the magnetic energy in the transformer winding is completely converted into electrical energy, if Q2 is still in the conducting state, the voltage on the output capacitor COut of the output terminal VObuck of the Buck structure power supply passes through the loop formed by the transformer and Q2, generating a reverse current on the primary side of the transformer. The reverse currents in the secondary winding and the primary winding form a forward converter.

[0017] Q2 is driven by a signal complementary to the PWM, that is, Q2 is off when Q1 is on, and Q2 is on when Q1 is off. In this mode, it is called FCCM (forced continuous current mode). In the FCCM mode, after the PWM controls Q1 to turn off, the inductor current continues to decrease. If it drops to zero and the PWM still controls Q1 to be in the off state, at this time Q2 is in the on state, then a reverse current will be generated in the inductor until the PWM controls Q1 to turn on, controls Q2 to turn off. At this time, the current in the inductor still flows in the reverse direction, feeding back energy to the bus input terminal until the reverse current in the inductor drops to zero, or the PWM controls Q1 to turn off, and at the same time controls Q2 to turn on; if the reverse current in the inductor drops to zero and Q1 still remains on and Q2 remains off, then the current in the inductor starts to rise from zero, and the inductor current is positive until the PWM controls Q1 to turn off, and at the same time controls Q2 to turn on; if the reverse current in the inductor does not drop to zero, the PWM controls Q1 to turn off, and at the same time When Q2 is turned on, the current in the inductor continues to flow in the reverse direction. Therefore, in the FCCM mode, there are three different forms of current in the inductor of the Buck-structured power supply: the first is a continuous forward current, and the magnitude of the current changes periodically with the PWM; the second is that the current in the inductor alternates between forward and reverse, and its period is the same as the PWM period; the third is a continuous reverse current in the inductor, and the magnitude of the reverse current changes periodically with the PWM. The average current in the inductor is called the operating point of the FCCM mode circuit. When the operating point is positive, energy flows from the input terminal Vin to the output terminal VObuck; when the operating point is negative, energy flows from VObuck to Vin; when the operating point is zero, there is no energy transfer between Vin and VObuck. This Buck-structured power converter that can transfer energy bidirectionally is called a bidirectional DCDC conversion circuit.

[0018] As described above, when operating in the FCCM mode, the Buck-structured power converter actually becomes a bidirectional DCDC power converter in which energy can be transferred from the input terminal to the output terminal or from the output terminal to the input terminal.

[0019] In the FCCM mode, when Q1 is turned on and Q2 is turned off, a forward current flows through the primary winding of the transformer, and the magnetic energy in the transformer increases. When Q1 is turned off and Q2 is turned on, the magnetic energy in the transformer is demanded by the primary winding through Q2 and continues to charge COut. At the same time, the secondary winding charges CIOut through D2. When the magnetic energy in the transformer is completely released and drops to zero, if Q2 remains turned on and Q2 remains turned off, then COut forms a reverse current in the primary winding of the transformer through the loop composed of Q2 and the primary winding of the transformer. At this time, the secondary winding of the transformer operates in the forward power supply mode, and the induced electromotive force of the secondary winding continues to charge CIOut through D2. Therefore, in the FCCM mode, the isolated power supply output by the secondary winding can provide a higher output power.

[0020] Embodiment 2 Based on the above Embodiment 1, as Figure 3The isolated power supply with a Buck structure disclosed in this embodiment uses a MOS switch Q3 to replace the rectifying diode of the secondary winding of the transformer. Q3 operates in the FCCM mode and is kept on and off simultaneously with Q2. Among the three ports of Vin, IVOut, and VObuck, three independent bidirectional DCDC conversion circuits are formed by pairwise combinations. The voltages of the three ports of Vin, IVOut, and VObuck depend on the duty cycle of the PWM and the turns ratio of the primary and secondary windings of the transformer. When the load of a certain port is large, the energy flowing out of it increases. When there is a net inflow of energy into a certain port, the bidirectional DCDC conversion mechanism causes the energy to flow to other ports. When there is an inflow of energy into both the IVOut and VObuck ports, the bidirectional DCDC conversion mechanism causes the energy to flow to the Vin input terminal.

[0021] In the embodiment of the present disclosure, when Q3 operates in the FCCM mode, Q3 is kept off when Q1 is on, and Q3 is on when Q1 is off. In this operating state, the IVout terminal is similar to the VObuck terminal on the primary side. During the period when Q3 is on and Q1 is off, when the magnetic energy in the transformer drops to zero, the energy on CIOut can form a reverse current through Q3 and the secondary winding of the transformer, and convert the electrical energy into magnetic energy in the transformer. When the PWM controls Q1 to turn on in the next cycle, When controlling Q2 and Q3 to turn off, the magnetic energy in the transformer feeds back energy to the bus input terminal Vin through Q1. Therefore, when the power output loop formed by the secondary winding operates in the FCCM mode, it also constitutes an isolated bidirectional DCDC converter. In the case where IVOut absorbs energy from the outside, this bidirectional structure allows energy to be transferred from the IVout port to the Vin and VObuck terminals.

[0022] Based on the isolated power supply with a Buck structure disclosed in this embodiment, in specific applications, such as Figure 4 As shown, when the transformer includes two secondary windings, each secondary winding uses MOS switches Q3 and Q4 to replace the rectifying diodes, and the MOS switches used to replace the rectifying diodes all operate in the FCCM mode and are kept on and off simultaneously with Q2. Then, between each port of the secondary output and VObuck and Vin, multiple DCDC bidirectional conversion circuits are formed by pairwise combinations.

[0023] The multi-channel isolated output power supply formed by multiple secondary windings simultaneously has the characteristic of bidirectional energy transmission. In this case, energy can be transferred between the primary winding output terminal VObuck, the bus input terminal Vin, and all secondary output terminals, IVout, IVout2, and more output terminals. The direction of energy transfer depends on the amount of energy absorbed or output by each port.

[0024] This multi-to-multi energy transfer characteristic is completely determined by the circuit itself and does not require an additional control circuit to control the energy transfer direction. Under ideal conditions, that is, without considering the leakage inductance of the transformer, the distributed resistance, and the forward voltage drop of the diode (the conduction voltage of the MOS switch tube), the voltage at each port will be strictly stable at the state set by the circuit, that is: the ratio of VObuck to the output voltages of multiple secondary sides is the same as the ratio of the number of turns of their corresponding windings, and the voltage ratio of VObuck to Vin is equal to the duty cycle of PWM. In actual engineering, various factors such as the internal resistance of the transformer, the leakage inductance of the transformer, the distributed resistance of the circuit, the conduction voltage drop of the MOS switch tube, and the delay time of the switch tube turning on and off need to be considered.

[0025] Under ideal conditions, the isolated power supply with multiple outputs has a very high cross-regulation rate, and its output voltage will not be affected by the load change. The entire circuit only needs to adjust the PWM through the feedback at the VObuck terminal on the primary side to achieve a high-precision voltage regulation effect. It should be noted that in actual engineering, higher cross-regulation rate and voltage regulation effect need to be obtained through the selection of devices and the improvement of processes.

[0026] Embodiment 3 As Figure 5 shown, this embodiment uses an isolated positive and negative power supply in FCCM mode, where the control chip uses the SGM63600 controller of Siling Micro. Its switching frequency, conversion mode, etc. are set by peripheral components. In the figure, R1, R4, R5, R6, C1, C2, C3, C4, C5 are necessary peripheral devices, and the SGM63600 component manual can be referred to. Cb and Db are the bootstrap diodes and bootstrap capacitors for the upper-arm MOS drive. RS is the current sampling resistor. The SGM63600 uses external MOS switch tubes. In the figure, Q1 and Q2 are the upper and lower-arm MOS switch tubes respectively. R2 and R3 form a feedback network to realize the feedback regulation of the output of the Buck-structured power supply. When R2 = 180k and R3 = 10k, Vout1 is about 12.5V; the transformer T1 uses an ECP10 magnetic core, with 11 turns in the primary winding and 12 turns in both secondary windings. D2 and D3 are Schottky diodes, which rectify the two secondary windings respectively and are connected in series to output positive and negative power supplies. C5 and C7 are output rectifying and filtering capacitors. L1, C6 and L2, C7 respectively form two LC filters to further filter the output voltage. Finally, Vo- is -15V and Vo+ is +15V. Since the FCCM mode is used on the primary side, as Figure 5When using a diode rectifier on the secondary side, a better cross-regulation rate than that of a conventional flyback power supply can still be obtained, and there is no need to use secondary-side feedback. Instead, a stable voltage output can be achieved only by using non-isolated feedback on the primary side. When the input voltage Vin is between 20V and 40V, the isolated output is ±15V, and the current is not less than 300mA. At the same time, when the load deviation between the positive and negative outputs is greater than 50%, the output voltage difference does not exceed 1.5%.

Claims

1. A Buck structure isolated power supply, characterized in that: In an isolated power converter that uses the primary winding of a transformer as the inductor of a Buck structure power converter, a MOS switch tube Q2 is used to replace the freewheeling diode of the Buck structure power supply, and the Buck structure power supply is operated in FCCM mode; during the PWM off period, Q2 is driven complementary to PWM. Driven to turn on, the magnetic energy in the transformer winding forms a standard Buck power converter freewheeling process on the primary side, and a flyback power converter is formed on the secondary side of the transformer. The magnetic energy of the transformer converts energy to the primary and secondary windings at the same time, and VOBuck and IVOut are proportional to the number of turns of the primary and secondary windings of the transformer. When the magnetic energy in the transformer winding is completely converted into electrical energy, if Q2 is still in the on state, the voltage on the output capacitor COut of the output terminal VObuck of the Buck structure power supply passes through the loop formed by the transformer and Q2, and generates a reverse current on the primary side of the transformer. The reverse current of the secondary winding and the primary winding constitutes a forward power converter.

2. The Buck structure isolated power supply according to claim 1, characterized in that: The rectifier diode of the secondary winding of the transformer is replaced by the MOS switch tube Q3, and Q3 works in FCCM mode, keeping it turned on and off at the same time as Q2. Between the three ports of Vin, IVOut and VObuck, two by two are combined to form three independent bidirectional DCDC conversion circuits.

3. The Buck structure isolated power supply according to claim 2, characterized in that: The voltages of the three ports Vin, IVOut and VObuck depend on the duty cycle of PWM and the turns ratio of the primary and secondary sides of the transformer; when a port has a large load, its outflow energy increases; when a port has a net energy inflow, the bidirectional DCDC conversion mechanism causes the energy to flow to other ports, and when energy flows into both the IVOut and VObuck ports, the bidirectional DCDC conversion mechanism causes the energy to flow to the Vin input terminal.

4. The Buck structure isolated power supply according to claim 2, characterized in that: The transformer includes multiple secondary windings, each of which uses a MOS switch tube to replace the rectifier diode, and the MOS switch tubes used to replace the rectifier diode all work in FCCM mode, keeping Q2 turned on and off at the same time, so that each port of the secondary output and VObuck and Vin are combined in pairs to form multiple DCDC bidirectional conversion circuits.

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