CN101604919A - A Synchronous Rectification Buck-Flyback Converter - Google Patents

Abstract

The invention provides a synchronous rectification Buck-Flyback converter, which is suitable for the auxiliary power supply design of primary and secondary side isolation working voltage required by various control chips in the power supply, including synchronous rectification Buck converter, Flyback converter and Buck synchronous Rectification control circuit; the output voltage of the synchronous rectification Buck converter provides the working voltage required by various control chips on the primary side; the output voltage of the Flyback converter provides the isolated working voltage required by various control chips on the secondary side; the Buck synchronous rectification control The circuit is used to provide the synchronous rectification control signal required by the synchronous rectification Buck converter. The present invention is different from the existing topology that can only provide a single output voltage of the primary side or the secondary side, and it can provide the output voltage isolated from the primary side and the secondary side at the same time. The output voltage amplitude of the secondary side can be set by the output voltage of the primary side, and the circuit The structure is simple, the stress of the device is low, and it has the advantages of good voltage stabilization effect and high efficiency under certain load conditions.

Description

A Synchronous Rectification Buck-Flyback Converter

technical field

The invention relates to a DC switching power supply converter, in particular to the technical field of an auxiliary power supply suitable for DC/DC digital power supply modules.

Background technique

As the functions of electronic devices become more and more complex, and the management of wider loads, lower output voltages, and synchronization of multiple power sources, DSP/FPGA-controlled digital power modules have become a popular research direction in recent years. Although the digital power supply can provide more powerful monitoring functions, the standby power required by digital control chips such as DSP/FPGA is also greatly increased. In standby mode, the digital power supply not only needs to provide the operating voltage required by the primary side control chip to meet the communication and monitoring functions, including fault management, over-current protection, and shutdown avoidance, to ensure remote diagnosis and continuous system reliability. In addition, it is necessary to provide the working voltage required by the secondary digital chip control to provide functions such as output voltage, timing control, and current sharing. PCB space is very precious in high power density power module design, how to design an auxiliary power supply with simple structure and high efficiency has become one of the key issues faced by digital module power supply design.

Contents of the invention

purpose of invention

Aiming at the characteristics of modern digital power supply control chips with large static operating current, high standby power consumption, and the need to provide isolated output voltages for various control chips on the primary and secondary sides, the present invention proposes a new type of synchronous rectification Buck-Flyback converter to provide digital The power block controls the auxiliary power required by the chip to simplify design and increase efficiency.

Technical solutions:

The present invention adopts following technical scheme for realizing above-mentioned purpose of the invention:

The synchronous rectification Buck-Flyback converter of the present invention is used to provide primary and secondary side isolated working voltages for various control chips in the power supply, including a synchronous rectification Buck converter, a Flyback converter and a Buck synchronous rectification control circuit, wherein the synchronous The output voltage of the rectified Buck converter is used to provide the working voltage required by various control chips on the primary side; the output voltage of the Flyback converter is used to provide the isolated working voltage required by various control chips on the secondary side; the Buck synchronous rectification control circuit is used In order to provide the required synchronous rectification control signal of the synchronous rectification Buck converter; the synchronous rectification Buck-Flyback converter also includes a transformer L1, the transformer L1 has three windings and shares a magnetic core, i.e. the primary winding, the first secondary winding and the second secondary winding, the primary winding of the transformer L1 is set in the synchronous rectification Buck converter, the first secondary winding of the transformer L1 is set in the Flyback converter, and the second secondary winding of the transformer L1 is set in the Buck synchronous rectification In the control circuit, the voltage applied to the primary winding of the transformer L1 in the synchronous rectification Buck converter is respectively coupled to the first secondary winding of the transformer L1 in the Flyback converter and the second secondary winding of the transformer L1 in the Buck synchronous rectification control circuit through the transformer L1. secondary winding.

The synchronous rectification Buck converter in the synchronous rectification Buck-Flyback converter of the present invention consists of a switch control chip IC1, a first capacitor C1, a first resistor R1, a second resistor R2, a second capacitor C2, a third capacitor C3, and a third resistor R3, the fourth resistor R4, the freewheeling tube Q1, the fourth capacitor C4 and the primary winding of the transformer L1, wherein one end of the first capacitor C1 is connected to the positive pole of the power supply, one end of the first resistor R1 and the eighth end of the switch control chip IC1 respectively. The other end of the first capacitor C1 is connected to the negative pole of the power supply, one end of the second resistor R2 and the fourth pin of the switch control chip IC1, and the other end of the first resistor R1 is connected to the sixth pin of the switch control chip IC1. pin connection, the other end of the second resistor R2 is connected to the third pin of the switch control chip IC1, one end of the second capacitor C2 is connected to the seventh pin of the switch control chip IC1, and the other end is connected to the primary ground; the switch control The second pin of the chip IC1 is connected to one end of the third capacitor C3, and the other end of the third capacitor C3 is respectively connected to the first pin of the switch control chip IC1, one end of the primary winding of the transformer L1, and the drain of the freewheeling tube Q1 connection, the two ends of the primary winding of the transformer L1 are respectively connected to one end of the third resistor R3 and the positive pole of the fourth capacitor C4, and the other end of the third resistor R3 is respectively connected to the fifth pin of the switch control chip IC1 and the fourth resistor R4 One end of the fourth resistor R4 is connected to the negative pole of the fourth capacitor C4 and the source of the freewheeling tube Q1 respectively, and then connected to the primary ground, and the gate of the freewheeling tube Q1 is connected to the output terminal of the Buck synchronous rectification control circuit connect.

The Flyback converter in the synchronous rectification Buck-Flyback converter of the present invention is composed of the third diode D3, the sixth capacitor C6, and the first secondary winding of the transformer L1 connected in series, wherein the anode of the third diode D3 is connected to the transformer The 4 terminals of the first secondary winding of L1 are connected, the cathode of the third diode D3 is connected to the positive pole of the sixth capacitor C6, the 3 terminals of the first secondary winding of the transformer L1 are connected to the negative pole of the sixth capacitor C6 and then connected to the secondary side land.

The Buck synchronous rectification control circuit in the synchronous rectification Buck-Flyback converter of the present invention is composed of the first diode D1, the second diode D2, the fifth capacitor C5, the fifth resistor R5, the PNP transistor Q2, and the second pair of transformer L1 side winding, wherein the cathode of the first diode D1 is respectively connected to the output terminal of the synchronous Back control circuit, that is, the gate of Q1, and the emitter of the PNP transistor Q2, and the anode of the first diode D1 is respectively connected to the fifth capacitor C5 One end of the fifth resistor R5 and the cathode of the second diode D2 are connected, the other end of the fifth resistor R5 is respectively connected to the other end of the fifth capacitor C5 and the base of the PNP transistor Q2, and the second diode The anode of D2 is connected to terminal 6 of the second secondary winding of transformer L1, and terminal 5 of the second secondary winding of transformer L1 is connected to the collector of PNP transistor Q2 and connected to the primary ground.

In the synchronous rectification Buck-Flyback converter of the present invention, terminal 1 of the primary winding of the transformer L1, terminal 3 of the first secondary winding, and terminal 5 of the second secondary winding are terminals with the same name.

According to the above solution, the synchronous rectification Buck-Flyback converter is composed of a primary side synchronous rectification Buck converter, a secondary side Flyback converter and a Buck synchronous rectification control circuit. The transformer L1 can not only provide the electrical isolation function of the primary side and the secondary side, but also serve as the output inductor of the synchronous rectification Buck converter, the energy storage inductor of the Flyback converter and the function of providing synchronous rectification control signals. Since the primary-side synchronous rectification Buck converter always works in the continuous state of the inductor current, its duty cycle D is guaranteed, even if the synchronous rectification Buck converter or Flyback converter works in the no-load state, the output voltages of the primary and secondary sides are also constant. can remain stable. The output voltage of the synchronous rectification Buck converter is set by its control circuit. The output voltage of the secondary Flyback converter is controlled by the output voltage of the primary synchronous rectification Buck converter, and the output voltage value of the secondary side can be adjusted by the turns ratio between the primary winding and the first secondary winding of transformer L1 .

According to the above scheme, when the main switching tube of the synchronous rectification Buck converter is turned on, the diode D3 of the Flyback converter bears the reverse voltage, and the transformer L1 does not transmit energy to the secondary side. When the freewheel switch tube of the synchronous rectification Buck converter is turned on, the diode D3 of the Flyback converter is forward-conducting, and the transformer L1 transmits energy to the secondary side.

Beneficial effect

1. It can provide the stable output voltage of the primary side and the secondary side isolation at the same time to meet the working voltage required by various control chips of the primary side and the secondary side.

2. Since the auxiliary power device of the invention works in a switch mode instead of a nonlinear mode, the work efficiency is greatly improved. Regardless of whether the power module is in standby mode or normal operation mode, the auxiliary power supply can be directly used for power supply, without the need to design additional auxiliary power supply and switching circuits.

3. The output voltage of the secondary side does not need complex control circuit settings, and its amplitude is directly set by the output voltage of the primary side through the coil ratio.

4. The auxiliary power supply has fewer working components, low voltage stress of power components, and simple design, which reduces the cost and space requirements on the PCB board.

Description of drawings

Fig. 1 is a traditional auxiliary power supply design in the prior art.

Fig. 2 is a schematic block diagram of the circuit of the present invention.

Fig. 3 is a circuit block diagram of the present invention.

Detailed ways

Embodiments of the present invention are further described below in conjunction with the accompanying drawings:

As shown in Figure 1, the traditional auxiliary power supply sets the base voltage of the triode through the voltage regulator D1, so that the triode or MOSFET works in the linear region to obtain the power supply voltage required by the primary side control chip, and at the same time provides the secondary voltage through the forward circuit. The isolated working voltage required by the side control chip is shown in Figure 1. Since the static operating current of the digital control chip is tens of milliamperes, plus the operating current required by other various auxiliary control chips, the total static current flowing through the primary triode is about 0.1A. The power module works in a wide input voltage range (such as 36V ~ 75V). When the input voltage is 75V and the module power supply is in standby mode, the power consumption generated by the triode is as high as several watts because it works in a linear state. In addition, in order to improve the working efficiency of the power supply module, when the digital power supply module is working normally, it is generally necessary to design an additional auxiliary power supply circuit to switch the auxiliary power supply during standby to reduce power consumption. Therefore, it is difficult to meet the requirements of high power density digital power modules for efficiency and PCB space.

As shown in Figure 2 and Figure 3, the synchronous rectification Buck-Flyback converter of the present invention includes a synchronous rectification Buck converter, a Flyback converter, and a Buck synchronous rectification control circuit, wherein the synchronous rectification Buck converter is used to provide various types of primary side control The working voltage required by the chip; the Flyback converter is used to provide the isolated working voltage required by various control chips on the secondary side; the Buck synchronous rectification control circuit is used to provide the synchronous rectification control signal required by the synchronous rectification Buck converter; the input voltage enters the synchronous The input terminal of the rectification Buck converter generates an output voltage of 10V on the primary side. The structure of the synchronous rectification Buck converter includes a first capacitor C1, a MosFET inside the switch control chip IC1 (as the upper tube of the Buck converter), and The first resistor R1 for fixed on-time timing, the second resistor R2 for internal MosFET current limit setting, the second capacitor C2 for internal MosFET drive circuit power supply, and the third capacitor for internal MosFET drive voltage boost C3, the third resistor R3 and the fourth resistor R4 of the output voltage sampling circuit, the freewheeling tube Q1, the fourth capacitor C4 used for output voltage filtering, and the primary winding of the transformer L1, etc. The set output voltage of the primary side is 10V .

The synchronous driving control signal circuit of the freewheeling tube Q1, that is, the Buck synchronous rectification control circuit consists of the first diode D1, the second diode D2, the fifth capacitor C5, the fifth resistor R5, the PNP transistor Q2, and the second transformer L1 Composition of the secondary winding.

The structure of the secondary Flyback converter consists of the third diode D3, the sixth capacitor C6, and the first secondary winding of the transformer L1 connected in series, and the first secondary winding of the transformer L1 outputs a stable voltage of 8V.

The above embodiments are composed of high-performance low-cost integrated chips and peripheral circuits. The switch control chip IC1 is a high-frequency step-down control chip LM5009. Its switching frequency can reach up to 600Khz, and the allowable range of input voltage is 9.5V~ 95V, can output a maximum current of 150mA, and its working environment temperature is -40 degrees to +125 degrees. The chip contains a 2% high-precision 2.5V reference operational amplifier to ensure the stability of the output voltage. The circuit adopts the current hysteresis control technology of timing conduction, and no compensation loop design is required. At the same time, the chip integrates Buck upper transistor MosFET, current limiting function, standby function, etc., which reduces the design cost and the complexity of the peripheral circuit, and reduces the design difficulty.

Working principle and working process:

The synchronous rectification Buck-Flyback converter is composed of a synchronous rectification Buck converter, a Flyback converter and a Buck synchronous rectification control circuit. In the figure, the transformer L1 not only provides the electrical isolation function, but also the primary winding of the transformer L1 serves as the output filter inductor of the synchronous rectification Buck converter, the first secondary winding of the transformer L1 serves as the energy storage inductor of the Flyback converter, and the second secondary winding of the transformer L1 Provides a synchronous rectification self-driven signal for the freewheeling transistor Q1 of the synchronous rectification Buck converter. The primary winding and the two secondary windings of the transformer L1 share a magnetic core, and terminals 1, 3 and 5 of the three windings of the transformer L1 are terminals with the same names. Since the synchronous rectification Buck-Flyback always works in the continuous state of the inductor current, its duty cycle D is relatively large. This ensures that even if Buck or Flyback works in a no-load state, its output voltage V _O2 can also remain stable. The output voltage V _O2 of the Flyback is controlled by the output voltage V _O1 of the primary Buck, and the size of V _O2 can be adjusted by the coil ratio between the primary winding and the first secondary winding of the transformer L1.

When the freewheeling tube Q1 is turned off, the voltage V _{L1 (1, 2)} applied to the primary winding of the transformer L1 in the synchronous rectification Buck converter is V _in -V _o1 . At this time, the first voltage of the transformer L1 in the Flyback converter is The voltage V _{L1 (3, 4)} on the secondary winding is positive, so the third diode D3 is cut off, and the maximum reverse voltage on the third diode D3 is lower than that of the traditional Flyback converter. The load working current of the secondary side is provided by the sixth capacitor C6. Since the second secondary winding generates a positive voltage V _{L1 (5, 6)} , the fifth capacitor C5 plays a role in accelerating the conduction of the PNP transistor Q2, so a low level is generated on the gate of the freewheeling transistor Q1 to keep it off state.

When the flywheel Q1 is turned on, the voltage V _{L1 (1, 2)} applied to the primary winding of the transformer L1 in the synchronous rectification Buck converter is -V _O1 . At the same time, the voltage V _{L1 (3, 4)} on the first secondary winding of the transformer L1 in the Flyback converter is negative, and its amplitude is set by the output voltage of the primary side, specifically, the output voltage of the primary side -V _O1 divided by The coil transformation ratio between the primary winding of the transformer L1 and the first secondary winding of the transformer L1. At this time, the third diode D3 is turned on, and the energy stored in the magnetic field of the transformer L1 is released through the third diode D3. On the one hand, it charges the sixth capacitor C6, and on the other hand, it supplies power to the load. When the load on the secondary side is light and the current of the Flyback converter is critical or discontinuous, the third diode D3 is turned off with zero current to obtain higher efficiency. The second secondary winding of the transformer L1 generates a negative voltage V _L1(5,6) , the fifth capacitor C5 accelerates the closing of the PNP transistor Q2, and at the same time the second secondary winding of the transformer L1 passes through the first diode D1, The second diode D2 generates a negative voltage V _{L1 (5, 6 )} on the gate of the freewheeling transistor Q1 to turn on the freewheeling transistor Q1 .

The invention adopts a high-performance and low-priced integrated control chip, which greatly reduces the design difficulty of a synchronous rectification Buck-Flyback converter, and obtains better control characteristics with less peripheral circuits. Since the converter works in a switching state, the efficiency of the auxiliary power supply is guaranteed. Therefore, there is no need to design the switching circuit of the auxiliary power supply of the main converter in different working modes, which greatly saves the circuit space of the PCB board, and is especially suitable for the design of the auxiliary power supply of the digital power module with high power density.

Claims (5)

1. A synchronous rectification Buck-Flyback converter, which is used to provide primary and secondary side isolated working voltages for various control chips in a power supply, and is characterized in that it includes a synchronous rectification Buck converter, a Flyback converter and a Buck synchronous rectification Control circuit, in which the output voltage of the synchronous rectification Buck converter is used to provide the working voltage required by various control chips on the primary side; the output voltage of the Flyback converter is used to provide the isolated working voltage required by various control chips on the secondary side; The synchronous rectification control circuit is used to provide the synchronous rectification control signal required by the synchronous rectification Buck converter; the synchronous rectification Buck-Flyback converter also includes a transformer L1, the transformer L1 has three windings and shares a magnetic core, that is, the primary winding , the first secondary winding and the second secondary winding, the primary winding of the transformer L1 is set in the synchronous rectification Buck converter, the first secondary winding of the transformer L1 is set in the Flyback converter, and the second secondary winding of the transformer L1 Set in the Buck synchronous rectification control circuit, the voltage applied to the primary winding of the transformer L1 in the synchronous rectification Buck converter is respectively coupled to the first secondary winding of the transformer L1 in the Flyback converter and the Buck synchronous rectification control circuit through the transformer L1 The second secondary winding of the transformer L1. 2. The synchronous rectification Buck-Flyback converter according to claim 1, characterized in that: the synchronous rectification Buck converter consists of a switch control chip IC1, a first capacitor C1, a first resistor R1, a second resistor R2, and a second capacitor C2, the third capacitor C3, the third resistor R3, the fourth resistor R4, the freewheeling tube Q1, the fourth capacitor C4 and the primary winding of the transformer L1, wherein one end of the first capacitor C1 is respectively connected to the positive pole of the power supply and the first resistor R1 One end of the first capacitor C1 is connected to the eighth pin of the switch control chip IC1, the other end of the first capacitor C1 is respectively connected to the negative pole of the power supply, one end of the second resistor R2 and the fourth pin of the switch control chip IC1, and the first resistor R1 The other end is connected to the sixth pin of the switch control chip IC1, the other end of the second resistor R2 is connected to the third pin of the switch control chip IC1, and one end of the second capacitor C2 is connected to the seventh pin of the switch control chip IC1 , the other end is connected to the primary ground; the second pin of the switch control chip IC1 is connected to one end of the third capacitor C3, and the other end of the third capacitor C3 is respectively connected to the first pin of the switch control chip IC1 and the primary winding of the transformer L1 Terminal 1 of the freewheeling tube Q1 is connected to the drain. Terminals 2 of the primary winding of the transformer L1 are respectively connected to one terminal of the third resistor R3 and the positive pole of the fourth capacitor C4. The other terminal of the third resistor R3 is respectively connected to the switch control chip IC1. The 5th pin and one end of the fourth resistor R4 are connected; the other end of the fourth resistor R4 is respectively connected to the negative pole of the fourth capacitor C4 and the source of the freewheeling tube Q1, and then connected to the primary ground, and the gate of the freewheeling tube Q1 The pole is connected with the output end of the Buck synchronous rectification control circuit. 3. The synchronous rectification Buck-Flyback converter according to claim 1, characterized in that: the Flyback converter is composed of the third diode D3, the sixth capacitor C6, and the first secondary winding of the transformer L1 connected in series, wherein The anode of the third diode D3 is connected to the 4-terminal of the first secondary winding of the transformer L1, the cathode of the third diode D3 is connected to the anode of the sixth capacitor C6, and the 3-terminal of the first secondary winding of the transformer L1 is connected to the first secondary winding of the transformer L1. The negative poles of the six capacitors C6 are connected to the secondary ground. 4. The synchronous rectification Buck-Flyback converter according to claim 1, characterized in that: the Buck synchronous rectification control circuit consists of a first diode D1, a second diode D2, a fifth capacitor C5, and a fifth resistor R5 , PNP transistor Q2, and the second secondary winding of the transformer L1, wherein the cathode of the first diode D1 is respectively connected to the output terminal of the synchronous Buck control circuit, that is, the gate of Q1, and the emitter of the PNP transistor Q2, and the first diode The anode of the tube D1 is respectively connected to one end of the fifth capacitor C5, one end of the fifth resistor R5, and the cathode of the second diode D2, and the other end of the fifth resistor R5 is respectively connected to the other end of the fifth capacitor C5, the PNP transistor Q2 The anode of the second diode D2 is connected to terminal 6 of the second secondary winding of the transformer L1, and terminal 5 of the second secondary winding of the transformer L1 is connected to the collector of the PNP transistor Q2 and then connected to the primary ground. 5. The synchronous rectification Buck-Flyback converter according to claim 1, characterized in that: terminal 1 of the primary winding of the transformer L1, terminal 3 of the first secondary winding, and terminal 5 of the second secondary winding are end of the same name.

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