A bidirectional magnetic isolation feedback circuit including synchronous rectification timing transfer

Abstract

The present invention discloses a bidirectional magnetic isolation feedback circuit including synchronous rectification timing transfer in the fields of isolation feedback circuits and synchronous rectification drives, which comprises a bidirectional magnetic isolation feedback unit, a pulse adjustment unit, and a synchronous rectification timing transfer unit. The pulse adjustment unit generates a rectangular pulse signal for driving transformer T, modulates the duty cycle and timing of the driving pulse, and simultaneously controls and configures the dead zone between the driving pulse signal and the driving signal of switch Q2; the synchronous rectification timing transfer unit conditions the synchronous rectification driving timing transferred to the secondary of transformer T; the bidirectional magnetic isolation feedback unit is used to transfer the primary synchronous rectification timing signal to the secondary and transfer the secondary error amplified signal to the primary. The present invention can accurately achieve the isolated transmission of error signals, realize high-performance feedback and closed-loop control, has the advantages of high portability and low design difficulty, and is applicable to high-reliability and high-efficiency application scenarios under various powers.

Description

Technical Field

[0001] The present invention relates to the fields of isolated feedback circuits and synchronous rectification drives, and specifically to a bidirectional magnetic isolation feedback circuit including synchronous rectification timing transfer. Background Art

[0002] Opto-coupler isolation feedback is the most widely used in industrial applications and has the advantages of simplicity and fewer components. However, limited by the inherent defects of the opto-coupler, the aging problems of its light-emitting diodes and photosensitive devices, the CTR (Current Transfer Ratio) will change with temperature and service time, and its service life and reliability are far inferior to magnetic isolation feedback. In high-reliability and high-quality application scenarios (such as aerospace and aviation power supplies), magnetic feedback technology must be used. Magnetic isolation feedback is not affected by temperature and time drift and is stable and reliable.

[0003] Magnetic isolation feedback uses a high-frequency switching quantity to drive a feedback magnetic transformer, and transforms the sampled quantity on the secondary side to the primary side through the transformer for closed-loop control. Currently, the commonly used magnetic feedback technologies mainly focus on the chips of the IR, VPT, and TI UC1901 series. These technologies have their own advantages and disadvantages: the magnetic feedback technology of the IR series has more components and requires a current source to be generated on the primary side, occupying a relatively large power supply space; the magnetic feedback technology of the VPT series requires two magnetic rings and has a relatively large volume; the magnetic feedback technology of the TI series requires a dedicated control chip, and high-quality chips are expensive and difficult to obtain.

[0004] As Figure 1 shown, a Chinese patent, a bidirectional transmission magnetic isolation feedback circuit (Publication No.: CN206850674U), discloses a magnetic feedback technology that can perform bidirectional transmission. Its carrier signal is taken from the oscillation signal of the PWM of the DC / DC converter, avoiding mutual interference caused by different operating frequencies. And when the DC / DC converter is in different input voltage and different load operating states, its oscillation signal is stable and there is no need to add a "dummy load". However, the above patent does not have the function of synchronous rectification timing adjustment and transfer.

[0005] Synchronous rectification technology refers to a technology that uses a power MOSFET tube with an extremely low on-resistance as a rectifying diode to replace the traditional rectifying diode to reduce the loss of the rectifying circuit and improve the efficiency of the converter. Synchronous rectification technology is an important means to improve the efficiency of DC-DC converters. How to properly design the synchronous rectification drive circuit and control timing is the core of synchronous rectification technology.

[0006] The currently commonly used synchronous rectifier drive technologies mainly include three categories: self-driving of transformer windings, primary signal transfer to secondary drive, and dedicated secondary drive ICs. Among them, the self-driving technology of windings has an unfixed drive voltage, which is limited by the input and output voltages, with a narrow application range, poor scalability, and relatively poor reliability; the primary signal transfer to secondary drive scheme requires a dedicated isolation transformer for signal isolation transmission, and it is difficult to adjust the drive dead zone, occupying more components; the dedicated secondary drive IC has a low operating frequency and requires auxiliary peripheral circuits, and high-quality grade chips are expensive and difficult to purchase.

[0007] The traditional magnetic isolation feedback circuit uses 1 isolation transformer, and the synchronous rectification timing transfer also uses 1 isolation transformer, that is, two isolation transformers are used to complete magnetic isolation feedback and synchronous rectification timing control respectively. Specifically, first, magnetic isolation feedback control is performed, and then a PWM2 signal with a dead zone relative to PWM1 is generated by using other dead zone generation circuits, and then it is isolated and transmitted by using the isolation transformer to drive the secondary synchronous rectifier. That is, these two parts of the circuit, the magnetic isolation feedback circuit and the synchronous rectification timing transfer circuit, are independent and irrelevant, and most of the components used to implement the functions do not overlap or share. Summary of the Invention

[0008] The purpose of the present invention is to provide a bidirectional magnetic isolation feedback circuit including synchronous rectification timing transfer to solve the problems proposed in the above background technology.

[0009] To achieve the above purpose, the present invention provides the following technical solutions:

[0010] A bidirectional magnetic isolation feedback circuit including synchronous rectification timing transfer, comprising a bidirectional magnetic isolation feedback unit. The bidirectional magnetic isolation feedback unit includes a transformer T, an error sampling and amplifying circuit, and a triode Q4. The input end of the error sampling and amplifying circuit is connected to a voltage dividing circuit of the output voltage of the DC-DC conversion unit. The base of the triode Q4 is connected to the output end of the error sampling and amplifying circuit, the emitter is connected to the cathode of a diode D4 and then to the opposite-name end of the secondary winding of the transformer T, and the collector is connected to the secondary ground. The same-name end of the secondary winding of the transformer T is connected to the cathode of a diode D3 and then to the secondary ground; the primary winding of the transformer is connected to a level conversion circuit.

[0011] It also includes a pulse adjustment unit and a synchronous rectification timing transfer unit;

[0012] The pulse adjustment unit is configured to output a narrow pulse earlier than the PWM1 signal to the primary winding of the transformer T by comparing the oscillation signal generated by the PWM controller N2 and the voltage dividing circuit of the reference voltage Vref at the two input ends of the comparator U1, so as to be transferred to the secondary winding through the transformer T to generate a PWM2 signal;

[0013] The PWM1 signal is generated by the PWM controller N2, and the PWM controller N2 generates the dead time between the PWM1 signal and the PWM2 signal by changing the peripheral parameters;

[0014] The synchronous rectification timing transfer unit is configured to turn off the synchronous rectifier SR2 in the DC-DC conversion unit through the high level of the PWM2 signal, and turn on the synchronous rectifier SR2 through the low level of the PWM2 signal.

[0015] As an improved scheme of the present invention, in order to provide stable secondary auxiliary power supply on the secondary side of the transformer T, the opposite-named end of the secondary winding of the transformer T is sequentially connected to the cathode of the diode D6, the capacitor C3, and then to the cathode of the diode D5 and the secondary auxiliary power supply V CCS , the anode of the diode D5 is connected to the same-named end of the secondary winding of the transformer T; a resistor Ron is connected between the cathode of the diode D5 and the base of the triode Q4, and a capacitor C2 is connected between the base and the secondary ground.

[0016] As an improved scheme of the present invention, in order to convert the level transferred from the secondary side of the transformer T to the primary side into a positive level, the level conversion circuit includes a diode S D , a capacitor C S / H , a resistor R IB , R IA , the same-named end of the primary winding of the transformer T is sequentially connected in series with the diode S D , the resistor R IB , R IA and then connected to the reference voltage Vref, the cathode of the diode S D is connected to the transformer T, and the anode is grounded through the capacitor C S / H .

[0017] As an improved scheme of the present invention, the synchronous rectification timing transfer unit includes a triode Q1 and a field effect transistor Q3. The base of the triode Q1 is connected to the same-named end of the secondary winding of the transformer T, the collector is connected to the secondary ground, the emitter is connected to the cathode of the diode D2 and then to the same-named end of the secondary winding of the transformer T, and the other path is connected to the gate of the field effect transistor Q3. The source of the field effect transistor Q3 is connected to the secondary ground. A resistor R8 is connected between the source and the gate of the field effect transistor Q3, and a resistor R7 is connected between the base and the collector of the triode Q1.

[0018] As an improvement scheme of the present invention, in order to facilitate the adjustment of the duty cycle of the PWM1 signal input to the primary side of the transformer T, the pulse adjustment unit further includes a duty cycle limiting circuit, and the duty cycle limiting circuit includes a triode Q2. One end of the emitter of the triode Q2 is connected to the primary auxiliary power supply VCC, and the other end is connected to the output end of the comparator U1 through the series resistors R4 and R5. The base is connected to the common end of the resistors R4 and R5, and the collector is connected to the same-named end of the primary winding of the transformer T through the resistor R9.

[0019] As an improvement scheme of the present invention, in order to facilitate the adjustment of the duty cycle of the PWM1 signal input to the primary side of the transformer T, a capacitor C1 and a resistor R6 are sequentially connected between the output end of the comparator U1 and the base of the triode Q2.

[0020] As an improvement scheme of the present invention, the error sampling and amplifying circuit includes an operational amplifier U2, capacitors CHS, CFS and a resistor RF. The output end of the operational amplifier U2 is connected to the base of the triode Q4. The capacitor CHS is connected between the negative input end and the output end of the operational amplifier U2, and the two ends of the capacitor CHS are connected in parallel with the series-connected capacitor CFS and resistor RF. The positive input end of the operational amplifier U2 is connected to the secondary ground through the capacitor C0, and the negative input end is connected to the output end of the DC-DC conversion unit through a voltage dividing circuit.

[0021] As an improvement scheme of the present invention, the error sampling and amplifying circuit includes a voltage regulator N1, capacitors C HS 、C FS and a resistor RF. The positive pole of the voltage regulator N1 is connected to the secondary ground, the reference terminal is connected to the output end of the DC-DC conversion unit through a second voltage dividing circuit, the capacitor C HS is connected between the negative pole and the reference terminal of the voltage regulator N1, and the two ends of the capacitor C HS are connected in parallel with the series-connected capacitor C FS and the resistor RF. The negative pole of the voltage regulator N1 is also connected to the base of the triode Q4 in one path, and to the secondary auxiliary power supply V CCS .

[0022] Beneficial effects: The present invention drives a small transformer T with a narrow pulse signal of a configurable fixed duty cycle and amplitude, and through the shunt circuit of the diode, enables the transformer T to work in different working modes, achieving the purpose of isolating and transmitting the synchronous rectification drive timing signal and the loop feedback signal. Description of the Drawings

[0023] Figure 1 It is a circuit structure diagram of a bidirectional transmission magnetic isolation feedback circuit disclosed in the prior art;

[0024] Figure 2 It is a circuit structure diagram of the present invention;

[0025] Figure 3 Another circuit structure diagram of the present invention;

[0026] Figure 4 It is the circuit structure diagram of the first embodiment of the connection of the pulse adjustment unit, synchronous rectification timing transfer unit and bidirectional magnetic isolation feedback unit of the present invention;

[0027] Figure 5 It is the circuit structure diagram of the second embodiment of the connection of the pulse adjustment unit, synchronous rectification timing transfer unit and bidirectional magnetic isolation feedback unit of the present invention;

[0028] Figure 6 It is the circuit structure diagram of the third embodiment of the connection of the pulse adjustment unit, synchronous rectification timing transfer unit and bidirectional magnetic isolation feedback unit of the present invention;

[0029] Figure 7 It is the circuit structure diagram of the fourth embodiment of the connection of the pulse adjustment unit, synchronous rectification timing transfer unit and bidirectional magnetic isolation feedback unit of the present invention;

[0030] Figure 8 It is the circuit diagram of the transformer T of the present invention operating in the quasi-forward mode;

[0031] Figure 9 It is the circuit diagram of the transformer T of the present invention operating in the quasi-flyback DCM mode (magnetic core reset);

[0032] Figure 10 It is the circuit diagram of the transformer T of the present invention operating in the quasi-flyback DCM mode (after magnetic core reset);

[0033] Figure 11 For the transformer T of the present invention Figures 8 - 10 in the operating mode of

[0034] Figure 12 It is the schematic diagram of the PWM controller N2 of the present invention and the waveform diagram of the output oscillation signal;

[0035] Figure 13 It is the dead-time control waveform diagram of the PWM1 signal and the PWM2 signal under the oscillation signal output by the PWM controller N2 of the present invention.

[0036] In the figure: 1 - pulse adjustment unit; 2 - synchronous rectification timing transfer unit; 3 - bidirectional magnetic isolation feedback unit; 4 - DC-DC conversion unit. Detailed implementation manners

[0037] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0038] The present invention is applied to a DC-DC conversion unit. Refer to Figures 2 - 3 , the DC-DC conversion unit includes a PWM controller N2, a transformer T1, a field effect transistor S1 and a field effect transistor SR2. The PWM controller N2 outputs a PWM1 signal to the gate of the field effect transistor S1, and the field effect transistor S1 transmits the PWM1 signal to the field effect transistor SR2 through a magnetic isolation transformer. The drain of the field effect transistor Q3 is connected to the gate of the field effect transistor S2. The model of the control chip of the PWM controller N2 can be selected as UC1843 or UC1803, etc.

[0039] As Figure 2 shown, an implementation structure of the DC-DC conversion unit is: it further includes a field effect transistor SR1. The gate of the field effect transistor SR1 and the drain of the field effect transistor SR2 are both connected to the same-name end of the secondary winding of the transformer T1. One path of the drain of the field effect transistor SR1 is connected to the different-name end of the secondary winding of the transformer T1, and the other path is connected to the gate of the field effect transistor SR2 through a diode. The sources of the field effect transistors SR1 and SR2 are commonly connected to the secondary ground. This implementation structure is a forward winding self-driven synchronous rectification topology, and the present application can also be applied to flyback synchronous rectification topology control.

[0040] As Figure 3 shown, another implementation structure of the DC-DC conversion unit is: the drain of the field effect transistor SR2 is connected to the same-name end of the secondary winding of the transformer T1, the gate is connected to the different-name end of the secondary winding of the transformer T1, and the drain is connected to the secondary ground.

[0041] The implementation structure of the DC-DC conversion unit is not an improvement of the present application, and will not be elaborated herein.

[0042] Embodiment 1. A bidirectional magnetic isolation feedback circuit including synchronous rectification timing transfer provided by the present invention includes a bidirectional magnetic isolation feedback unit. The bidirectional magnetic isolation feedback unit includes a transformer T, an error sampling and amplifying circuit and a triode Q4. The input end of the error sampling and amplifying circuit is connected to a voltage dividing circuit of the output voltage of the DC-DC conversion unit. The base of the triode Q4 is connected to the output end of the error sampling and amplifying circuit, the emitter is connected to the cathode of the diode D4 and then connected to the different-name end of the secondary winding of the transformer T, and the collector is connected to the secondary ground. The same-name end of the secondary winding of the transformer T is connected to the cathode of the diode D3 and then connected to the secondary ground; the primary winding of the transformer is connected to a level conversion circuit.

[0043] Preferably, the level conversion circuit includes a diode S D , a capacitor C S / H , a resistor R IB , R IA . The same-name ends of the primary winding of the transformer T are successively connected in series with the diode S D , the resistor R IB , R IA and then connected to the reference voltage Vref. The cathode of the diode S D is connected to the transformer T, and the anode is grounded through the capacitor C S / H .

[0044] Specifically, the reference voltage Vref is provided by the PWM controller N2. The resistors R IB , R IA are voltage-dividing resistors, and the capacitor C S / H is a sampling capacitor. The level conversion circuit is mainly used to convert the VS / H (negative level) transferred from the secondary side to the primary side of the transformer T into a VFB level (positive level of about 2.5V), and then send it to the inverting input terminal of the operational amplifier inside the PWM controller N2 to be compared with the internal reference (non-inverting input terminal), thereby controlling the duty cycle of the PWM1 signal output by the PWM controller N2 to achieve closed-loop feedback of the power supply and form a loop feedback circuit.

[0045] This circuit further includes a pulse adjustment unit and a synchronous rectification timing transfer unit.

[0046] The pulse adjustment unit is configured to output a narrow pulse advanced than the PWM1 signal to the primary winding of the transformer T by connecting the two input terminals of the comparator U1 to the oscillation signal generated by the PWM controller N2 and the voltage-dividing circuit of the reference voltage Vref respectively, so as to generate a PWM2 signal through the transformer T and transfer it to the secondary winding.

[0047] The PWM1 signal is generated by the PWM controller N2, and the PWM controller N2 generates a dead time between the PWM1 signal and the PWM2 signal by changing the peripheral parameters.

[0048] The synchronous rectification timing transfer unit is configured to turn off the synchronous rectifier SR2 in the DC-DC conversion unit through the high level of the PWM2 signal and turn on the synchronous rectifier SR2 through the low level of the PWM2 signal.

[0049] Embodiment 2. Preferably, an implementation manner of the synchronous rectification timing transfer unit includes a triode Q1 and a field effect transistor Q3. The triode Q1 is a PNP triode. The base of the triode Q1 is connected to the same-name end of the secondary winding of the transformer T, the collector is connected to the secondary ground, and one path of the emitter is connected to the cathode of the diode D2 and then to the same-name end of the secondary winding of the transformer T, and the other path is connected to the gate of the field effect transistor Q3. The source of the field effect transistor Q3 is connected to the secondary ground. A resistor R8 is connected between the source and the gate of the field effect transistor Q3, and a resistor R7 is connected between the base and the collector of the triode Q1.

[0050] The synchronous rectification timing conditioning unit is used for the logic conversion (turning on or off the synchronous rectifier SR2) of the PWM2 signal transmitted to the secondary of the transformer T and the improvement of the driving ability. The high level in the PWM2 signal at the anode of the diode D2 (and on the secondary of the transformer T) is used to turn on the field effect transistor Q3, which is converted into a low-level signal of PWM2 through the field effect transistor Q3 and is used to turn off the synchronous rectifier SR2; the low level in the PWM2 signal at the anode of the diode D2 is used to turn on the triode Q1, thereby turning off the field effect transistor Q3, releasing the gate pull-down state of the synchronous rectifier SR2, and making the gate of the synchronous rectifier SR2 in a high impedance state.

[0051] Specifically, the pulse adjustment unit includes a comparator U1. The positive input terminal of the comparator U1 is connected to the oscillation signal generated by the PWM controller N2, the negative input terminal is connected to the reference voltage Vref through a voltage dividing circuit, and the output terminal is connected to the same-name end of the primary winding of the transformer T. The different-name end of the primary winding of the transformer T is grounded.

[0052] Embodiment 3. Preferably, as Figure 4 shown, the pulse adjustment unit further includes a duty cycle limiting circuit. The duty cycle limiting circuit includes a triode Q2. One end of the emitter of the triode Q2 is connected to the primary auxiliary power supply VCC, and the other end is connected to the output terminal of the comparator U1 through series resistors R4 and R5. The base is connected to the common terminal of the resistors R4 and R5, and the collector is connected to the same-name end of the primary winding of the transformer T through a resistor R9.

[0053] By configuring the peripheral parameters of the positive and negative inputs of the comparator U1, the pulse duty cycle generated by the comparator U1 can be adjusted, and the function of controlling and limiting the duty cycle of the output signal of the comparator U1 can be achieved. In this embodiment, the duty cycle of the switching transistor Q2 is the same as that of the comparator U1. Therefore, by means of this duty cycle limiting circuit, the duty cycle of the switching transistor Q2 can be adjusted, and further the duty cycle of the transformer T can be adjusted.

[0054] Embodiment 4. Preferably, as Figure 5As shown, on the basis of Embodiment 3, a capacitor C1 and a resistor R6 are sequentially connected between the output terminal of the comparator U1 and the base of the triode Q2. The capacitor C1 and the resistor R6 additionally add a duty cycle limiting circuit, which can be used to limit the conduction time (duty cycle) of the triode Q2.

[0055] In Embodiment 3, when the RC oscillation signal input to the comparator U1 is abnormal, the duty cycle of the comparator U1 is large, and the duty cycle of the triode Q2 is also large, which may cause the transformer T to saturate and is not easy to adjust. However, in this embodiment, by adding the capacitor C1 and the resistor R6, the duty cycle of the triode Q2 can be directly limited, and then the duty cycle of the transformer T can be limited, preventing the transformer T from saturating due to the wide duty cycle pulse generated by the misoperation of the comparator U1, and improving the reliability.

[0056] Embodiment 5, as Figure 6 shown, optionally, an implementation structure of the error sampling and amplifying circuit includes an operational amplifier U2, capacitors C HS , C FS and a resistor RF. The output terminal of the operational amplifier U2 is connected to the base of the triode Q4. The capacitor C HS is connected between the negative input terminal and the output terminal of the operational amplifier U2, and the two ends of the capacitor C HS are connected in parallel with the serially connected capacitor C FS and the resistor RF. The positive input terminal of the operational amplifier U2 is connected to the secondary ground through the capacitor C0, and the negative input terminal is connected to the output terminal of the DC-DC conversion unit through a voltage dividing circuit.

[0057] The error sampling and amplifying circuit performs voltage division sampling on the output voltage Vo of the DC-DC conversion unit and outputs the sampled voltage signal to the negative input terminal of the operational amplifier U2. A reference is set at the positive input terminal of the operational amplifier U2, and after comparison and error amplification, an error amplification signal is output to the base of the triode Q4. The capacitors C HS , C FS and the resistor RF form a loop compensation circuit, which is used to adjust the stability of the power supply loop of the bidirectional magnetic isolation feedback circuit and optimize the dynamic performance.

[0058] Embodiment 6, as Figure 7 shown, optionally, another implementation structure of the error sampling and amplifying circuit includes a voltage regulator N1, capacitors C HS , C FS and a resistor RF. The positive electrode of the voltage regulator N1 is connected to the secondary ground, the reference terminal is connected to the output terminal of the DC-DC conversion unit through a second voltage dividing circuit, the capacitor C HS is connected between the negative electrode and the reference terminal of the voltage regulator N1, and the two ends of the capacitor C HS are connected in parallel with the serially connected capacitor C FSThe negative electrode of the voltage regulator N1 is also connected to the base of the triode Q4 through the resistor RF, and the other path is connected to the secondary auxiliary power supply V through the resistor R5. CCS .

[0059] Embodiment 7. Optionally, the non - same - name ends of the secondary winding of the transformer T are sequentially connected to the cathode of the diode D6, the capacitor C3, then to the cathode of the diode D5 and the secondary auxiliary power supply V. CCS The anode of the diode D5 is connected to the same - name end of the secondary winding of the transformer T; a resistor Ron is connected between the cathode of the diode D5 and the base of the triode Q4, and a capacitor C2 is connected between the base and the secondary ground.

[0060] A secondary auxiliary voltage source is formed on the capacitor C3, which is formed by being powered by the comparator U1 and transmitted through the isolation transformer T. The base of the triode Q4 is connected to V through the resistor Ron CCS for pulling up the output end of the operational amplifier U2. The capacitor C2 is connected to the output end of the operational amplifier U2, which plays the role of stabilizing the error amplification signal VEA and improving the dynamic response speed. Pulling up the output of the operational amplifier U2 is to provide an initial error amplification signal. After being transmitted to the primary of the transformer T, the PWM controller N2 is enabled to output PWM. If this error signal is initially at a low level, the control loop will control the PWM controller N2 not to output the PWM1 signal, and the entire circuit cannot start closed - loop operation.

[0061] In this embodiment, the pulse adjustment unit generates a rectangular pulse signal for driving the transformer T, modulates the duty cycle and timing of the driving pulse, and simultaneously controls and configures the dead zone between the driving pulse signal and the driving signal of the switch Q2 on the primary side of the transformer T; the synchronous rectification timing transfer unit conditions the synchronous rectification driving timing transmitted to the secondary of the transformer T for the turn - off control of the synchronous rectifier SR2 on the secondary side winding of the transformer T1; the bidirectional magnetic isolation feedback unit is used to transfer the primary energy of the transformer T to the secondary, and generate a stable secondary auxiliary power supply V CCS , transfer the primary synchronous rectification timing signal to the secondary, and at the same time transfer the secondary error amplification signal obtained by the error sampling and amplification circuit to the primary.

[0062] The bidirectional magnetic isolation feedback unit enables the unit circuit to work in different working modes through the diode shunt circuit composed of the transformer T and D3, D4 and D5, D6, transfers the synchronous rectification driving timing and the auxiliary power supply from the primary to the secondary, and then transfers the secondary error amplification signal to the primary to achieve bidirectional signal transfer.

[0063] In this embodiment, the comparator U1 is a high - speed comparator, the triodes Q1, Q2, Q4 are all PNP triodes, the transformer T is a small - volume signal isolation transformer; the oscillation signal is a triangular wave output by the internal clock control circuit of the PWM controller N2, and the divided voltage V of the reference voltage Vrefset It is used to control the output flip threshold and duty cycle of the comparator U1; the PWM controller N2 outputs the PWM1 signal, and the PWM1 signal is the gate drive pulse of the field effect transistor S1. The signal output by the field effect transistor Q3 to the gate of the field effect transistor SR2 is the PWM2 signal, and the PWM2 signal is the synchronous rectification timing control signal transmitted to the secondary. Before the field effect transistor S1 is turned on, the field effect transistor SR2 is turned off in advance.

[0064] The specific principle of this embodiment is described as follows:

[0065] 1. Establishment of the secondary auxiliary power supply and magnetic isolation transmission of the error signal

[0066] In the pulse adjustment unit, the oscillation signal (RC signal) is compared with the Vset level, and the comparator U1 generates a rectangular wave to control the on-off of the triode Q2 (the frequency is the switching frequency, and the duty cycle is controlled by the Vset level). According to the on-off situation of the triode Q2, the magnetic isolation feedback process of the transformer T in one cycle can be divided into 3 working states. Figure 11 It is the waveform diagram of the transformer T in the following three working states.

[0067] 1) Quasi-forward mode: As Figure 8 shown, when the triode Q2 is turned on, the primary side of the transformer T bears a positive voltage and starts to be magnetized. The magnetizing current starts to increase from 0. At the same time, the diodes D5 and D6 are turned on, and the transformer T charges the capacitor C3. The diodes D3 and D4 are cut off, and the triode Q4 is cut off. The primary auxiliary power supply VCC creates a stable secondary auxiliary power supply V CCS through the transformer T for the secondary winding, V CCS = VCC - V D5 - V D6 - V Q1(CE) , and the sampling switch diode SD is cut off.

[0068] 2) Quasi - flyback CCM mode (core reset): As Figure 9 shown, when the triode Q2 is turned off, the polarities of the primary and secondary windings of the transformer T are reversed, generating a reverse electromotive force. The diodes D5 and D6 are cut off, and the path of the secondary winding is switched. The diodes D3 and D4 are turned on, and the triode Q4 is turned on. The voltage between V D —V B is clamped, and the current flows from the winding V D , through the diode D4, the EB junction (PN junction) of the triode Q4, the capacitor C2, and the diode D3 back to the winding V B . The diode S D on the primary side of the transformer T is turned on, and the capacitor C S / H samples and holds the error amplification signal V EA transmitted from the secondary side of the transformer T.

[0069] V D -V B = V D4 +V Q4(EB) +V EA +V D3

[0070] V A = V B -V D = -(V D4 +V Q4(EB) +V EA +V D3 )

[0071] V S / H = V A +V SD = -(V D4 +V Q4(EB) +V EA +V D3 ) + V SD

[0072] The sampled and held signal V S / H is negative. It is converted to a level of about 2.5V by the level shift circuit and sent to the internal error amplifier of the PWM controller N2 to complete the feedback closed loop. The reference voltage V ref provides a positive voltage bias for the shift circuit, and then through the voltage dividing resistors R IA and R IB the appropriate V FB level is obtained.

[0073] 3) Quasi - flyback DCM mode (after core reset): As Figure 10 shown, after the transformer T completes magnetic reset, all the energy is transferred. Diodes D5, D6, D3, D4 are all cut off, and the triode Q2 is cut off. The residual leakage inductance L of the transformer T, the CE junction capacitance of the triode Q2, and the line resistance form an LRC damped oscillation, and the leakage inductance energy is dissipated.

[0074] 2. Synchronous rectification timing dead - zone control

[0075] Using the RC signal generated by the PWM controller N2, a dead - zone is generated between the PWM1 signal and the PWM2 signal to ensure that the field - effect transistor SR2 is turned off before the primary - side switching field - effect transistor S1 is turned on. The specific implementation process is analyzed as follows:

[0076] As Figures 12 - 13As shown, resistor RT and capacitor CT are the resistor-capacitor components configured around PWM controller N2, which are used to control the frequency of PWM controller N2 and the RC triangular wave generated by PWM controller N2. The product of resistor RT and capacitor CT determines the frequency of the triangular wave. When the frequencies are the same, if the configured capacitance CT is large, the slope of the falling edge of the triangular wave is small and the falling time is long; if the capacitance CT is small, the slope of the falling edge of the triangular wave is large and the falling time is short. When the signal of capacitor CT starts to rise, PWM controller N2 turns on the PWM output (i.e., PWM1). PWM1 starts to drive power transformer T1 to transfer energy to the secondary side. When PWM1 is turned off, the energy transfer within this cycle ends. The duty cycle of PWM1 is determined by the loop feedback circuit.

[0077] By configuring different RT and CT parameters, the slope of the falling edge of the triangular wave is controlled. The time of the falling edge determines the maximum dead time that PWM2 can be advanced ahead of PWM1 for design.

[0078] Utilizing the falling edge of the RC signal output by PWM controller N2, before the PWM1 signal is turned on, the PWM2 signal is established in advance and transmitted to the secondary side of transformer T through magnetic isolation transformer T1 to turn off field effect transistor SR2, forming dead time control. When the level of the falling edge of the RC signal is lower than the divided voltage Vsef sampled by comparator U1, comparator U1 outputs a low level and triode Q2 conducts, and transformer T works. When the RC signal enters the rising edge and the voltage is greater than the divided voltage Vsef, comparator U1 outputs a high level and transformer T does not work. Therefore, a synchronous rectification timing control signal that advances the PWM1 signal can be obtained using the pulse adjustment unit. The dead time Δt is jointly determined by resistor RT, capacitor CT, and the reference voltage Vref set by PWM controller N2.

[0079] In addition to being controlled by the level of the negative input terminal Vset of comparator U1 and the configured RC signal at the positive input terminal, the duty cycle d of the PWM2 signal is restricted by capacitor C1, resistors R6, R4, and R5 in the duty cycle limiting circuit at the output terminal of comparator U1, which can limit the conduction time of triode Q2. Therefore, not only the dead time between the PWM1 signal and the PWM2 signal is controllable, but also the maximum duty cycle of the PWM2 control signal is controllable.

[0080] The synchronous rectification control signal PWM2 is transmitted to the secondary side. The synchronous rectification timing transfer unit turns off the field effect transistor SR2 in advance before the field effect transistor S1 is turned on, avoiding the common connection between the primary and secondary sides of the transformer T1. When the PWM2 signal is ahead of the PWM1 signal and is at a high level, after passing through the diode D2, it drives the field effect transistor Q3 to conduct, and the gate of the field effect transistor SR2 is pulled low, turning off the field effect transistor SR2. When the PWM2 signal turns to a low level, the triode Q1 conducts, pulling the gate of the field effect transistor Q3 low, turning off the field effect transistor Q3, and the synchronous rectification timing transfer unit has no effect on the field effect transistor SR2, and self-driving control can be used to turn on SR2.

[0081] The present invention drives a small isolated transformer through a narrow pulse signal with a configurable fixed duty cycle and amplitude, and through a shunt circuit of diodes, enables the transformer T to operate in different operating modes, completes the establishment of the secondary auxiliary power supply, and achieves the purpose of isolating and transmitting the synchronous rectification drive timing signal and the loop feedback signal.

[0082] The beneficial effects of the present invention are as follows:

[0083] 1. The present invention uses a bidirectional magnetic isolation feedback circuit instead of an optocoupler isolation feedback, avoiding the influence of the optocoupler lifespan, performance degradation, and batch inconsistency on product design, and can accurately achieve the isolation transmission of error signals, realizing high-performance feedback and closed-loop control.

[0084] 2. The present invention provides a stable auxiliary power supply for the secondary side of the transformer T before the output voltage is established. The secondary auxiliary power supply is decoupled from the DC / DC output voltage, reducing the complexity of the loop feedback design and the difficulty of the soft start design; at the same time, the use of an auxiliary power supply independent of the output voltage can design output constant current control to provide relatively accurate overcurrent protection for the secondary side.

[0085] 3. The coupling degree of the bidirectional magnetic isolation feedback unit, pulse adjustment unit, synchronous rectification timing transfer unit and DC-DC conversion unit of the present invention is low, and the bidirectional magnetic isolation feedback unit has high portability and is not affected by factors such as input voltage, output voltage, and power, and is applicable to high-reliability and high-efficiency application scenarios under various powers.

[0086] 4. The transformer T is used to transmit the primary drive timing to the secondary side simultaneously for the switching timing control of the synchronous rectifier (field effect transistor SR2), reducing one transformer for synchronous rectification timing transmission compared to traditional solutions.

[0087] 5. The voltage value and duty cycle of the narrow pulse transmitted by the transformer T are fixed and not affected by the DC-DC conversion unit, simplifying the design difficulty of the transformer T, and a small-sized magnetic ring can be used.

[0088] Although this specification is described in terms of embodiments, not every embodiment contains only one independent technical solution. This narrative style of the specification is only for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

[0089] In the description of the present invention, it should be noted that relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprising", "including" or any other variant thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements not only includes those elements, but also includes other elements not expressly listed, or elements inherent to such process, method, article or device. Without further limitation, an element defined by the phrase "comprising a..." does not exclude the presence of additional identical elements in the process, method, article or device comprising the element.

[0090] In the description of the present invention, it should also be noted that the orientation or positional relationship indicated by terms such as "upper", "lower", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship in which the inventive product is customarily placed during use. It is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention.

[0091] In the description of the present invention, it should also be noted that unless otherwise clearly specified and defined, the terms "arranged", "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection, an electrical connection; it can be directly connected, or indirectly connected through an intermediate medium, and it can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0092] Therefore, the above description is only a preferred embodiment of the present application and is not used to limit the scope of implementation of the present application; that is, all equivalent transformations made according to the scope of the claims of the present application are within the protection scope of the claims of the present application.

Claims

1. A bidirectional magnetic isolation feedback circuit including synchronous rectification timing transfer, comprising a bidirectional magnetic isolation feedback unit. The bidirectional magnetic isolation feedback unit includes a transformer T, an error sampling and amplifying circuit, and a triode Q4. The input end of the error sampling and amplifying circuit is connected to a voltage dividing circuit of the output voltage of the DC-DC conversion unit. The base of the triode Q4 is connected to the output end of the error sampling and amplifying circuit. The emitter is connected to the cathode of a diode D4 and then to the opposite-named end of the secondary winding of the transformer T. The collector is connected to the secondary ground. The same-named end of the secondary winding of the transformer T is connected to the cathode of a diode D3 and then to the secondary ground. The primary winding of the transformer is connected to a level conversion circuit, and is characterized in that, it further includes a pulse adjustment unit and a synchronous rectification timing transfer unit; The pulse adjustment unit is configured to output a narrow pulse earlier than the PWM1 signal to the primary winding of the transformer T by connecting the two input ends of a comparator U1 to an oscillation signal generated by a PWM controller N2 and a voltage dividing circuit of a reference voltage Vref respectively, so as to be transferred to the secondary winding through the transformer T to generate a PWM2 signal; The PWM1 signal is generated by the PWM controller N2, and the PWM controller N2 generates a dead time between the PWM1 signal and the PWM2 signal by changing peripheral parameters; The synchronous rectification timing transfer unit is configured to turn off a synchronous rectifier SR2 in the DC-DC conversion unit through the high level of the PWM2 signal, and turn on the synchronous rectifier SR2 through the low level of the PWM2 signal; The non - common ends of the secondary winding of the transformer T are sequentially connected to the cathode of the diode D6, the capacitor C3, and then to the cathode of the diode D5 and the secondary auxiliary power supply V CCS , the anode of the diode D5 is connected to the common end of the secondary winding of the transformer T; a resistor Ron is connected between the cathode of the diode D5 and the base of the triode Q4, and a capacitor C2 is connected between the base and the secondary ground; The level conversion circuit includes diode S D , capacitor C S / H , resistor R IB , R IA . The same-name ends of the primary winding of the transformer T are sequentially connected in series with diode S D , resistor R IB , R IA and then connected to the reference voltage Vref. The cathode of diode S D is connected to the transformer T, and the anode is grounded through capacitor C S / H ; The synchronous rectification timing transfer unit includes a triode Q1 and a field effect transistor Q3. The base of the triode Q1 is connected to the same-named end of the secondary winding of the transformer T. The collector is connected to the secondary ground. One path of the emitter is connected to the cathode of a diode D2 and then to the same-named end of the secondary winding of the transformer T. The other path is connected to the gate of the field effect transistor Q3. The source of the field effect transistor Q3 is connected to the secondary ground. A resistor R8 is connected between the source and the gate of the field effect transistor Q3, and a resistor R7 is connected between the base and the collector of the triode Q1; The pulse adjustment unit further includes a duty cycle limiting circuit. The duty cycle limiting circuit includes a triode Q2. One end of the emitter of the triode Q2 is connected to the primary auxiliary power supply VCC, and the other end is connected to the output end of the comparator U1 through series resistors R4 and R5. The base is connected to the common end of the resistors R4 and R5. The collector is connected to the same-named end of the primary winding of the transformer T through a resistor R9.

2. The bidirectional magnetic isolation feedback circuit including synchronous rectification timing transfer according to claim 1, wherein A capacitor C1 and a resistor R6 are sequentially connected between the output end of the comparator U1 and the base of the triode Q2.

3. A bidirectional magnetic isolation feedback circuit including synchronous rectification timing transfer according to claim 1, characterized in that, The error sampling and amplifying circuit includes an operational amplifier U2, capacitors C HS , C FS and a resistor RF. The output terminal of the operational amplifier U2 is connected to the base of the triode Q4. The capacitor C HS is connected between the negative input terminal and the output terminal of the operational amplifier U2, and capacitors C HS are connected in parallel at both ends of the capacitor C FS and the resistor RF. The positive input terminal of the operational amplifier U2 is connected to the secondary ground through the capacitor C0, and the negative input terminal is connected to the output terminal of the DC-DC conversion unit through a voltage dividing circuit.

4. A bidirectional magnetic isolation feedback circuit including synchronous rectification timing transfer according to claim 1, characterized in that The error sampling and amplifying circuit includes a voltage regulator N1, capacitors C HS , C FS and a resistor RF. The positive electrode of the voltage regulator N1 is connected to the secondary ground, and the reference terminal is connected to the output terminal of the DC-DC conversion unit through a second voltage dividing circuit. The capacitor C HS is connected between the negative electrode of the voltage regulator N1 and the reference terminal, and capacitors C HS are connected in parallel at both ends of the capacitor C FS and the resistor RF. The negative electrode of the voltage regulator N1 is also connected to the base of the triode Q4 on one path, and to the secondary auxiliary power supply V CCS .

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