Magnetic isolation feedback method with auxiliary power supply

Abstract

The invention discloses a magnetic isolation feedback method with auxiliary power supply, and relates to the technical field of high-reliability application switching power supplies, and the method comprises the steps: carrying out the chopping of a power supply voltage at a primary side through a drive circuit, and transmitting a secondary side feedback voltage signal through a modulation transformer; feedback signal transmission in a forward mode and auxiliary power supply output in a flyback mode are achieved on the secondary side through a clamping circuit and a demagnetizing circuit, so that the secondary side control circuit can still obtain stable power supply support under the condition that output voltage is not established or abnormal. Compared with a traditional photoelectric coupler feedback scheme, the reliability in a strong irradiation environment can be remarkably improved due to the fact that irradiation-insensitive discrete components are adopted; meanwhile, a special control chip is not needed, the circuit is more flexible, and the cost and the size are reduced; the magnetic isolation feedback method is especially suitable for the high-reliability application switching power supply field of spaceflight, medical treatment, nuclear industry and the like.

Description

Technical Field

[0001] The invention relates to the technical field of high-reliability application switching power supplies, in particular to a magnetic isolation feedback method with auxiliary power supply. Background Art

[0002] Existing switching power supplies generally use optocouplers to achieve isolated feedback between the primary and secondary sides. However, in high-reliability applications such as aerospace, medical equipment, and nuclear industry where strong radio waves, high-energy particles, or other strong electromagnetic radiation exist, optocouplers are easily affected by radiation, causing light decay or failure, which leads to loop gain drift and power supply output imbalance, making it difficult to meet stringent reliability requirements.

[0003] Therefore, in order to improve the adaptability in strong radiation environments, it is necessary to explore an isolated feedback method that is insensitive to radiation and long-term stable; in this context, the magnetic transformer can be used as a device with strong radiation resistance to replace the optocoupler to achieve secondary side signal isolation transmission in a high-reliability environment; if an auxiliary power supply channel can be added on the basis of magnetic isolation feedback, even when the switching power supply output is not established or is in abnormal states such as short circuit or overvoltage protection, the secondary side sampling and protection circuit can maintain normal operation, further enhancing the safety and applicability of the entire power supply system. Summary of the invention

[0004] In view of the above existing problems, the present invention is proposed.

[0005] The present invention provides a magnetic isolation feedback method with auxiliary power supply to solve the problem that a conventional switching power supply using a photoelectric coupler feedback technology is difficult to meet the use requirements in a strong radiation environment.

[0006] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0007] An embodiment of the present invention provides a magnetic isolation feedback method with auxiliary power supply, which includes:

[0008] Step S1, chopping the primary power supply voltage Vcc through a driving circuit at the primary side to form an AC square wave carrier signal, and inputting the AC square wave carrier signal to the primary winding LP1 of the modulation transformer;

[0009] Step S2, on the secondary side, the signals sensed on the secondary windings LS3 and LS4 of the modulation transformer are clamped by a clamping circuit so that the voltage peak value thereof is jointly determined by the secondary side feedback voltage Vf-Secondary and the voltage drop of the corresponding device;

[0010] Step S3, performing peak detection and rectification on the AC signal coupled to the primary secondary winding LP2 by the modulation transformer through a peak detection circuit, and obtaining a DC signal reflecting the change of the secondary feedback voltage on the holding capacitor;

[0011] Step S4, using a regulating circuit to adjust the amplitude of the DC signal obtained in step S3 to meet the voltage input requirement of the primary PWM control circuit;

[0012] Step S5, when the primary winding of the modulation transformer is turned off, the energy stored in the modulation transformer is transferred to the secondary side in a flyback manner by using a demagnetization circuit, and an auxiliary power supply voltage Vss is formed by rectification and filtering;

[0013] Step S6, providing the auxiliary power supply voltage Vss to the feedback control circuit of the secondary side, so that when the output voltage has not been established or an abnormality occurs (such as short circuit, overvoltage protection), the sampling and protection functions of the secondary side can still be maintained;

[0014] Step S7, the feedback signal obtained by sampling the secondary side is transmitted to the PWM control circuit of the primary side through the above-mentioned magnetic isolation feedback process, so as to realize closed-loop regulation of the switching power supply.

[0015] As a preferred solution of the magnetic isolation feedback method with auxiliary power supply described in the present invention, the driving circuit includes a switch tube Q2, driving resistors R4, R5 and a switching speed improvement capacitor C4, wherein the on and off of Q2 is controlled by the primary side driving square wave; when Q2 is turned on, the primary side power supply voltage Vcc is chopped into an AC square wave and transmitted through the primary winding LP1 of the modulation transformer.

[0016] As a preferred solution of the magnetic isolation feedback method with auxiliary power supply described in the present invention, the peak detection circuit includes diodes D1 and D2 connected in series and a holding capacitor C1, which are used to perform peak detection on the forward signal sensed by the secondary winding LP2 of the modulation transformer, and output the acquired DC voltage signal to the regulation circuit.

[0017] As a preferred solution of the magnetic isolation feedback method with auxiliary power supply described in the present invention, the regulation circuit includes a voltage regulator D3, a current limiting resistor R1, a filter capacitor C2 and a PWM comparator input resistor R2, wherein the voltage regulator D3 stabilizes or attenuates the DC level on the capacitor C1 after peak detection so that the voltage signal meets the input requirements of different PWM control chips.

[0018] As a preferred solution of the magnetic isolation feedback method with auxiliary power supply described in the present invention, the clamping circuit includes a PNP transistor Q1 and series diodes D4, D5, D6, and D8. During the conduction period of the drive circuit, the conduction of Q1 causes the voltage peak on the secondary windings LS3 and LS4 to be clamped by the secondary feedback voltage Vf-Secondary and the PN junction voltage drop, thereby determining the peak level of the output signal.

[0019] As a preferred solution of the magnetic isolation feedback method with auxiliary power supply described in the present invention, the demagnetization circuit includes diodes D9, D7 and filter capacitor C6. During the shutdown period of the drive circuit, the energy stored in the modulation transformer is reversely induced by the secondary windings LS3 and LS4, rectified by the diode D9 and stored in the filter capacitor C6 to form the auxiliary power supply voltage Vss on the secondary side.

[0020] As a preferred solution of the magnetic isolation feedback method with auxiliary power supply described in the present invention, the secondary windings LS3 and LS4 of the modulation transformer are a plurality of windings in parallel structure, which are used to improve the ability of the demagnetization circuit to transfer energy to the filter capacitor C6, thereby meeting the maximum power supply current required by different secondary control circuits.

[0021] As a preferred solution of the magnetic isolation feedback method with auxiliary power supply described in the present invention, the driving circuit adopts NPN transistor Q2 to realize chopping, and MOSFET can also be used in combination with the corresponding driving circuit to realize the function of converting the primary power supply voltage Vcc into a high-frequency AC square wave.

[0022] As a preferred solution of the magnetic isolation feedback method with auxiliary power supply described in the present invention, the element used to adjust the DC level on the capacitor C1 in the regulation circuit is not limited to the voltage regulator D3, and the demodulated voltage signal can also be attenuated or amplified by resistor division or capacitor division.

[0023] As a preferred solution of the magnetic isolation feedback method with auxiliary power supply described in the present invention, multiple diodes are connected in series in both the secondary side clamping circuit and the demagnetization circuit to reduce the leakage current under reverse bias conditions, improve the accuracy and stability of the circuit, and ensure that the magnetic isolation feedback and auxiliary power supply functions are not completely lost in the event of a single point failure.

[0024] The beneficial effects of the present invention are:

[0025] The present invention adopts a magnetic isolation feedback solution in which transformers, diodes, triodes, resistors and capacitors are all radiation-insensitive devices, which can effectively avoid the light decay or performance degradation problems encountered by the optocoupler in a strong radiation environment, and greatly improve the immunity in high-energy radiation environments such as total dose and single particle. Since there is no light decay effect of the optocoupler, the stability of the feedback loop gain can be maintained during long-term use, thereby ensuring the reliability and consistency of the output voltage of the switching power supply.

[0026] Compared with the magnetic isolation feedback method that uses a dedicated control chip for modulation and demodulation, the present invention is completely based on discrete components for modulation and demodulation. Not only is the hardware structure more flexible and controllable, but also because it no longer requires a dedicated radiation-sensitive chip, the radiation resistance of the overall circuit can be further enhanced. At the same time, the selection and procurement of discrete devices are relatively more flexible, and have obvious advantages in cost and volume, which is particularly suitable for harsh environments and high-reliability applications.

[0027] When the primary winding of the transformer is turned on, the present invention adopts a forward working mode to transmit the secondary voltage signal, so that the primary side can quickly follow the changes in the secondary voltage and accurately realize closed-loop control; when the primary winding is turned off, the transformer storage energy is converted into a secondary auxiliary power supply voltage Vss in a flyback mode; the auxiliary power supply can provide an independent voltage-stabilized power supply for the sampling and amplifying circuit, protection circuit, etc. of the secondary side, so that the switching power supply can still maintain the continuous operation of the secondary side monitoring and protection functions under abnormal conditions such as short circuit, overvoltage, etc. when the output voltage is not established or short circuit, overvoltage, etc. occur, which greatly broadens the use scenarios and improves the overall reliability and fault tolerance. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

[0029] Figure 1 It is a schematic diagram of the framework of the magnetic isolation feedback method with auxiliary power supply of the present invention.

[0030] Figure 2 This is a principle circuit diagram of the magnetic isolation feedback method with auxiliary power supply of the present invention.

[0031] Figure 3 It is a node waveform diagram of the magnetic isolation feedback method of the present invention in a simulation environment. DETAILED DESCRIPTION

[0032] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the accompanying drawings.

[0033] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0034] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The term "in one embodiment" that appears in different places in this specification does not necessarily refer to the same embodiment, nor does it refer to a separate or selective embodiment that is mutually exclusive with other embodiments.

[0035] The object of the present invention is to provide a method for modulating and demodulating a signal using a transformer, thereby transmitting a secondary side feedback voltage signal to a primary side control circuit to complete a closed-loop control of a power supply:

[0036] This method can be applied to various isolated switching power supplies, and is applicable to various topologies such as flyback, forward, and bridge. The entire circuit is built and implemented by discrete devices, abandoning the constraints of traditional magnetic isolation control chips, and has advantages in circuit cost, stability, board area, etc.

[0037] On the other hand, the power supply of the feedback control circuit on the secondary side of the switching power supply often comes from the output voltage. However, before the output voltage is established, or the output voltage is abnormal, such as short-circuit protection, overvoltage protection, etc., it cannot provide stable power supply;

[0038] The present invention can provide an independent auxiliary power supply for the secondary side sampling feedback circuit on the basis of realizing magnetic isolation feedback, so that even in the above-mentioned abnormal situation, the auxiliary power supply can continue to supply power, thereby maintaining the sampling feedback and various output protection functions of the secondary side of the switching power supply.

[0039] Example 1, reference Figure 1 and Figure 2 , this embodiment provides a magnetic isolation feedback method with auxiliary power supply, wherein:

[0040] The circuit of the feedback method includes: a driving circuit, a peak detection circuit, and a regulating circuit on the primary side, a clamping circuit and a demagnetization circuit on the secondary side, and a modulation transformer for isolating the primary and secondary sides;

[0041] The input signal of the feedback method circuit mostly comes from the sampling feedback circuit on the secondary side, which is usually implemented by TL431 or op amp. The output signal of this circuit is provided to the PWM control circuit, such as various analog or digital PWM chips. The auxiliary power supply Vss of this circuit is provided to various control circuits on the secondary side of the switching power supply for power supply.

[0042] Driving circuit: The driving square wave controls the NPN transistor to chop the DC voltage into an AC square wave, which flows through the modulation transformer to become a carrier signal. The driving square wave can be changed using the PWM driving waveform or other high-frequency waveforms, which determines the operating frequency of the modulation transformer; among them: C4 is used to improve the switching speed of the transistor, R5 is the driving resistor, R5 and R4 divide the driving waveform to set the turn-on voltage of the transistor, and R4 can also be used for the discharge of the NPN gate. Q2 is the chopped switch tube. The opening and closing of Q2 can chop the primary power supply Vcc from DC to AC square wave, which is used as the carrier signal of the modulation transformer. The carrier signal flows through the LP1 winding of the modulation transformer; C5 is a filter capacitor, which can filter the high-frequency ripple generated by the modulation transformer to reduce the impact on the primary power supply Vcc voltage.

[0043] Peak detection circuit: can demodulate the AC voltage signal coupled from the modulation transformer into a DC voltage signal; wherein: D1 and D2 are used to detect the peak level in the LP2 winding and isolate the AC carrier, C1 is a holding capacitor, and since the LP2 winding and the secondary LP3 / LP4 winding work in a forward-excitation mode, the voltage signal on the LP2 winding can instantly reflect the voltage signal on the LP3 / LP4 winding.

[0044] Regulation circuit: The amplitude of the demodulated DC voltage signal can be increased or decreased to meet the requirements of different PWM control circuits; wherein: the D3 voltage regulator can attenuate and adjust the level signal on the holding capacitor C1 to meet the requirements of different PWM control circuits; R1 is the current limiting resistor of the voltage regulator, C2 is used to filter high-frequency spikes, and R2 is the input resistor of the PWM comparator.

[0045] Clamping circuit: can make the voltage amplitude in the modulation transformer be adjusted accordingly according to the feedback voltage generated in the sampling feedback circuit; wherein: in the Q2 turn-on stage, the current flows into the primary winding LP1 dot-marked end, and the secondary windings LS3 and LS4 dot-marked ends are sensed as high level, at this time D4, D5, D6, D8 are turned on, and the PNP tube Q1 is also turned on, and the voltage signal on LS3 and LS4 is clamped by Q1, and its voltage peak is determined by the secondary feedback voltage Vf-Secondary, the Q1 emitter voltage drop and the PN junction voltage drop of D4, D5, D6, and D7; C3 is a holding capacitor.

[0046] Demagnetization circuit: It can dissipate the energy in the modulation transformer in each cycle to ensure that the transformer will not be saturated, and convert the energy into auxiliary power supply; wherein: in the Q2 disconnection stage, the current of the primary winding LP1 is suddenly interrupted, resulting in the reverse induced voltage on the winding, and the secondary windings LS3 and LS4 dot-marked ends are sensed as low level. At this time, D9 and D7 are turned on, and the energy stored in the transformer is rectified into DC output through D9, and C6 is an energy storage filter capacitor; in this stage, the energy stored in the modulation transformer is transferred to the filter capacitor, and energy is provided to the secondary power supply Vss while demagnetizing the transformer.

[0047] In addition, the present invention uses two windings LS3 and LS4 in parallel as the secondary winding, and this function can also be achieved by using one winding or multiple windings;

[0048] The present invention utilizes a demagnetization circuit to provide auxiliary power supply for the secondary side. If auxiliary power supply is not required, other demagnetization methods (such as resistance dissipation, etc.) can also realize the main function of the present invention (i.e., magnetic isolation feedback);

[0049] The present invention uses a triode as a driving switch tube of the magnetic modulation transformer, and can also use a MOS tube or a corresponding driving circuit to achieve the same function;

[0050] The present invention adopts a voltage regulator as a modulation circuit, and can also adopt a resistor voltage division method to achieve the same function.

[0051] Experimental Example 1, reference Figure 3 , is an experimental example of the present invention. To verify the feasibility and performance of the above circuit, the feedback circuit is tested in a simulation environment, and the waveforms of key nodes are collected, such as Figure 3 As shown;

[0052] The main observation signals include:

[0053] Vf-Secondary (red waveform): is the simulated secondary feedback voltage input signal, which is simulated here with a 10kHz sawtooth wave;

[0054] Vf-Primary (blue waveform): is the primary feedback voltage signal, which is isolated by the modulation transformer and obtained after passing through the peak detection and regulation circuit;

[0055] Vss (green waveform): is the secondary auxiliary power supply output voltage, which is formed by releasing the energy stored in the modulation transformer to the filter capacitor C6 through the demagnetization circuit when Q2 is turned off;

[0056] According to the simulation waveform, we can see:

[0057] Vf-Primary (blue curve) can quickly follow the changes of Vf-Secondary (red curve), and the waveforms of the two are basically the same; by replacing the voltage regulator tube or adjusting the resistor divider, its DC bias can also be changed to adapt to different types of PWM control chips;

[0058] Vss (green curve) is a DC voltage of about 8V; its ripple size depends on the transformer operating frequency, the duty cycle of the transformer energy transfer and the capacity of the filter capacitor C6; its voltage level is mainly determined by the primary side Vcc, the circuit working duty cycle and the maximum load current demand of the secondary side;

[0059] When the secondary side has an abnormality such as a short circuit or overvoltage, which causes the Vf-Secondary signal to be abnormal or the main output power supply is insufficient, the auxiliary power supply Vss can still be relied on to provide power for the secondary side control circuit, thereby maintaining the normal execution of the protection and feedback functions.

[0060] Through the above experimental example 1, it can be seen that the present invention uses a modulation transformer to combine high-frequency forward and flyback, which not only realizes the magnetic isolation transmission of the secondary side feedback voltage signal, but also outputs auxiliary power in the demagnetization stage;

[0061] Compared with optocoupler feedback, the present invention has obvious advantages in radiation resistance and long-term reliability;

[0062] Compared with a dedicated magnetic isolation control chip, the present invention can be composed of discrete components, has high reliability, low cost and is not limited by the specifications of a single chip, and is more suitable for high-reliability occasions (such as aerospace, medical, nuclear industry, etc.).

[0063] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A magnetic isolation feedback method with auxiliary power supply, characterized in that: include, Step S1, chopping the primary power supply voltage Vcc through a driving circuit at the primary side to form an AC square wave carrier signal, and inputting the AC square wave carrier signal to the primary winding LP1 of the modulation transformer; Step S2, on the secondary side, the signals sensed on the secondary windings LS3 and LS4 of the modulation transformer are clamped by a clamping circuit so that the voltage peak value thereof is jointly determined by the secondary side feedback voltage Vf-Secondary and the voltage drop of the corresponding device; Step S3, performing peak detection and rectification on the AC signal coupled to the primary secondary winding LP2 by the modulation transformer through a peak detection circuit, and obtaining a DC signal reflecting the change of the secondary feedback voltage on the holding capacitor; Step S4, using a regulating circuit to adjust the amplitude of the DC signal obtained in step S3; Step S5, when the primary winding of the modulation transformer is turned off, the energy stored in the modulation transformer is transferred to the secondary side in a flyback manner by using a demagnetization circuit, and an auxiliary power supply voltage Vss is formed by rectification and filtering; Step S6, providing the auxiliary power supply voltage Vss to the feedback control circuit of the secondary side; Step S7, the feedback signal obtained by sampling the secondary side is transmitted to the PWM control circuit of the primary side through the above-mentioned magnetic isolation feedback process.

2. A magnetic isolation feedback method with auxiliary power supply as claimed in claim 1, characterized in that: The driving circuit includes a switch tube Q2, driving resistors R4, R5 and a switching speed improvement capacitor C4, wherein the on and off of Q2 is controlled by the primary driving square wave; when Q2 is turned on, the primary supply voltage Vcc is chopped into an AC square wave and transmitted through the primary winding LP1 of the modulation transformer.

3. A magnetic isolation feedback method with auxiliary power supply as claimed in claim 2, characterized in that: The peak detection circuit includes diodes D1 and D2 connected in series and a holding capacitor C1, which is used to perform peak detection on the forward signal sensed by the secondary winding LP2 of the modulation transformer and output the acquired DC voltage signal to the regulation circuit.

4. A magnetic isolation feedback method with auxiliary power supply as claimed in claim 3, characterized in that: The regulating circuit includes a voltage regulator tube D3, a current limiting resistor R1, a filter capacitor C2 and a PWM comparator input resistor R2, wherein the voltage regulator tube D3 performs voltage stabilization or attenuation regulation on the DC level on the capacitor C1 after peak value detection.

5. A magnetic isolation feedback method with auxiliary power supply as claimed in claim 4, characterized in that: The clamping circuit includes a PNP transistor Q1 and series diodes D4, D5, D6, and D8. During the conduction period of the drive circuit, the conduction of Q1 causes the voltage peaks on the secondary windings LS3 and LS4 to be clamped by the secondary feedback voltage Vf-Secondary and the PN junction voltage drop.

6. A magnetic isolation feedback method with auxiliary power supply as claimed in claim 5, characterized in that: The demagnetization circuit includes diodes D9, D7 and filter capacitor C6. During the shutdown period of the drive circuit, the energy stored in the modulation transformer is reversely induced by the secondary windings LS3 and LS4, rectified by the diode D9 and stored in the filter capacitor C6 to form an auxiliary power supply voltage Vss on the secondary side.

7. A magnetic isolation feedback method with auxiliary power supply as claimed in claim 6, characterized in that: The secondary windings LS3 and LS4 of the modulation transformer are a plurality of windings in parallel structure, which are used to improve the ability of the demagnetization circuit to transfer energy to the filter capacitor C6.

8. A magnetic isolation feedback method with auxiliary power supply as claimed in claim 7, characterized in that: The driving circuit uses an NPN transistor Q2 to achieve chopping, or uses a MOSFET in conjunction with a corresponding driving circuit.

9. A magnetic isolation feedback method with auxiliary power supply as claimed in claim 8, characterized in that: The element used for adjusting the DC level on the capacitor C1 in the regulating circuit is not limited to the voltage regulator D3, or the demodulated voltage signal is attenuated or amplified by means of resistor voltage division or capacitor voltage division.

10. A magnetic isolation feedback method with auxiliary power supply as claimed in claim 9, characterized in that: In both the secondary side clamping circuit and the demagnetization circuit, a plurality of diodes are connected in series.

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