CN113595370A

CN113595370A - Dynamic tracking quasi-resonant valley bottom conduction circuit and method and primary side feedback switching power supply

Info

Publication number: CN113595370A
Application number: CN202110834882.1A
Authority: CN
Inventors: 向磊; 唐波; 马强; 许刚颖; 王磊
Original assignee: Chengdu Chip Rail Microelectronics Co ltd
Current assignee: Chengdu Chip Rail Microelectronics Co ltd
Priority date: 2021-07-23
Filing date: 2021-07-23
Publication date: 2021-11-02
Anticipated expiration: 2041-07-23
Also published as: CN113595370B

Abstract

The invention discloses a dynamic tracking quasi-resonance valley bottom conduction circuit, a method and a primary side feedback switching power supply, comprising a precise demagnetization signal detection circuit, a quasi-resonance time generation circuit, a first valley signal generation circuit and a quasi-resonance logic circuit; the precise demagnetization signal detection circuit is connected with the precise resonance time generation circuit and the first wave trough signal generation circuit, and the precise resonance time generation circuit and the first wave trough signal generation circuit are connected with the precise resonance time generation circuit; on the basis of the accurate demagnetization signal detection circuit, the invention detects more accurate trough voltage signals by calculating the period of damping oscillation after the demagnetization time and integrating various load states through the accurate resonance logic circuit, so that each time the power switch tube is switched on, the trough voltage signals are in real troughs, the switching loss of the MOSFET of the power switch tube can be reduced, and the system efficiency is improved.

Description

Dynamic tracking quasi-resonant valley bottom conduction circuit and method and primary side feedback switching power supply

Technical Field

The invention relates to the field of switch power supply design, in particular to a dynamic tracking quasi-resonant valley conduction circuit, a method and a primary side feedback switch power supply.

Background

With the widespread use of new energy efficiency standards, the efficiency requirements of the switching power supply in the market field are higher and higher. The application scene that adopts accurate resonance valley bottom to switch on is increasingly popularized, uses accurate resonance valley bottom to switch on and can effectively improve switching power supply's efficiency, reduces switching power supply temperature rise, provides switching power supply power density.

It is well known that the losses of the switching power supply are mainly due to the turn-on and turn-off processes of the power switching tube MOSFET. In the on and off processes of the power switch tube MOSFET, the switching power supply has an overlapping interval, so that loss can be generated. Corresponding to a flyback switching power supply, a power switch tube MOSFET is turned off when the current of a primary winding is maximum, and the turn-off loss of the MOSFET is obtained. When the MOSFET of the power switch tube is turned off, the energy stored on the mutual inductance transfers to the secondary, the secondary diode is conducted, and the current of the secondary winding charges the output load and the output capacitor through the diode. When the energy transfer on the mutual inductance is finished, the secondary diode is cut off, and a part of energy still can generate damped damping oscillation between the coupling inductor and the parasitic capacitor of the power switch tube MOSFET by taking the direct-current voltage after the alternating-current bridge rectification as the reference until the power switch tube MOSFET is started next time. Generally, when the MOSFET is turned on again, the DRAIN voltage DRAIN of the MOSFET may be at a lower level, or the DRAIN voltage DRAIN may be at a high level, and then the conduction loss of the power switch tube MOSFET is generated.

This increase in losses with increasing power limits on the one hand the maximum operating efficiency; on the other hand, since the voltage and current rapidly change in a short time during the conversion, a large switching noise is also generated, resulting in a large electromagnetic interference. To address the above shortcomings, the prior art gradually adopted the quasi-resonant mode. By means of the resonance technology, the DRAIN voltage DRAIN of the power switch tube MOSFET is conducted at the minimum voltage, namely the valley voltage, so that the high-energy transmission mode of the square wave switch power supply can be kept, the switching loss can be reduced, and the efficiency of the switch power supply is improved.

However, when the mutual-inductance energy transfer is over, the DRAIN voltage of the MOSFET generates damped ringing with reference to the dc voltage after ac bridge rectification, and the valley voltage at the DRAIN end is not constant but gradually attenuated. Because DRAIN is high voltage, the conventional resonance technology does not directly detect DRAIN terminal voltage, but detects feedback terminal FB voltage. Similarly, the FB voltage is also damped and oscillated with zero voltage as a reference, and when the negative voltage degree of the FB is particularly severe, the negative voltage is inevitably clamped by the PN junction voltage in the process, so that the FB is clamped at minus 0.6V at the first few valleys, and the valley bottom voltage of the FB end gradually increases as the amplitude of the damped oscillation decreases. In the conventional resonance technology, the FB terminal voltage is compared with a fixed bias voltage, such as 100mV, and the valley voltage of the FB terminal is not detected, and the corresponding DRAIN terminal is not the valley voltage. The purpose that the quasi-resonance valley bottom conducts is not completely reached in the existing scheme.

Disclosure of Invention

The invention aims to overcome the defects of the prior art, and provides a dynamic tracking quasi-resonant valley bottom conduction circuit, a method and a primary side feedback switching power supply, which can reduce the switching loss of a power switching tube MOSFET and improve the system efficiency.

The purpose of the invention is realized by the following scheme:

a dynamic tracking quasi-resonance valley bottom conducting circuit comprises a precise demagnetization signal detection circuit, a quasi-resonance time generation circuit, a first valley signal generation circuit and a quasi-resonance logic circuit; the accurate demagnetization signal detection circuit is connected with the accurate resonance time generation circuit and the first wave trough signal generation circuit, and the accurate resonance time generation circuit and the first wave trough signal generation circuit are connected with the accurate resonance time generation circuit.

Furthermore, the input end of the accurate demagnetization signal detection circuit is connected to the feedback end FB and the internal bias voltage VB, and a high-pass filter circuit is provided for detecting the voltage drop of the FB and generating an accurate demagnetization signal.

Furthermore, the input end of the accurate resonance time generation circuit is connected with an accurate demagnetization signal and an internal fixed time TEST.

Furthermore, the input end of the first trough signal generating circuit is connected to the feedback end FB and the accurate demagnetization signal output by the accurate demagnetization signal detecting circuit, and a current comparing circuit is arranged for detecting a rising state of a first trough at the end voltage of the FB and generating a first trough bottom signal TFA, wherein the TFA is a high pulse signal.

Further, the input end of the quasi-resonant logic circuit is connected with the output signal QB or QSET signal of the quasi-resonant time generation circuit and the output signal TFA of the first valley signal generation circuit.

Further, the device comprises an error amplifier, a frequency modulation time generating circuit, a PWM (pulse-width modulation) starting logic circuit, a turn-off time generating circuit and a PWM logic circuit; the error amplifier is connected with the frequency modulation time generation circuit, the frequency modulation time generation circuit is connected with the PWM starting logic circuit, the PWM starting logic circuit is connected with the PWM logic circuit, and the PWM logic circuit is connected with the turn-off time generation circuit; the PWM opening logic circuit is connected with the quasi-resonance time generation circuit. In this embodiment, the error amplifier compares the feedback terminal voltage FB with the internal reference voltage VREF to obtain the error amplifier output voltage EA. And the frequency modulation time generating circuit obtains a frequency modulation time signal PFM according to different output voltages of the error amplifier. Wherein the PFM is active at a logic high level. And the PWM starting logic circuit is used for accessing a QR signal output by the quasi-resonance logic circuit to the input end of the PWM starting logic circuit, accessing an output signal PFM of the frequency modulation time generating circuit to the input end of the PWM starting logic circuit, and obtaining a PWMON logic signal through logic operation. When the PFM signal and the QR signal are detected to be high at the same time, the PWMON signal is triggered to be in a logic high level. And the turn-off time generating circuit is used for connecting the current detection resistor CS end into the turn-off time generating circuit and outputting a PWMOFF logic signal, wherein the effective PFMOFF is a high-level logic signal. And when the PWMON signal is at a logic high level, the PWM signal is triggered to be at a logic high level, the PFMOFF signal is at a logic high level, and the PWM signal is triggered to be at a logic low level. When the PWM signal is at a logic high level, the MOSFET of the power switch tube is controlled to be switched on; and when the PWM signal is at a logic low level, the MOSFET of the power switch tube is controlled to be closed.

A method for dynamically tracking a quasi-resonant valley-bottom conduction circuit, comprising the steps of: in the accurate demagnetization signal detection circuit, the FB peak voltage falling slope is detected in the complete damping attenuation period of the FB, a plurality of accurate demagnetization signals are sequentially generated, and the generated accurate demagnetization signals are logic high level signals.

Further, in the quasi-resonance time generation circuit, logic operation is performed on two adjacent accurate demagnetization signals to obtain a time difference value TEA of the two adjacent accurate demagnetization signals, and the damped oscillation period is TEA; then adding half of the time difference TEA to the TB time signal to calculate a valley bottom signal QB which is a high pulse signal; when the TN signal can not be detected, the TN-1 superposes the fixed offset time TSET at the moment, the resonance time generating circuit outputs a QSET signal and outputs QSET time, the QSET is a high pulse signal, and the fixed offset time TSET is larger than the damped oscillation period TEA.

Further, the quasi-resonant logic circuit judges to obtain a quasi-resonant logic signal QR according to a system state, and the method comprises the following steps:

if the system is in a first system state, namely a heavy-load system state, the needed PWM cycle of the system is short, the frequency is high, the effective PFM logic high level generated by the frequency modulation time generating circuit is triggered firstly, and the TFA high pulse signal is triggered later, then the second peak signal TB cannot be waited, at this moment, the quasi-resonance logic circuit outputs a QR signal which is a TFA signal, and the logic high level of the PWM signal is triggered immediately;

if the signal is in a second system state, namely in a loaded system state, when the PFM logic high level generated by the frequency modulation time generation circuit is triggered after a TFA high pulse signal, the signal needs to be sent out at an Nth wave trough when the TFA needs to be sent out, N is greater than 1, the quasi-resonance logic circuit outputs a QR signal which is a QN signal, and when the PFM logic high level and the QN are simultaneously high, the PWM signal high level is triggered;

if the system is in the third system state, namely in the light-load system state, the PWM frequency of the system is very small, the PWM period is very long, when the frequency modulation time generation circuit generates an effective PFM logic high level, the damping oscillation amplitude of the FB end is too small, and the demagnetization signal of TN +1 can not be detected after TN, then the TN signal is superimposed with the fixed offset time TSET, and at this time, the quasi-resonance logic circuit outputs the QR signal, namely the QSET at the moment when the TN is superimposed with the fixed offset time TSET.

A primary side feedback switch power supply comprises the dynamic tracking quasi-resonance valley bottom conduction circuit.

The invention has the beneficial effects that:

on the basis of an accurate demagnetization signal detection circuit, the invention detects a more accurate trough voltage signal by calculating the period of damping oscillation after demagnetization time and integrating various load states through an accurate resonance logic circuit, so that each time the power switch tube is switched on, the switching loss of the MOSFET of the power switch tube is reduced, and the system efficiency is improved.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without creative efforts.

FIG. 1 is a diagram of a typical flyback primary feedback AC/DC circuit topology; (ii) a

FIG. 2 is a diagram of a conventional quasi-resonant valley conducting circuit;

FIG. 3 is a diagram of a dynamic tracking quasi-resonant valley conducting circuit according to an embodiment of the present invention; (ii) a

Fig. 4 is a schematic diagram of a dynamic tracking quasi-resonant valley conduction signal according to an embodiment of the present invention.

Detailed Description

All features disclosed in all embodiments in this specification, or all methods or process steps implicitly disclosed, may be combined and/or expanded, or substituted, in any way, except for mutually exclusive features and/or steps.

A conventional primary side feedback AC/DC switching power supply topology is shown in fig. 2. The feedback terminal FB is compared with the fixed voltage VA, and when the FB voltage is less than VA, a high pulse QRA signal is generated. After demagnetization is finished, on one hand, the DRAIN voltage DRAIN of the power switch tube MOSFET starts to take the direct current voltage after bridge rectification as a central value, and the reflected voltage generated by the product of the output voltage plus the conduction voltage of the output diode and the turn ratio as an amplitude value starts to damp oscillation. The period of oscillation is related to the parasitic capacitance of the MOSFET driving the switch tube and the leakage inductance of the primary winding. The DRAIN voltage DRAIN of the power switching tube MOSFET is shown in fig. 4, and the oscillation frequency is not high and the oscillation amplitude is gradually attenuated.

On the other hand, after demagnetization is finished, the FB voltage takes zero as a reference point, the high-level voltage of the FB is an amplitude value, damped oscillation is started, and the oscillation frequency and the DRAIN terminal voltage DRAIN are kept consistent. In the initial stage of the damped oscillation, the valley bottom voltage of the FB is clamped near minus 0.6V, the oscillation amplitude is gradually reduced along with the increase of the damped oscillation time, the negative voltage of the FB at the trough end is gradually increased, meanwhile, the positive voltage of the FB at the crest end is also gradually reduced, and when the turn-off time of the PWM is too long, the FB damped oscillation amplitude tends to zero.

The conventional resonant valley bottom conduction technology generally detects the voltage at the bottom of the feedback terminal FB to indirectly detect the voltage at the bottom of the DRAIN valley. In order to give consideration to the accuracy of FB valley bottom detection and ensure that the DRAIN terminal voltage approaches the valley as much as possible. The VA voltage is generally set above zero and below 100 mv. Then the corresponding detected DRAIN voltage is now close to the center value of the ringing, i.e. the dc voltage after bridge rectification of the ac voltage. When the alternating current voltage is AC264V, the bridge rectification voltage can reach 380V. At this time, there is a certain distance from the true valley conduction.

To achieve the above object, as shown in fig. 3 to 4, an embodiment of the present invention provides a dynamic tracking quasi-resonant valley bottom conducting circuit, which includes a precise demagnetization signal detection circuit, a quasi-resonant time generation circuit, a first valley signal generation circuit, and a quasi-resonant logic circuit; the accurate demagnetization signal detection circuit is connected with the accurate resonance time generation circuit and the first wave trough signal generation circuit, and the accurate resonance time generation circuit and the first wave trough signal generation circuit are connected with the accurate resonance time generation circuit.

The dynamic tracking quasi-resonant valley bottom conducting circuit of the embodiment can not directly compare the FB voltage of the feedback end with the fixed voltage. But according to the principle that the frequency is kept unchanged in the damped oscillation stage, the result is necessarily at the valley moment by calculating the time between adjacent peaks, namely the damped oscillation period, and then superposing half the period at the peak moment.

The feedback end FB and the fixed bias voltage VB are introduced into the accurate demagnetization signal detection circuit, the fixed bias voltage VB is not compared with the FB in a COMP mode, the falling slope of the FB voltage is judged through an internal high-pass filter, when the FB voltage rapidly falls by a certain amplitude at the peak time, the TA is triggered to be a high pulse signal, and each peak time of the FB can be detected. The high pulse signals of TA, TB and the like are input into the quasi-resonance time generation circuit, and the difference value of TB and TA can be obtained through logic operation or analog circuit calculation, and the difference value is the period of the damped oscillation. And continuously superposing the TB high pulse signal in the quasi-resonance time generation circuit for half of the period to obtain the QB signal. QB is the calculated valley high pulse signal.

An output signal TA of the accurate demagnetization signal detection circuit is introduced into the first trough signal generation circuit. The feedback end FB voltage is in the first damped oscillation period, the trough voltage is clamped to minus 0.6V by the PN junction voltage, after the FB detects the TA, the FB voltage drops rapidly, and through a first trough signal generating circuit, when the FB voltage rises to be greater than minus 0.6V or so, a high pulse signal TFA can be generated.

And introducing a high pulse signal QB and a high pulse signal TFA into the quasi-resonant logic circuit to carry out state judgment. In the first system state, under the condition of heavy load, the PWM cycle required by the system is short, the frequency is high, the effective PFM logic high level generated by the frequency modulation time generating circuit is triggered first, and the TFA high pulse signal is triggered later, so that the second peak signal TB cannot be waited, at the moment, the quasi-resonance logic circuit outputs the QR signal which is the TFA signal, and the logic high level of the PWM signal is triggered immediately. In the second system state, the PFM logic high level generated by the fm time generation circuit is triggered after the TFA high pulse signal, and when the TFA needs the nth (N >1) wave trough to send wave (i.e., send wave when the minimum voltage is reached), the quasi-resonant logic circuit outputs the QR signal, i.e., the QN signal, and when the PFM logic high level and the QN are simultaneously high, the PWM signal high level is triggered. In the third system state, when the load state is very light, the PWM frequency of the system is very small, and the PWM period is very long, when the frequency modulation time generation circuit generates an effective PFM logic high level, the FB terminal damping oscillation amplitude is too small, and after TN, the demagnetization signal of TN +1 cannot be detected any more, then the TN signal is superimposed with the fixed offset time TSET, and at this time, the quasi-resonant logic circuit outputs a QR signal, which is the time QSET when TN is superimposed with the fixed offset time TSET. Because the third system state is in a load state and is very light-loaded, the whole PWM period is very long, the PWM wave-emitting frequency is very small, the power loss of the MOSFET switching loss of the power switch tube is relatively small at the moment, the system can not be started at a wave trough at the moment, and the quasi-resonance state can not be triggered to be started at the moment.

Other embodiments than the above examples may be devised by those skilled in the art based on the foregoing disclosure, or by adapting and using knowledge or techniques of the relevant art, and features of various embodiments may be interchanged or substituted and such modifications and variations that may be made by those skilled in the art without departing from the spirit and scope of the present invention are intended to be within the scope of the following claims.

The functionality of the present invention, if implemented in the form of software functional units and sold or used as a stand-alone product, may be stored in a computer readable storage medium. Based on such understanding, the technical solution of the present invention may be embodied in the form of a software product, which is stored in a storage medium, and all or part of the steps of the method according to the embodiments of the present invention are executed in a computer device (which may be a personal computer, a server, or a network device) and corresponding software. And the aforementioned storage medium includes: various media capable of storing program codes, such as a usb disk, a removable hard disk, or an optical disk, exist in a read-only Memory (RAM), a Random Access Memory (RAM), and the like, for performing a test or actual data in a program implementation.

Claims

1. A dynamic tracking quasi-resonance valley bottom conducting circuit is characterized by comprising a precise demagnetization signal detection circuit, a quasi-resonance time generation circuit, a first valley signal generation circuit and a quasi-resonance logic circuit; the accurate demagnetization signal detection circuit is connected with the accurate resonance time generation circuit and the first wave trough signal generation circuit, and the accurate resonance time generation circuit and the first wave trough signal generation circuit are connected with the accurate resonance time generation circuit.

2. The dynamic tracking quasi-resonant valley bottom conduction circuit according to claim 1, wherein the input terminal of the precise demagnetization signal detection circuit is connected to the feedback terminal FB and the internal bias voltage VB, and a high pass filter circuit is provided for detecting the FB voltage drop and generating the precise demagnetization signal.

3. The dynamic tracking quasi-resonant valley conducting circuit according to claim 2, wherein the input terminal of the quasi-resonant time generating circuit is connected to the precise demagnetization signal and the internal fixed time TEST.

4. The dynamic tracking quasi-resonant valley bottom on-state circuit as claimed in claim 3, wherein the input terminal of the first valley signal generating circuit is connected to the feedback terminal FB and the accurate demagnetization signal outputted by the accurate demagnetization signal detecting circuit, and a current comparing circuit is provided for detecting the rising state of the first valley at the FB terminal and generating a first valley bottom signal TFA, which is a high pulse signal.

5. The dynamic tracking quasi-resonant valley bottom on circuit according to claim 4, wherein the input terminal of the quasi-resonant logic circuit is connected to the output signal QB or QSET signal of the quasi-resonant time generation circuit and the output signal TFA of the first valley bottom signal generation circuit.

6. The dynamic tracking quasi-resonant valley bottom conduction circuit according to any one of claims 1 to 5, comprising an error amplifier, a frequency modulation time generation circuit, a PWM turn-on logic circuit, a turn-off time generation circuit and a PWM logic circuit; the error amplifier is connected with the frequency modulation time generation circuit, the frequency modulation time generation circuit is connected with the PWM starting logic circuit, the PWM starting logic circuit is connected with the PWM logic circuit, and the PWM logic circuit is connected with the turn-off time generation circuit; the PWM opening logic circuit is connected with the quasi-resonance time generation circuit.

7. A method for dynamically tracking a quasi-resonant valley-conducting circuit according to claim 6, comprising the steps of: in the accurate demagnetization signal detection circuit, the FB peak voltage falling slope is detected in the complete damping attenuation period of the FB, a plurality of accurate demagnetization signals are sequentially generated, and the generated accurate demagnetization signals are logic high level signals.

8. The method for dynamically tracking the quasi-resonant valley conducting circuit according to claim 7, wherein in the quasi-resonant time generating circuit, the logic operation is performed on two adjacent accurate demagnetization signals to obtain a time difference value TEA between the two adjacent accurate demagnetization signals, and a damped oscillation period is TEA; then adding half of the time difference TEA to the TB time signal to calculate a valley bottom signal QB which is a high pulse signal; when the TN signal can not be detected, the TN-1 superposes the fixed offset time TSET at the moment, the resonance time generating circuit outputs a QSET signal and outputs QSET time, the QSET is a high pulse signal, and the fixed offset time TSET is larger than the damped oscillation period TEA.

9. The method of dynamically tracking a quasi-resonant valley-bottom conduction circuit according to claim 7, wherein a quasi-resonant logic signal QR is obtained in the quasi-resonant logic circuit according to a system state judgment, comprising the steps of:

if the logic high level of the effective PFM generated by the frequency modulation time generating circuit is triggered firstly and then triggered by the TFA high pulse signal in the first system state, namely in the heavy-load system state, the second peak signal TB is not waited at the moment, and the quasi-resonance logic circuit outputs the QR signal which is the TFA signal at the moment and triggers the logic high level of the PWM signal;

if the system state is the third system state, namely the light-load system state, when the frequency modulation time generating circuit generates an effective PFM logic high level, the TN signal is superposed with the fixed offset time TSET, and at the moment, the quasi-resonance logic circuit outputs the QR signal, namely the time QSET at which the TN is superposed with the fixed offset time TSET.

10. A primary-side feedback switching power supply comprising the circuit of claim 6.