CN114583962A - Power supply control system for zero voltage switching - Google Patents
Power supply control system for zero voltage switching Download PDFInfo
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- CN114583962A CN114583962A CN202011389355.6A CN202011389355A CN114583962A CN 114583962 A CN114583962 A CN 114583962A CN 202011389355 A CN202011389355 A CN 202011389355A CN 114583962 A CN114583962 A CN 114583962A
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- 229910044991 metal oxide Inorganic materials 0.000 claims description 3
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M3/00—Conversion of dc power input into dc power output
- H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
- H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
- H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
- H02M3/325—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal
- H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
- H02M3/33507—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of the output voltage or current, e.g. flyback converters
- H02M3/33523—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of the output voltage or current, e.g. flyback converters with galvanic isolation between input and output of both the power stage and the feedback loop
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/02—Conversion of ac power input into dc power output without possibility of reversal
- H02M7/04—Conversion of ac power input into dc power output without possibility of reversal by static converters
- H02M7/12—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/21—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
- H02M7/217—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
- Y02B70/00—Technologies for an efficient end-user side electric power management and consumption
- Y02B70/10—Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes
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Abstract
The invention provides a power supply control system for zero voltage switching, which comprises a power supply controller, a rectifying unit, a power supply unit, a transformer unit, a primary side switching unit, an auxiliary switching unit, an output unit and a current sensing unit, wherein the power supply controller is used for realizing flyback conversion, and the power supply controller comprises a power supply pin, a grounding pin, a primary driving pin, a voltage sensing pin, an auxiliary driving pin and an auxiliary winding sensing pin. In particular, the invention controls the auxiliary switching unit to influence the primary side winding by the auxiliary winding to reduce the drain voltage of the primary side switching unit, so that the primary side switching unit is switched on when the drain voltage of the primary side switching unit is the lowest voltage, thereby greatly reducing the switching loss and improving the power conversion efficiency.
Description
Technical Field
The invention relates to a power supply control system for zero voltage switching, in particular to a power supply control system which utilizes an auxiliary switching unit to be connected to an auxiliary winding, and a power supply controller to generate an auxiliary driving signal to control the opening and closing of the auxiliary switching unit, so that a primary side winding is influenced by the auxiliary winding to reduce the drain voltage of the primary side switching unit, and the primary side switching unit can be opened only when the drain voltage of the primary side switching unit generated by the power supply controller is the lowest voltage or is close to zero voltage, thereby greatly reducing the switching loss and improving the power supply conversion efficiency.
Background
With the progress of electronic technology and semiconductor process, various electronic products with more powerful functions and high integration are continuously provided by end-product related practitioners, and different electronic devices require specific power supplies to provide required power, such as Integrated Circuits (ICs) requiring low voltage direct current of 1.2V, electric motors requiring direct current of 12V, and backlight modules requiring high voltage power supplies of hundreds of volts or more, so that high-quality and high-efficiency power conversion devices are required as power supplies to meet the required power supplies.
Among the current Power supplies, the Switching Power Supply (Switching Power Supply) with Pulse Width Modulation (PWM) is one of the most common methods, because a relatively high Power conversion efficiency can be achieved. Taking Flyback power converter as an example, the Flyback power converter mainly includes a power controller, a transformer, a switching unit, a current sensing resistor, a secondary side rectifier and an output capacitor, and the transformer includes a primary side winding and a secondary side winding, wherein the power controller, the primary side winding, the switching unit and the current sensing resistor are connected in series to form a primary side loop, and the secondary side winding, the secondary side rectifier and the output capacitor are connected in series to form a secondary side loop. The power controller generates a PWM driving signal to drive a switching unit such as a power transistor connected to the transformer, and the PWM driving signal has a high-speed switching frequency, and can periodically and rapidly turn on and off the switching unit to achieve the purpose of conducting and cutting off the current flowing through the primary side winding and the switching unit of the transformer, and convert the input voltage into different output voltages by means of the electromagnetic induction between the primary side winding and the secondary side winding of the transformer and a preset winding ratio, and the different output voltages are used as a power supply to supply power to an external load, thereby achieving the power conversion function.
In addition, the primary side winding is composed of Magnetizing Inductance (Magnetizing Inductance) and leakage Inductance, the leakage Inductance is generated because the primary side Magnetic Flux (Magnetic Flux) cannot be coupled to the secondary side, the stored energy must be transferred to other places for consumption, and the energy in the leakage Inductance is the cause of the generation of a very large Voltage Spike (Voltage Spike) when the drain of the switching unit is turned off and cut off.
When the switching unit is turned on, a current flows through the primary side winding, that is, the input power source stores energy in the primary side winding. When the switching unit is turned off, since the energy stored in the leakage inductance cannot be coupled to the secondary side, an LC resonance is formed with the capacitance between the drain and the source of the switching unit, and a voltage spike is generated between the drain and the source of the switching unit. After LC resonance, the voltage across the drain and the source starts to slowly drop from the peak value to a certain fixed value, called Knee (Knee), which indicates that the energy stored in the exciting inductor is completely released, at this time, the current on the secondary side is completely zero and is in an open circuit state, wherein the circuit on the primary side forms an RLC resonant tank, generates an underdamped resonance or ringing and has a resonant frequency, so that the time of the valley bottom can be predicted according to the resonant frequency.
Further, when the switching unit is rapidly turned on and off by the PWM driving signal in a periodic manner, discontinuity, such as current and voltage, may occur in the related electrical signals, thereby causing switching loss and reducing the overall power conversion efficiency. For example, if the switching cell can be turned on when the drain-source voltage is lowest, i.e., the valley voltage (valley), the switching loss can be greatly reduced. Therefore, in the prior art, the switching unit is usually turned on only when the drain-source cross voltage of the switching unit is lowered to a low voltage and the current of the exciting inductor is zero, which is generally called quasi-resonance (QR) switching or valley-bottom switching, mainly because the energy loss is less when the switching unit is turned on, which can reduce the switching loss.
Usually, quasi-resonant switching or valley switching is performed by estimating the time when the knee occurs and calculating the time for the valley switching according to the frequency of ringing, which is used as the time point for opening the switching unit, or selecting a valley at a certain time, such as the third valley. Although the switching-on mode can reduce the switching loss moderately, the characteristics of each electrical component affect the time of the knee and the frequency of ringing, so that the switching-on mode needs to be adjusted or calculated in cooperation with the current circuit, otherwise, the switching-on mode cannot be switched accurately at the valley bottom to open the switching unit. Further, when the load is light, it is necessary to open a little later, but when the load is heavy, it is necessary to open a little earlier.
It is obvious that any component change or electrical characteristic change in the circuit needs to be readjusted or calculated to open the time, which is inconvenient in practical application, so that the above prior art has disadvantages in that the optimal open time required for different load levels is different according to the change of application environment, and the power controller cannot be predicted and dynamically adjusted to set the corresponding open time in advance, and thus it is difficult to meet most of the existing application fields in practice.
Therefore, there is a need for a power control system with zero voltage switching, in which an auxiliary switching unit is connected to an auxiliary winding, and a power controller generates an auxiliary driving signal to control the auxiliary switching unit to turn on and off, so that the auxiliary winding affects a primary side winding to reduce a drain voltage of the primary side switching unit, so that the primary side switching unit is turned on when the drain voltage of the primary side switching unit is at a minimum voltage or close to zero voltage, thereby greatly reducing switching loss and improving power conversion efficiency.
Disclosure of Invention
The main objective of the present invention is to provide a power control system for zero voltage switching, which comprises a power controller, a rectifying unit, a power unit, a transformer unit, a primary side switching unit, an auxiliary switching unit, an output unit and a current sensing unit, wherein the power controller is used for implementing a flyback power conversion function, and comprises a power pin, a ground pin, a primary driving pin, a voltage sensing pin, an auxiliary driving pin and an auxiliary winding sensing pin, wherein the transformer unit comprises a primary side winding, an auxiliary winding and a secondary side winding, which are coupled to each other, and the primary side switching unit and the auxiliary switching unit may comprise a mos transistor, or a gan field effect transistor, or a sic-mos transistor.
The rectifying unit receives an external input power supply and generates a rectifying power supply after rectification, the rectifying unit is connected to the grounding potential through the auxiliary capacitor, and the power supply unit also receives the external input power supply and generates and outputs power supply voltage to the power supply pin after processing for the power supply controller to operate.
The transformer unit comprises a primary side winding, an auxiliary winding and a secondary side winding which are coupled with each other, wherein one end of the primary side winding is connected with the rectifying unit and used for receiving rectified power.
The drain of the primary side switching unit is connected with the other end of the primary side winding, the gate of the primary side switching unit is connected with the primary driving pin, and the source of the primary side switching unit is connected with the voltage sensing pin.
One end of the current sensing unit is connected to the voltage sensing pin, and the other end of the current sensing unit is connected to the ground potential, and the voltage sensing pin generates a current sensing signal.
The drain of the auxiliary switching unit is connected with the rectifying unit to receive the rectified power, the gate of the auxiliary switching unit is connected with the auxiliary driving pin, the source of the auxiliary switching unit is connected with one end of the auxiliary winding and the auxiliary winding sensing pin, and the other end of the auxiliary winding is connected with the grounding potential. In addition, the source of the auxiliary switching unit generates an auxiliary winding voltage corresponding to the drain voltage of the primary side switching unit, and particularly, the drain voltage refers to the voltage of the drain of the primary side switching unit.
Furthermore, the drain of the auxiliary switching unit is connected to the ground potential via the auxiliary capacitor.
One end of the output unit is connected to one end of the secondary side winding for generating an output power supply and supplying power to a load connected to the output unit, and the other end of the secondary side winding is connected to a ground potential.
The power controller generates a primary driving signal and an auxiliary driving signal by performing a zero voltage switching operation, wherein the primary driving signal is transmitted to the primary driving pin, and the auxiliary driving signal is transmitted to the auxiliary driving pin. Essentially, the primary driving signal is a Pulse Width Modulation (PWM) signal, has a PWM frequency, and includes a periodic turn-on level and a turn-off level for periodically turning on or off the primary-side switching unit, wherein the turn-on level is a sustain turn-on time and the turn-off level is a sustain turn-off time, and particularly, the PWM frequency is determined according to a load level of a load, and the turn-on time is determined according to an output power.
Specifically, the zero-point voltage switching operation includes: the primary side switching unit detects and judges whether the voltage of the auxiliary winding is reduced to the knee part or not when the auxiliary switching unit is closed after the auxiliary switching unit is closed; when the auxiliary winding voltage is decreased to the knee, the time between the turning-off of the primary side switching unit and the decrease of the auxiliary winding voltage to the knee is taken as the demagnetization time, and the turn-on delay time is calculated; driving an auxiliary driving signal to open the auxiliary switching unit after waiting for the opening delay time, and setting, adjusting or calculating an auxiliary conduction time; after waiting for the auxiliary on-time, driving an auxiliary driving signal to close the auxiliary switching unit, and calculating an interval time; finally, after waiting for the interval time, the primary driving signal is driven to turn on the primary side switching unit.
Therefore, the turn-off time of the primary-side switching unit includes a demagnetization time, a turn-on delay time, an auxiliary turn-on time, and an interval time.
In general, the invention uses the auxiliary switching unit to connect to the auxiliary winding, and the power controller generates the auxiliary driving signal to control the on and off of the auxiliary switching unit, and then the auxiliary winding affects the primary side winding, and reduces the drain voltage of the primary side switching unit, so that the primary driving signal generated by the power controller can open the primary side switching unit when the drain voltage of the primary side switching unit is the lowest voltage or is close to zero voltage, thereby greatly reducing the switching loss and improving the power conversion efficiency.
Drawings
Fig. 1 is a system diagram of a power control system for zero-point voltage switching according to an embodiment of the present invention.
Fig. 2 is a waveform diagram illustrating the operation of a zero-voltage switching power control system according to an embodiment of the present invention.
Fig. 3 is a simplified waveform diagram illustrating the operation of a zero voltage switching power control system according to an embodiment of the present invention.
Description of reference numerals:
10-a power supply controller;
20-a rectifying unit;
21-a power supply unit;
30-a transformer unit;
50-an output unit;
60-a current sensing unit;
CA-auxiliary capacitance;
CB-auxiliary capacitance;
IDS — primary side switching cell current;
IP-primary side current;
IS-secondary side current;
LA-auxiliary winding;
LP-primary side winding;
LS — secondary side winding;
QA-auxiliary switching unit;
QP — primary side switching unit;
RL-load;
T1-Power Pin;
t2-ground pin;
t3-primary drive pin;
T4-Voltage sense Pin;
t5-auxiliary drive pin;
t6-auxiliary winding sense pin;
VAC-external input power;
VCS-current sense signal;
VDD-supply voltage;
VDP-drain voltage;
VGA-auxiliary drive signal;
VGND-ground potential;
VGP-primary drive signal;
a Vb-rectified power supply;
VOUT-output power;
VZVS — auxiliary winding voltage;
TSW PWM-frequency period;
TPON-on time;
TPOFF-off time;
TFW-demagnetization time;
TD-opening delay time;
TAON-auxiliary on time;
TDEAD-interval time;
k-knee.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in detail with reference to the accompanying drawings and specific embodiments.
Fig. 1 and fig. 2 are a system schematic diagram and an operation waveform diagram of a power control system for zero voltage switching according to a first embodiment of the present invention. As shown in fig. 1 and 2, the power control system for zero-point voltage switching according to the first embodiment of the present invention includes a power controller 10, a rectifying unit 20, a power unit 21, a transformer unit 30, a primary side switching unit QP, an auxiliary switching unit QA, an output unit 50, and a current sensing unit 60, and is configured to implement a Flyback (Flyback) power conversion function.
Specifically, the power controller 10 includes a power pin T1, a ground pin T2, a primary driving pin T3, a voltage sensing pin T4, an auxiliary driving pin T5 and an auxiliary winding sensing pin T6, and the transformer unit 30 may include a primary side winding LP, an auxiliary winding LA and a secondary side winding LS coupled to each other, and the primary side switching unit QP and the auxiliary switching unit QA may include Metal-Oxide-Semiconductor (MOS) transistors, gallium nitride (gan) nitride (FET), or silicon carbide-Metal Oxide Semiconductor field effect transistors (SiC-MOSFET).
Further, the rectifying unit 20 receives an external input power VAC and rectifies the external input power VAC to generate a rectified power Vb, and particularly, the rectifying unit 20 is further connected to a ground potential VGND through an auxiliary capacitor CB for providing a filtering effect on the rectified power Vb, and the power supply unit 21 also receives the external input power VAC, processes the rectified power to generate and output a power voltage VDD, and receives the power voltage VDD through a power pin T1 to operate the power supply controller 10.
In addition, one end of the primary winding LP is connected to the rectifying unit 20 for receiving the rectified power Vb, the drain of the primary switching unit QP is connected to the other end of the primary winding LP, the gate of the primary switching unit QP is connected to the primary driving pin T3, and the source of the primary switching unit QP is connected to the voltage sensing pin T4.
One end of the current sensing unit 60 is connected to the voltage sensing pin T4, and the other end of the current sensing unit 60 is connected to the ground voltage VGND, and generates the current sensing signal VCS at the voltage sensing pin T4.
The drain of the auxiliary switching unit QA is connected to the power unit 21 for receiving the rectified power Vb, the gate of the auxiliary switching unit QA is connected to the auxiliary driving pin T5, the source of the auxiliary switching unit QA is connected to one end of the auxiliary winding LA and the auxiliary winding sensing pin T6, and the other end of the auxiliary winding LA is connected to the ground potential VGND. In addition, the drain of the auxiliary switching unit QA is further connected to the ground potential VGND via an auxiliary capacitor CA. Furthermore, the source of the auxiliary switching unit QA generates an auxiliary winding voltage VZVS, wherein the auxiliary winding voltage VZVS corresponds to the drain voltage of the primary side switching unit QP, and the drain voltage refers to the voltage of the drain of the primary side switching unit QP.
One end of the output unit 50 is connected to one end of the secondary side winding LS for generating an output power source VOUT and supplying power to a load RL connected to the output unit 50, and the other end of the secondary side winding LS is connected to a ground potential VGND.
More specifically, the power controller 10 performs a zero voltage switching operation to generate the primary driving signal VGP and the auxiliary driving signal VGA, wherein the primary driving signal VGP is transmitted to the primary driving pin T3, and the auxiliary driving signal VGA is transmitted to the auxiliary driving pin T5.
The primary driving signal VGP is substantially a Pulse Width Modulation (PWM) signal, has a PWM frequency or a PWM period TSW, and includes a periodic on level and an off level for periodically turning on or off the primary-side switching unit QP, where the on level is maintained for the on time TPON and the off level is maintained for the off time TPOFF. In particular, the PWM frequency or the PWM period TSW is determined according to the load level of the load RL, and the on-time TPON is determined according to the output power VOUT, and since the selection of the PWM frequency and the on-time TPON are in the prior art of the switching of the flyback power, they will not be explained in detail further below.
More specifically, the zero-point voltage switching operation includes the following steps. Note, however, that since the auxiliary winding voltage VZVS itself corresponds to the drain voltage VDP of the primary-side switching unit QP, the following operation performed by using the auxiliary winding voltage VZVS is actually directed to the drain voltage VDP of the primary-side switching unit QP.
First, the primary side switching unit QP detects and determines whether the auxiliary winding voltage VZVS drops to a Knee (Knee) K when the auxiliary switching unit QA turns off after turning off, wherein the Knee K is an inflection point at which the auxiliary winding voltage VZVS changes to a steeper and sharper dropping curve after undergoing an approximately linear drop. Generally, the turning point of the knee K indicates that the Demagnetization of the transformer unit 30 is completed, and the determination method can be implemented by detecting whether the falling slope of the auxiliary winding voltage VZVS is greater than a predetermined slope value, which belongs to the prior art and will not be described in detail hereinafter.
When the auxiliary winding voltage VZVS falls to the knee K, the time between the turn-off of the primary-side switching unit QP to the fall of the auxiliary winding voltage VZVS to the knee K is taken as a demagnetization time TFW, and the entire period of the demagnetization time TFW may be generally referred to as a Free-rolling phase (Free-rolling phase), after which the auxiliary winding voltage VZVS enters an underdamped resonance, which may be generally referred to as a resonance phase (Oscillation phase), and immediately thereafter, the opening delay time TD is calculated or set. After waiting for the opening delay time TD, the auxiliary driving signal VGA is driven to open the auxiliary switching unit QA, and then the auxiliary on-time TAON is generated by setting, adjusting or calculating.
After waiting for the auxiliary on-time TAON, the auxiliary driving signal VGA is driven to turn off the auxiliary switching unit QA, and then, a preset interval time TDEAD is waited, preferably, the interval time TDEAD is preset to be between 150ns and 250ns, and then, the primary driving signal VGP is driven to turn on the primary side switching unit QP, in other words, the primary side switching unit QP and the auxiliary switching unit QA are not simultaneously turned on but are separated by the interval time TDEAD. Then, the primary switching unit QP is turned off after maintaining the on-time TPON, so as to complete the periodic operations of the primary driving signal VGP and the auxiliary driving signal VGA.
In general, the turn-off time TPOFF includes a demagnetization time TFW, a turn-on delay time TD, an auxiliary turn-on time TAON, and an interval time TDEAD, and the auxiliary switching unit Q is turned on after the demagnetization time TFW and the turn-on delay time TD have elapsed after the primary side switching unit QP is turned off, and is turned off after the auxiliary turn-on time TAON is maintained, and particularly, the primary side switching unit QP is then turned on after the interval time TDEAD has elapsed.
Furthermore, the main purpose of the auxiliary driving signal VGA is to reduce the drain voltage of the primary switch unit QP, that is, the drain voltage of the primary switch unit QP can be greatly reduced when the primary switch unit QP is turned on, even approaching zero voltage, so as to reduce the switching loss and further improve the overall power conversion efficiency. It is obvious that the drain voltage of the primary side switching unit QP is decreased as the auxiliary on-time TAON is increased, but too much auxiliary on-time TAON causes the inter-time TDEAD to be too small to ensure that the primary side switching unit QP and the auxiliary switching unit QA are not turned on at the same time, so that the auxiliary on-time TAON can have the maximum value and the drain voltage of the primary side switching unit QP has the minimum value under the condition that the inter-time TDEAD must satisfy the requirement of 150ns to 250 ns.
Therefore, the auxiliary on-time TAON can be set, adjusted or calculated according to the requirements of the application system, so that it is very flexible in practical application. Of course, compared with the conventional flyback converter, the present invention uses the auxiliary driving signal VGA, so that the power consumption is further increased, but after actual measurement, the power consumption of the auxiliary driving signal VGA is still much smaller than the reduced switching loss.
As mentioned above, the auxiliary on-time TAON can be generated by setting, adjusting or calculating, and further, by utilizing an adjustable setting operation, an adaptive adjusting operation or a calculating operation, respectively, and is individually described as follows.
The adjustable setting operation is to individually set the auxiliary on-time TAON according to the voltage of the external input power VAC, which may include 90, 115, and 230VAC, and the load level of the load RL, which may include very light load, medium load, and full load. In general, the auxiliary on time TAON is set to be longer as the voltage of the external input power supply VAC is higher, and is set to be shorter as the load degree is heavier.
Alternatively, the adjustable setting operation may be performed by first setting the auxiliary on-time TAON to a certain initial on-time when the voltage of the external input power VAC is 90VAC, and setting the corresponding auxiliary on-time TAON in an equal-scale amplification manner according to the voltage of the external input power VAC by using the initial on-time when the voltage of the external input power VAC is 115 VAC or 230 VAC. In other words, the auxiliary on time TAON is set in equal proportion to the voltage of the external input power VAC.
If the adaptive adjustment operation is used, the method includes determining whether the auxiliary winding voltage VZVS is lower than a threshold voltage value, and changing the auxiliary on-time TAON in a cycle by cycle manner when the auxiliary winding voltage VZVS is not lower than the threshold voltage value until the auxiliary winding voltage VZVS is lower than the threshold voltage value. Since the auxiliary winding voltage VZVS decreases with the increase of the auxiliary turn-on time TAON, in practice, the auxiliary turn-on time TAON is first shorter and gradually increased to make the auxiliary winding voltage VZVS lower than the threshold voltage value, and the primary side switching unit QP is turned on and turned on.
Referring to fig. 3, a simplified waveform diagram of the operation of the zero-point voltage switching power control system according to the embodiment of the present invention is similar to fig. 2, but the period of the under-damped resonance is shortened and simplified, and the above-mentioned calculation operation includes calculating according to the following calculation formula to set the auxiliary turn-on time, which is shown as the auxiliary turn-on time in this case
In which V isbFor a rectified power supply, VorIs the maximum amplitude voltage, T, of the drain voltage VDP of the primary side switching unit QP at the under-damped resonancerThe period of the under-damped resonance. The above calculation formula is derived mainly according to the law of conservation of energy, and includes:
wherein L ismIs the inductance value of the primary side winding LP, IzvspkIs the current peak value, C, of the excitation current Img of the transformer unit 30ossIs the parasitic capacitance of the drain of the primary side switch unit QP.
In addition, another simple way to calculate the auxiliary on-time is: the auxiliary on-time is equal to (voltage of the external input power supply × P1) + P2, where P1 is a first parameter, P2 is a second parameter, and the first parameter is between 0.98 and 0.99ns, and the second parameter is between 31.1 and 31.9 ns. It is noted that the calculation formula essentially utilizes the linear increase of the auxiliary on-time TAON with the voltage of the external input power VAC to achieve the reduction of the drain voltage of the primary side switching unit QP, thereby reducing the switching loss.
In summary, the present invention is characterized in that the auxiliary switching unit is connected to the auxiliary winding, and the power controller generates the auxiliary driving signal to control the on/off of the auxiliary switching unit, so that the auxiliary winding affects the primary side winding to reduce the drain voltage of the primary side switching unit, so that the primary side switching unit can be turned on only when the drain voltage of the primary side switching unit is the lowest voltage or close to zero voltage, thereby greatly reducing the switching loss and improving the power conversion efficiency.
Further, for a general flyback system capable of only performing low voltage switching, a higher coil ratio is mainly used, or a quasi-resonant controller is used to perform switching to turn on and conduct when the drain voltage of the primary side switching unit drops to a valley low voltage, if Zero Voltage Switching (ZVS) is to be performed, an ACF or AHB architecture is required, or additional windings are required, which may cause a large increase in cost and may not be practical, and in contrast, the present invention is to share the auxiliary winding LA, or to combine with the synchronous rectification control of the secondary side to adjust the ZVS control signal according to the input voltage and load or coil ratio of the overall system, and to slowly adjust the ZVS control signal to the optimum ZVS switching point by a preset width, thereby improving the overall power conversion efficiency of the system.
While the preferred embodiments of the present invention have been described, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the following claims.
Claims (7)
1. A power control system for zero voltage switching, which is used for realizing a flyback power conversion function, is characterized by comprising:
a power controller including a power pin, a ground pin, a primary drive pin, a voltage sensing pin, an auxiliary drive pin, and an auxiliary winding sensing pin;
the rectifier unit receives and rectifies an external input power supply to generate a rectified power supply, and is connected to a grounding potential through an auxiliary capacitor;
the power supply unit receives the external input power supply, generates and outputs a power supply voltage after processing, and the power supply pin receives the power supply voltage to supply the power supply controller to operate;
a transformer unit including a primary side winding, an auxiliary winding and a secondary side winding coupled to each other, one end of the primary side winding being connected to the rectifying unit to receive the rectified power;
a primary side switching unit, a drain of the primary side switching unit is connected with the other end of the primary side winding, a gate of the primary side switching unit is connected with the primary driving pin, and a source of the primary side switching unit is connected with the voltage sensing pin;
one end of the current sensing unit is connected to the voltage sensing pin, the other end of the current sensing unit is connected to the grounding potential, and the voltage sensing pin generates a current sensing signal;
an auxiliary switching unit, a drain of the auxiliary switching unit being connected to the power supply unit to receive the power supply voltage, a gate of the auxiliary switching unit being connected to the auxiliary driving pin, a source of the auxiliary switching unit being connected to one end of the auxiliary winding and the auxiliary winding sensing pin, another end of the auxiliary winding being connected to the ground potential, the source of the auxiliary switching unit generating an auxiliary winding voltage, the auxiliary winding voltage being a drain voltage corresponding to the primary side switching unit, the drain voltage being a voltage of the drain of the primary side switching unit, the drain of the auxiliary switching unit being further connected to the ground potential via an auxiliary capacitor; and
an output unit, one end of which is connected to one end of the secondary side winding, for generating an output power and supplying power to a load connected to the output unit, and the other end of the secondary side winding is connected to the ground potential;
wherein the power controller performs a zero voltage switching operation to generate a primary driving signal and an auxiliary driving signal, the primary driving signal is transmitted to the primary driving pin, the auxiliary driving signal is transmitted to the auxiliary driving pin, the primary driving signal is a Pulse Width Modulation (PWM) signal, has a PWM frequency, and includes a periodic turn-on level and a turn-off level for periodically turning on or off the primary side switching unit, the turn-on level maintains a turn-on time, the turn-off level maintains a turn-off time, the PWM frequency is determined according to a load level of the load, the turn-on time is determined according to the output power, the zero voltage switching operation includes:
the primary side switching unit detects and judges whether the voltage of the auxiliary winding is reduced to knee or not when the auxiliary switching unit is closed after being closed;
when the auxiliary winding voltage drops to the knee, a time between turning off of the primary side switching unit and the auxiliary winding voltage drop to the knee is taken as a demagnetization time, and the primary side switching unit enters an under damped resonance and an on delay time is calculated by the power controller;
after waiting for the opening delay time, driving the auxiliary driving signal to open the auxiliary switching unit, and setting, adjusting or calculating an auxiliary conduction time;
after waiting for the auxiliary conduction time, driving the auxiliary driving signal to close the auxiliary switching unit, and calculating an interval time; and
and after waiting the interval time, driving the primary driving signal to turn on the primary side switching unit, wherein the turn-off time comprises the demagnetization time, the turn-on delay time, the auxiliary conduction time and the interval time.
2. The power control system of claim 1, wherein the primary-side switching unit and the auxiliary switching unit comprise a metal oxide semiconductor MOS transistor, or a gallium nitride field effect transistor GaN FET, or a silicon carbide-metal oxide semiconductor field effect transistor SiC-MOSFET.
3. The power control system of claim 1, wherein the voltage of the external input power source comprises 90, 115 and 230Vac, the load levels comprise an ultra light load, a medium load and a full load, and the auxiliary turn-on time is generated by an adjustable setting operation, and the adjustable setting operation is to set the auxiliary turn-on time according to the voltage of the external input power source and the load levels.
4. The power control system of claim 3, wherein the voltage of the external input power source comprises 90, 115 and 230Vac, the load level comprises an ultra light load, a medium load and a full load, and the auxiliary turn-on time is generated by an adjustable setting operation, wherein the adjustable setting operation is to set the auxiliary turn-on time as an initial turn-on time when the voltage of the external input power source is 90Vac, and to set the corresponding auxiliary turn-on time in an equal-proportion amplification manner according to the voltage of the external input power source by using the initial turn-on time when the voltage of the external input power source is 115 or 230 Vac.
5. The power control system of claim 1, wherein the auxiliary turn-on time is generated by an adaptive adjustment operation, and the adaptive adjustment operation comprises: and judging whether the auxiliary winding voltage is lower than a threshold voltage value, and changing the cycle by cycle in a cycle-to-cycle manner to set the auxiliary conduction time when the auxiliary winding voltage is not lower than the threshold voltage value until the auxiliary winding voltage is lower than the threshold voltage value.
6. The system of claim 1, wherein the auxiliary turn-on time is generated by a calculation operation, and the calculation operation comprises: setting the auxiliary conduction time by calculating according to the following calculation formula
7. The system of claim 1, wherein the auxiliary turn-on time is generated by a calculation operation, and the calculation operation comprises: the auxiliary turn-on time is calculated according to the following calculation formula, where the auxiliary turn-on time is (the voltage of the external input power supply × P1) + P2, P1 is a first parameter, P2 is a second parameter, the first parameter is between 0.98 and 0.99ns, and the second parameter is between 31.1 and 31.9 ns.
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