A switching power supply fast charging system and its opto - coupler - less secondary - side control method

Abstract

The present invention discloses a switching power supply fast charging system and a method for controlling the secondary side without an optocoupler, which relates to the field of switching power supplies. The primary side controller of the switching power supply fast charging system of the present invention includes a primary side drive control unit, a primary side turn-on signal receiving unit, and a current peak control unit; the secondary side controller includes a synchronous rectifier drive control unit, a primary side turn-on signal transmitting unit, a protocol detection unit, a constant voltage control unit, a constant current control unit, and a secondary side drive control unit. The present invention detects and controls the output voltage and current on the secondary side, and the secondary side transmits the turn-on information to the primary side through transformer coupling, realizing the control of the output voltage and current by the secondary side without an optocoupler and without special packaging, achieving the goal of high precision and low cost. At the same time, the switching power supply fast charging system of the present invention can easily achieve zero voltage turn-on of the primary side power tube, reducing the turn-on loss and improving the system efficiency.

Description

Technical Field

[0001] The present invention relates to the technical field of switching power supplies, and particularly to a switching power supply fast charging system and a method for controlling the secondary side without an optocoupler thereof. Background Art

[0002] Switching power supplies have advantages such as small size and high conversion efficiency, and their application fields are constantly expanding, including chargers, adapters, etc. Switching power supplies controlled on the primary side (or called the primary) are widely used because they do not require an optocoupler, have simple control, and low cost.

[0003] In recent years, major countries in the world have put forward higher and higher requirements for the conversion efficiency of switching power supplies. To meet the latest EU energy efficiency class requirements (phase II) and the US Department of Energy level VI energy efficiency requirements, synchronous rectification technology is generally adopted in switching power supplies to improve efficiency. With the rapid development of mobile phone fast charging, not only are the accuracy requirements for the output voltage and output current of chargers getting higher and higher, but also it is required that the output power of the charger is no longer fixed, and the output voltage and current need to be adjusted according to the mobile phone load. For chargers that meet the USB PD 3.0 specification, the output voltage variation range is 3V to 21V, and the minimum voltage interval is 20mV. These requirements bring many challenges to the application of switching power supplies controlled on the primary side.

[0004] The traditional charger circuit of a switching power supply controlled on the primary side includes an AC input port (the AC voltage range is generally 85VAC to 265VAC), a rectifier bridge (converting the AC voltage VAC into a DC voltage VIN), an input capacitor, a transformer, a primary side controller, a primary side power switch tube, a secondary side (or called the secondary) synchronous rectification power switch tube, an output capacitor, a secondary side controller, an output port, etc. Its output voltage and current are both controlled by the primary side controller, which detects and samples the voltage of the auxiliary winding coupling the secondary output voltage, compares the sampled value with the level in the controller, and generates a turn-on signal after error amplification to control the output voltage to be constant. The secondary side controller is only used for synchronous rectification control. This scheme has its output voltage controlled by the primary side controller, does not require an optocoupler, has simple control, and low cost, and is widely used in switching power supply applications with single output voltage and current requirements.

[0005] However, in the case of fast charging, there are requirements for switching the output voltage and current at the load end. Since the primary side controller cannot obtain its conversion information in real time, it is difficult to meet the requirements. In an existing switched-mode power supply fast charging system circuit with primary side control, the voltage and current requirements at the load end are detected by a protocol detection unit on the secondary side. Then, the voltage and current information sending unit encodes the voltage and current requirement information and controls the on and off of the switching transistor through the secondary side drive control unit. The information is transmitted to the primary side through the transformer. After the voltage and current information receiving unit on the primary side detects the voltage and current information, it is transmitted to the constant voltage and constant current module for adjustment, and then the on of the primary side switching transistor is controlled to meet the changes at the load end. However, the output voltage accuracy of this primary side control method is limited by the error of sampling the output voltage on the primary side, and generally can only meet the mass production accuracy of + / -5%, making it difficult to achieve higher voltage accuracy.

[0006] In addition, in an existing switched-mode power supply fast charging system circuit with opto-isolatorless secondary side control, the primary side controller and the secondary side controller are placed in the same package. Its output voltage is directly detected and regulated by the secondary side controller. Therefore, higher voltage accuracy can be guaranteed, reaching the mass production level of + / -2.5%. However, it requires a special package, resulting in a higher system cost. Summary of the Invention

[0007] In view of the problems raised in the above background art, the present invention provides a switched-mode power supply fast charging system and an opto-isolatorless secondary side control method thereof to improve the output voltage accuracy and reduce the system cost without the need for an opto-isolator and special packaging.

[0008] To achieve the above object, the present invention provides the following solutions:

[0009] A switched-mode power supply fast charging system includes:

[0010] An input port, coupled to an AC input voltage VAC;

[0011] A first rectifier, coupled to the input port, converting the AC voltage into a DC voltage;

[0012] An input capacitor, coupled to the first rectifier, filtering the DC voltage output by the first rectifier;

[0013] An output terminal capacitor, coupled to the output port;

[0014] An output port, providing voltage and current to the load, including protocol terminals;

[0015] A transformer, including a first winding, a second winding, and a third winding; the first winding is coupled to the input capacitor and the primary side power switch transistor; the second winding is coupled to the output terminal capacitor and the secondary side power switch transistor; the third winding is coupled to a voltage dividing resistor;

[0016] The primary - side power switch is coupled to the primary - side controller, the first winding of the transformer, and the primary - side current - sensing resistor;

[0017] The secondary - side power switch is coupled to the secondary - side controller and the second winding of the transformer;

[0018] The primary - side controller includes a primary - side drive control unit, a primary - side turn - on signal receiving unit, and a current - peak control unit;

[0019] The primary - side drive control unit is used to control the turn - on and turn - off of the primary - side power switch. The turn - on signal PRI_ON_EN of the primary - side power switch is obtained from the primary - side turn - on signal receiving unit, and the turn - off signal is generated by the current - peak control unit;

[0020] The primary - side turn - on signal receiving unit is used to detect the turn - on information sent from the secondary - side by detecting the voltage at the common terminal of the voltage - dividing resistors, and generate the turn - on signal PRI_ON_EN of the primary - side power switch to control the turn - on of the primary - side power switch;

[0021] The current - peak control unit is used to detect the current flowing through the primary - side current - sensing resistor and compare it with the current - peak level to control the peak value of the primary - side current;

[0022] The secondary - side controller includes a synchronous - rectification drive control unit, a primary - side turn - on signal sending unit, a protocol - detection unit, a constant - voltage control unit, a constant - current control unit, and a secondary - side drive control unit;

[0023] The synchronous - rectification drive control unit is used to detect the drain voltage of the secondary - side power switch and generate a drive signal SR_ON to control the turn - on of the secondary - side power switch during transformer demagnetization rectification;

[0024] The primary - side turn - on signal sending unit is used to generate a primary - side turn - on signal PRI_ON according to the constant - voltage control signal CV_EN and the constant - current control signal CC_EN output by the constant - voltage control unit and the constant - current control unit, and transmit it to the secondary - side drive control unit to control the turn - on of the secondary - side power switch for an additional preset time except during rectification, and then transmit the turn - on information to the primary - side through transformer coupling;

[0025] The protocol - detection unit is used to communicate with the load terminal by detecting the protocol terminal at the output port, obtain the output voltage and current information of the load terminal through protocol detection, and generate a constant - voltage level CV_REF and transmit it to the constant - voltage control unit, and generate a constant - current level CC_REF and transmit it to the constant - current control unit;

[0026] The constant voltage control unit is used to directly sample the output voltage on the secondary side and compare it with the constant voltage level CV_REF to generate a constant voltage control signal CV_EN;

[0027] The constant current control unit is used to directly sample the output current on the secondary side or indirectly calculate the output current on the secondary side to generate a constant current control signal CC_EN;

[0028] The secondary side drive control unit is used to control the turn-on and turn-off of the secondary side power switch tube according to the drive signal SR_ON of the synchronous rectification drive control unit and the primary side turn-on signal PRI_ON of the primary side turn-on signal sending unit.

[0029] Optionally, the constant current control unit directly detects the voltage of the output current detection resistor and compares it with the constant current level CC_REF to generate a constant current control signal CC_EN.

[0030] Optionally, the constant current control unit uses the formula IO = (1 / 2) * IPK * NPS * TONS / TSW to control the output current IO by controlling the switching period TSW to generate a constant current control signal CC_EN; where IPK is the peak value of the primary side current; NPS is the turn ratio of the first winding and the second winding of the transformer; TONS is the rectification time of the secondary side power switch tube.

[0031] Optionally, the primary side turn-on signal sending unit includes an AND gate, a pulse width control unit, and a flip-flop; the first and second input ports of the AND gate are respectively coupled to the output end of the constant voltage control unit and the output end of the constant current control unit; the output end of the AND gate is coupled to the input end of the pulse width control unit and the second input port of the flip-flop, and the output end of the pulse width control unit is coupled to the first input port of the flip-flop; the output end of the flip-flop is used as the output end of the primary side turn-on signal sending unit and is coupled to the secondary side drive control unit.

[0032] Optionally, the pulse width control unit includes a current source, a second switch, a second capacitor, and a second comparator; the output end of the current source is coupled to the first port of the second switch, and the second port of the second switch and the first port of the second capacitor are coupled to the first input port of the second comparator; the control end of the second switch is coupled to the output end of the AND gate in the primary side turn-on signal sending unit; the second port of the second capacitor is coupled to the ground; the second input port of the second comparator is coupled to a third level; the output end of the second comparator is used as the output end of the pulse width control unit and is coupled to the first input port of the flip-flop in the primary side turn-on signal sending unit.

[0033] Optionally, the primary - side turn - on signal receiving unit includes a first voltage - controlled current source, a second voltage - controlled current source, a DEMAG unit, a first switch, a first comparator, and a first capacitor; the common terminal of the voltage - dividing resistors is coupled to the input terminal of the DEMAG unit, the control terminal of the first voltage - controlled current source, and the control terminal of the second voltage - controlled current source; the output terminal of the first voltage - controlled current source, the output terminal of the second voltage - controlled current source, the second port of the first switch, and the first input port of the first comparator are all coupled to the first port of the first capacitor; the first port of the first switch is coupled to the first level Vref1; the control port of the first switch is coupled to the output terminal of the DEMAG unit; the second input port of the first comparator is coupled to the second level Vref2; the output terminal of the first comparator is used as the output terminal of the primary - side turn - on signal receiving unit and is coupled to the primary - side drive control unit.

[0034] A method for opto - coupler - less secondary - side control is applied to the above - mentioned switched - mode power supply fast - charging system. The opto - coupler - less secondary - side control method detects and controls the output voltage and current on the secondary side, and the secondary side transfers the turn - on information to the primary side through transformer coupling, including:

[0035] The protocol detection unit detects the protocol terminals in the output port to obtain voltage and current information, and generates a constant - voltage level CV_REF and a constant - current level CC_REF according to the voltage and current information, and transmits them to the constant - voltage control unit and the constant - current control unit respectively;

[0036] The constant - voltage control unit directly samples the secondary - side output voltage and compares it with the constant - voltage level CV_REF to generate a constant - voltage control signal CV_EN;

[0037] The constant - current control unit directly samples the secondary - side output current or indirectly calculates the secondary - side output current, and generates a constant - current control signal CC_EN based on the constant - current level CC_REF;

[0038] The primary - side turn - on signal sending unit generates a turn - on signal PRI_ON according to the constant - voltage control signal CV_EN and the constant - current control signal CC_EN and transmits it to the secondary - side drive control unit. Through the secondary - side drive control unit, the secondary - side power switch tube is controlled to be turned on additionally for a preset time, and through transformer coupling, the turn - on information is transmitted to the primary - side controller;

[0039] The primary - side turn - on signal receiving unit detects the voltage at the common terminal of the voltage - dividing resistors coupled to the third winding of the transformer. After detecting the turn - on information sent from the secondary side, it generates a turn - on signal PRI_ON_EN for the primary - side power switch tube to control the turn - on of the primary - side power switch tube, realizing opto - coupler - less secondary - side control.

[0040] Optionally, when both the constant voltage control signal CV_EN and the constant current control signal CC_EN are 1, the AND gate output EN of the primary side turn-on signal sending unit is 1, setting the flip-flop to 1. At the same time, the pulse width control unit starts timing. When the timing reaches the set value, the flip-flop is set to 0. The output PRI_ON of the flip-flop, which is the pulse width, is transmitted to the secondary side drive control unit to control the secondary side power transistor to conduct additionally for this pulse width. This additional conduction is coupled to the third winding of the transformer through the transformer to complete the transmission process of the turn-on information.

[0041] Optionally, when the AND gate output EN is 1, the second switch is closed, and the current source starts to charge the second capacitor. When the voltage of the second capacitor is charged above the third level Vref3, the second comparator outputs Tstop as 1, setting the flip-flop of the primary side turn-on signal sending unit to 0 and ending the turn-on signal PRI_ON.

[0042] Optionally, before the turn-on information is sent from the secondary side, the voltage PRI_ON_DET of the first capacitor in the primary side turn-on signal receiving unit is always lower than the second level Vref2, and PRI_ON_EN always remains 0. After the turn-on information is sent from the secondary side, PRI_ON_DET is charged above the second level Vref2, and the turn-on signal PRI_ON_EN output by the first comparator becomes 1. The turn-on signal PRI_ON_EN is transmitted to the primary side drive control unit. After the secondary side turn-on information is sent, the primary side power switch transistor is immediately turned on.

[0043] According to the specific embodiments provided by the present invention, the following technical effects are disclosed:

[0044] The present invention provides a switching power supply fast charging system and a method for controlling the secondary side without an optocoupler. The primary side controller includes a primary side drive control unit, a primary side turn-on signal receiving unit, and a current peak control unit. The secondary side controller includes a synchronous rectification drive control unit, a primary side turn-on signal sending unit, a protocol detection unit, a constant voltage control unit, a constant current control unit, and a secondary side drive control unit. The present invention detects and controls the output voltage and current on the secondary side. The secondary side transmits the turn-on information to the primary side through transformer coupling, realizing the control of the output voltage and current on the secondary side without an optocoupler and special packaging, achieving the goal of high precision and low cost. At the same time, the switching power supply fast charging system of the present invention can easily achieve zero voltage turn-on of the primary side power transistor, reducing the turn-on loss and improving the system efficiency. Description of the Drawings

[0045] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the accompanying drawings required in the embodiments. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other accompanying drawings can be obtained based on these drawings.

[0046] Figure 1 It is a circuit schematic diagram of a switching power supply fast charging system of the present invention;

[0047] Figure 2 It is the main waveform diagram of the switching power supply fast charging system of the present invention;

[0048] Figure 3 It is a circuit schematic diagram of the primary side turn-on signal sending unit of the present invention;

[0049] Figure 4 It is a circuit schematic diagram of the primary side turn-on signal receiving unit of the present invention;

[0050] Figure 5 It is the main working waveform diagram of the primary side turn-on signal receiving unit of the present invention;

[0051] Figure 6 It is a circuit schematic diagram of the pulse width control unit of the present invention;

[0052] Figure 7 It is the waveform diagram of zero-voltage turn-on of the primary side power switch tube. Specific embodiments

[0053] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

[0054] The purpose of the present invention is to provide a switching power supply fast charging system and a method for controlling the secondary side without an optocoupler, so as to improve the output voltage accuracy and reduce the system cost without the need for an optocoupler and special packaging.

[0055] To make the above objects, features, and advantages of the present invention more clearly understood, the present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0056] Figure 1 It is a circuit schematic diagram of a switching power supply fast charging system of the present invention. See Figure 1, the switching power supply fast charging system includes: an input port IN, a first rectifier 40, a primary side controller 41, a secondary side controller 42, an input capacitor 43, a primary side power switch 44, a primary side current sensing resistor 45, a voltage dividing resistor 46, a transformer 47, a secondary side power switch 48, an output terminal capacitor 49, and an output port OUT.

[0057] Among them, the input port IN is coupled to the AC input voltage VAC. The first rectifier 40 is coupled to the input port IN and converts the AC voltage VAC into a DC voltage VIN. The input capacitor 43 is coupled to the first rectifier 40 and filters the DC voltage VIN output by the first rectifier 40. The output terminal capacitor 49 is coupled to the output port OUT. The output port OUT provides voltage and current to the load and includes protocol terminals. The transformer 47 includes a first winding NP, a second winding NS, and a third winding NA; the first winding NP is coupled to the input capacitor 43 and the primary side power switch 44; the second winding NS is coupled to the output terminal capacitor 49 and the secondary side power switch 48; the third winding NA is coupled to the voltage dividing resistor 46. The primary side power switch 44 is coupled to the primary side controller 41, the first winding NP of the transformer, and the primary side current sensing resistor 45. The secondary side power switch 48 is coupled to the secondary side controller 42 and the second winding NS of the transformer.

[0058] Specifically, as Figure 1 shown, one end of the input capacitor 43 is connected to the first rectifier 40, and the other end of the input capacitor 43 is grounded. One end of the first winding NP of the transformer is connected to one end of the input capacitor 43, and the other end of the first winding NP of the transformer is connected to the drain of the primary side power switch 44. One end of the second winding NS of the transformer is connected to one end of the output terminal capacitor 49, and the other end of the second winding NS of the transformer is connected to the drain of the secondary side power switch 48; the other end of the output terminal capacitor 49 is connected to the source of the secondary side power switch 48. One end of the third winding NA of the transformer is connected to one end of the voltage dividing resistor 46, and the other end of the third winding NA of the transformer is grounded; the other end of the voltage dividing resistor 46 is grounded.

[0059] Referring to Figure 1 , the primary side controller 41 includes a primary side drive control unit 411, a primary side turn-on signal receiving unit 412, and a current peak control unit 413.

[0060] Among them, the primary side drive control unit 411 is connected to the gate of the primary side power switch 44 and is used to control the turn-on and turn-off of the primary side power switch 44; the turn-on signal PRI_ON_EN of the primary side power switch 44 is obtained from the primary side turn-on signal receiving unit 412, and the turn-off signal SD is generated by the current peak control unit 413.

[0061] The primary - side turn - on signal receiving unit 412 is connected to the common terminal of the voltage - dividing resistor 46, and is used to detect the turn - on information sent from the secondary side by detecting the voltage VS at the common terminal of the voltage - dividing resistor 46, and generate a turn - on signal PRI_ON_EN for the primary - side power switch tube 44 to control the turn - on of the primary - side power tube 44.

[0062] The current peak control unit 413 is connected to one end of the primary - side current - detecting resistor 45 and the source electrode of the primary - side power switch tube 44, and the other end of the primary - side current - detecting resistor 45 is grounded. The current peak control unit 413 is used to detect the current flowing through the primary - side current - detecting resistor 45 and compare it with the current peak level to control the peak value of the primary - side current IP.

[0063] The secondary - side controller 42 includes a synchronous rectification drive control unit 421, a primary - side turn - on signal sending unit 422, a protocol detection unit 423, a constant - voltage control unit 424, a constant - current control unit 425, and a secondary - side drive control unit 426.

[0064] Among them, the synchronous rectification drive control unit 421 is connected to the drain of the secondary - side power switch tube 48, and is used to detect the drain voltage DET of the secondary - side power switch tube 48 and generate a drive signal SR_ON to control the turn - on of the secondary - side power switch tube 48 during the demagnetization rectification of the transformer 47.

[0065] The primary - side turn - on signal sending unit 422 is used to generate a primary - side turn - on signal PRI_ON according to the constant - voltage control signal CV_EN and the constant - current control signal CC_EN output by the constant - voltage control unit 424 and the constant - current control unit 425, and transmit it to the secondary - side drive control unit 426 to control the turn - on of the secondary - side power switch tube 48 for an additional short preset time except during rectification, and then transmit the turn - on information to the primary side through the coupling of the transformer 47.

[0066] The protocol detection unit 423 is connected to the protocol terminal of the output port OUT, and is used to communicate with the load terminal by detecting the protocol terminal of the output port OUT, obtain the output voltage and current information of the load terminal through protocol detection, and generate a constant - voltage level CV_REF and transmit it to the constant - voltage control unit 424, and generate a constant - current level CC_REF and transmit it to the constant - current control unit 425.

[0067] The constant - voltage control unit 424 is used to directly sample the secondary - side output voltage VO and compare it with the constant - voltage level CV_REF to generate a constant - voltage control signal CV_EN.

[0068] The constant current control unit 425 is used to directly sample the secondary side output current IO or indirectly calculate the secondary side output current IO to generate a constant current control signal CC_EN. The present invention is not limited to a specific constant current control method.

[0069] Among them, the method of directly sampling the secondary side output current IO means that the constant current control unit 425 directly detects the current IO of the output current detection resistor and compares it with the constant current reference level CC_REF to generate a constant current control signal CC_EN.

[0070] The method of indirectly calculating the secondary side output current IO means that the constant current control unit 425 uses the formula IO = (1 / 2) * IPK * NPS * TONS / TSW to control the output current IO by controlling the switching period TSW and generate a constant current control signal CC_EN; where IPK is the peak value of the primary side current, which is a fixed value; NPS is the turn ratio of the first winding NP and the second winding NS of the transformer; TONS is the rectification time of the secondary side power switch tube. In the discontinuous and critical operating modes, IPK is fixed and TONS is also fixed. Therefore, only by controlling the switching period TSW can the output current IO be controlled to generate a constant current control signal CC_EN.

[0071] The secondary side drive control unit 426 is connected to the gate of the secondary side power switch tube 48 and is used to control the turn-on and turn-off of the secondary side power switch tube 48 according to the drive signal SR_ON of the synchronous rectification drive control unit 421 and the primary side turn-on signal PRI_ON of the primary side turn-on signal sending unit 422.

[0072] The entire process of generating, transmitting, and receiving turn-on information is as follows: The protocol detection unit 423 detects the protocol terminals in the output port OUT, obtains voltage and current information, and generates a constant voltage level CV_REF and a constant current level CC_REF, which are respectively transmitted to the constant voltage control unit 424 and the constant current control unit 425. The constant voltage control unit 424 and the constant current control unit 425 detect and control the output voltage VO and current IO on the secondary side and generate control signals CV_EN and CC_EN. Then, the primary side turn-on signal sending unit 422 generates a primary side turn-on signal PRI_ON. The primary side turn-on signal PRI_ON is used to additionally turn on the secondary side power switch 48 for a short period of time through the secondary drive control unit 426. Through the coupling of the transformer 47, the turn-on information is transmitted to the primary side controller 41. The primary side turn-on signal receiving unit 412 detects the common terminal voltage VS of the voltage dividing resistor 46 coupled to the third winding NA of the transformer. After detecting the turn-on information sent from the secondary side, it generates a turn-on signal PRI_ON_EN for the primary side power switch 44 to control the turn-on of the primary side power switch 44. During this process, the system output voltage VO and current IO are detected and controlled by the secondary side controller 42, and the turn-on information is transmitted to the primary side through the transformer 47 to control the turn-on of the primary side power switch 44, realizing secondary side control without an optocoupler.

[0073] Figure 2 This is the main waveform diagram of the switching power supply fast charging system of the present invention. In the figure, CC_EN is the constant current control signal output by the constant current control unit 425, and CC_EN = 1 indicates that the constant current control condition is satisfied. CV_EN is the constant voltage control signal output by the constant voltage control unit 424, and CV_EN = 1 indicates that the constant voltage control condition is satisfied. PRI_ON is the primary side turn-on signal output by the primary side turn-on signal sending unit 422. When both the constant voltage and constant current conditions are satisfied, that is, when both CV_EN and CC_EN are 1, PRI_ON = 1. VOUT is the drive voltage of the primary side power switch 44, which is output by the primary side controller 41. DRI is the drive voltage of the secondary side power switch 48, which is sent by the secondary side controller 42 according to the drive signal SR_ON of the secondary side rectification and the primary side turn-on signal PRI_ON. VS is the common terminal voltage of the voltage dividing resistor 46 coupled to the third winding NA of the transformer.

[0074] As Figure 2As shown, when the output is at a constant voltage, CC_EN of the constant current control unit 425 is 1. When CV_EN of the constant voltage control unit 424 is 1, primary side turn-on information is generated. The primary side turn-on signal sending unit 422 sends a narrow pulse signal PRI_ON to the secondary side drive control unit 426, and the secondary side drive control unit 426 outputs DRI to control the secondary side power switch tube 48 to turn on for a short period of time. The transformer 47 couples this turn-on information to the third winding NA of the transformer. After detecting the turn-on information by detecting the common terminal voltage VS of the voltage dividing resistors 46, the primary side turn-on signal receiving unit 412 in the primary and secondary side controller 41 generates PRI_ON_EN to the primary side drive control unit 411 to control the primary side power switch tube 44 to turn on immediately. This process is the process of the secondary side transmitting the turn-on information to the primary side and turning on the primary side power switch tube 44.

[0075] Figure 1 In the fast charging system of the switching power supply of the present invention as shown, sending and transmitting the primary side turn-on signal is the key point of the present invention. Therefore, for the primary side drive control unit 411 and the current peak control unit 413 in the primary side controller 41, and the synchronous rectification drive control unit 421, protocol detection unit 423, constant voltage control unit 424, constant current control unit 425, and secondary side drive control unit 426 in the secondary side controller 42, no more detailed introduction will be given. Only the implementation of the primary side turn-on signal sending unit 422 in the secondary controller 42 and the primary side turn-on signal receiving unit 412 in the primary side controller 41 will be described in detail.

[0076] Figure 3 is a circuit schematic diagram of the primary side turn-on signal sending unit of the present invention, as Figure 3 shown, the primary side turn-on signal sending unit 422 includes an AND gate 4221, a pulse width control unit 4222, and a flip-flop 4223. Among them, the first and second input ports of the AND gate 4221 are respectively coupled to the output terminals of the constant voltage control unit 424 and the constant current control unit 425, that is, coupled to the constant voltage control signal CV_EN and the constant current control signal CC_EN respectively. The output terminal of the AND gate 4221 generates an enable signal EN, which is coupled to the input terminal of the pulse width control unit 4222 and the second input port of the flip-flop 4223; the output terminal of the pulse width control unit 4222 generates a timing end signal Tstop, which is coupled to the first input port of the flip-flop 4223; the output terminal of the flip-flop 4223 serves as the output terminal of the primary side turn-on signal sending unit 422 to generate the PRI_ON primary side turn-on signal, which is coupled to the secondary side drive control unit 426.

[0077] When both the constant voltage and constant current control signals CV_EN and CC_EN are 1, the AND gate 4221 outputs EN as 1, setting the flip-flop 4223 to 1. Meanwhile, the pulse width control unit 4222 starts timing. Once the timing reaches the set value, the flip-flop 4223 is set to 0, and the output PRI_ON of the flip-flop 4223 is this pulse width. PRI_ON is transmitted to the secondary side drive control unit 426, which can control the secondary side power transistor 48 to conduct additionally for this pulse width. This additional conduction is coupled to the third winding NA of the transformer 47 through the transformer 47, and this process is the transmission process of the turn-on signal.

[0078] The primary side turn-on signal receiving unit 412 determines whether to turn on the primary side power switch transistor 44 by detecting the common terminal voltage of the voltage-dividing resistor 46 coupled to the third winding NA of the transformer. Figure 4 It is a circuit schematic diagram of the primary side turn-on signal receiving unit of the present invention. Refer to Figure 4 The primary side turn-on signal receiving unit 412 includes a first voltage-controlled current source 4121, a second voltage-controlled current source 4122, a DEMAG unit 4123, a first switch SW1, a first comparator 4124, and a first capacitor C1. The common terminal of the voltage-dividing resistor 46 is coupled to the input terminal of the DEMAG unit 4123, the control terminal of the first voltage-controlled current source 4121, and the control terminal of the second voltage-controlled current source 4122. The output terminal of the first voltage-controlled current source 4121, the output terminal of the second voltage-controlled current source 4122, the second port of the first switch SW1, and the first input port of the first comparator 4124 are all coupled to the first port of the first capacitor C1. The first port of the first switch SW1 is coupled to the first level Vref1. The control port of the first switch SW1 is coupled to the output terminal of the DEMAG unit 4123. The second input port of the first comparator 4124 is coupled to the second level Vref2. The output terminal of the first comparator 4124 serves as the output terminal of the primary side turn-on signal receiving unit 412, generating the turn-on signal PRI_ON_EN of the primary side power switch transistor 44 and coupling it to the primary side drive control unit 411.

[0079] Figure 4 In, PRI_ON_DET is the voltage of the first capacitor C1; VS+ is the positive voltage on the common terminal voltage VS of the voltage-dividing resistor 46, generally output and coupled to the third winding NA of the transformer during secondary side rectification, and is proportional to the output voltage VO; VS- is the negative voltage of VS, generally when the primary side power switch transistor 44 conducts, the input capacitor 43 voltage VIN is coupled to the third winding NA of the transformer, and its absolute value is proportional to VIN; DEMAG_P is a narrow pulse generated by the DEMAG unit 4123 when VS crosses the 0 point downward.

[0080] During the time period when neither the primary - side nor the secondary - side power transistors are operating after the secondary demagnetization ends, the volt - second difference on the common terminal voltage VS of the voltage - dividing resistors 46 is detected. Under normal circumstances, the volt - seconds of adjacent positive and negative half - cycles on VS are basically equivalent. If the secondary side is turned on for an additional short period of time, the volt - seconds of the positive half - cycle will be greater than those of the previous negative half - cycle, thereby determining whether there is an additional turn - on on the secondary side to send the primary - side turn - on signal. As Figure 4 shown, when VS crosses the 0 - point downward, the narrow pulse DEMAG_P generated sets PRI_ON_DET to Vref1. During the negative half - cycle of VS, a current proportional to the negative voltage of VS is generated to discharge the first capacitor C1. During the positive half - cycle of VS, a current proportional to the positive voltage of VS is generated to charge the first capacitor C1. In the absence of other interference, the volt - seconds of adjacent positive and negative half - cycles on VS are basically equivalent. Therefore, the voltage of PRI_ON_DET is near Vref1, generally less than Vref2 (Vref2 > Vref1), and the first comparator 4124 outputs PRI_ON_EN = 0. When the secondary side sends a turn - on signal, the positive half - cycle of VS will be maintained until the turn - on signal ends, the charging time of C1 is extended, PRI_ON_DET is above Vref2, greater than Vref2, and the first comparator 4124 outputs PRI_ON_EN = 1. This signal is transmitted to the primary - side drive control unit 411 to control the turn - on of the primary - side power switch transistor 44.

[0081] Figure 5 This is the main working waveform diagram of the primary - side turn - on signal receiving unit of the present invention. In the figure, PRI_ON_DET is the voltage of the first capacitor C1, DEMAG_P is the narrow pulse generated when VS crosses the 0 - point downward, which is the output of the DEMAG unit 4123, and other signals are the same as those in Figure 4 As Figure 5 shown, before the secondary side sends a turn - on signal, the voltage PRI_ON_DET of the first capacitor C1 is always lower than Vref2, and PRI_ON_EN always remains 0. When the secondary side sends a turn - on signal, PRI_ON_DET is charged above Vref2, and the output of the first comparator 4124, PRI_ON_EN, changes to 1. This signal is transmitted to the primary - side drive control unit 411. After the secondary turn - on signal is sent, the primary - side power switch transistor 44 is immediately turned on. Through the transmission of the turn - on signals on the primary and secondary sides in this way, the secondary - side control can be achieved without an optocoupler and without special packaging, achieving the goal of high precision and low cost.

[0082] Figure 6 This is the circuit schematic diagram of the pulse - width control unit of the present invention. Refer to Figure 6, the pulse width control unit 4222 includes a current source I1, a second switch SW2, a second capacitor C2, and a second comparator 42221; the output terminal of the current source I1 is coupled to the first port of the second switch SW2, and the second port of the second switch SW2 and the first port of the second capacitor C2 are coupled to the first input port of the second comparator 42221; the control terminal of the second switch SW2 is coupled to the output terminal of the AND gate 4221 in the primary side turn-on signal sending unit 422, that is, coupled to the enable signal EN; the second port of the second capacitor C2 is coupled to ground; the second input port of the second comparator 42221 is coupled to the third level Vref3; the output terminal of the second comparator 42221 serves as the output terminal of the pulse width control unit 4222, generating a timing end signal Tstop that is coupled to the first input port of the flip-flop 4223 in the primary side turn-on signal sending unit 422.

[0083] When the output EN of the AND gate 4221 with the output of the constant voltage and constant current control unit as the input is 1, the second switch SW2 is closed, and the current source I1 starts to charge the second capacitor C2. When the voltage VC2 of C2 is charged above the third level Vref3, the second comparator 42221 outputs Tstop as 1, setting the flip-flop 4223 in the primary side turn-on signal sending unit 422 to 0 and ending the turn-on signal.

[0084] In addition, by the way of the secondary side being turned on a short time in advance to notify the primary side to turn on, zero voltage turn-on of the primary side can be achieved, greatly reducing the turn-on loss and improving the efficiency. Figure 7 It is the waveform diagram of zero voltage turn-on of the primary side power switch tube. In the figure, IP is the current flowing into the primary side winding NP of the transformer, IS is the current flowing out of the secondary side winding NS of the transformer, Vdrain is the drain voltage of the primary side power switch tube 44, and VIN is the voltage of the input capacitor 43.

[0085] As Figure 7 shown, in the t0 - t1 stage, the secondary side sends a turn-on message to the primary side, and the secondary side current IS reversely stores energy in the transformer 47. At the moment t1, the turn-on message sending ends, and the secondary reverse current IS flybacks to the primary side. At this time, the primary side current IP is the most negative. In the t1 - t2 stage, the negative IP transfers energy to the primary side input capacitor 43. The primary side power switch tube 44 is in the off state, but its parasitic diode conducts, and the drain voltage Vdrain of the primary side power switch tube 44 is close to 0 potential. If the primary side power switch tube 44 is turned on, it is zero voltage turn-on. At the moment t2, the primary side power switch tube 44 is turned on with zero voltage. By the moment t3, IP changes from negative to positive, and the input terminal IN starts to transfer the energy stored in the transformer 47 to the output terminal OUT.

[0086] Based on the above-mentioned switching power supply fast charging system, the present invention further provides a method for secondary side control without optocoupler, including:

[0087] The protocol detection unit detects the protocol terminals in the output port to obtain voltage and current information, and generates a constant voltage level CV_REF and a constant current level CC_REF according to the voltage and current information, and transmits them to the constant voltage control unit and the constant current control unit respectively;

[0088] The constant voltage control unit directly samples the secondary side output voltage and compares it with the constant voltage level CV_REF to generate a constant voltage control signal CV_EN;

[0089] The constant current control unit directly samples the secondary side output current or indirectly calculates the secondary side output current, and generates a constant current control signal CC_EN based on the constant current level CC_REF;

[0090] The primary side turn-on signal sending unit generates a turn-on signal PRI_ON according to the constant voltage control signal CV_EN and the constant current control signal CC_EN and transmits it to the secondary side drive control unit. The secondary side power switch tube is controlled to be turned on additionally for a preset time through the secondary drive control unit, and the turn-on information is transmitted to the primary side controller through transformer coupling;

[0091] The primary side turn-on signal receiving unit detects the common terminal voltage of the voltage dividing resistors coupled to the third winding of the transformer. After detecting the turn-on information sent from the secondary side, it generates a turn-on signal PRI_ON_EN for the primary side power switch tube to control the turn-on of the primary side power switch tube, realizing the secondary side control without optocoupler.

[0092] Wherein, when both the constant voltage control signal CV_EN and the constant current control signal CC_EN are 1, the AND gate output EN of the primary side turn-on signal sending unit is 1, the flip-flop is set to 1, and at the same time the pulse width control unit starts timing. When the timing arrives, the flip-flop is set to 0, and the output PRI_ON of the flip-flop is the pulse width. The turn-on signal PRI_ON is transmitted to the secondary side drive control unit to control the secondary side power tube to conduct additionally for this pulse width; this additional conduction will be coupled to the third winding of the transformer through the transformer to complete the transmission process of the turn-on information.

[0093] Wherein, when the AND gate output EN is 1, the second switch is closed, and the current source starts to charge the second capacitor. When the voltage of the second capacitor is charged above the third level Vref3, the second comparator outputs Tstop as 1, and the flip-flop of the primary side turn-on signal sending unit is set to 0, ending the turn-on signal PRI_ON.

[0094] Among them, before the secondary side sends out the turn-on information, the voltage PRI_ON_DET of the first capacitor in the primary side turn-on signal receiving unit is always lower than the second level Vref2, and PRI_ON_EN always maintains 0; when the secondary side sends out the turn-on information, PRI_ON_DET is charged above the second level Vref2, and the turn-on signal PRI_ON_EN output by the first comparator becomes 1; the turn-on signal PRI_ON_EN is transmitted to the primary side drive control unit. After the secondary side turn-on information is sent, the primary side power switch is immediately turned on.

[0095] The fast charging system of the switching power supply and its opto-isolatorless secondary side control method of the present invention do not require an opto-isolator and special packaging, have low cost, and directly detect and control constant voltage and constant current on the secondary side with high precision. At the same time, the short-time turn-on signal sent by the secondary side can easily achieve zero-voltage turn-on of the primary side power switch.

[0096] In this specification, each embodiment is described in a progressive manner. The key point of each embodiment is the difference from other embodiments. The same or similar parts among the embodiments can be referred to each other.

[0097] Specific examples are used in this article to elaborate on the principle and implementation of the present invention. The description of the above embodiments is only used to help understand the method and its core idea of the present invention; at the same time, for those of ordinary skill in the art, according to the idea of the present invention, there will be changes in the specific implementation and application scope. In summary, the content of this specification should not be construed as a limitation to the present invention.

Claims

1. A switching power supply fast charging system, characterized in that, it includes: An input port, coupled to an AC input voltage VAC; A first rectifier, coupled to the input port, converting the AC voltage into a DC voltage; An input capacitor, coupled to the first rectifier, filtering the DC voltage output by the first rectifier; An output terminal capacitor, coupled to the output port; An output port, providing voltage and current to a load, including protocol terminals; A transformer, including a first winding, a second winding, and a third winding; The first winding, coupled to the input capacitor and a primary side power switch; The second winding, coupled to the output terminal capacitor and a secondary side power switch; The third winding, coupled to a voltage dividing resistor; A primary side power switch, coupled to a primary side controller, the first winding of the transformer, and a primary side current detection resistor; A secondary side power switch, coupled to a secondary side controller and the second winding of the transformer; A primary side controller, including a primary side drive control unit, a primary side turn-on signal receiving unit, and a current peak control unit; The primary side drive control unit is used to control the turn-on and turn-off of the primary side power switch; the turn-on signal PRI_ON_EN of the primary side power switch is obtained from the primary side turn-on signal receiving unit, and the turn-off signal is generated by the current peak control unit; The primary side turn-on signal receiving unit is used to detect the turn-on information sent from the secondary side by detecting the voltage at the common terminal of the voltage dividing resistor, generating the turn-on signal PRI_ON_EN of the primary side power switch to control the turn-on of the primary side power transistor; The current peak control unit is used to detect the current flowing through the primary side current detection resistor and compare it with the current peak level to control the peak value of the primary side current; A secondary side controller, including a synchronous rectification drive control unit, a primary side turn-on signal sending unit, a protocol detection unit, a constant voltage control unit, a constant current control unit, and a secondary side drive control unit; The synchronous rectification drive control unit is used to detect the drain voltage of the secondary side power switch and generate a drive signal SR_ON to control the turn-on of the secondary side power switch during transformer demagnetization rectification; The primary side turn-on signal sending unit is used to generate a primary side turn-on signal PRI_ON according to the constant voltage control signal CV_EN and the constant current control signal CC_EN output by the constant voltage control unit and the constant current control unit, transmit it to the secondary side drive control unit to control the turn-on of the secondary side power switch for an additional preset time except during rectification, and then transmit the turn-on information to the primary side through transformer coupling; The protocol detection unit is used to communicate with the load terminal by detecting the protocol terminals of the output port, obtain the output voltage and current information of the load terminal by detecting the protocol, and generate a constant voltage level CV_REF to transmit to the constant voltage control unit, and generate a constant current level CC_REF to transmit to the constant current control unit; The constant voltage control unit is used to directly sample the secondary side output voltage and compare it with the constant voltage level CV_REF to generate a constant voltage control signal CV_EN; The constant current control unit is configured to directly sample the secondary side output current or indirectly calculate the secondary side output current to generate a constant current control signal CC_EN; The secondary side drive control unit is configured to control the turn-on and turn-off of the secondary side power switch according to the drive signal SR_ON of the synchronous rectifier drive control unit and the primary side turn-on signal PRI_ON of the primary side turn-on signal sending unit; The primary side turn-on signal receiving unit includes a first voltage-controlled current source, a second voltage-controlled current source, a DEMAG unit, a first switch, a first comparator, and a first capacitor; the common terminal of the voltage-dividing resistors is coupled to the input terminal of the DEMAG unit, the control terminal of the first voltage-controlled current source, and the control terminal of the second voltage-controlled current source; the output terminal of the first voltage-controlled current source, the output terminal of the second voltage-controlled current source, the second port of the first switch, and the first input port of the first comparator are all coupled to the first port of the first capacitor; the first port of the first switch is coupled to a first level Vref1; the control port of the first switch is coupled to the output terminal of the DEMAG unit; the second input port of the first comparator is coupled to a second level Vref2; the output terminal of the first comparator serves as the output terminal of the primary side turn-on signal receiving unit and is coupled to the primary side drive control unit.

2. The switch-mode power supply fast charging system according to claim 1, wherein, the constant current control unit directly detects the voltage of the output current detection resistor and compares it with a constant current level CC_REF to generate a constant current control signal CC_EN.

3. The switch-mode power supply fast charging system according to claim 1, wherein, the constant current control unit uses the formula IO = (1 / 2) * IPK * NPS * TONS / TSW to control the output current IO by controlling the switching period TSW and generates a constant current control signal CC_EN; where IPK is the peak value of the primary side current; NPS is the turn ratio of the first winding and the second winding of the transformer; TONS is the rectification time of the secondary side power switch.

4. The switch-mode power supply fast charging system according to claim 1, wherein, the primary side turn-on signal sending unit includes an AND gate, a pulse width control unit, and a flip-flop; the first and second input ports of the AND gate are respectively coupled to the output terminal of the constant voltage control unit and the output terminal of the constant current control unit; the output terminal of the AND gate is coupled to the input terminal of the pulse width control unit and the second input port of the flip-flop, and the output terminal of the pulse width control unit is coupled to the first input port of the flip-flop; the output terminal of the flip-flop serves as the output terminal of the primary side turn-on signal sending unit and is coupled to the secondary side drive control unit.

5. The switch-mode power supply fast charging system according to claim 4, wherein, the pulse width control unit includes a current source, a second switch, a second capacitor, and a second comparator; the output terminal of the current source is coupled to the first port of the second switch, and the second port of the second switch and the first port of the second capacitor are coupled to the first input port of the second comparator; The control terminal of the second switch is coupled to the output terminal of the AND gate in the primary-side turn-on signal sending unit; the second terminal of the second capacitor is coupled to ground; the second input terminal of the second comparator is coupled to the third level; the output terminal of the second comparator serves as the output terminal of the pulse width control unit and is coupled to the first input terminal of the flip-flop in the primary-side turn-on signal sending unit.

6. A method for controlling a secondary side without an optocoupler, characterized in that, applied to the switching power supply fast charging system described in claim 1, the method for controlling the secondary side without an optocoupler detects and controls the output voltage and current on the secondary side, and the secondary side transfers the turn-on information to the primary side through transformer coupling, including: The protocol detection unit detects the protocol terminal in the output port to obtain voltage and current information, and generates a constant voltage level CV_REF and a constant current level CC_REF according to the voltage and current information, and transmits them to the constant voltage control unit and the constant current control unit respectively; The constant voltage control unit directly samples the secondary side output voltage and compares it with the constant voltage level CV_REF to generate a constant voltage control signal CV_EN; The constant current control unit directly samples the secondary side output current or indirectly calculates the secondary side output current, and generates a constant current control signal CC_EN based on the constant current level CC_REF; The primary-side turn-on signal sending unit generates a turn-on signal PRI_ON according to the constant voltage control signal CV_EN and the constant current control signal CC_EN and transmits it to the secondary-side drive control unit. Through the secondary drive control unit, the secondary-side power switch tube is controlled to be turned on additionally for a preset time, and through transformer coupling, the turn-on information is transmitted to the primary-side controller; The primary-side turn-on signal receiving unit detects the common terminal voltage of the voltage dividing resistors coupled to the third winding of the transformer. After detecting the turn-on information sent from the secondary side, it generates a turn-on signal PRI_ON_EN for the primary-side power switch tube to control the turn-on of the primary-side power switch tube, realizing the control of the secondary side without an optocoupler.

7. The method for controlling a secondary side without an optocoupler according to claim 6, characterized in that, When both the constant voltage control signal CV_EN and the constant current control signal CC_EN are 1, the output EN of the AND gate in the primary-side turn-on signal sending unit is 1, setting the flip-flop to 1. At the same time, the pulse width control unit starts timing. When the timing arrives, the flip-flop is set to 0. The output PRI_ON of the flip-flop is the pulse width, and the turn-on signal PRI_ON is transmitted to the secondary-side drive control unit to control the secondary-side power tube to conduct additionally for this pulse width; This additional conduction will be coupled to the third winding of the transformer through the transformer to complete the transmission process of the turn-on information.

8. The method for controlling a secondary side without an optocoupler according to claim 7, characterized in that, When the output EN of the AND gate is 1, the second switch is closed, and the current source starts to charge the second capacitor. When the voltage of the second capacitor is charged above the third level Vref3, the second comparator outputs Tstop as 1, setting the flip-flop in the primary-side turn-on signal sending unit to 0, ending the turn-on signal PRI_ON.

9. The method for controlling a secondary side without an optocoupler according to claim 7, characterized in that, Before the turn-on information is sent on the secondary side, the voltage PRI_ON_DET of the first capacitor in the primary-side turn-on signal receiving unit is always lower than the second level Vref2, and PRI_ON_EN always remains at 0; when the turn-on information is sent on the secondary side, PRI_ON_DET is charged above the second level Vref2, and the turn-on signal PRI_ON_EN output by the first comparator becomes 1; the turn-on signal PRI_ON_EN is transmitted to the primary-side drive control unit. After the secondary turn-on information is sent, the primary-side power switch is immediately turned on.

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