A constant power charging power supply

Abstract

The present invention discloses a constant-power charging power supply, which includes a flyback power supply at the front end and a constant-power control circuit at the rear end. The flyback power supply uses a PWM controller to control the conduction and cutoff of the switch, and the constant-power control circuit is connected to the voltage feedback pin of the PWM controller; the constant-power control circuit includes a constant-power circuit, a constant-power comparison circuit, a reference source generation circuit, and a low-voltage constant-power deviation correction circuit that are electrically connected in sequence; the constant-power comparison circuit is implemented by a first operational amplifier and its follower circuit, and the reference source generation circuit is implemented by a second operational amplifier and its follower circuit. The constant-power charging power supply of the present application is implemented by using operational amplifiers instead of active multipliers or MCU chips, and is especially suitable for medium and small power applications. It not only greatly reduces the manufacturing cost, is easy to implement, has very good practical significance, but also can greatly improve the accuracy of constant power without too many algorithms.

Description

Technical Field

[0001] The present invention relates to the technical field of electronic circuits, and specifically to a constant power charging power supply suitable for medium and small power. Background Art

[0002] At present, the charging power supplies on the market can be divided into three situations according to the power size: 1. For relatively small power, Method 1 is to directly perform addition operations on current and voltage using an operational amplifier. The power of this method is relatively inaccurate; Method 2 is to use some chips, which can only operate in a narrow range relatively; 2. For slightly larger power, a multiplier is generally used, but the cost increases a lot; 3. For even larger power, an MCU is used to collect current and voltage, then perform multiplication, and then make corresponding adjustments. Among the above methods, the first case is only applicable to small power and occasions with low requirements for constant power accuracy. The second and third cases are applicable to occasions with low cost requirements and high accuracy requirements.

[0003] For example, the invention patent with the authorization announcement number CN105322637 B discloses a capacitor charging method and device with the characteristics of constant power input and constant current output. The constant power of this invention is achieved by adding a temporary energy storage link. Through the calculation module of the chip, the bus voltage and the voltage of the temporary energy storage capacitor are kept constant within a resonant cycle, so as to achieve constant power charging. As described above, this invention not only has high costs, but also has a complex calculation algorithm, which leads to a complex circuit structure, greatly increasing the cost and difficulty of manufacturing the circuit board. Summary of the Invention

[0004] A brief overview of the embodiments of the present invention is given below to provide a basic understanding of certain aspects of the present invention. It should be understood that the following overview is not an exhaustive overview of the present invention. It is not intended to identify the key or important parts of the present invention, nor is it intended to limit the scope of the present invention. Its purpose is only to present certain concepts in a simplified form as a prelude to the more detailed description to be discussed later.

[0005] According to one aspect of the present application, a constant power charging power supply is provided, which includes a flyback power supply at the front end and a constant power control circuit at the rear end. The flyback power supply uses a PWM controller to control the on and off of the switch, and the constant power control circuit is connected to the voltage feedback pin of the PWM controller. Among them, the constant power control circuit includes a constant power circuit, a constant power comparison circuit, a reference source generation circuit, and a low-voltage constant power deviation correction circuit that are electrically connected in sequence; the constant power comparison circuit is implemented by a first operational amplifier and its follower circuit, and the reference source generation circuit is implemented by a second operational amplifier and its follower circuit.

[0006] Preferably, the constant power charging power supply further includes a feedback circuit connected in series between the flyback power supply and the constant power control circuit. The feedback circuit is used for electrical isolation between the flyback power supply and the constant power control circuit while transmitting signals.

[0007] The constant power comparison circuit includes a first operational amplifier, resistor R20, resistor R21, resistor R24, resistor R25, resistor R37, and capacitor C11. The output terminal of the first operational amplifier is connected to the constant power circuit. One path of the positive input terminal of the first operational amplifier is grounded after being connected in series with resistor R24, and the other path is connected to the output terminal of the second operational amplifier after being connected in series with resistor R25. A resistor R20 is connected in series between the negative input terminal and the output terminal of the first operational amplifier. One path of the negative input terminal of the first operational amplifier is grounded after being connected in series with capacitor C11, and the other path is connected to the first end of resistor R37 and the first end of resistor R21. The second end of resistor R37 is connected to the flyback power supply, and the second end of resistor R21 is connected to the low-voltage constant power deviation correction circuit and the flyback power supply.

[0008] The reference source generation circuit includes a second operational amplifier, resistor R26, resistor R35, resistor R36, resistor R43, resistor R47, capacitor C13, capacitor C15, and a three-terminal voltage regulator IC3. The output terminal and the negative input terminal of the second operational amplifier are connected in series with resistor R47. The positive input terminal of the second operational amplifier is connected to the first end of resistor R26, the first end of capacitor C13, the ground terminal of the three-terminal voltage regulator IC3, and the output voltage terminal of the three-terminal voltage regulator IC3 after being connected in series with resistor R35. The second end of resistor R26 is connected to VCC, the second end of capacitor C13 is grounded, and the input voltage terminal of the three-terminal voltage regulator IC3 is grounded; the negative input terminal of the second operational amplifier is connected to the low-voltage constant power deviation correction circuit after being connected in series with resistor R43.

[0009] Further, the constant power circuit includes a series-connected resistor R22 and a zener diode D5. The first end of resistor R22 is connected to the feedback circuit, the second end of resistor R22 is connected to the positive end of the zener diode D5, and the negative end of the zener diode D5 is connected to the constant power comparison circuit (the output terminal of the first operational amplifier).

[0010] Preferably, the low-voltage constant power deviation correction circuit includes a zener diode D6, resistor R46, and resistor R38. The positive end of the zener diode D6 is connected to the reference source generation circuit (the second end of resistor R43), the negative end of the zener diode D6 is connected to the constant power comparison circuit (the second end of resistor R21) after being connected in series with resistor R46, and the other path is grounded after being connected in series with resistor R38.

[0011] Preferably, the feedback circuit is implemented by an optocoupler and its follower circuit.

[0012] In the above circuit, the first operational amplifier is used for constant power comparison, and the second operational amplifier is used to generate a reference source, which is used to correct the constant power deviation after the output voltage drops. The zener diode D5 is used for constant power operation, and the zener diode D6 is used to correct the low-voltage constant power deviation. The first operational amplifier detects the output voltage and current, and based on the reference source of the second operational amplifier for feedback, after compensating the voltage and current, the product of the voltage and current forms a constant, thus realizing the high-precision constant power power supply of the present application.

[0013] A multiplier is an active non-linear device that realizes the multiplication function of two analog signals (voltage or current). An operational amplifier is actually a high-gain direct-coupled amplifier circuit. When a certain form of deep negative feedback is applied to it, it can complete mathematical operations such as addition, subtraction, integration, and differentiation. The constant power charging power supply of the present application is implemented using an operational amplifier instead of an active multiplier or an MCU chip, and is particularly suitable for medium and small power applications. It not only greatly reduces the manufacturing cost, is easy to implement, has very good practical significance, but also can greatly improve the constant power accuracy without excessive algorithms. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The present invention can be better understood by referring to the description given below in conjunction with the accompanying drawings, in which the same or similar reference numerals are used throughout the drawings to denote the same or similar components. The accompanying drawings, together with the following detailed description, are included in this specification and form a part of this specification, and are further used to illustrate the preferred embodiments of the present invention and to explain the principles and advantages of the present invention. In the drawings:

[0015] Figure 1 is the circuit schematic diagram of the front-end flyback power supply in the embodiment of the constant power charging power supply of the present invention;

[0016] Figure 2 is the circuit schematic diagram of the front-end constant power control circuit in the embodiment of the constant power charging power supply of the present invention;

[0017] Figure 3 is the circuit schematic diagram of the front-end feedback circuit in the embodiment of the constant power charging power supply of the present invention;

[0018] Figure 4 is the equivalent circuit schematic diagram of the embodiment of the constant power charging power supply of the present invention;

[0019] Figure 5 is the simulation diagram of the embodiment of the constant power charging power supply of the present invention;

[0020] Figure 6 is the simulation result data of the embodiment of the constant power charging power supply of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0021] Embodiments of the present invention will be described below with reference to the accompanying drawings. Elements and features described in one drawing or one embodiment of the present invention may be combined with elements and features shown in one or more other drawings or embodiments. It should be noted that, for the sake of clarity, representations and descriptions of components and processes that are irrelevant to the present invention and known to those of ordinary skill in the art are omitted in the drawings and the description.

[0022] In the description of the present invention, it should be understood that the terms "first", "second", "third" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance.

[0023] In the description of the present invention, it should be noted that unless otherwise clearly specified and defined, the terms "mounted", "connected", "coupled" should be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or an integral connection; it may be a mechanical connection or an electrical connection; it may be directly connected or indirectly connected through an intermediate medium, and it may be the communication inside two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0024] The object of the present invention is to provide a constant power supply that is applicable to medium and small power and can achieve high precision. Specifically, refer to Figures 1-3 , the constant power charging power supply in this embodiment includes a flyback power supply at the front end, a constant power control circuit at the rear end, and a feedback circuit connected in series between the flyback power supply and the constant power control circuit. The feedback circuit is used to transmit signals while providing electrical isolation between the flyback power supply and the constant power control circuit.

[0025] As Figure 1 shown, the flyback power supply uses a PWM controller IC1 to control the conduction and turn-off of the switch. As Figure 2 and Figure 3 shown, the constant power control circuit is connected to the voltage feedback pin PB of the PWM controller through the feedback circuit.

[0026] Refer to Figure 2 , the constant power control circuit includes a constant power circuit, a constant power comparison circuit, a reference source generation circuit, and a low-voltage constant power deviation correction circuit that are electrically connected in sequence; the constant power comparison circuit is implemented by a first operational amplifier and its follower circuit, and the reference source generation circuit is implemented by a second operational amplifier and its follower circuit.

[0027] Specifically, refer to Figure 2, the constant power circuit includes a series-connected resistor R22 and a zener diode D5. The first end of the resistor R22 is connected to the feedback circuit, the second end of the resistor R22 is connected to the positive end of the zener diode D5, and the negative end of the zener diode D5 is connected to the output end of the first operational amplifier IC2B of the constant power comparison circuit.

[0028] The constant power comparison circuit includes a first operational amplifier IC2B, resistors R20, R21, R24, R25, R37, and a capacitor C11. The output end of the first operational amplifier IC2B is connected to the constant power circuit. The positive input end of the first operational amplifier IC2B is grounded through a series-connected resistor R24, and is also connected to the output end of the second operational amplifier through a series-connected resistor R25. A resistor R20 is connected in series between the negative input end and the output end of the first operational amplifier IC2B. The negative input end of the first operational amplifier IC2B is grounded through a series-connected capacitor C11, and is also connected to the first end of the resistor R37 and the first end of the resistor R21. The second end of the resistor R37 is connected to the flyback power supply, and the second end of the resistor R21 is connected to the low-voltage constant power deviation correction circuit (resistor R46) and the voltage output end Vo2 of the flyback power supply. The first operational amplifier IC2B is used for constant power comparison.

[0029] The reference source generation circuit includes a second operational amplifier IC2A, resistors R26, R35, R36, R43, R47, capacitors C13, C15, and a three-terminal voltage regulator IC3. The output end and the negative input end of the second operational amplifier IC2A are connected in series with the resistor R47. The positive input end of the second operational amplifier IC2A is connected to the first end of the resistor R26, the first end of the capacitor C13, the ground terminal of the three-terminal voltage regulator IC3, and the output voltage terminal of the three-terminal voltage regulator IC3 through a series-connected resistor R35. The second end of the resistor R26 is connected to VCC, the second end of the capacitor C13 is grounded, and the input voltage terminal of the three-terminal voltage regulator IC3 is grounded. The negative input end of the second operational amplifier IC2A is connected to the low-voltage constant power deviation correction circuit (zener diode D6) through a series-connected resistor R43. The second operational amplifier IC2A is used for generating a reference source to correct the constant power deviation after the output voltage drops, and the zener diode D5 is used for constant power operation. In this embodiment, from VCC to the three-terminal voltage regulator IC3, the three-terminal voltage regulator IC3 generates a reference voltage of 2.5V through the power supply voltage to the resistor R26. Then, it is divided by R46 and R38, the deviation is converted through the diode and R43, and is supplied to the third pin of the second operational amplifier IC2A through the current-limiting resistor R35. Then, it is amplified by the second operational amplifier IC2A and the resistor R47 to form a corrected reference. Then, the corrected reference is compared with the voltage and current to achieve constant power.

[0030] The low-voltage constant-power deviation correction circuit includes a zener diode D6, a resistor R46, and a resistor R38. The positive terminal of the zener diode D6 is connected to the reference source generation circuit (the second terminal of the resistor R43). The negative terminal of the zener diode D6 is connected to the constant-power comparison circuit (the second terminal of the resistor R21) after being serially connected with the resistor R46, and is grounded after being serially connected with the resistor R38. The zener diode D6 is used to correct the low-voltage constant-power deviation.

[0031] See Figure 3 , and the feedback circuit is implemented by an optocoupler. Specifically, the feedback circuit includes an optocoupler U1, a resistor R27, a resistor R28, a resistor R29, a resistor R30, a resistor R33, a resistor R34, a capacitor C14, and a three-terminal voltage regulator U2. The first output terminal of the optocoupler U1 is connected to the voltage feedback pin PB of the PWM controller. The second output terminal of the optocoupler U1 is grounded. The first input terminal of the optocoupler U1 is connected to the power supply VCC after being serially connected with the resistor R27, and is connected to the second output terminal of the optocoupler U1, the first terminal of the resistor R22 in the constant-power circuit, the first terminal of the capacitor C14, and the output voltage terminal of the three-terminal voltage regulator U2 after being serially connected with the resistor R28. The input voltage terminal of the three-terminal voltage regulator U2 is grounded. A parallel-connected resistor R33 and resistor R34 are serially connected between the grounded terminal and the input voltage terminal of the three-terminal voltage regulator U2. The grounded terminal of the three-terminal voltage regulator U2 is connected to the second terminal of the capacitor C14 after being serially connected with the resistor R30, and is connected to the voltage output terminal Vo2 of the flyback power supply after being serially connected with the resistor R29.

[0032] The following introduces the theoretical basis for obtaining a constant power. According to Figure 4 the simplified schematic diagram, to achieve constant power, there is:

[0033] Po = Uo * Io = (Uo + dU) * (Io + dI) = Uo * Io + Uo * dI + Io * dU + dU * dI;

[0034] Among them, dU * dI is a double integral term and is ignored, thus obtaining the following formula:

[0035] dU / dI = -U0 / Io.

[0036] The following elaborates in detail the principle of the operational amplifier part: To achieve constant power, that is, the output feedback amount is basically unchanged, that is, the sampling change values of voltage and current need to cancel each other out. Then, the sampling current sample Us = Io * R14, and the current voltage is Uo = U * R38 / (R38 + R46). That is, Us + Uo is a constant, that is, Io * R14 + U * R38 / (R38 + R46) is a constant.

[0037] Similarly, if a small current is also a constant on this basis, then (Io + dI)*R14 + (U*R38 / (R38 + R46)) is also a constant. Subtracting the above two equations, that is, after taking the differential, we can get R14*dI + dU*R38 / (R38 + R46) = 0. Substituting it into dU / dI = -U0 / Io, we can obtain: Uo / Io = Rs*(R1 + R2) / R2.

[0038] Therefore, as long as the ratio of Rs*(R1 + R2) / R2 is Uo / Io, constant power can be achieved. Then, for any fixed output voltage and current, once the voltage and current are determined, constant power can be achieved by adjusting Rs, R1, and R2.

[0039] Based on the above principle, this application adds some optimizations to make the linearity of power better and achieve constant power within a relatively wide range. The front end of this application is a conventional flyback power supply, which will not be elaborated here. This application mainly realizes constant power through a constant power control circuit composed of an operational amplifier at the back end and other circuits. The first operational amplifier IC2B is used for constant power comparison, detecting the output voltage and current, and performing feedback based on the reference source generated by the second operational amplifier IC2A. After compensating the voltage and current through the operational amplifier and correcting the constant power deviation after the output voltage drops, the product of voltage and current becomes a constant, thus achieving constant power. Figure 5 This is the simulation diagram of the circuit of this application. Figure 6 This is the simulation result. From the values (Vref) in the table, it can be seen that through the optimized design of the constant power circuit in this application, constant power is achieved within a relatively wide range. Compared with the prior art, it is not only easy to implement, but also can obtain high-precision constant power on the basis of greatly reducing costs, so it has very good practical significance.

[0040] It should be emphasized that the term "including / containing" when used herein refers to the presence of features, elements, steps or components, but does not exclude the presence or addition of one or more other features, elements, steps or components.

[0041] Although the present invention has been disclosed above through the description of specific embodiments of the present invention, it should be understood that all the above embodiments and examples are exemplary and not restrictive. Those skilled in the art can design various modifications, improvements or equivalents to the present invention within the spirit and scope of the appended claims. These modifications, improvements or equivalents should also be considered to be included within the protection scope of the present invention.

Claims

1. A constant power charging power supply, characterized in that: It includes a flyback power supply at the front end and a constant power control circuit at the back end. The flyback power supply uses a PWM controller to control the on and off of the switch, and the constant power control circuit is connected to the voltage feedback pin of the PWM controller; The constant power control circuit includes a constant power circuit, a constant power comparison circuit, a reference source generation circuit, and a low-voltage constant power deviation correction circuit that are electrically connected in sequence. The constant power comparison circuit is implemented using a first operational amplifier and its follower circuit, and the reference source generation circuit is implemented using a second operational amplifier and its follower circuit; This constant power charging power supply also includes a feedback circuit connected in series between the flyback power supply and the constant power control circuit. The feedback circuit is used to transmit signals while providing electrical isolation between the flyback power supply and the constant power control circuit; The constant power comparison circuit includes a first operational amplifier, resistor R20, resistor R21, resistor R24, resistor R25, resistor R37, and capacitor C11. The output terminal of the first operational amplifier is connected to the constant power circuit. One path of the positive input terminal of the first operational amplifier is grounded after being serially connected with resistor R24, and the other path is connected to the output terminal of the second operational amplifier after being serially connected with resistor R25. A resistor R20 is serially connected between the negative input terminal and the output terminal of the first operational amplifier. One path of the negative input terminal of the first operational amplifier is grounded after being serially connected with capacitor C11, and the other path is connected to the first end of resistor R37 and the first end of resistor R21. The second end of resistor R37 is connected to the flyback power supply, and the second end of resistor R21 is connected to the low-voltage constant power deviation correction circuit and the flyback power supply; The reference source generation circuit includes a second operational amplifier, resistor R26, resistor R35, resistor R36, resistor R43, resistor R47, capacitor C13, capacitor C15, and a three-terminal voltage regulator IC3. The output terminal and the negative input terminal of the second operational amplifier are serially connected with resistor R47. The positive input terminal of the second operational amplifier is serially connected with resistor R35 and then connected to the first end of resistor R26, the first end of capacitor C13, the ground terminal of the three-terminal voltage regulator IC3, and the output voltage terminal of the three-terminal voltage regulator IC3. The second end of resistor R26 is connected to VCC, the second end of capacitor C13 is grounded, and the input voltage terminal of the three-terminal voltage regulator IC3 is grounded. The negative input terminal of the second operational amplifier is serially connected with resistor R43 and then connected to the low-voltage constant power deviation correction circuit; The low-voltage constant power deviation correction circuit includes a zener diode D6, resistor R46, and resistor R38. The positive end of the zener diode D6 is connected to the reference source generation circuit. The negative end of the zener diode D6 is serially connected with resistor R46 and then connected to the constant power comparison circuit, and is also serially connected with resistor R38 and then grounded; The feedback circuit is implemented using an optocoupler and its follower circuit.

2. The constant power charging power supply according to claim 1, characterized in that: The constant power circuit includes a serially connected resistor R22 and zener diode D5. The first end of resistor R22 is connected to the feedback circuit, the second end of resistor R22 is connected to the positive end of the zener diode D5, and the negative end of the zener diode D5 is connected to the constant power comparison circuit.

3. The constant power charging power supply according to claim 1, characterized in that: The feedback circuit includes an optocoupler U1, resistors R27, R28, R29, R30, R33, R34, a capacitor C14, and a three-terminal voltage regulator U2. The first output terminal of the optocoupler U1 is connected to the voltage feedback pin PB of the PWM controller. The second output terminal of the optocoupler U1 is grounded. One path of the first input terminal of the optocoupler U1 is connected to the power supply VCC after being serially connected with the resistor R27, and the other path is connected to the second output terminal of the optocoupler U1, the first terminal of the resistor R22 in the constant power circuit, the first terminal of the capacitor C14, and the output voltage terminal of the three-terminal voltage regulator U2 after being serially connected with the resistor R28. The input voltage terminal of the three-terminal voltage regulator U2 is grounded. A parallel connection of the resistor R33 and the resistor R34 is serially connected between the grounded terminal and the input voltage terminal of the three-terminal voltage regulator U2. One path of the grounded terminal of the three-terminal voltage regulator U2 is connected to the second terminal of the capacitor C14 after being serially connected with the resistor R30, and the other path is connected to the voltage output terminal Vo2 of the flyback power supply after being serially connected with the resistor R29.

Images