Isolation charging circuit with feedback function and charging method

Abstract

This application discloses an isolated charging circuit and method with feedback function, belonging to the field of circuit technology. A knee detector converts the voltage difference between the input voltage and the drain voltage into a ramp feedback signal and outputs it to a constant voltage controller. A zero-crossing signal generated at the end of demagnetization of the flyback converter is also output to the constant voltage controller. Under the control of the zero-crossing signal, the constant voltage controller samples and holds the drain voltage at the knee, compares the obtained voltage feedback signal with a voltage reference signal to generate a constant voltage control signal, and outputs it to a selector. During the power switch turn-off period, the constant current controller generates a current feedback signal based on the peak current on the primary winding, compares it with a current reference signal to generate a constant current control signal, and outputs it to the selector. The selector outputs either a constant voltage control signal or a constant current control signal to control charging. This application can achieve constant voltage and constant current charging, reduce circuit area, and improve charging efficiency.

Description

Technical Field

[0001] This application relates to the field of circuit technology, and in particular to an isolated charging circuit and charging method with feedback function. Background Technology

[0002] With the widespread use of portable electronic devices, power tools, energy storage systems, and various battery-powered devices, higher demands are being placed on battery charging technology. To ensure electrical safety and meet the matching requirements between different voltage levels, electrical isolation is typically required in the charging circuit to prevent direct electrical coupling between the input terminal and the battery terminal. In isolated charging circuits, precise control of the output voltage and current is crucial for ensuring safe and efficient battery charging.

[0003] like Figure 1 The isolated charging circuit shown consists of an isolation conversion stage and a subsequent charging management stage. The primary side employs a full-bridge topology composed of power switches S1-S4 to convert the DC input V... IN The current is inverted into high-frequency alternating current and fed into the primary winding of the transformer. The secondary winding of the transformer uses a center-tapped winding structure, and is equipped with a synchronous rectifier circuit consisting of S5 and S6 for energy recovery and rectification. After the energy is coupled to the secondary winding via the transformer, it undergoes secondary regulation through an independent constant current / constant voltage charging module, and is finally output to the battery terminal V. CP With V CN between.

[0004] However, the above charging circuit has the following drawbacks: First, the lack of high-speed and effective real-time feedback loops on both sides of the isolation barrier means the primary-side controller cannot sense the secondary-side charging status, and the open-loop control limits the system's response speed and adjustment accuracy. Second, the reliance on a separate constant current / constant voltage charging module in the subsequent stage results in a distinct two-stage transformation characteristic in the entire energy transfer path. This not only increases circuit complexity and the number of components but also causes energy loss to accumulate at multiple stages, reducing overall power conversion efficiency and increasing system size and heat dissipation costs. Summary of the Invention

[0005] This application provides an isolated charging circuit and charging method with feedback function to solve the problems of slow dynamic response and low adjustment accuracy caused by the lack of real-time feedback, as well as the problems of complex structure and low efficiency caused by relying on a separate downstream constant current / constant voltage module. The technical solution is as follows: According to a first aspect of this application, an isolated charging circuit with feedback function is provided, the isolated charging circuit including a knee detector, a constant voltage controller, a constant current controller and a selector; The knee detector is used to collect the voltage difference between the input voltage and the drain voltage of the power switch in the flyback converter, convert the voltage difference into a ramp feedback signal and output it to the constant voltage controller; the knee detector is also used to generate a zero-crossing signal when the flyback converter demagnetizes, and output the zero-crossing signal to the constant voltage controller. The constant voltage controller is used to sample and hold the drain voltage at the knee point under the control of the zero crossover signal, compare the obtained voltage feedback signal with the preset voltage reference signal to generate a constant voltage control signal, and output the constant voltage control signal to the selector. The constant current controller is used to generate a current feedback signal based on the peak current on the primary winding of the flyback converter during the off-time of the power switch, compare the current feedback signal with a preset current reference signal to generate a constant current control signal, and output the constant current control signal to the selector. The selector is used to determine the signal with the largest voltage difference between the constant voltage control signal and the constant current control signal as the target control signal, and outputs the target control signal to the power switch. When the target control signal is a constant voltage control signal, it is used to adjust the duty cycle of the control signal of the power switch to achieve constant voltage charging; when the target control signal is a constant current control signal, it is used to adjust the duty cycle of the control signal of the power switch to achieve constant current charging.

[0006] In one possible implementation, the knee detector includes a first amplifier, a second amplifier, a transistor, a first resistor, and a second resistor; The first end of the first resistor serves as the first input terminal of the knee detector. The second end of the first resistor is connected to the inverting input terminal of the first amplifier, the inverting input terminal of the second amplifier, and the emitter of the transistor. The non-inverting input terminals of the first amplifier and the second amplifier serve as the second input terminals of the knee detector. The output terminal of the first amplifier is connected to the base of the transistor. The collector of the transistor is connected to the first end of the second resistor and serves as the first output terminal of the knee detector. The second end of the second resistor is grounded, and the output terminal of the second amplifier serves as the second output terminal of the knee detector.

[0007] In one possible implementation, the knee detector is further configured to: convert the voltage difference between the input voltage and the drain voltage of the power switch into a ramp current via the first resistor; control the first amplifier to drive the transistor to convert the ramp current into a ramp feedback signal via the second resistor; and output the ramp feedback signal to the constant voltage controller; and control the second amplifier to generate a zero-crossing signal at the end of the flyback converter demagnetization based on the voltage difference between the input voltage and the drain voltage of the power switch; and output the zero-crossing signal to the constant voltage controller.

[0008] In one possible implementation, the constant voltage controller includes a first switch, a second switch, an inverter, a peak ramp detection module, a sample-and-hold module, and a third comparator; The first terminal of the first switch serves as the first input terminal of the constant voltage controller and is connected to the first output terminal of the knee detector. The second terminal of the first switch is connected to the first terminal of the second switch and the input terminal of the peak ramp detection module. The control terminal of the first switch is connected to the output terminal of the inverter. The second terminal of the second switch is grounded. The control terminal of the second switch, after being connected to the input terminal of the inverter, serves as the second input terminal of the constant voltage controller and is connected to the control signal terminal of the power switch. The output terminal of the peak ramp detection module is connected to the first input terminal of the sample-and-hold module. The second input terminal of the sample-and-hold module serves as the third input terminal of the constant voltage controller and is connected to the second output terminal of the knee detector. The output terminal of the sample-and-hold module is connected to the inverting input terminal of the third comparator. The non-inverting input terminal of the third comparator is connected to the voltage reference terminal. The output terminal of the third comparator serves as the output terminal of the constant voltage controller.

[0009] In one possible implementation, the constant voltage controller is further configured to: control the first switch to close and the second switch to open when the control signal of the power switch is a low-level signal, so that the ramp feedback signal is output to the peak ramp detection module; and, when the drain voltage is determined to have reached the knee point based on the zero-crossing signal, control the sample-and-hold module to perform sample-and-hold processing on the signal output by the peak ramp detection module, control the third comparator to compare the obtained voltage feedback signal with a preset voltage reference signal to generate a constant voltage control signal, and output the constant voltage control signal to the selector.

[0010] In one possible implementation, the constant current controller includes a peak current detection module, a shutdown period detection module, an adjustable current source, a third switch, a third resistor, a buffer, and a fourth amplifier. The input terminal of the peak current detection module serves as the first input terminal of the constant current controller and is connected to the drain of the power switch. The output terminal of the peak current detection module is connected to the control terminal of the adjustable current source. The output terminal of the adjustable current source is connected to the first terminal of the third switch. The control terminal of the third switch is connected to the output terminal of the off-time detection module. The input terminal of the off-time detection module serves as the second input terminal of the constant current controller and is connected to the control signal terminal of the power switch. The second terminal of the third switch is connected to the first terminal of the third resistor and the input terminal of the buffer. The second terminal of the third resistor is grounded. The output terminal of the buffer is connected to the inverting input terminal of the fourth amplifier. The non-inverting input terminal of the fourth amplifier is connected to the reference current terminal. The output terminal of the fourth amplifier serves as the output terminal of the constant current controller.

[0011] In one possible implementation, the constant current controller is further configured to: control the third switch to close when the off-time detection module detects that the power switch is off, so that the peak current output by the adjustable current source flows through the third resistor and generates a voltage signal on the third resistor; control the buffer to buffer the voltage signal and output a current feedback signal; control the fourth amplifier to compare the current feedback signal with a preset current reference signal to generate a constant current control signal, and output the constant current control signal to the selector.

[0012] In one possible implementation, the selector includes a first diode, a second diode, and a drive current source; The cathode of the first diode serves as the first input terminal of the selector and is connected to the output terminal of the constant voltage controller. The anode of the first diode, together with the anode of the second diode and the output terminal of the drive current source, serves as the output terminal of the selector. The cathode of the second diode serves as the second input terminal of the selector and is connected to the output terminal of the constant current controller.

[0013] In one possible implementation, the selector is further configured to: when the voltage difference of the constant voltage control signal is greater than the voltage difference of the constant current control signal, output the constant voltage control signal to the power switch transistor, so as to adjust the duty cycle of the control signal of the power switch transistor through the constant voltage control signal to achieve constant voltage charging; and when the voltage difference of the constant current control signal is greater than the voltage difference of the constant voltage control signal, output the constant current control signal to the power switch transistor, so as to adjust the duty cycle of the control signal of the power switch transistor through the constant current control signal to achieve constant current charging.

[0014] According to a second aspect of this application, an isolated charging method with feedback function is provided, the method comprising: The knee detector collects the voltage difference between the input voltage and the drain voltage of the power switch in the flyback converter, converts the voltage difference into a ramp feedback signal, and outputs it to the constant voltage controller; the knee detector generates a zero-crossing signal when the flyback converter demagnetizes, and outputs the zero-crossing signal to the constant voltage controller. Under the control of the zero-crossing signal, the constant voltage controller samples and holds the drain voltage at the knee point, compares the obtained voltage feedback signal with the preset voltage reference signal to generate a constant voltage control signal, and outputs the constant voltage control signal to the selector. During the off-time of the power switch, the constant current controller generates a current feedback signal based on the peak current on the primary winding of the flyback converter, compares the current feedback signal with a preset current reference signal to generate a constant current control signal, and outputs the constant current control signal to the selector. The selector determines the signal with the largest voltage difference between the constant voltage control signal and the constant current control signal as the target control signal, and outputs the target control signal to the power switch. When the target control signal is a constant voltage control signal, it is used to adjust the duty cycle of the control signal of the power switch to achieve constant voltage charging. When the target control signal is a constant current control signal, it is used to adjust the duty cycle of the control signal of the power switch to achieve constant current charging.

[0015] The beneficial effects of the technical solution provided in this application include at least the following: During the off-time of the power switch, the constant current controller directly generates a current feedback signal based on the peak current on the primary winding of the flyback converter. It can complete the current parameter acquisition required for constant current charging without relying on the auxiliary winding. This eliminates the need for the auxiliary winding and its related peripheral circuits, reduces the area of ​​the flyback converter, and is beneficial for the miniaturization and integration of the charging circuit.

[0016] Integrating the constant voltage controller and constant current controller into the same isolated charging circuit allows the circuit to respond to the different stages of battery charging. In the initial charging phase, the constant voltage controller operates, charging the battery with a constant voltage; in the later stages, the constant current controller operates, charging the battery with a constant current. This eliminates the need for a separate charging management module on the secondary side, simplifying the circuit structure.

[0017] The selector directly identifies the signal with the larger voltage difference between the constant voltage control signal and the constant current control signal as the target control signal and outputs it to the power switch to adjust its duty cycle. No additional mode judgment logic is required. The automatic identification and switching between the constant voltage stage and the constant current stage can be completed by simply using the voltage difference between the two control signals. The response speed is fast and the charging efficiency is improved. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a structural block diagram of an isolated charging circuit with feedback function in related technologies; Figure 2 This is a structural block diagram of an isolated charging circuit with feedback function provided in one embodiment of this application; Figure 3 This is a charging waveform diagram of the constant voltage stage provided in one embodiment of this application; Figure 4 This is a charging waveform diagram of the constant current stage provided in one embodiment of this application; Figure 5 This is a flowchart of an isolated charging method with feedback function provided in one embodiment of this application. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the implementation methods of this application will be further described in detail below with reference to the accompanying drawings.

[0021] like Figure 2 The diagram illustrates a structural block diagram of an isolated charging circuit with feedback functionality according to an embodiment of this application. This isolated charging circuit with feedback functionality may include: a knee detector 210, a constant voltage controller 220, a constant current controller 230, and a selector 240.

[0022] The input terminal of the knee detector 210 is connected to both ends of the primary winding in the flyback converter, and the output terminal of the knee detector 210 is connected to the input terminal of the constant voltage controller 220. Based on this connection, the knee detector 210 is used to acquire the input voltage V. IN With the power switch M in the flyback converter L Drain voltage V SW voltage difference V FLK The voltage difference V FLKConverted into ramp feedback signal V SNS The output is then sent to the constant voltage controller 220; the knee detector 210 is also used to generate a zero-crossing signal V at the end of flyback converter demagnetization. Z The zero-crossing signal V Z Output to constant voltage controller 220.

[0023] The input terminal of the constant voltage controller 220 is also connected to the power switch M in the flyback converter. L control signal terminal V PWM The constant voltage controller 220 is connected to the selector 240. Based on this connection, the constant voltage controller 220 is used to control the voltage output of the zero-crossing signal V. Z Under the control of [the system], the drain voltage V at the knee point is [affected]. SW Perform sample-and-hold processing to obtain the voltage feedback signal V. FB With the preset voltage reference signal V THCV After comparison, a constant voltage control signal is generated and output to selector 240.

[0024] The input terminals of the constant current controller 230 are respectively connected to the power switching transistor M L The drain and power switch M L control signal terminal V PWM The constant current controller 230 is connected to the selector 240. Based on this connection, the constant current controller 230 is used to control the power switching transistor M. L During the off-time (1-D), based on the peak current I on the primary winding of the flyback converter... PK Generate current feedback signal V IFB The current feedback signal V IFB With the preset current reference signal V THCC After comparison, a constant current control signal is generated and output to selector 240. Here, D represents the control signal V. PWM The duty cycle, that is, the control signal V during time period D. PWM A high-level signal is used to control the power switch M. L On; during the 1-D time period, the control signal V PWM A low-level signal is used to control the power switch M. L Turn off.

[0025] The output of selector 240 is connected to power switch M L The controller is connected. Based on this connection, selector 240 is used to determine the signal with the largest pressure difference between the constant pressure control signal and the constant current control signal as the target control signal V. C , target control signal V C Output to power switching transistor ML Among them, when the target control signal V C When it is a constant voltage control signal, the constant voltage control signal is used to regulate the power switching transistor M. L The duty cycle of the control signal is adjusted to achieve constant voltage charging; when the target control signal V... C When it is a constant current control signal, the constant current control signal is used to regulate the power switching transistor M. L The duty cycle of the control signal is adjusted to achieve constant current charging.

[0026] The structure and working principle of each component in the charging circuit are explained below.

[0027] (1) Knee point detector 210 Knee detector 210 includes a first amplifier AMP1, a second amplifier AMP2, a transistor Q, and a first resistor R. FB Second resistor R SNS Among them, the first resistor R FB The first terminal serves as the first input terminal of the knee detector 210, and the first resistor R FB The second terminal is connected to the inverting input terminal of the first amplifier AMP1, the inverting input terminal of the second amplifier AMP2, and the emitter of the transistor Q. The non-inverting input terminals of the first amplifier AMP1 and the second amplifier AMP2 serve as the second input terminals of the knee detector 210. The output terminal of the first amplifier AMP1 is connected to the base of the transistor Q, and the collector of the transistor Q is connected to the second resistor R. SNS The first end is connected and serves as the first output terminal of the knee detector 210, and the second resistor R SNS The second terminal is grounded, and the output terminal of the second amplifier AMP2 serves as the second output terminal of the knee detector 210.

[0028] Knee detector 210 is also used to: convert input voltage V IN With power switching transistor M L Drain voltage V SW voltage difference V FLK Through the first resistor R FB Converted into a ramp current, it controls the first amplifier AMP1 to drive the transistor Q, which then transmits the ramp current through the second resistor R. SNS Converted to ramp feedback signal V SNS and the ramp feedback signal V SNS The output is sent to the constant voltage controller 220; and the second amplifier AMP2 is controlled according to the input voltage V. IN With power switching transistor M L Drain voltage V SW The voltage difference generates a zero-crossing signal V at the end of flyback converter demagnetization. Z and the zero-crossing signal VZ Output to constant voltage controller 220.

[0029] During the constant voltage charging phase, the knee detector 210 monitors the input voltage V in real time. IN With power switching transistor M L Drain voltage V SW Voltage difference V between FLK According to the transformation principle of the flyback converter, the voltage difference V... FLK With output voltage V OUT The following proportional relationship exists between them: V FLK = N×V OUT Where N is the primary-to-secondary turns ratio. Then, the knee detector 210 transmits the voltage difference V. FLK Through the first resistor R FB Converted into a ramp current, it controls the first amplifier AMP1 to drive the transistor Q, which then transmits the ramp current through the second resistor R. SNS Converted to ramp feedback signal V SNS The slope feedback signal V SNS The voltage signal is a systematic reference, and its amplitude is related to the output voltage V. OUT Proportional, that is, V SNS =(R SNS / R FB )×V FLK =(R SNS ×N / R FB )×V OUT .

[0030] The second amplifier AMP2 in the knee detector 210 detects the drain voltage V. SW The characteristic point that generates a zero-crossing signal V at the end of flyback converter demagnetization. Z The zero-crossing signal V Z It can accurately reflect the instant when demagnetization ends.

[0031] Knee point detector 210 will send ramp feedback signal V SNS and zero-crossing signal V Z The signals are output to the constant voltage controller 220. The ramp feedback signal V... SNS Used to represent output voltage information, zero-crossing signal V Z Used to trigger the constant voltage controller 220 to perform sample-and-hold processing at the knee point.

[0032] (2) Constant pressure controller 220 The constant voltage controller 220 includes a first switch S1, a second switch S2, an inverter INV, a peak ramp detection module, a sample-and-hold module, and a third comparator AMP3. The first terminal of the first switch S1 serves as the first input terminal of the constant voltage controller 220 and is connected to the first output terminal of the knee detector 210. The second terminal of the first switch S1 is connected to the first terminal of the second switch S2 and the input terminal of the peak ramp detection module. The control terminal of the first switch S1 is connected to the output terminal of the inverter INV. The second terminal of the second switch S2 is grounded. The control terminal of the second switch S2, after being connected to the input terminal of the inverter INV, serves as the second input terminal of the constant voltage controller 220 and is connected to the power switch M. L control signal terminal V PWM The peak ramp detection module's output is connected to the first input of the sample-and-hold module. The second input of the sample-and-hold module serves as the third input of the constant voltage controller 220 and is connected to the second output of the knee detector 210. The output of the sample-and-hold module is connected to the inverting input of the third comparator AMP3. The non-inverting input of the third comparator AMP3 is connected to the voltage reference terminal. The output of the third comparator AMP3 serves as the output of the constant voltage controller 220.

[0033] The constant voltage controller 220 is also used for: when the power switching transistor M L control signal V PWM When the signal is low, the first switch S1 is closed and the second switch S2 is open, so that the ramp feedback signal V... SNS The output is sent to the peak slope detection module and denoted as V. SWR ; and, when based on the zero-crossing signal V Z Determine the drain voltage V SW When the knee point is reached, the control sample-and-hold module performs sample-and-hold processing on the signal output by the peak ramp detection module, and controls the third comparator AMP3 to obtain the voltage feedback signal V. SWR With the preset voltage reference signal V THCV After comparison, a constant voltage control signal is generated and output to selector 240.

[0034] During the constant voltage charging phase, the power switch M... L After shutdown, the flyback converter enters the demagnetization process. At this time, the ramp feedback signal V output by the knee detector 210... SNS With drain voltage V SW Synchronous decrease. When the flyback converter demagnetization ends, the drain voltage V... SW A knee point is detected. The second amplifier AMP2 in the knee point detector 210 detects the knee point and outputs a high-level zero-crossing signal V. Z A high-level zero-crossing signal V ZThe sample-and-hold module is triggered to feed back the ramp signal V at the knee point. SNS Sample and hold processing is performed to obtain the voltage feedback signal V. FB Since the sampling time coincides with the exact moment demagnetization ends, before leakage inductance resonance begins, the sampled voltage feedback signal V... FB It can accurately reflect the output voltage V OUT Then, the sample-and-hold module will use the voltage feedback signal V FB The output is sent to the third comparator AMP3, which then outputs the voltage feedback signal V. FB With the preset voltage reference signal V THCV After comparison, a constant voltage control signal is generated and output to selector 240. This constant voltage control signal is used to regulate the power switching transistor M. L The duty cycle makes the output voltage V OUT It stabilizes at the preset value.

[0035] Figure 3 The charging waveform during the constant voltage phase is shown. Figure 3 As can be seen from this, the zero-crossing signal V Z The rising edge occurs at the drain voltage V SW At the knee point, the sample-and-hold module samples the ramp feedback signal V at that moment. SWR Sampling was performed to ensure the voltage feedback signal V FB The accuracy of the output voltage V. OUT With voltage reference signal V THCV The following conditions must be met between them: V OUT = (V THCV ×R FB ) / (N×R SNS ), where N is the primary-to-secondary turn ratio.

[0036] (3) Constant current controller 230 The constant current controller 230 includes a peak current detection module, a turn-off period detection module, and an adjustable current source I. PKS Third switch S3, third resistor R PKS The system includes a buffer and a fourth amplifier AMP4; the input terminal of the peak current detection module serves as the first input terminal of the constant current controller 230, and is connected to the power switch M. L The drain of the peak current detection module is connected to the adjustable current source I. PKS Connected to the control terminal, adjustable current source I PKS The output terminal is connected to the first terminal of the third switch S3, the control terminal of the third switch S3 is connected to the output terminal of the off-time detection module, and the input terminal of the off-time detection module serves as the second input terminal of the constant current controller 230, connected to the power switch M. L control signal terminal V PWMConnected, the second terminal of the third switch S3 is connected to the third resistor R. PKS The first terminal is connected to the input terminal of the buffer, and the third resistor R PKS The second terminal is grounded, the output terminal of the buffer is connected to the inverting input terminal of the fourth amplifier AMP4, the non-inverting input terminal of the fourth amplifier AMP4 is connected to the reference current terminal, and the output terminal of the fourth amplifier AMP4 serves as the output terminal of the constant current controller 230.

[0037] The constant current controller 230 is also used to: when the off-time detection module detects the power switch M L When turned off, the third switch S3 is closed to allow the adjustable current source I to... PKS The peak output current flows through the third resistor S3, generating a voltage signal across it; the control buffer buffers the voltage signal and then outputs a current feedback signal V. IFB The fourth amplifier AMP4 controls the current feedback signal V. IFB With the preset current reference signal V THCC After comparison, a constant current control signal is generated and output to selector 240.

[0038] During the constant current charging phase, the peak current detection module monitors the current of the primary winding in real time. When the primary winding current reaches its peak value, the peak current detection module controls the adjustable current source to output a peak current corresponding to the magnitude of the peak current.

[0039] When the shutdown period detection module detects the power switch M L When turned off, the constant current controller 230 controls the third switch S3 to close. At this time, the adjustable current source I... PKS The peak output current flows through the third resistor R PKS In the third resistor R PKS A voltage signal is established. After processing the voltage signal, the buffer generates a current feedback signal V. IFB Among them, the current feedback signal V IFB Amplitude and peak current I PKS It is directly proportional, thus indirectly reflecting the output current I. OUT Size.

[0040] The buffer will feed back the current signal V IFB The output is connected to the inverting input of the fourth amplifier AMP4, and the non-inverting input of the fourth amplifier AMP4 is connected to a preset current reference signal V. THCC Then, the fourth amplifier AMP4 feeds back the current feedback signal V. IFB With the preset current reference signal V THCC After comparison, a constant current control signal is generated and output to selector 240. When the current feedback signal V... IFBThe current reference signal V is higher than the preset value. THCC When, it indicates that the output current I OUT The value is too high; in this case, the power switch M needs to be reduced. L The duty cycle is adjusted to reduce the output current I. OUT When the current feedback signal V IFB The current reference signal V is lower than the preset value. THCC When, it indicates that the output current I OUT The value is too low; in this case, the power switching transistor M needs to be increased. L The duty cycle is adjusted to increase the output current I. OUT .

[0041] Figure 4 The charging waveform during the constant current phase is shown, with the primary winding current I... P Rise to peak current I in each switching cycle PK The output current I decreases afterward. OUT With peak current I PK The relationship between I and OUT =(N×I PK ) / [2×(1-D)], where N is the primary-secondary turn ratio and D is the duty cycle.

[0042] (4) Selector 240 Selector 240 includes a first diode D1, a second diode D2, and a drive current source I. B In this configuration, the cathode of the first diode D1 serves as the first input terminal of the selector 240 and is connected to the output terminal of the constant voltage controller 220. The anode of the first diode D1 is connected to the anode of the second diode D2 and the drive current source I. B The output terminal of the first diode is connected to the output terminal of the second diode D2, which serves as the output terminal of the second diode D2. The cathode of the second diode D2 serves as the second input terminal of the second diode D2, which is connected to the output terminal of the constant current controller 230.

[0043] Selector 240 is also used to: when the voltage difference of the constant voltage control signal is greater than the voltage difference of the constant current control signal, output the constant voltage control signal to the power switching transistor M. L In order to regulate the power switching transistor M through a constant voltage control signal L control signal V PWM The duty cycle is adjusted to achieve constant voltage charging; when the voltage difference of the constant current control signal is greater than that of the constant voltage control signal, the constant current control signal is output to the power switch M. L In order to regulate the power switching transistor M through a constant current control signal L control signal V PWM The duty cycle is adjusted to achieve constant current charging.

[0044] Drive current source I BA bias current is provided to the first diode D1 and the second diode D2, causing them to operate near their conduction thresholds. When the voltage difference of the constant voltage control signal is greater than the voltage difference of the constant current control signal, the forward voltage drop of the first diode D1 meets the conduction condition, and the first diode D1 conducts, outputting the constant voltage control signal to the power switch M. L At the control terminal, the charging circuit operates in the constant voltage charging stage. When the voltage difference of the constant current control signal is less than the voltage difference of the constant voltage control signal itself, the forward voltage drop of the second diode D2 meets the conduction condition, and the second diode D2 conducts, outputting the constant current control signal to the power switch M. L At the control terminal, the charging circuit operates in the constant current charging stage. Thus, selector 240 automatically selects the signal with the larger voltage difference as the target control signal output based on the voltage difference between the constant voltage control signal and the constant current control signal, achieving automatic switching between the constant voltage charging stage and the constant current charging stage without the need for additional mode judgment logic.

[0045] In summary, the isolated charging circuit with feedback function provided in this application embodiment allows the constant current controller to directly generate a current feedback signal based on the peak current on the primary winding of the flyback converter during the off-time of the power switch. This eliminates the need for auxiliary windings to collect the current parameters required for constant current charging, thereby eliminating the need for auxiliary windings and related peripheral circuits, reducing the area of ​​the flyback converter, and facilitating the miniaturization and integration of the charging circuit.

[0046] Integrating the constant voltage controller and constant current controller into the same isolated charging circuit allows the circuit to respond to the different stages of battery charging. In the initial charging phase, the constant voltage controller operates, charging the battery with a constant voltage; in the later stages, the constant current controller operates, charging the battery with a constant current. This eliminates the need for a separate charging management module on the secondary side, simplifying the circuit structure.

[0047] The selector directly identifies the signal with the larger voltage difference between the constant voltage control signal and the constant current control signal as the target control signal and outputs it to the power switch to adjust its duty cycle. No additional mode judgment logic is required. The automatic identification and switching between the constant voltage stage and the constant current stage can be completed by simply using the voltage difference between the two control signals. The response speed is fast and the charging efficiency is improved.

[0048] like Figure 5 The diagram illustrates a flowchart of an isolated charging method with feedback functionality according to an embodiment of this application. The isolated charging method with feedback functionality includes: Step 501: The knee detector collects the voltage difference between the input voltage and the drain voltage of the power switch in the flyback converter, converts the voltage difference into a ramp feedback signal and outputs it to the constant voltage controller; the knee detector generates a zero-crossing signal when the flyback converter demagnetizes and outputs the zero-crossing signal to the constant voltage controller.

[0049] Specifically, the knee detector converts the voltage difference between the input voltage and the drain voltage of the power switch into a ramp current through a first resistor, controls the first amplifier to drive the transistor to convert the ramp current into a ramp feedback signal through a second resistor, and outputs the ramp feedback signal to the constant voltage controller; and the knee detector controls the second amplifier to generate a zero-crossing signal at the end of the flyback converter demagnetization based on the voltage difference between the input voltage and the drain voltage of the power switch, and outputs the zero-crossing signal to the constant voltage controller.

[0050] Step 502: Under the control of the zero-crossing signal, the constant voltage controller samples and holds the drain voltage at the knee point, compares the obtained voltage feedback signal with the preset voltage reference signal to generate a constant voltage control signal, and outputs the constant voltage control signal to the selector.

[0051] Specifically, when the control signal of the power switch is a low-level signal, the constant voltage controller controls the first switch to close and the second switch to open, so that the ramp feedback signal is output to the peak ramp detection module; and when the drain voltage reaches the knee point according to the zero-crossing signal, the constant voltage controller controls the sample-and-hold module to sample and hold the signal output by the peak ramp detection module, controls the third comparator to compare the obtained voltage feedback signal with the preset voltage reference signal and generate a constant voltage control signal, and outputs the constant voltage control signal to the selector.

[0052] Step 503: During the off-time of the power switch, the constant current controller generates a current feedback signal based on the peak current on the primary winding of the flyback converter. After comparing the current feedback signal with a preset current reference signal, a constant current control signal is generated and output to the selector.

[0053] Specifically, when the shutdown period detection module detects that the power switch is turned off, the constant current controller controls the third switch to close, so that the peak current output by the adjustable current source flows through the third resistor and generates a voltage signal on the third resistor; the control buffer buffers the voltage signal and outputs a current feedback signal; the control fourth amplifier compares the current feedback signal with the preset current reference signal to generate a constant current control signal, and outputs the constant current control signal to the selector.

[0054] Step 504: The selector determines the signal with the largest voltage difference between the constant voltage control signal and the constant current control signal as the target control signal, and outputs the target control signal to the power switch. When the target control signal is a constant voltage control signal, the constant voltage control signal is used to adjust the duty cycle of the control signal of the power switch to achieve constant voltage charging. When the target control signal is a constant current control signal, the constant current control signal is used to adjust the duty cycle of the control signal of the power switch to achieve constant current charging.

[0055] Specifically, when the voltage difference of the constant voltage control signal is greater than the voltage difference of the constant current control signal, the selector outputs the constant voltage control signal to the power switching transistor, so as to adjust the duty cycle of the control signal of the power switching transistor through the constant voltage control signal to achieve constant voltage charging; when the voltage difference of the constant current control signal is greater than the voltage difference of the constant voltage control signal, the selector outputs the constant current control signal to the power switching transistor, so as to adjust the duty cycle of the control signal of the power switching transistor through the constant current control signal to achieve constant current charging.

[0056] In summary, the isolated charging method with feedback function provided in this application embodiment allows the constant current controller to directly generate a current feedback signal based on the peak current on the primary winding of the flyback converter during the off-time of the power switch. This eliminates the need for auxiliary windings to collect the current parameters required for constant current charging, thereby eliminating the need for auxiliary windings and related peripheral circuits, reducing the area of ​​the flyback converter, and facilitating the miniaturization and integration of the charging circuit.

[0057] Integrating the constant voltage controller and constant current controller into the same isolated charging circuit allows the circuit to respond to the different stages of battery charging. In the initial charging phase, the constant voltage controller operates, charging the battery with a constant voltage; in the later stages, the constant current controller operates, charging the battery with a constant current. This eliminates the need for a separate charging management module on the secondary side, simplifying the circuit structure.

[0058] The selector directly identifies the signal with the larger voltage difference between the constant voltage control signal and the constant current control signal as the target control signal and outputs it to the power switch to adjust its duty cycle. No additional mode judgment logic is required. The automatic identification and switching between the constant voltage stage and the constant current stage can be completed by simply using the voltage difference between the two control signals. The response speed is fast and the charging efficiency is improved.

[0059] Those skilled in the art will understand that all or part of the steps of the above embodiments can be implemented by hardware or by a program instructing related hardware. The program can be stored in a computer-readable storage medium, such as a read-only memory, a disk, or an optical disk.

[0060] The above description is not intended to limit the embodiments of this application. Any adjustments, equivalent substitutions, improvements, etc., made within the spirit and principles of the embodiments of this application should be included within the protection scope of the embodiments of this application.

Claims

1. An isolated charging circuit with feedback function, characterized in that, The isolated charging circuit includes a knee detector, a constant voltage controller, a constant current controller, and a selector; The knee detector is used to collect the voltage difference between the input voltage and the drain voltage of the power switch in the flyback converter, and converts the voltage difference into a ramp feedback signal and outputs it to the constant voltage controller. The knee detector is also used to generate a zero-crossing signal when the flyback converter is demagnetized and output the zero-crossing signal to the constant voltage controller. The constant voltage controller is used to sample and hold the drain voltage at the knee point under the control of the zero crossover signal, compare the obtained voltage feedback signal with the preset voltage reference signal to generate a constant voltage control signal, and output the constant voltage control signal to the selector. The constant current controller is used to generate a current feedback signal based on the peak current on the primary winding of the flyback converter during the off-time of the power switch, compare the current feedback signal with a preset current reference signal to generate a constant current control signal, and output the constant current control signal to the selector. The selector is used to determine the signal with the largest voltage difference between the constant voltage control signal and the constant current control signal as the target control signal, and outputs the target control signal to the power switch. When the target control signal is a constant voltage control signal, it is used to adjust the duty cycle of the control signal of the power switch to achieve constant voltage charging; when the target control signal is a constant current control signal, it is used to adjust the duty cycle of the control signal of the power switch to achieve constant current charging.

2. The isolated charging circuit with feedback function according to claim 1, characterized in that, The knee detector includes a first amplifier, a second amplifier, a transistor, a first resistor, and a second resistor; The first end of the first resistor serves as the first input terminal of the knee detector. The second end of the first resistor is connected to the inverting input terminal of the first amplifier, the inverting input terminal of the second amplifier, and the emitter of the transistor. The non-inverting input terminals of the first amplifier and the second amplifier serve as the second input terminals of the knee detector. The output terminal of the first amplifier is connected to the base of the transistor. The collector of the transistor is connected to the first end of the second resistor and serves as the first output terminal of the knee detector. The second end of the second resistor is grounded, and the output terminal of the second amplifier serves as the second output terminal of the knee detector.

3. The isolated charging circuit with feedback function according to claim 2, characterized in that, The knee detector is further configured to: convert the voltage difference between the input voltage and the drain voltage of the power switch into a ramp current via the first resistor; control the first amplifier to drive the transistor to convert the ramp current into a ramp feedback signal via the second resistor; and output the ramp feedback signal to the constant voltage controller; and control the second amplifier to generate a zero-crossing signal at the end of the flyback converter demagnetization based on the voltage difference between the input voltage and the drain voltage of the power switch; and output the zero-crossing signal to the constant voltage controller.

4. The isolated charging circuit with feedback function according to claim 1, characterized in that, The constant pressure controller includes a first switch, a second switch, an inverter, a peak ramp detection module, a sample-and-hold module, and a third comparator; The first terminal of the first switch serves as the first input terminal of the constant voltage controller and is connected to the first output terminal of the knee detector. The second terminal of the first switch is connected to the first terminal of the second switch and the input terminal of the peak ramp detection module. The control terminal of the first switch is connected to the output terminal of the inverter. The second terminal of the second switch is grounded. The control terminal of the second switch, after being connected to the input terminal of the inverter, serves as the second input terminal of the constant voltage controller and is connected to the control signal terminal of the power switch. The output terminal of the peak ramp detection module is connected to the first input terminal of the sample-and-hold module. The second input terminal of the sample-and-hold module serves as the third input terminal of the constant voltage controller and is connected to the second output terminal of the knee detector. The output terminal of the sample-and-hold module is connected to the inverting input terminal of the third comparator. The non-inverting input terminal of the third comparator is connected to the voltage reference terminal. The output terminal of the third comparator serves as the output terminal of the constant voltage controller.

5. The isolated charging circuit with feedback function according to claim 4, characterized in that, The constant voltage controller is further configured to: when the control signal of the power switch is a low-level signal, control the first switch to close and the second switch to open, so that the ramp feedback signal is output to the peak ramp detection module; Furthermore, when the drain voltage reaches the knee point based on the zero-crossing signal, the sample-and-hold module is controlled to perform sample-and-hold processing on the signal output by the peak ramp detection module, and the third comparator is controlled to compare the obtained voltage feedback signal with the preset voltage reference signal to generate a constant voltage control signal, and the constant voltage control signal is output to the selector.

6. The isolated charging circuit with feedback function according to claim 1, characterized in that, The constant current controller includes a peak current detection module, a turn-off period detection module, an adjustable current source, a third switch, a third resistor, a buffer, and a fourth amplifier; The input terminal of the peak current detection module serves as the first input terminal of the constant current controller and is connected to the drain of the power switch. The output terminal of the peak current detection module is connected to the control terminal of the adjustable current source. The output terminal of the adjustable current source is connected to the first terminal of the third switch. The control terminal of the third switch is connected to the output terminal of the off-time detection module. The input terminal of the off-time detection module serves as the second input terminal of the constant current controller and is connected to the control signal terminal of the power switch. The second terminal of the third switch is connected to the first terminal of the third resistor and the input terminal of the buffer. The second terminal of the third resistor is grounded. The output terminal of the buffer is connected to the inverting input terminal of the fourth amplifier. The non-inverting input terminal of the fourth amplifier is connected to the reference current terminal. The output terminal of the fourth amplifier serves as the output terminal of the constant current controller.

7. The isolated charging circuit with feedback function according to claim 6, characterized in that, The constant current controller is further configured to: when the off-time detection module detects that the power switch is off, control the third switch to close so that the peak current output by the adjustable current source flows through the third resistor and generates a voltage signal on the third resistor; control the buffer to buffer the voltage signal and output a current feedback signal; control the fourth amplifier to compare the current feedback signal with a preset current reference signal to generate a constant current control signal, and output the constant current control signal to the selector.

8. The isolated charging circuit with feedback function according to claim 1, characterized in that, The selector includes a first diode, a second diode, and a drive current source; The cathode of the first diode serves as the first input terminal of the selector and is connected to the output terminal of the constant voltage controller. The anode of the first diode, together with the anode of the second diode and the output terminal of the drive current source, serves as the output terminal of the selector. The cathode of the second diode serves as the second input terminal of the selector and is connected to the output terminal of the constant current controller.

9. The isolated charging circuit with feedback function according to claim 8, characterized in that, The selector is further configured to: when the voltage difference of the constant voltage control signal is greater than the voltage difference of the constant current control signal, output the constant voltage control signal to the power switch transistor, so as to adjust the duty cycle of the control signal of the power switch transistor through the constant voltage control signal to achieve constant voltage charging; and when the voltage difference of the constant current control signal is greater than the voltage difference of the constant voltage control signal, output the constant current control signal to the power switch transistor, so as to adjust the duty cycle of the control signal of the power switch transistor through the constant current control signal to achieve constant current charging.

10. An isolated charging method with feedback function, characterized in that, The method includes: The knee detector collects the voltage difference between the input voltage and the drain voltage of the power switch in the flyback converter, converts the voltage difference into a ramp feedback signal, and outputs it to the constant voltage controller; the knee detector generates a zero-crossing signal when the flyback converter demagnetizes, and outputs the zero-crossing signal to the constant voltage controller. Under the control of the zero-crossing signal, the constant voltage controller samples and holds the drain voltage at the knee point, compares the obtained voltage feedback signal with the preset voltage reference signal to generate a constant voltage control signal, and outputs the constant voltage control signal to the selector. During the off-time of the power switch, the constant current controller generates a current feedback signal based on the peak current on the primary winding of the flyback converter, compares the current feedback signal with a preset current reference signal to generate a constant current control signal, and outputs the constant current control signal to the selector. The selector determines the signal with the largest voltage difference between the constant voltage control signal and the constant current control signal as the target control signal, and outputs the target control signal to the power switch. When the target control signal is a constant voltage control signal, it is used to adjust the duty cycle of the control signal of the power switch to achieve constant voltage charging. When the target control signal is a constant current control signal, it is used to adjust the duty cycle of the control signal of the power switch to achieve constant current charging.

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