Constant current switching power supply system and its control circuit and control method

Abstract

A constant current switching power supply system and its control circuit and control method are provided. The constant current switching power supply system includes an inductor and a power switch. The control circuit is configured to: generate a current sampling signal associated with the current detection signal based on a pulse width modulation signal for controlling the on and off of the power switch and a current detection signal characterizing the inductor current flowing through the inductor; and generate a pulse width modulation signal based on the current sampling signal, a demagnetization detection signal characterizing the demagnetization of the inductor, and a reference voltage. The current sampling signal is the current detection signal itself when the pulse width modulation signal is at a first logic level, and is a sampling signal generated by sampling the current detection signal when the pulse width modulation signal is at a second logic level.

Description

Technical Field

[0001] This invention relates to the field of circuits, and more specifically to a constant current switching power supply system and its control circuit and control method. Background Technology

[0002] A switching power supply, also known as a switching converter or switching power supply, is a type of power supply. The function of a switching power supply is to convert a voltage level to the voltage or current required by the user through different architectures (e.g., flyback, buck, or boost architectures). Summary of the Invention

[0003] According to an embodiment of the present invention, a control circuit for a constant current switching power supply system includes an inductor and a power switch. The control circuit is configured to: generate a current sampling signal associated with the current detection signal based on a pulse width modulation signal for controlling the on and off of the power switch and a current detection signal characterizing the inductor current flowing through the inductor; and generate a pulse width modulation signal based on the current sampling signal, a demagnetization detection signal characterizing the demagnetization of the inductor, and a reference voltage, wherein the current sampling signal is the current detection signal itself when the pulse width modulation signal is at a first logic level, and is a sampling signal generated by sampling the current detection signal when the pulse width modulation signal is at a second logic level.

[0004] According to an embodiment of the present invention, a control method for a constant current switching power supply system includes an inductor and a power switch. The control method includes: generating a current sampling signal associated with the current detection signal based on a pulse width modulation signal for controlling the on and off of the power switch and a current detection signal characterizing the inductor current flowing through the inductor; and generating a pulse width modulation signal based on the current sampling signal, a demagnetization detection signal characterizing the demagnetization of the inductor, and a reference voltage. The current sampling signal is the current detection signal itself when the pulse width modulation signal is at a first logic level, and is a sampling signal generated by sampling the current detection signal when the pulse width modulation signal is at a second logic level.

[0005] The constant current switching power supply system according to an embodiment of the present invention includes the control circuit described above. Attached Figure Description

[0006] The invention can be better understood from the following description of specific embodiments of the invention in conjunction with the accompanying drawings, wherein:

[0007] Figure 1 An example circuit diagram of a constant current switching power supply system for LED lighting according to an embodiment of the present invention is shown.

[0008] Figure 2 It shows Figure 1 The timing diagram of multiple signals in the constant current switching power supply system is shown.

[0009] Figure 3 It shows Figure 1 The circuit diagram shown is an example of the constant current control module.

[0010] Figure 4 It shows the relationship with Figure 3 The timing diagram shown is for multiple signals related to the sampling control unit.

[0011] Figure 5 It shows Figure 1 The circuit diagram shown is another example of the implementation of the constant current control module.

[0012] Figure 6 It shows the relationship with Figure 5 The timing diagram shown is for multiple signals related to the sampling control unit.

[0013] Figure 7 It shows Figure 5 The circuit diagram shown is an example implementation of the error amplifier. Detailed Implementation

[0014] The features and exemplary embodiments of various aspects of the present invention will now be described in detail. Numerous specific details are set forth in the following detailed description to provide a thorough understanding of the invention. However, it will be apparent to those skilled in the art that the invention may be practiced without requiring some of these specific details. The following description of embodiments is merely intended to provide a better understanding of the invention by illustrating examples of the invention. The invention is by no means limited to any specific configurations and algorithms presented below, but covers any modifications, substitutions, and improvements to elements, components, and algorithms without departing from the spirit of the invention. Well-known structures and techniques are not shown in the drawings and the following description in order to avoid unnecessarily obscuring the invention.

[0015] In recent years, light-emitting diodes (LEDs) have been widely used in all aspects of social production and life due to their advantages over traditional incandescent lamps, halogen lamps, or fluorescent lamps, such as long lifespan, low cost, and small size. The brightness of an LED is mainly controlled by the current flowing through it, so high-precision constant current control is the key to designing constant current switching power supply systems for LED lighting.

[0016] Figure 1 An example circuit diagram of a constant current switching power supply system 100 for LED lighting according to an embodiment of the present invention is shown. Figure 1As shown, the constant current switching power supply system 100 adopts a BUCK architecture, mainly including a rectifier BD1, an input capacitor C1, a diode D1, an inductor L1, an output load capacitor C2, a power switch Q1, a current sensing resistor R1, and a control chip U100. The system bus voltage VIN supplies power to the control chip U100 via the HV pin of the control chip U100. The control chip U100 outputs a gate drive signal Gate for driving the power switch Q1 to turn on and off based on the current sensing signal CS, which characterizes the inductor current IL (not shown in the figure) flowing through the inductor L1.

[0017] like Figure 1 As shown, the control chip U100 includes a low-dropout regulator (LDO) module 102, a demagnetization detection module 104, a constant current control module 106, and a driver module 108. Specifically: the low-dropout regulator module 102 supplies power to the internal circuitry of the control chip U100 based on the system bus voltage VIN; the demagnetization detection module 104 generates a demagnetization detection signal Dem characterizing the demagnetization status of inductor L1 based on the gate drive signal Gate, and outputs the demagnetization detection signal Dem to the constant current control module 106. (It should be understood that the demagnetization detection module 104 detects the demagnetization status of inductor L1 in a specific way.) Not limited to this, the demagnetization detection module 104 can also generate a demagnetization detection signal Dem based on demagnetization detection related signals received from the outside via chip pins; the constant current control module 106 generates a pulse width modulation signal PWM for controlling the on and off of the power switch Q1 based on the reference voltage Vref, the demagnetization detection signal Dem, and the current detection signal CS, and outputs the pulse width modulation signal PWM to the driver module 108; the driver module 108 generates a gate drive signal Gate based on the pulse width modulation signal PWM and outputs the gate drive signal Gate to the gate of the power switch Q1.

[0018] exist Figure 1 In the constant current switching power supply system 100 shown, the power switch Q1 is in the on state when the pulse width modulation signal PWM is at a logic high level, and in the off state when the pulse width modulation signal PWM is at a logic low level; the reference voltage Vref is used to control the magnitude of the system output current Iout of the constant current switching power supply system 100; the demagnetization detection signal Dem is used for system constant current control, and also to control the constant current switching power supply system 100 to operate in discontinuous conduction mode (DCM) or quasi-resonant (QR) mode; the current detection signal CS is used to realize the closed-loop constant current control of the constant current switching power supply system 100. Here, the design value of the system output current Iout can be expressed by the following Equation 1:

[0019] Equation 1

[0020] exist Figure 1In the constant current switching power supply system 100 shown, constant current control is mainly achieved by utilizing the approximately triangular waveform characteristic of the inductor current IL flowing through inductor L1 during one switching cycle of power switch Q1. However, due to the use of a common-ground BUCK architecture, the current sensing resistor R1 cannot detect the inductor current IL flowing through inductor L1 when power switch Q1 is in the off state. Therefore, in the traditional constant current control scheme, constant current control is achieved by obtaining the peak voltage CS_peak of the current sensing signal CS before power switch Q1 changes from the on state to the off state and the demagnetization time of inductor L1, and then performing triangle area calculation based on these two factors.

[0021] Figure 2 It shows Figure 1 The timing diagram of multiple signals in the constant current switching power supply system 100 is shown. (See figure.) Figure 2 As shown, the inductor current IL flowing through inductor L1 exhibits an approximately triangular waveform characteristic during one switching cycle of power switch Q1 (i.e., the duration Ton when the gate drive signal Gate is at a logic high level + the duration Toff when the gate drive signal Gate is at a logic low level); and during the period when power switch Q1 is in the off state (i.e., during the duration Toff when the gate drive signal Gate is at a logic low level), the current detection signal CS is 0V.

[0022] Because the system bus voltage VIN is not an ideal DC voltage but exhibits power frequency fluctuations, the inductor current IL flowing through inductor L1 does not increase linearly ideally during the duration Ton when power switch Q1 is in the on state. Specifically, the inductor current IL flowing through inductor L1 when power switch Q1 is in the on state can be expressed by the following Equation 2:

[0023] Equation 2

[0024] Among them, I L_Ton This represents the inductor current flowing through inductor L1 when power switch Q1 is in the on state. Vin represents the system bus voltage VIN, Vout represents the system output voltage, and L represents the inductance of inductor L1. Equation 2 shows that when the system bus voltage VIN is low and close to the system output voltage, the relative linear distortion of the inductor current IL becomes more severe.

[0025] Since the system output current Iout is the inductor current I flowing through inductor L1 when power switch Q1 is in the on state. L_Ton And the inductor current I flowing through inductor L1 when power switch Q1 is in the off state L_ToffThe sum of these factors means that when the system bus voltage VIN is low, there is a significant deviation between the actual and design values ​​of the system output current Iout. Furthermore, the system output current Iout varies with the system bus voltage VIN. In particular, when the power factor of the constant current switching power supply system 100 is high, the input bus voltage VIN exhibits an M-wave shape, meaning that within one AC frequency cycle, the system bus voltage VIN varies from approximately 0V to 1.4 times the AC line voltage. Changes in the AC line voltage have a greater impact on the accuracy of the system output current Iout, indicating that the line voltage regulation capability of the constant current switching power supply system 100 is poor. Therefore, improving the constant current control accuracy of the constant current switching power supply system 100, especially its line voltage regulation capability, is an urgent problem to be solved.

[0026] In view of the above, a constant current control scheme according to an embodiment of the present invention is proposed, wherein constant current control is performed in stages according to the on / off state of power switch Q1 and the change of inductor current IL flowing through inductor L1, so as to eliminate the error caused by the distortion of inductor current IL flowing through inductor L1 and improve the accuracy of constant current control.

[0027] Combination Figure 2 It can be seen that the distortion of the inductor current IL flowing through inductor L1 mainly occurs during the duration Ton when power switch Q1 is in the on state. However, during the duration Toff when power switch Q1 is in the off state, the inductor current IL flowing through inductor L1 has a basically linear relationship with the demagnetization time of inductor L1. Therefore, staged constant current control is an optimized constant current control scheme. That is, when power switch Q1 is in the on state, the current detection signal CS is not sampled and the integral operation is directly performed based on the current detection signal CS. When power switch Q1 is in the off state, peak sampling combined with integral operation is used. This allows the main information of the inductor current IL to be completely detected by the control chip U100 and participate in the calculation of the system output current Iout during a complete switching cycle of power switch Q1. This makes the system output current Iout more in line with the ideal design equation 1 and almost does not change with the system bus voltage VIN.

[0028] The constant current control scheme according to embodiments of the present invention mainly consists of Figure 1The constant current control module 106 shown is implemented. Specifically, the constant current control module 106 can be configured to: generate a current sampling signal CS_sample associated with the current detection signal CS based on the pulse width modulation signal PWM used to control the on and off of the power switch Q1 and the current detection signal CS characterizing the inductor current IL flowing through the inductor L1; and generate the pulse width modulation signal PWM based on the current sampling signal CS, the demagnetization detection signal Dem characterizing the demagnetization of the inductor L1, and the reference voltage Vref, wherein the current sampling signal CS_sample is the current detection signal CS itself when the pulse width modulation signal PWM is at a first logic level (e.g., logic high level), and is a sampling signal generated by sampling the current detection signal CS when the pulse width modulation signal PWM is at a second logic level (e.g., logic low level).

[0029] In some embodiments, the constant current control module 106 may be further configured to generate a turn-off control signal PWM_off for controlling the power switch Q1 to change from the on state to the off state based on the current sampling signal CS_sample and the reference voltage Vref.

[0030] In some embodiments, the constant current control module 106 may be further configured to use the demagnetization detection signal Dem as a turn-on control signal for controlling the power switch Q1 to change from the off state to the on state.

[0031] In some embodiments, the constant current control module 106 may be further configured to: generate an error compensation signal CMP based on the current sampling signal CS_sample and the reference voltage Vref; generate a ramp signal Ramp based on the pulse width modulation signal PWM or the current detection signal CS; and generate a turn-off control signal PWM_off based on the error compensation signal CMP and the ramp signal Ramp.

[0032] Figure 3 It shows Figure 1 The circuit diagram shown illustrates an example implementation of the constant current control module 106. Figure 3As shown, the constant current control module 106 includes a sampling control unit U200, an error amplifier U201, a ramp generation unit U202, a comparator U203, an RS flip-flop U204, and a capacitor C203. Specifically: the sampling control unit U200 receives a current detection signal CS, generates a current sampling signal CS_sample based on the current detection signal CS, and outputs the current sampling signal CS_sample to the error amplifier U201; the two inputs of the error amplifier U201 receive a reference voltage Vref and the current sampling signal CS_sample, respectively, amplify the error between the current sampling signal CS_sample and the reference voltage Vref to generate an error amplification signal, and output the error amplification signal to the capacitor C203; the capacitor C203 integrates the error amplification signal to generate an error compensation signal CMP, and outputs the error compensation signal CMP to the comparator U203; the ramp generation unit U202 receives a pulse width modulation signal (PWM) or an electric current sensor (RCS) sensor (RCS). The current detection signal CS generates a ramp signal Ramp based on the pulse width modulation signal PWM or the current detection signal CS, and outputs the ramp signal Ramp to comparator U203. The two inputs of comparator U203 receive the error compensation signal CMP and the ramp signal Ramp respectively, and generate a shutdown control signal PWM_off based on the error compensation signal CMP and the ramp signal Ramp, and output the shutdown control signal PWM_off to RS flip-flop U204. The two inputs of RS flip-flop U204 receive the shutdown control signal PWM_off and the demagnetization detection signal Dem respectively, and generate a pulse width modulation signal PWM based on the shutdown control signal PWM_off and the demagnetization detection signal Dem, and output the pulse width modulation signal PWM to driver module 1028. The shutdown control signal PWM_off controls the pulse width modulation signal PWM to change from logic high level to logic low level, and the demagnetization detection signal Dem controls the pulse width modulation signal PWM to change from logic low level to logic high level.

[0033] Furthermore, such as Figure 3 As shown, the sampling control unit U200 includes switches K201, K202, and K203, and capacitors C201 and C202. Capacitors C201 and C202 have the same capacitance value. The switching on and off of switches K201 and K203 is controlled by a pulse width modulation (PWM) signal, while the switching on and off of switch K202 is controlled by a switch control signal SW1. Here, switches K201 and K203 are in the on state when the PWM signal is at a logic high level and in the off state when the PWM signal is at a logic low level; switch K202 is in the on state when the switch control signal SW1 is at a logic high level and in the off state when the switch control signal SW1 is at a logic low level.

[0034] Figure 4It shows the relationship with Figure 3 The timing diagram shown is for multiple signals related to the sampling control unit U200. (See diagram for example.) Figure 4 As shown, the rising edge of the switch control signal SW1 (the moment when the logic level changes from low to high) has a preset time delay (t1~t2 in the figure) compared to the rising edge of the pulse width modulation signal PWM. The falling edge of the switch control signal SW1 (the moment when the logic level changes from high to low) coincides with the falling edge of the pulse width modulation signal PWM. Through the sampling control circuit U200, when the pulse width modulation signal PWM is at a logic high level, the complete current detection signal CS can be used as a current sampling signal CS_sample and input to the error amplifier U201. When the pulse width modulation signal PWM is at a logic low level, the peak voltage CS_peak of the current detection signal CS is sampled and the current sampling signal CS_sample obtained by dividing by 2 is input to the error amplifier U201.

[0035] Specifically, such as Figure 3 and Figure 4 As shown, when the pulse width modulation signal PWM is at a logic high level (t0~t1), switches K201 and K203 are in the on state, switch K202 is in the off state, and the current detection signal CS is directly input to the input terminals of capacitor C201 and error amplifier U201. The voltage across capacitor C202 is Vc202=0V, and the voltage across capacitor C201 is Vc201=Vcs_sample=Vcs. During the peak sampling stage (t1~t2) when the pulse width modulation signal PWM is at a logic low level, switches K201, K202, and K203 are all in the off state. The peak voltage CS_peak of the current detection signal CS is stored at the input terminals of capacitor C201 and error amplifier U201. The voltage at the terminal Vc202 = 0V, and the voltage across capacitor C201 Vc201 = Vcs_sample = Vcs_peak; during the peak value "divided by 2" operation phase (t2~t3) when the pulse width modulation signal PWM is at a logic low level, switches K201 and K203 are in the off state, and switch K202 is in the on state. The peak voltage CS_peak stored on capacitor C201 is regulated by capacitor C202 through switch K202. Since the capacitance values ​​of capacitors C201 and C202 are equal, and the initial voltage of capacitor C202 is 0V, the peak voltage CS_peak can be "divided by 2" at this time, that is, Vc201 = Vc202 = Vcs_sample = Vcs_peak / 2.

[0036] It can be seen that, in combination Figure 3 and Figure 4In the described embodiment, the constant current control module 106 may be further configured to: when the pulse width modulation signal PWM is at a logic low level, generate a current sampling signal CS_sample by sampling the peak voltage CS_peak of the current detection signal CS and performing a "division by 2" operation on the sampling result; generate an error compensation signal CMP by amplifying the error between the current sampling signal CS_sample and the reference voltage Vref; and generate a turn-off control signal PWM_off by comparing the error compensation signal CMP with the ramp signal Ramp.

[0037] Figure 5 It shows Figure 1 The circuit diagram shows another example implementation of the constant current control module 106. (See diagram below.) Figure 5 As shown, the constant current control module 106 includes a sampling control unit U300, an error amplifier U301, a ramp generation unit U302, a comparator U303, an RS flip-flop U304, and a capacitor C303. The sampling control unit U300 processes the current detection signal CS in the same way as the sampling control unit U200 when the pulse width modulation signal PWM is at a logic high level. However, when the pulse width modulation signal PWM is at a logic low level, it only samples the peak voltage CS_peak of the current detection signal CS without performing the "divide by 2" operation. The "divide by 2" operation for the peak voltage CS_peak is implemented by the error amplifier U301. Furthermore, the processing of the ramp generation unit U302, comparator U303, RS flip-flop U304, and capacitor C303 is similar to that of the sampling control unit U200. Figure 4 The corresponding units shown are the same, so they will not be described again. Figure 6 It shows the relationship with Figure 5 The timing diagram shown is related to multiple signals of the sampling control unit U300.

[0038] Figure 7 It shows Figure 6 The circuit diagram shown is an example implementation of the error amplifier U300. Figure 7 As shown, the error amplifier U301 performs the "division by 2" operation on the current sampling signal CS_sample through two resistors R502 and R503 with equal resistance, switch K501, and pulse width modulation signal PWM, and amplifies the error between the "division by 2" operation result and the reference voltage Vref.

[0039] It can be seen that, in combination Figures 5 to 7In the described embodiment, the constant current control module 106 may be further configured to: generate a current sampling signal CS_sample by sampling the peak voltage CS_peak of the current detection signal CS when the pulse width modulation signal PWM is at a logic low level; generate an error compensation signal CMP by performing a "division by 2" operation on the current sampling signal CS_sample and amplifying the error between the operation result and the reference voltage Vref; and generate a turn-off control signal PWM_off by comparing the error compensation signal CMP with the ramp signal Ramp.

[0040] Such as combination Figures 1 to 7 The control method for the constant current switching power supply system 100 includes: generating a current sampling signal CS_sample associated with the current detection signal CS based on a pulse width modulation signal PWM for controlling the on and off of the power switch Q1 and a current detection signal CS characterizing the inductor current IL flowing through the inductor L1; and generating a pulse width modulation signal PWM based on the current sampling signal CS_sample, a demagnetization detection signal Dem characterizing the demagnetization of the inductor L1, and a reference voltage Vref, wherein the current sampling signal CS_sample is the current detection signal CS itself when the pulse width modulation signal PWM is at a first logic level, and is a sampling signal generated by sampling the current detection signal CS when the pulse width modulation signal PWM is at a second logic level.

[0041] Furthermore, the specific details and combinations of the control method according to embodiments of the present invention Figures 1 to 7 The corresponding content of the control chip U100 is similar, and will not be repeated here.

[0042] In summary, the control circuit and control method for a constant current switching power supply system according to the embodiments of the present invention perform constant current control in stages based on the on / off state of power switch Q1 and the change of inductor current IL flowing through inductor L1, which can eliminate the error caused by the distortion of inductor current IL flowing through inductor L1 and improve the accuracy of constant current control.

[0043] This invention can be implemented in other specific forms without departing from its spirit and essential characteristics. For example, the algorithm described in a particular embodiment can be modified without departing from the basic spirit of the invention. Therefore, the present embodiments are to be regarded as exemplary rather than limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description, and all changes falling within the meaning and scope of the claims and their equivalents are thus included within the scope of the invention.

Claims

1. A control circuit for a constant current switching power supply system, wherein, The constant current switching power supply system includes an inductor and a power switch, and the control circuit is configured as follows: A current sampling signal associated with the current detection signal is generated based on the pulse width modulation signal used to control the on and off of the power switch and the current detection signal characterizing the inductor current flowing through the inductor. as well as The pulse width modulation signal is generated based on the current sampling signal, the demagnetization detection signal characterizing the demagnetization of the inductor, and the reference voltage, wherein... The current sampling signal is the current detection signal itself when the pulse width modulation signal is at the first logic level, and is a sampling signal generated by sampling the current detection signal when the pulse width modulation signal is at the second logic level. When the pulse width modulation signal is at the second logic level, the current sampling signal is generated by sampling the peak voltage of the current detection signal and performing a "divide by 2" operation on the sampling result.

2. The control circuit according to claim 1 is further configured as follows: Based on the current sampling signal and the reference voltage, a shutdown control signal is generated to control the power switch to change from the on state to the off state.

3. The control circuit according to claim 2 is further configured as follows: An error compensation signal is generated based on the current sampling signal and the reference voltage; Based on the pulse width modulation signal or the current detection signal, a ramp signal is generated; and The shutdown control signal is generated based on the error compensation signal and the ramp signal.

4. The control circuit according to claim 3 is further configured as follows: The error compensation signal is generated by amplifying the current sampling signal and the reference voltage.

5. The control circuit according to claim 3, further configured as follows: The error compensation signal is generated by dividing the current sampling signal by 2 and amplifying the error between the result and the reference voltage.

6. The control circuit according to claim 3 is further configured as follows: The shutdown control signal is generated by comparing the error compensation signal and the ramp signal.

7. The control circuit according to claim 1, further configured as follows: The demagnetization detection signal is used as a conduction control signal to control the power switch to change from the off state to the on state.

8. A control method for a constant current switching power supply system, wherein, The constant current switching power supply system includes an inductor and a power switch, and the control method includes: Based on a pulse-width modulation signal used to control the on / off state of the power switch and a current detection signal characterizing the inductor current flowing through the inductor, a current sampling signal associated with the current detection signal is generated; and The pulse width modulation signal is generated based on the current sampling signal, the demagnetization detection signal characterizing the demagnetization of the inductor, and the reference voltage, wherein... The current sampling signal is the current detection signal itself when the pulse width modulation signal is at the first logic level, and is a sampling signal generated by sampling the current detection signal when the pulse width modulation signal is at the second logic level. When the pulse width modulation signal is at the second logic level, the current sampling signal is generated by sampling the peak voltage of the current detection signal and performing a "divide by 2" operation on the sampling result.

9. The control method according to claim 8, wherein, The process of generating the pulse width modulation signal includes: Based on the current sampling signal and the reference voltage, a shutdown control signal is generated to control the power switch to change from the on state to the off state.

10. The control method according to claim 9, wherein, The process of generating the shutdown control signal includes: An error compensation signal is generated based on the current sampling signal and the reference voltage; Based on the pulse width modulation signal or the current detection signal, a ramp signal is generated; and The shutdown control signal is generated based on the error compensation signal and the ramp signal.

11. The control method according to claim 10, wherein, The error compensation signal is generated by amplifying the current sampling signal and the reference voltage.

12. The control method according to claim 10, wherein, The error compensation signal is generated by dividing the current sampling signal by 2 and amplifying the error between the result and the reference voltage.

13. The control method according to claim 10, wherein, The shutdown control signal is generated by comparing the error compensation signal and the ramp signal.

14. The control method according to claim 8, wherein the process of generating the pulse width modulation signal includes: The demagnetization detection signal is used as a conduction control signal to control the power switch to change from the off state to the on state.

15. A constant current switching power supply system, comprising the control circuit according to any one of claims 1 to 7.

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