Constant current switching power supply system and control chip and control method thereof

Abstract

Provided are a constant-current switching power supply system, a control chip thereof, and a control method thereof. The constant-current switching power supply system includes an inductor and a power switch. The control chip is configured to generate a constant-current control reference voltage based on a demagnetization detection signal representing a demagnetization condition of the inductor, a pulse width modulation signal for controlling the power switch to turn on and turn off, and an adjustment reference voltage; generate a turn-off control signal for controlling the power switch to change from a turn-on state to a turn-off state based on the constant-current control reference voltage and a current feedback signal representing an inductor current flowing through the inductor; generate a turn-on control signal for controlling the power switch to change from the turn-off state to the turn-on state based on the demagnetization detection signal; and generate the pulse width modulation signal based on the turn-off control signal and the turn-on control signal.

Description

Technical Field

[0001] This invention relates to the field of integrated circuits, and more specifically to a constant current switching power supply system and its control chip 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 chip for a constant current switching power supply system includes an inductor and a power switch. The control chip is configured to: generate a constant current control reference voltage based on a demagnetization detection signal characterizing the demagnetization of the inductor, a pulse width modulation signal for controlling the on and off states of the power switch, and an adjusted reference voltage; generate a turn-off control signal for controlling the power switch to change from an on state to an off state based on the constant current control reference voltage and a current feedback signal characterizing the inductor current flowing through the inductor; generate a turn-on control signal for controlling the power switch to change from an off state to an on state based on the demagnetization detection signal; and generate a pulse width modulation signal based on the turn-off control signal and the turn-on control signal.

[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 constant current control reference voltage based on a demagnetization detection signal characterizing the demagnetization of the inductor, a pulse width modulation signal for controlling the on and off states of the power switch, and adjusting a reference voltage; generating a turn-off control signal for controlling the power switch to change from an on state to an off state based on the constant current control reference voltage and a current feedback signal characterizing the inductor current flowing through the inductor; generating a turn-on control signal for controlling the power switch to change from an off state to an on state based on the demagnetization detection signal; and generating a pulse width modulation signal based on the turn-off control signal and the turn-on control signal.

[0005] The constant current switching power supply system according to an embodiment of the present invention includes the control chip 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 dimmable LED lighting according to an embodiment of the present invention is shown.

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

[0009] Figure 3 It shows Figure 1 The diagram shows the waveforms of multiple signals in a constant current switching power supply system.

[0010] Figure 4 It shows Figure 1 The example circuit diagram of the constant current control module is shown.

[0011] Figure 5 yes Figure 4 The example circuit diagram shown is for the reference voltage generation unit.

[0012] Figure 6 An example circuit diagram of a constant current switching power supply system for non-dimmable LED lighting according to an embodiment of the present invention is shown. Detailed Implementation

[0013] 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.

[0014] 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.

[0015] Figure 1 An example circuit diagram of a constant current switching power supply system 100 for dimmable 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 102. The line voltage VIN supplies power to the control chip 102 via the HV pin. The control chip 102 outputs a gate drive signal Gate to drive the power switch Q1 to turn on and off, based on the dimming control signal DIM used to adjust the brightness of the LED and the current feedback signal CS characterizing the inductor current IL (not shown in the figure) flowing through the inductor L1.

[0016] like Figure 1 As shown, the control chip 102 includes a low-dropout regulator (LDO) module 1022, a dimming control module 1024, a demagnetization detection module 1026, a constant current control module 1028, and a driver module 1030. Specifically: the LDO module 1022 supplies power to the internal circuitry of the control chip 102 based on the line voltage VIN; the dimming control module 1024 generates an adjustment reference voltage Vdim based on the dimming control signal DIM and a predetermined reference voltage Vref, and outputs the adjustment reference voltage Vdim to the constant current control module 1028; the demagnetization detection module 1026 generates a demagnetization detection signal Dem characterizing the demagnetization status of the inductor L1 based on the gate drive signal Gate, and outputs the demagnetization detection signal Dem to the constant current control module 1030. The control module 1028 (it should be understood that the demagnetization detection module 1026 detects the demagnetization of inductor L1 in a manner not limited to this; the demagnetization detection module 1026 can also generate a demagnetization detection signal Dem based on receiving demagnetization detection related signals from the outside via chip pins); the constant current control module 1028 generates a pulse width modulation signal PWM for controlling the on and off of power switch Q1 based on adjusting the reference voltage Vdim, the demagnetization detection signal Dem, and the current feedback signal CS, and outputs the pulse width modulation signal PWM to the driver module 1030; the driver module 1030 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 power switch Q1. Here, the dimming control signal DIM can be a DC voltage signal or a pulse width modulation pulse signal; the demagnetization detection signal Dem participates in the system constant current control, and simultaneously controls the constant current switching power supply system 100 to operate in discontinuous conduction mode (DCM) or quasi-resonant (QR) mode; the current feedback signal CS is used to realize the closed-loop constant current control of the constant current switching power supply system 100.

[0017] exist Figure 1 In the constant current switching power supply system 100 shown, due to the adoption of a common ground BUCK architecture, the current sensing resistor R1 cannot detect the inductor current IL flowing through the inductor L1 when the power switch Q1 is in the off state. Figure 2 It shows Figure 1 The diagram shows the operating waveforms of multiple signals in the constant current switching power supply system 100. Here, Gate represents the gate drive signal used to turn power switch Q1 on and off, IL represents the inductor current flowing through inductor L1, and CS represents the current feedback signal characterizing the inductor current IL flowing through inductor L1 (i.e., the voltage across the current sensing resistor R1). Figure 2 As shown, the current feedback signal CS is 0V when the power switch Q1 is in the off state.

[0018] exist Figure 1 In the constant current switching power supply system 100 shown, the constant current control module 1028 can perform calculations based on the peak voltage of the current feedback signal CS before the power switch Q1 changes from the on state to the off state and the demagnetization time of the inductor L1 to achieve constant current control of the system. However, the actual circuit of the control chip 102 will generate a certain amount of error in the sampling and signal processing of the peak voltage of the current feedback signal CS. In particular, when using the adjustment of the reference voltage Vdim for analog dimming, the peak voltage of the current feedback signal CS used to achieve low-brightness LED lighting is low and is easily affected by the input offset voltage of the internal circuit of the control chip 102, which leads to a further increase in constant current control error and further affects the constant current accuracy.

[0019] Figure 3 It shows Figure 1 The diagram shows the operating waveforms of multiple signals in the constant current switching power supply system 100. Here, Gate represents the gate drive signal used to drive the power switch Q1 to turn on and off, Dem represents the demagnetization detection signal characterizing the demagnetization of inductor L1, IL represents the inductor current flowing through inductor L1, and CS represents the current feedback signal characterizing the inductor current IL flowing through inductor L1 (i.e., the voltage across the current sensing resistor R1).

[0020] exist Figure 1 In the constant current switching power supply system 100 shown, the system output current Iout is the average value of the inductor current IL flowing through inductor L1 during one switching cycle of power switch Q1. Figure 3 As shown, assuming that the total current IL of the inductor L1 during the period Ton when the power switch Q1 is in the on state is S1, and the total current during the period Tdem when the inductor L1 is in the demagnetized state is S2, then the system output current Iout of the constant current switching power supply system 100 satisfies the following relationship (Equation 1), where t is one switching cycle of the power switch Q1.

[0021]

[0022] according to Figure 3 It can be seen that, Figure 1 The constant current switching power supply system 100 shown operates in discontinuous mode (DCM) or quasi-resonant critical mode (QR). During each switching cycle of power switch Q1, the inductor current IL flowing through inductor L1 increases from 0A. Correspondingly, S1 and S2 can be considered as integrals of the triangular waveform area of ​​the inductor current IL flowing through inductor L1. Thus, the relationship between the total current S1 flowing through inductor L1 during the period Ton when power switch Q1 is in the on state and the total current S2 flowing through inductor L1 during the period Tdem when inductor L1 is in the demagnetized state satisfies Equation 2.

[0023]

[0024] Substituting equation 2 into equation 1, we obtain equation 3.

[0025]

[0026] According to Equation 3, if the current feedback signal CS is integrated over the entire switching cycle of power switch Q1, the integration result is S1 / (Ton+Toff). The ratio of this integration result to the system output current Iout is Ton / (Ton+Tdem). In the constant current switching power supply system 100, the system output current Iout can be obtained by performing Equation 4 transformation between the constant current control reference voltage Vref_cc of the integrating amplifier and the adjustment reference voltage Vdim (Equation 5).

[0027]

[0028] In Equation 5, Iout is the system output current of the constant current switching power supply system 100, and Rcs is the resistance value of the current sensing resistor R1.

[0029]

[0030] Based on the above considerations, a constant current control method and its specific implementation circuit for the constant current control module 1028 are proposed. In this method, it is not necessary to sample the peak voltage of the current feedback signal CS, thereby avoiding the error caused by signal sampling. Furthermore, the circuit error is further reduced by simplifying the signal calculation process through the equivalent circuit, thus improving the accuracy of constant current control.

[0031] In some embodiments, the constant current control module 1028 can be configured to: generate a constant current control reference voltage Vref_cc based on a demagnetization detection signal Dem characterizing the demagnetization of inductor L1, a pulse width modulation signal PWM for controlling the on and off states of power switch Q1, and an adjustment of reference voltage Vdim; generate a turn-off control signal for controlling power switch Q1 to change from an on state to an off state based on the constant current control reference voltage Vref_cc and a current feedback signal CS characterizing the inductor current IL flowing through inductor L1; generate a turn-on control signal for controlling power switch Q1 to change from an off state to an on state based on the demagnetization detection signal Dem; and generate a pulse width modulation signal PWM based on the turn-off control signal and the turn-on control signal.

[0032] In some embodiments, the constant current control module 1028 may be further configured to: generate an error characterization signal by amplifying the error between the constant current control reference voltage Vref_cc and the current feedback signal CS; generate a compensation control signal by integrating the error characterization signal over a complete switching cycle of the power switch Q1; and generate a turn-off control signal by comparing the compensation control signal with the current feedback signal CS.

[0033] In some embodiments, the constant current control module 1028 may be further configured to level-shift the compensation control signal before comparing it with the current feedback signal CS.

[0034] In some embodiments, the constant current control reference voltage Vref_cc is proportional to the regulated reference voltage Vdim. For example, the ratio between the constant current control reference voltage Vref_cc and the regulated reference voltage Vdim is equal to the ratio between the duration Ton of the power switch Q1 being in the on state and the following time, which is the sum of the duration Ton of the power switch Q1 being in the on state and the duration Tdem of the inductor L1 being in the demagnetized state.

[0035] In some embodiments, the constant current control module 1028 may be further configured to: generate a chopped reference voltage by chopping the adjustment reference voltage Vdim using the pulse width modulation signal PWM and the demagnetization detection signal Dem; and generate a constant current control reference voltage Vref_cc by low-pass filtering the chopped reference voltage.

[0036] Figure 4 It shows Figure 1 The example circuit diagram of the constant current control module 1028 is shown. Figure 4As shown, the constant current control module 1028 includes a reference voltage generation unit 402, an error amplifier 404, a level shifting circuit 406, a comparator 408, a turn-off time control unit 410, and an RS flip-flop 412. Specifically: the reference voltage generation unit 402, based on the adjusted reference voltage Vdim, the pulse width modulation signal PWM, and the demagnetization detection signal Dem, performs calculations according to Equation 4 and outputs a constant current control reference voltage Vref_cc; the error amplifier amplifies the error between the current feedback signal CS and the constant current control reference voltage Vref_cc to generate an error characterization signal; capacitor C401 integrates the error characterization signal within one switching cycle (Ton+Toff) of power switch Q1 to generate a compensation control signal CMP; the level shifting circuit... 406 performs a level shift on the compensation control signal CMP to adjust its dynamic range; comparator 408 compares the level-shifted compensation control signal CMP with the current feedback signal CS to generate a turn-off control signal PWM_F; the turn-off control signal PWM_F is coupled to the input of RS flip-flop 412 to control the pulse width modulation signal PWM output by RS flip-flop 412 from logic 1 to logic 0; the turn-off time control unit 410 generates a turn-on control signal PWM_R based on the demagnetization detection signal Dem; the turn-on control signal PWM_R is coupled to the other input of RS flip-flop 412 to control the pulse width modulation signal PWM output by RS flip-flop 412 from logic 0 to logic 1. Figure 1 It can be seen that the pulse width modulation signal PWM controls the power switch Q1 to turn on and off after being driven by the driver module 1030. When the pulse width modulation signal PWM is at logic 1 level, the power switch Q1 is in the on state, and when the pulse width modulation signal PWM is at logic 0 level, the power switch Q1 is in the off state. Figure 1 The constant current switching power supply system 100 shown can be precisely adjusted according to Equation 5 by controlling the constant current control module 1022 and combining other circuits and peripheral devices.

[0037] Figure 5 yes Figure 4 The example circuit diagram of the reference voltage generation unit 402 is shown. Figure 5As shown, the reference voltage generation unit 402 includes an amplifier 501, switches 502 and 503, a resistor 504, and a capacitor 505. The positive input terminal of amplifier 501 is connected to the adjusted reference voltage Vdim, and its negative input terminal and output terminal are connected to form a buffer structure. The output of amplifier 501 is connected to switch 502. One end of switch 502 is connected to the output of amplifier 501, and the other end is connected to switch 503 and resistor 504. The control signal for switch 502 is a pulse width modulation (PWM) signal. When the PWM signal is logic 1, switch 502 is in the ON state; when the PWM signal is logic 0, switch 503 is in the OFF state. When the level is 0, switch 502 is in the off state; one end of switch 503 is connected to switch 502 and resistor 504, and the other end is connected to ground. The control signal of switch 503 is the demagnetization detection signal Dem. When the demagnetization detection signal Dem is at logic 1, switch 503 is in the on state; when the demagnetization detection signal Dem is at logic 0, switch 503 is in the off state; one end of resistor 504 is connected to switches 502 and 503, and the other end is connected to capacitor 505 and constant current control reference voltage Vref_cc; one end of capacitor 505 is connected to resistor 504 and constant current control reference voltage Vref_cc, and the other end is connected to ground. In the reference voltage generation unit 402, the regulated reference voltage Vdim is coupled to one end of the switch 502 after passing through the amplifier 501. The switching on and off of the switches 502 and 503 is controlled by the pulse width modulation signal PWM and the demagnetization detection signal Dem to achieve the chopping process of the regulated reference voltage Vdim. The resistor 504 and the capacitor 505 together form a low-pass filter to filter the chopped reference voltage Vchop into a DC signal, that is, the constant current control reference voltage Vref_cc, thereby realizing the circuit operation of Equation 2.

[0038] It should be noted that the constant current control method and circuit implementation described above are not limited to... Figure 1 The constant current switching power supply system 100 shown is also applicable to constant current switching power supply systems used for non-dimmable LED lighting, simply by replacing the adjustable reference voltage Vdim inside the control chip with a predetermined reference voltage Vref.

[0039] Figure 6 An example circuit diagram of a constant current switching power supply system 600 according to another embodiment of the present invention is shown. Figure 6As shown, the control chip 602 for the constant current switching power supply system 600 includes a low dropout regulator (LDO) module 6022, a demagnetization detection module 6026, a constant current control module 6028, and a driver module 6030 (excluding the dimming control module). The constant current control module 6028 generates a pulse width modulation signal PWM for controlling the on and off of the power switch Q1 based on a predetermined reference voltage Vref (i.e., the predetermined reference voltage Vref is used as the adjustment reference voltage Vdim), a demagnetization detection signal Dem, and a current feedback signal CS, and outputs the pulse width modulation signal PWM to the driver module 6030. The specific implementation of the other modules of the constant current switching power supply system 600 and the constant current control module 6028 is similar to the corresponding part in the constant current switching power supply system 100, so it will not be described in detail.

[0040] In summary, the control chip and control method for a constant current switching power supply system according to embodiments of the present invention do not require sampling of the peak voltage of the current feedback signal CS, thereby avoiding errors caused by signal sampling. Furthermore, the simplification of the signal calculation process through equivalent circuits further reduces circuit errors and improves the accuracy of constant current control.

[0041] 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 chip 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 chip is configured as follows: A constant current control reference voltage is generated based on a demagnetization detection signal characterizing the demagnetization of the inductor, a pulse width modulation signal for controlling the on and off of the power switch, and an adjustment reference voltage, wherein the constant current control reference voltage is proportional to the adjustment reference voltage. An error characterization signal is generated by amplifying the error of the constant current control reference voltage and the current feedback signal characterizing the inductor current flowing through the inductor. A compensation control signal is generated by integrating the error characterization signal over a complete switching cycle of the power switch. A turn-off control signal for controlling the power switch to change from an on state to an off state is generated by comparing the compensation control signal with the current feedback signal. The compensation control signal is level-shifted before comparing it with the current feedback signal. Based on the demagnetization detection signal, a conduction control signal is generated to control the power switch to change from an off state to an on state; and The pulse width modulation signal is generated based on the shutdown control signal and the turn-on control signal.

2. The control chip according to claim 1, wherein, The ratio between the constant current control reference voltage and the adjustment reference voltage is equal to the ratio between the duration of the power switch being in the on state and the following time, which is the sum of the duration of the power switch being in the on state and the duration of the inductor being in the demagnetized state.

3. The control chip according to claim 1, wherein, The control chip is further configured as follows: By using the pulse width modulation signal and the demagnetization detection signal to chop the adjustment reference voltage, a chopped reference voltage is generated. The constant current control reference voltage is generated by low-pass filtering the chopped reference voltage.

4. The control chip according to claim 1, wherein, The control chip is further configured as follows: The adjustment reference voltage is generated based on the dimming control signal used to adjust the luminous brightness of the light-emitting diode and a predetermined reference voltage.

5. The control chip according to claim 1, wherein, The adjusted reference voltage is a predetermined reference voltage.

6. 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: A constant current control reference voltage is generated based on a demagnetization detection signal characterizing the demagnetization of the inductor, a pulse width modulation signal for controlling the on and off of the power switch, and an adjustment reference voltage, wherein the constant current control reference voltage is proportional to the adjustment reference voltage. An error characterization signal is generated by amplifying the error of the constant current control reference voltage and the current feedback signal characterizing the inductor current flowing through the inductor. A compensation control signal is generated by integrating the error characterization signal over a complete switching cycle of the power switch. A turn-off control signal for controlling the power switch to change from an on state to an off state is generated by comparing the compensation control signal with the current feedback signal. The compensation control signal is level-shifted before comparing it with the current feedback signal. Based on the demagnetization detection signal, a conduction control signal is generated to control the power switch to change from an off state to an on state; and The pulse width modulation signal is generated based on the shutdown control signal and the turn-on control signal.

7. The control method according to claim 6, wherein, The ratio between the constant current control reference voltage and the adjustment reference voltage is equal to the ratio between the duration of the power switch being in the on state and the following time, which is the sum of the duration of the power switch being in the on state and the duration of the inductor being in the demagnetized state.

8. The control method according to claim 6, wherein, The process of generating the constant current control reference voltage includes: By chopping the adjusted reference voltage using the pulse width modulation signal and the demagnetization detection signal, a chopped reference voltage is generated; and The constant current control reference voltage is generated by low-pass filtering the chopped reference voltage.

9. The control method according to claim 6, further comprising: The adjustment reference voltage is generated based on the dimming control signal used to adjust the luminous brightness of the light-emitting diode and a predetermined reference voltage.

10. The control method according to claim 9, wherein, The adjusted reference voltage is a predetermined reference voltage.

11. A constant current switching power supply system, comprising a control chip for a constant current switching power supply system as described in any one of claims 1 to 5.

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