Constant current circuit, switching power supply and lighting device operating in DCM mode

Abstract

This invention discloses a constant current circuit, a switching power supply, and a lighting device operating in DCM mode. The constant current circuit operating in DCM mode includes: an error sampling circuit, whose first input terminal is connected to the output terminal of the switching transistor, and whose second input terminal is used to connect to a reference power supply, for collecting the average current flowing through the inductor, and outputting a corresponding error detection signal based on the deviation between the average current and the reference power supply; and an effective duty cycle modulation circuit, whose first sampling terminal is connected to the output terminal of the error sampling circuit, whose second sampling terminal is electrically connected to the first switching transistor, and whose output terminal is used to connect to the driving module. This invention improves the stability of the inductor's operation in the switching power supply, thereby improving the working performance and reliability of the switching power supply.

Description

Technical Field

[0001] This invention relates to the field of constant current dimming technology, and particularly to a constant current circuit, switching power supply, and lighting device operating in DCM mode. Background Technology

[0002] Currently, because the inductor current always reaches 0 during the switching cycle in DCM mode, meaning the inductor is properly "reset," its switching losses are lower than other LED driving modes, making it a common choice for power switches. However, in DCM mode, traditional switching power supplies are prone to fluctuations in the current flowing through the inductor due to temperature or repeated switching, leading to instability in the inductor's operation and generating significant noise and EMI interference, thus affecting the power supply's performance and reliability. Summary of the Invention

[0003] The main objective of this invention is to provide a constant current circuit, a switching power supply, and a lighting device operating in DCM mode, aiming to improve the stability of inductor operation in the switching power supply, thereby improving the working performance and reliability of the switching power supply.

[0004] To achieve the above objectives, the present invention proposes a constant current circuit operating in DCM mode, applied to a switching power supply. The switching power supply includes an inductor, a first switching transistor, and a driving module. The inductor and the first switching transistor are connected in series between the DC power supply and ground. The driving module is connected to the controlled terminal of the first switching transistor. The constant current circuit operating in DCM mode includes:

[0005] An error sampling circuit has its first input terminal connected to the output terminal of the switching transistor, and its second input terminal connected to a reference power supply. It is used to collect the average current flowing through the inductor and output a corresponding error detection signal based on the deviation between the average current and the reference power supply.

[0006] An effective duty cycle modulation circuit has a first sampling terminal connected to the output terminal of the error sampling circuit, a second sampling terminal for electrical connection to the first switching transistor, and an output terminal for connection to the driving module. The effective duty cycle modulation circuit is also used to control the driving module to adjust the dead time of the first switching transistor according to the received error detection signal when the first switching transistor enters the dead time period based on the detected operating parameters of the first switching transistor, so as to keep the average current flowing through the inductor at a preset current value.

[0007] Optionally, the first switch has an on-time period, an off-time period, and a dead-time period during operation. The error sampling circuit is specifically used to collect the detection voltage corresponding to the current flowing through the inductor when the first switch is in the on-time period, to collect the leakage voltage corresponding to the leakage of the inductor when the first switch is in the off-time period, and to collect the 0 voltage corresponding to the demagnetization of the inductor when the first switch is in the dead-time period. The circuit also detects the average current flowing through the inductor based on the current flowing through the inductor, the leakage voltage, and the 0 voltage.

[0008] Optionally, the error sampling circuit includes:

[0009] A current sampling resistor is connected in series between the output terminal of the switching transistor and ground to output the corresponding sampling voltage.

[0010] A switch group, wherein the first input terminal of the switch group is used to connect to the leakage voltage, the second input terminal of the switch group is connected to the current sampling resistor, and the third input terminal of the switch group is grounded, and the switch group is used to output a corresponding current sampling signal according to the connected leakage voltage, the sampling voltage and the 0 voltage;

[0011] A transconductance amplifier, wherein the positive input terminal of the transconductance amplifier is connected to the output terminal of the switch group, and the negative input terminal of the transconductance amplifier is used to connect to the first reference voltage, and is used to compare the received detection voltage with the first reference voltage and output the corresponding error current;

[0012] An integrator, the input of which is connected to the output of the transconductance amplifier, and the output of which is connected to the input of the effective duty cycle modulation circuit, is used to integrate the error current output by the transconductance amplifier and output an error detection signal with a corresponding voltage value.

[0013] Optionally, the first switch has an on period, an off period, and a dead period when it is working, and the switch group includes a first switch, a second switch, and a third switch;

[0014] The first terminal of the first switch is used to connect to the bleed voltage, the first terminal of the second switch is electrically connected to the current sampling resistor, the second terminals of the first switch, the second terminal of the second switch, and the first terminal of the third switch are respectively connected to the non-inverting input terminal of the transconductance amplifier, and the second terminal of the third switch is grounded.

[0015] When the first switch is in the on period, the first switch is turned on, and the second switch and the third switch are closed; when the first switch is in the off period, the second switch is turned on, and the first switch and the third switch are closed; and when the first switch is in the dead period, the third switch is turned on, and the second switch and the first switch are closed.

[0016] Optionally, the constant current circuit operating in DCM mode includes:

[0017] A bleed voltage generating circuit is provided, wherein the input terminal of the bleed voltage generating circuit is electrically connected to the first switching transistor, and the output terminal of the bleed voltage generating circuit is connected to the input terminal of the sampling circuit. The bleed voltage generating circuit is used to collect the current flowing through the inductor during the conduction period of the first switching transistor, and to process the collected current signal to output the corresponding bleed voltage during the turn-off period of the first switching transistor.

[0018] Optionally, the bleed voltage generating circuit includes a first resistor, a second resistor, a third resistor, a second switching transistor, a first comparator, and a first capacitor;

[0019] The first end of the first resistor is connected to a DC power supply. The second end of the first resistor is connected to the drain of the second switching transistor. The controlled terminal of the second switching transistor is connected to the output terminal of the first comparator. The source of the second switching transistor is connected to the inverting input terminal of the first comparator and the first end of the second resistor. The second end of the second resistor is the output terminal of the bleed voltage generation circuit and is connected to the first end of the third resistor. The non-inverting input terminal of the first comparator is connected to a current sampling resistor and is connected to the first end of the first capacitor. The second end of the first capacitor, the second end of the third resistor, and the substrate pin of the first comparator are grounded.

[0020] Optionally, the effective duty cycle modulation circuit includes:

[0021] A signal conversion circuit, whose input terminal is connected to the output terminal of the error sampling circuit, is used to process the incoming error detection signal and output a corresponding second error current.

[0022] A demagnetization detection circuit, whose input terminal is connected to the controlled terminal of the first switching transistor, is used to output a corresponding demagnetization detection signal when the demagnetization of the inductor is detected to be complete based on the controlled terminal voltage of the first switching transistor.

[0023] The dead time adjustment circuit has its first input terminal electrically connected to the signal conversion circuit and its second input terminal connected to the output terminal of the signal conversion circuit. It is used to mirror the input second error current, discharge according to the second error current, and store the mirrored second error current again when the demagnetization detection signal is received.

[0024] The second comparator has its non-inverting input connected to the output of the dead time, its inverting input connected to the second reference voltage, and its output connected to the drive module. The second comparator is also used to control the drive module to turn on the first switch when it detects that the terminal voltage of the dead time adjustment circuit reaches the second reference voltage.

[0025] Optionally, the dead time adjustment circuit includes:

[0026] A current mirror group is electrically connected to the output terminal of the signal conversion circuit and is used to mirror the second error current and output the corresponding mirror current.

[0027] The second capacitor is connected to the non-inverting input of the second comparator and is used to output the corresponding voltage value according to the currently stored electrical energy.

[0028] A charge / discharge control circuit is provided, which is connected to a constant current power supply and is connected to the current mirror group, the second capacitor and the demagnetization detection circuit respectively. The charge / discharge control circuit is used to charge / discharge the second capacitor according to whether a demagnetization detection signal is received.

[0029] The present invention also proposes a switching power supply, which includes a BUCK circuit and the above-mentioned constant current circuit.

[0030] The input terminal of the BUCK circuit is used to connect to AC power. The BUCK circuit is electrically connected to the constant current circuit operating in DCM mode. The constant current circuit operating in DCM mode is used to collect the output current of the BUCK circuit and output a corresponding dead time adjustment signal so that the output current of the BUCK circuit is maintained at a preset current value.

[0031] The present invention also proposes a lighting device, including the above-mentioned switching power supply and light-emitting component, wherein the switching power supply is used to connect to AC power, and the light-emitting component is electrically connected to the switching power supply.

[0032] The technical solution of this invention, by setting an effective duty cycle modulation circuit 200, can output a corresponding dead time adjustment signal based on the received error detection signal when the current flowing through the inductor fluctuates. The dead time of the switching transistor in the current working cycle and subsequent working cycles is controlled by the driving circuit, realizing negative feedback adaptive adjustment of the length of the dead time period, keeping the effective duty cycle of the switching transistor in the switching power supply fixed, and keeping the current value flowing through the inductor constant. This avoids the inductor from generating a lot of noise and EMI interference due to unstable operation, thereby improving the stability of the inductor operation in the switching power supply, as well as the working performance and reliability of the switching power supply. Attached Figure Description

[0033] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0034] Figure 1 This is a schematic diagram of an embodiment of the constant current circuit of the present invention operating in DCM mode;

[0035] Figure 2 This is a schematic diagram of another embodiment of the constant current circuit of the present invention operating in DCM mode;

[0036] Figure 3 This is a circuit structure diagram of an embodiment of the constant current circuit of the present invention operating in DCM mode;

[0037] Figure 4 This is a circuit structure diagram of another embodiment of the constant current circuit of the present invention operating in DCM mode;

[0038] Figure 5 This is a circuit structure diagram of another embodiment of the constant current circuit of the present invention operating in DCM mode;

[0039] Figure 6 This is a schematic diagram of the leakage voltage generation circuit of the present invention;

[0040] Figure 7 This is a schematic diagram of the demagnetization detection circuit of the present invention;

[0041] Figure 8 This is a signal waveform diagram of an embodiment of the constant current circuit of the present invention operating in DCM mode.

[0042] Explanation of icon numbers:

[0043] label name label name 100 Error sampling circuit <![CDATA[R EA ]]> Integrating resistor 110 switch group <![CDATA[C EA ]]> Integrating capacitor 120 transconductance amplifier Deff Effective duty cycle 130 Integrator <![CDATA[T on ]]> Conducting period 200 Effective duty cycle modulation circuit <![CDATA[T dis ]]> Shutdown period 210 Signal conversion circuit <![CDATA[T s ]]> Dead Zone 220 Demagnetization detection circuit <![CDATA[I L ]]> Current flowing through the inductor 230 Dead time adjustment circuit <![CDATA[I average ]]> Average current flowing through the inductor 231 Current mirror group <![CDATA[I pk ]]> Peak current flowing through the inductor 232 Charge and discharge control circuit <![CDATA[V pk ]]> Peak voltage flowing through the inductor 300 Leakage voltage generation circuit <![CDATA[V cs ]]> Detection voltage OP1~OP2 First comparator ~ Second comparator <![CDATA[0.5V cs _p]]> Leakage voltage S1~S5 First Switch ~ Fifth Switch <![CDATA[V EA ]]> Integral voltage Q1~Q2 First switching transistor ~ Second switching transistor <![CDATA[I EA ]]> Second error current C1~C2 First capacitor ~ Second capacitor ZCOMP Demagnetization detection signal R1~R3 First resistor ~ Third resistor

[0044] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0045] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0046] Furthermore, in this invention, descriptions involving "first," "second," etc., are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of that feature. Additionally, the technical solutions of the various embodiments can be combined with each other, but only on the basis of being achievable by those skilled in the art. When the combination of technical solutions is contradictory or impossible to implement, such a combination of technical solutions should be considered non-existent and not within the scope of protection claimed by this invention.

[0047] This invention proposes a constant current circuit operating in DCM mode, applicable to switching power supplies.

[0048] Reference Figure 1 In one embodiment, the switching power supply includes an inductor, a first switching transistor Q1, and a driving module. The inductor and the first switching transistor Q1 are connected in series between the DC power supply and ground to form a current loop. The driving module is connected to the controlled terminal of the first switching transistor Q1. The constant current circuit operating in DCM mode includes:

[0049] The error sampling circuit 100 has its first input terminal connected to the output terminal of the switching transistor, and its second input terminal connected to a reference power supply. It is used to collect the average current flowing through the inductor and output a corresponding error detection signal based on the deviation between the average current and the reference power supply.

[0050] An effective duty cycle modulation circuit 200 has a first sampling terminal connected to the output terminal of the error sampling circuit 100, a second sampling terminal for electrical connection to the first switch Q1, and an output terminal for connection to the driving module. The effective duty cycle modulation circuit 200 is also used to control the driving module to adjust the dead time of the first switch Q1 according to the received error detection signal when the first switch Q1 enters the dead time period based on the detected operating parameters of the first switch Q1.

[0051] It should be noted that existing switching power supplies, during normal operation, perform PWM chopping on the input DC power according to the needs of the electrical equipment. By adjusting the duty cycle of the PWM signal, the output current is regulated. When current flows through an inductor, the inductor generates electrodynamic force due to electromagnetic effects, causing the inductor to oscillate under the influence of this force. This electrodynamic force doubles as the current increases. When fluctuations in current cause the electrodynamic force to surge to a certain level, electrons move irregularly, and the magnetic field changes, resulting in noise and EMI interference.

[0052] When a switching power supply outputs constant current in DCM mode, its internal switching transistor sequentially experiences three periods—on, off, and dead time—within one duty cycle. Figure 8 As shown, during the on-time of the first switch Q1, the current loop formed by the first switch Q1 and the inductor is connected, and the current flowing through the inductor gradually increases, that is, the inductor current gradually increases. During the off-time of the first switch Q1, the current loop formed by the first switch Q1 and the inductor is disconnected, and the current flowing through the inductor is discharged through the bleed circuit set in the switching power supply, so that the inductor current gradually decreases. When the inductor current drops to 0, the off-time of the first switch Q1 ends, and the dead time period in which the inductor current remains at 0 is entered.

[0053] In this embodiment, the error sampling circuit 100 includes two parts: sampling and error detection. Sampling can be performed using a current sampling resistor, and error detection can be performed using a transconductance amplifier 120, a comparator, or other operational amplifier devices. The error sampling circuit 100 collects the current flowing through the inductor during the on-time, off-time, and dead-time of the switching transistor to obtain the average current flowing through the inductor, which is the actual output current of the switching power supply. Based on the reference power supply, the corresponding error value is obtained, and an error detection signal characterizing this error value is output. The effective duty cycle modulation circuit 200 can be a composite circuit composed of multiple MOS transistors, capacitors, and other devices.

[0054] It is understandable that when a switching power supply operates at a specific frequency, fluctuations in the current flowing through the inductor will inevitably affect the time it takes for the inductor current to rise to its peak value and for the inductor to demagnetize. In other words, this will alter the ratio of the on-time, off-time, and dead-time periods, thus changing the effective duty cycle of the circuit. The effective duty cycle is:

[0055] Deff = (T on +T dis ) / (T on +T dis +T s ), Deff is the effective duty cycle, T on For the conduction period, T dis For the shutdown period, Ts This is a dead zone period.

[0056] Because the average current flowing through the inductor in DCM mode is:

[0057] I pk The peak current flowing through the inductor is mentioned here. It should be noted that the switching power supply has a peak current control circuit. During normal operation, once the current flowing through the coil reaches a preset peak value, the first switching transistor Q1 is turned off, stopping the current flowing through the coil from increasing. Therefore, the peak current flowing through the coil is always a constant value, i.e., I0. pk Since the value is constant, the average current flowing through the inductor is only related to the effective duty cycle Deff. When the effective duty cycle Deff changes, the average current I flowing through the inductor... average Things will also change.

[0058] Based on the formula for calculating the average current flowing through the inductor in the DCM mode, we can obtain the peak current I flowing through the coil. pk Assuming the value is constant, in order to ensure the average current I flowing through the inductor... average To maintain a constant effective duty cycle, the effective duty cycle Deff of the first switching transistor Q1 needs to be controlled to keep Deff at a constant value. Therefore, this invention sets up an effective duty cycle modulation circuit 200. When the current flowing through the inductor fluctuates, a corresponding dead time adjustment signal is output based on the received error detection signal. This signal is then used by the drive circuit to control the dead time of the switching transistor in the current working cycle and subsequent working cycles. By adjusting the dead time, the effective duty cycle of the switching transistor in the switching power supply is kept fixed, and the current flowing through the inductor is kept constant. This avoids the situation where current fluctuations cause a surge in electrodynamic force, leading to irregular movement of electrons and changes in the magnetic field, which can cause noise and EMI interference.

[0059] Specifically, during normal operation, the constant current circuit collects the average current flowing through the inductor via the error sampling circuit 100. If a sudden temperature change or repeated switching of the switching device causes fluctuations in the current flowing through the inductor, the average current detected by the error sampling circuit 100 will also change, and a corresponding error detection signal will be output to the effective duty cycle modulation circuit 200. The effective duty cycle modulation circuit 200 determines the error between the average current and the reference power supply based on the error detection signal, and then outputs a corresponding dead time adjustment signal based on the error to adjust the on-time, off-time, and dead time to ensure that the effective duty cycle remains constant.

[0060] When the average current is too high, the on-time, off-time, and dead-time all increase, resulting in Deff = (T on +T dis ) / (Ton +T dis +T s The average current decreases as the average current decreases. When the average current is smaller, the on-time, off-time, and dead-time all decrease, resulting in Deff = (T) / T. on +T dis ) / (T on +T dis +T s The increase in current leads to an increase in the average current.

[0061] For example, when the effective duty cycle modulation circuit 200 determines that the average current flowing through the inductor is too large based on the error detection signal, the peak current I flowing through the inductor... pk The effective duty cycle modulation circuit 200 outputs a dead-time adjustment signal, representing an extension of the dead-time, to the drive circuit. This causes the effective duty cycle Deff of the first switch Q1 to decrease when the drive circuit drives the first switch Q1, thereby reducing the output current. Similarly, when the average current flowing through the inductor is determined to be small based on the error detection signal, the effective duty cycle modulation circuit 200 outputs a dead-time adjustment signal, representing a shortening of the dead-time, to the drive circuit. This causes the effective duty cycle Deff of the first switch Q1 to increase when the drive circuit drives the first switch Q1, thereby increasing the output current.

[0062] This invention, by setting an effective duty cycle modulation circuit 200, can output a corresponding dead time adjustment signal based on the received error detection signal when the current flowing through the inductor fluctuates. The dead time of the switching transistor in the current working cycle and subsequent working cycles is controlled by the driving circuit, realizing negative feedback adaptive adjustment of the length of the dead time period. This keeps the effective duty cycle of the switching transistor in the switching power supply fixed, and keeps the current value flowing through the inductor constant. This avoids the inductor from generating a lot of noise and EMI interference due to unstable operation, thereby improving the stability of the inductor operation in the switching power supply, as well as the working performance and reliability of the switching power supply.

[0063] In one embodiment, the switching transistor has an on-time period, an off-time period, and a dead-time period during operation. The error sampling circuit 100 is specifically used to collect the detection voltage corresponding to the current flowing through the inductor when the first switching transistor Q1 is in the on-time period, to collect the leakage voltage corresponding to the leakage of the inductor when the first switching transistor Q1 is in the off-time period, and to collect the 0 voltage corresponding to the demagnetization of the inductor when the first switching transistor Q1 is in the dead-time period. The average current flowing through the inductor is detected based on the current flowing through the inductor, the leakage voltage, and the 0 voltage.

[0064] In this embodiment, when the switching transistor is working normally, the current flowing through the inductor gradually increases as the switching transistor is turned on and gradually decreases as the switching transistor is turned off, resulting in... Figure 8 The current waveform shown indicates that the current flowing through the inductor during the on-time, off-time, and dead-time of the switching transistor needs to be collected by the error sampling circuit 100 to obtain the average current flowing through the inductor, which characterizes the actual output current of the switching power supply.

[0065] When the error sampling circuit 100 is working, it cannot directly collect the current value in the current loop. It is necessary to convert the current value into a corresponding voltage signal through devices such as the current sampling resistor for collection. Therefore, the detection voltage, leakage voltage and 0 voltage corresponding to the inductor current in each working cycle are detected and integrated. Based on the voltage integration in each working cycle, the average voltage signal in the corresponding working cycle is obtained to characterize the average current flowing through the inductor.

[0066] Reference Figures 1 to 3 In one embodiment, the error sampling circuit 100 includes:

[0067] A current sampling resistor is connected in series between the output terminal of the switching transistor and ground to output the corresponding sampling voltage.

[0068] The switch group 110 has a first input terminal for receiving a leakage voltage, a second input terminal for connecting to the current sampling resistor, and a third input terminal for grounding. The switch group 110 is used to output a corresponding current sampling signal based on the received leakage voltage, the sampling voltage, and the 0 voltage.

[0069] A transconductance amplifier 120 is provided, with its positive input terminal connected to the output terminal of the switch group 110. The negative input terminal of the transconductance amplifier 120 is used to connect to the first reference voltage and to compare the received detection voltage with the first reference voltage, thereby outputting a corresponding error current.

[0070] Integrator 130, the input terminal of which is connected to the output terminal of transconductance amplifier 120, and the output terminal of integrator 130 is connected to the input terminal of effective duty cycle modulation circuit 200, is used to integrate the error current output by transconductance amplifier 120 and output an error detection signal with a corresponding voltage value.

[0071] In this embodiment, the switch group 110 can be composed of multiple switching devices such as MOSFETs and transistors; the transconductance amplifier 120 can perform differential processing on the input signal and output the corresponding current. That is, by setting the transconductance amplifier 120, the acquired detection voltage and the first reference voltage can be differentially processed to output the corresponding error current.

[0072] When the first switch Q1 is in the on-time period, the current loop between the inductor and the switch is connected, and the inductor current rises linearly. At this time, the switch group 110 connects the transconductance amplifier 120 to the current sampling circuit, so that the transconductance amplifier 120 receives the detection voltage output by the current sampling circuit. When the first switch Q1 is in the off-time period, the inductor begins to demagnetize, and the inductor current decreases linearly. At this time, the switch group 110 connects the transconductance amplifier 120 to the bleed voltage. When the first switch Q1 is in the dead time period, the inductor demagnetization ends, and the inductor current is 0. At this time, the switch group 110 grounds the non-inverting input terminal of the transconductance amplifier 120, completing the sampling of the inductor current for one cycle.

[0073] The transconductance amplifier 120 processes the acquired detection voltage, bleed voltage and 0 voltage to obtain the average voltage corresponding to the average current flowing through the inductor. The average voltage is compared with the first reference voltage, and the error between the two is output to the integrator 130 in the form of error current. The error current carrying error information is integrated to generate an error detection signal with the corresponding voltage value.

[0074] Optionally, the integrator 130 includes an integrating resistor R. EA and integrating capacitor C EA The output current error is input to the integrating resistor R. EA and integrating capacitor C EA Through the integrating resistor R EA After limiting the error current, it passes through the integrating capacitor C. EA Integrating the current carrying error information generates an integrated voltage V on the upper plate of the capacitor. EA Output as an error detection signal.

[0075] Optionally, the switching transistor has an on period, an off period, and a dead period when it is working, and the switch group 110 includes a first switch S1, a second switch S2, and a third switch S3;

[0076] The first terminal of the first switch S1 is used to connect to the bleed voltage, the first terminal of the second switch S2 is electrically connected to the current sampling resistor, the second terminals of the first switch S1, the second terminal of the second switch S2 and the first terminal of the third switch S3 are respectively connected to the non-inverting input terminal of the transconductance amplifier 120, and the second terminal of the third switch S3 is grounded.

[0077] When the first switch Q1 is in the on period, the first switch S1 is turned on, and the second switch S2 and the third switch S3 are turned off; when the first switch Q1 is in the off period, the second switch S2 is turned on, and the first switch S1 and the third switch S3 are turned off; and when the first switch Q1 is in the dead period, the third switch S3 is turned on, and the second switch S2 and the first switch S1 are turned off.

[0078] In this embodiment, when the first switch Q1 is in the on-time period, the current loop between the inductor and the switch is connected, and the inductor current rises linearly. At this time, the first switch S1 connects the transconductance amplifier 120 to the current sampling circuit, and the second switch S2 and the third switch S3 are disconnected, so that the transconductance amplifier 120 receives the detection voltage output by the current sampling circuit. When the first switch Q1 is in the off-time period, the inductor begins to demagnetize, and the inductor current decreases linearly. At this time, the second switch S2 is turned on, and the first switch S1 and the third switch S3 are disconnected, so that the transconductance amplifier 120 is connected to the leakage voltage. When the first switch Q1 is in the dead time period, the inductor demagnetization ends, and the inductor current is 0. At this time, the third switch S3 is turned on, and the first switch S1 grounds the non-inverting input terminal of the transconductance amplifier 120, thus completing the sampling of the inductor current for one cycle.

[0079] It should be noted that, referring to Figure 8 When the constant current circuit is applied to a switching power supply, its current sampling resistor is connected to the output terminal of the switching transistor. That is, when the first switching transistor Q1 is turned off, no current flows through the current sampling resistor. Therefore, the current sampling resistor cannot collect the current flowing through the inductor when the first switching transistor Q1 is in the off period and dead period.

[0080] Therefore, refer to Figure 1 and Figure 6 In one embodiment, the constant current circuit operating in DCM mode further includes:

[0081] A bleed voltage generating circuit 300 is provided. The input terminal of the bleed voltage generating circuit 300 is electrically connected to the first switching transistor Q1, and the output terminal of the bleed voltage generating circuit 300 is connected to the input terminal of the error sampling circuit 100. The bleed voltage generating circuit 300 is used to collect the current flowing through the inductor during the conduction period of the first switching transistor Q1, and to process the collected current signal to output the corresponding bleed voltage during the turn-off period of the first switching transistor Q1.

[0082] In this embodiment, when the first switch Q1 is turned on, the bleed voltage generating circuit 300 collects the current flowing through the inductor to obtain the average current flowing through the inductor. Since the current flowing through the inductor is almost symmetrical when rising and falling, the average value of the current flowing through the inductor when rising is equal to the average value when falling. Thus, the bleed voltage generating circuit 300 can take the average current during the turn-on period of the first switch Q1 as the average current during the turn-off period of the first switch Q1 and output the corresponding voltage signal as the bleed voltage output to simulate the current output during the turn-off period of the first switch Q1.

[0083] Optionally, the bleed voltage generating circuit 300 includes a first resistor R1, a second resistor R2, a third resistor R3, a second switch Q2, a first comparator OP1, and a first capacitor C1;

[0084] The first end of the first resistor R1 is connected to a DC power supply. The second end of the first resistor R1 is connected to the drain of the second switch Q2. The controlled end of the second switch Q2 is connected to the output of the first comparator OP1. The source of the second switch Q2 is connected to the inverting input of the first comparator OP1 and the first end of the second resistor R2. The second end of the second resistor R2 is the output of the bleed voltage generation circuit 300 and is connected to the first end of the third resistor R3. The non-inverting input of the first comparator OP1 is connected to a current sampling resistor and is connected to the first end of the first capacitor C1. The second end of the first capacitor C1, the second end of the third resistor R3, and the substrate pin of the first comparator OP1 are grounded.

[0085] In this embodiment, when the first switch Q1 is turned on, the current flowing through the inductor charges the first capacitor C1. At the end of the conducting period of the first switch Q1, the voltage across the first capacitor C1 represents the integral of the current during this operating cycle. Since the controlled terminal of the second switch Q2 is connected to the output terminal of the first comparator OP1, the output voltage of the second switch Q2 can be adjusted by regulating the voltage output of the first comparator OP1. The voltage output by the second switch Q2 is divided by resistors R2 and R3, which have two identical resistors, to output a leakage voltage representing the average current during the current operating cycle.

[0086] Therefore, when the current flowing through the inductor fluctuates, the voltage across the first capacitor C1 will also change accordingly, thereby adjusting the voltage output of the first comparator OP1, which in turn adjusts the voltage division value of the outputs of the second resistor R2 and the third resistor R3, i.e., the voltage value of the bleed voltage.

[0087] Reference Figures 1 to 7In one embodiment, the effective duty cycle modulation circuit 200 includes:

[0088] The signal conversion circuit 210, whose input terminal is connected to the output terminal of the error sampling circuit 100, is used to process the incoming error detection signal and output the corresponding second error current.

[0089] The demagnetization detection circuit 220 has its input terminal connected to the controlled terminal of the first switch Q1, and is used to output a corresponding demagnetization detection signal ZCOMP when the demagnetization of the inductor is detected to be finished based on the controlled terminal voltage of the first switch Q1.

[0090] The dead time adjustment circuit 230 has its first input terminal electrically connected to the signal conversion circuit 210 and its second input terminal connected to the output terminal of the signal conversion circuit 210. It is used to mirror the input second error current, discharge according to the second error current, and store the mirrored second error current again when the demagnetization detection signal ZCOMP is received.

[0091] The second comparator OP2 has its non-inverting input connected to the output of the dead time, its inverting input connected to the second reference voltage, and its output connected to the drive module. The second comparator OP2 is also used to control the drive module to turn on the first switch Q1 when the terminal voltage of the dead time adjustment circuit 230 is detected to reach the second reference voltage.

[0092] It should be noted that when the first switch Q1 is in the off state, the current in the inductor begins to drop to zero, that is, the inductor current begins to demagnetize. During the demagnetization process, due to the inductor's self-inductance, when the inductor current drops to zero, the voltage across the inductor will also drop to zero. Therefore, a demagnetization detection signal ZCOMP can be detected on the inductor, indicating that the inductor current has reached zero.

[0093] In this embodiment, the demagnetization detection circuit 220 can detect whether the current flowing through the inductor is 0, or it can detect the terminal voltage of the controlled terminal of the switching transistor. Optionally, the schematic diagram of the demagnetization detection circuit 220 used in this embodiment can be as follows: Figure 7 In this process, Vm is a set negative voltage. When the controlled terminal of the first switch Q1 is turned off and drops to 0, the input voltage of the first switch Q1 jumps to a negative voltage. Due to the existence of parasitic effects, the controlled terminal voltage also jumps to a negative voltage. When the controlled terminal voltage is less than the set Vm, a demagnetization detection signal ZCOMP is generated to determine that the inductor demagnetization has ended.

[0094] When the constant current circuit is working normally, the error detection signal output by the error sampling circuit 100 is converted into voltage and current by the signal conversion circuit 210, and the output is the second error current. The current value of the second error current IEA is positively correlated with the error represented by the error detection signal. The magnitude of the error represented by the error detection signal will automatically adjust the magnitude of the second error current IEA.

[0095] The dead-time adjustment circuit 230 mirrors the input second error current, converting it into a discharge current at a ratio of 1:M and a charging current at a ratio of 1:N, where M and N are both non-zero positive numbers. When the dead-time adjustment circuit 230 does not receive the demagnetization detection signal ZCOMP, it indicates that the first switch Q1 is either in the on or off period. The dead-time adjustment circuit 230 then discharges the stored energy until it receives the demagnetization detection signal ZCOMP, indicating that the first switch Q1 has entered the dead-time period and begins storing energy according to the charging current. This continues until the voltage value output by the dead-time adjustment circuit 230 reaches the second reference voltage again. The second comparator OP2 then outputs a dead-time end signal to the drive circuit, controlling the switch to turn on.

[0096] Since the dead time adjustment circuit 230 only discharges electrical energy during the on and off periods of the first switch Q1, when the off period of the first switch Q1 ends, that is, when the dead time adjustment circuit 230 receives the demagnetization detection signal ZCOMP, the voltage output by the dead time adjustment circuit 230 is the lowest value of the output voltage in one working cycle, that is, the valley voltage. Therefore, depending on the current value of the error current, the valley voltage after the dead time adjustment circuit 230 will also be different, so that when the dead time adjustment circuit 230 is charged again with a constant current, the time required to charge to the second reference voltage will also be different. Thus, the drive circuit can adjust the dead time according to the charging time of the dead time adjustment circuit 230.

[0097] Reference Figures 1 to 7 In one embodiment, the dead time adjustment circuit 230 includes:

[0098] Current mirror assembly 231, which is electrically connected to the output terminal of the signal conversion circuit 210, is used to mirror the second error current and output a corresponding mirrored current.

[0099] The second capacitor C2 is connected to the non-inverting input terminal of the second comparator OP2 and is used to output the corresponding voltage value according to the currently stored electrical energy.

[0100] The charge / discharge control circuit 232 is electrically connected to the current mirror group 231, and is also connected to the current mirror group 231, the second capacitor C2, and the demagnetization detection circuit 220. The charge / discharge control circuit 232 is used to charge / discharge the second capacitor C2 according to whether the demagnetization detection signal ZCOMP is received.

[0101] In this embodiment, the current mirror group 231 includes a first current mirror and a second current mirror. The first current mirror is electrically connected to the output terminal of the voltage-to-current conversion circuit and is used to mirror the second error current to output a corresponding first mirror current. The second current mirror is electrically connected to the first current mirror and is used to mirror the first mirror current to output a corresponding second mirror current.

[0102] The charging and discharging control circuit 232 includes a fourth switch S4 and a fifth switch S5;

[0103] The first end of the fourth switch S4 is electrically connected to the current mirror group 231, the second end of the fourth switch S4 is connected to the first end of the fifth switch S5 and the positive input end of the second comparator OP2, and the second end of the fifth switch S5 is electrically connected to the second current mirror.

[0104] Specifically, the first current mirror is a PMOS current mirror, and the integration voltage V EA The signal is converted to I through signal conversion circuit 210 and PMOS current mirror. EA The magnitude of the error will automatically adjust the second error current I. EA The size of the fifth switch S5. The fifth switch S5 is on during the conduction phase of the first switch Q1 and the time when the inductor current demagnetization ends. The fourth switch S4 is on during the dead time T, from the demagnetization detection signal ZCOMP to the time when the first switch Q1 is turned on again. s The internal signal is set to 1 for conduction. The specific signal logic is as follows: Figure 8 As shown. In T on During the phase, Son equals 1 for conduction, and is 0 for the rest of the time, in T... dis During stage S2, the circuit is active at a value of 1; otherwise, it is active at a value of 0. (This is in the context of time T.) s During stage S3, the circuit is active at a value of 1, and at other times it is active at a value of 0.

[0105] When S5 is turned on, the positive terminal of the second comparator OP2 discharges. If the reference voltage of the second comparator OP2 is 4V, then:

[0106] 4-V X =(MI EA )*(Ton+Tdis);

[0107] When S4 is on, the positive terminal of the second comparator OP2 is charged. When the positive terminal voltage reaches 4V, S4 is turned off, thus: 4-V X =NI EA *TS;

[0108] That is, 4-V is obtained X =(MI EA )*(Ton+Tdis)=NI EA *TS;

[0109] Since the effective duty cycle Deff = (Ton + Tdis) / (Ton + Tdis + Ts), we can obtain:

[0110] Deff=(Ton+Tdis) / (Ton+Tdis+Ts)=NI EA / (NI EA +MI EA ) = N / (N+M);

[0111] Because of the DCM working mode In equilibrium, when the average output current is constant, V pk and I EA The circuit current is constant. If the output current is too high, V... pk Constant, V EA Increase the current I after conversion by the voltage-to-current conversion circuit and the PMOS current mirror. EA Increase, I EA Increasing the duty cycle (Deff) will decrease the effective duty cycle, thus reducing the output current. Similarly, when the output current is low, V... pk Constant, V EA The current I is reduced by the voltage-to-current conversion circuit and the PMOS current mirror. EA Decrease, I EA Decreasing it will increase the effective duty cycle Deff, thereby increasing the output current.

[0112] The present invention also proposes a switching power supply, which includes a BUCK circuit and the above-mentioned constant current circuit operating in DCM mode.

[0113] The input terminal of the BUCK circuit is used to connect to AC power. The BUCK circuit is electrically connected to the constant current circuit operating in DCM mode. The constant current circuit operating in DCM mode is used to collect the output current of the BUCK circuit and output a corresponding dead time adjustment signal to adjust the output current of the BUCK circuit to maintain a preset current value. The specific structure of the constant current circuit operating in DCM mode is as described in the above embodiments. Since this switching power supply adopts all the technical solutions of all the above embodiments, it has at least all the beneficial effects brought by the technical solutions of the above embodiments, which will not be described in detail here.

[0114] The present invention also proposes a lighting device, including the above-described switching power supply and light-emitting component. The switching power supply is used to connect to AC power, and the light-emitting component is electrically connected to the switching power supply. The specific structure of the switching power supply is as described in the above embodiments. Since the lighting device adopts all the technical solutions of all the above embodiments, it has at least all the beneficial effects brought about by the technical solutions of the above embodiments, which will not be described in detail here.

[0115] The above description is merely an optional embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made using the contents of the present invention's specification and drawings under the inventive concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A constant current circuit operating in DCM mode, applied to a switching power supply, characterized in that, The switching power supply includes an inductor, a first switching transistor, and a driving module. The inductor and the first switching transistor are connected in series between the DC power supply and ground. The driving module is connected to the controlled terminal of the first switching transistor. The constant current circuit operating in DCM mode includes: An error sampling circuit has its first input terminal connected to the output terminal of the switching transistor, and its second input terminal connected to a reference power supply. It is used to collect the average current flowing through the inductor and output a corresponding error detection signal based on the deviation between the average current and the reference power supply. An effective duty cycle modulation circuit has a first sampling terminal connected to the output terminal of the error sampling circuit, a second sampling terminal for electrical connection to the first switching transistor, and an output terminal for connection to the driving module. The effective duty cycle modulation circuit is also used to control the driving module to adjust the dead time of the first switching transistor according to the received error detection signal when the first switching transistor enters the dead time period based on the detected operating parameters of the first switching transistor, so as to keep the average current flowing through the inductor at a preset current value. The effective duty cycle modulation circuit includes: A signal conversion circuit, whose input terminal is connected to the output terminal of the error sampling circuit, is used to process the incoming error detection signal and output a corresponding second error current. A demagnetization detection circuit, whose input terminal is connected to the controlled terminal of the first switching transistor, is used to output a corresponding demagnetization detection signal when the demagnetization of the inductor is detected to be complete based on the controlled terminal voltage of the first switching transistor. The dead time adjustment circuit has a first input terminal electrically connected to the signal conversion circuit and a second input terminal connected to the output terminal of the signal conversion circuit. It is used to mirror the input second error current, and when the first switch is in the on or off period and the dead time adjustment circuit does not receive the demagnetization detection signal, it discharges according to the second error current. When the demagnetization detection signal is received, it stores the mirrored second error current again. The second comparator has its non-inverting input connected to the output of the dead time adjustment circuit, its inverting input connected to the second reference voltage, and its output connected to the drive module. The second comparator is also used to control the drive module to turn on the first switch when it detects that the terminal voltage of the dead time adjustment circuit reaches the second reference voltage. The dead time adjustment circuit includes: A current mirror group is electrically connected to the output terminal of the signal conversion circuit and is used to mirror the second error current and output the corresponding mirror current. The second capacitor is connected to the non-inverting input of the second comparator and is used to output the corresponding voltage value according to the currently stored electrical energy. A charge / discharge control circuit is provided, which is connected to a constant current power supply and is connected to the current mirror group, the second capacitor and the demagnetization detection circuit respectively. The charge / discharge control circuit is used to charge / discharge the second capacitor according to whether a demagnetization detection signal is received.

2. The constant current circuit operating in DCM mode as described in claim 1, characterized in that, The first switching transistor has a conduction period, a turn-off period, and a dead time period during operation. The error sampling circuit is specifically used to collect the detection voltage corresponding to the current flowing through the inductor when the first switching transistor is in the conduction period, to collect the leakage voltage corresponding to the leakage of the inductor when the first switching transistor is in the turn-off period, and to collect the 0 voltage corresponding to the demagnetization of the inductor when the first switching transistor is in the dead time period. The circuit detects the average current flowing through the inductor based on the current flowing through the inductor, the leakage voltage, and the 0 voltage.

3. The constant current circuit operating in DCM mode as described in claim 2, characterized in that, The error sampling circuit includes: A current sampling resistor is connected in series between the output terminal of the switching transistor and ground to output the corresponding sampling voltage. A switch group, wherein the first input terminal of the switch group is used to connect to the bleed voltage, the second input terminal of the switch group is connected to the current sampling resistor, and the third input terminal of the switch group is grounded, and the switch group is used to output a corresponding current sampling signal according to the connected bleed voltage, the sampling voltage and the 0 voltage; A transconductance amplifier, wherein the positive input terminal of the transconductance amplifier is connected to the output terminal of the switch group, and the negative input terminal of the transconductance amplifier is used to connect to a first reference voltage, and is used to compare the received detection voltage with the first reference voltage and output the corresponding error current; An integrator, the input of which is connected to the output of the transconductance amplifier, and the output of which is connected to the input of the effective duty cycle modulation circuit, is used to integrate the error current output by the transconductance amplifier and output an error detection signal with a corresponding voltage value.

4. The constant current circuit operating in DCM mode as described in claim 3, characterized in that, The first switching transistor has an on period, an off period, and a dead period when it is working, and the switch group includes a first switch, a second switch, and a third switch; The first terminal of the first switch is used to connect to the bleed voltage, the first terminal of the second switch is electrically connected to the current sampling resistor, the second terminals of the first switch, the second terminal of the second switch, and the first terminal of the third switch are respectively connected to the non-inverting input terminal of the transconductance amplifier, and the second terminal of the third switch is grounded. When the first switch is in the conducting period, the first switch is turned on, and the second switch and the third switch are closed; When the first switch is in the off period, the second switch is turned on, and the first switch and the third switch are closed; Furthermore, when the first switch is in a dead time period, the third switch is turned on, and the second switch and the first switch are closed.

5. The constant current circuit operating in DCM mode as described in claim 3, characterized in that, The constant current circuit operating in DCM mode includes: A bleed voltage generating circuit is provided, wherein the input terminal of the bleed voltage generating circuit is electrically connected to the first switching transistor, and the output terminal of the bleed voltage generating circuit is connected to the input terminal of the sampling circuit. The bleed voltage generating circuit is used to collect the current flowing through the inductor during the conduction period of the first switching transistor, and to process the collected current signal to output the corresponding bleed voltage during the turn-off period of the first switching transistor.

6. The constant current circuit operating in DCM mode as described in claim 5, characterized in that, The leakage voltage generating circuit includes a first resistor, a second resistor, a third resistor, a second switching transistor, a first comparator, and a first capacitor; The first end of the first resistor is connected to a DC power supply. The second end of the first resistor is connected to the drain of the second switching transistor. The controlled terminal of the second switching transistor is connected to the output terminal of the first comparator. The source of the second switching transistor is connected to the inverting input terminal of the first comparator and the first end of the second resistor. The second end of the second resistor is the output terminal of the bleed voltage generation circuit and is connected to the first end of the third resistor. The non-inverting input terminal of the first comparator is connected to a current sampling resistor and is connected to the first end of the first capacitor. The second end of the first capacitor, the second end of the third resistor, and the substrate pin of the first comparator are grounded.

7. A switching power supply, characterized in that, The switching power supply includes a BUCK circuit and a constant current circuit operating in DCM mode as described in claims 1-6; The input terminal of the BUCK circuit is used to connect to AC power. The BUCK circuit is electrically connected to the constant current circuit operating in DCM mode. The constant current circuit operating in DCM mode is used to collect the output current of the BUCK circuit and output a corresponding dead time adjustment signal so that the output current of the BUCK circuit is maintained at a preset current value.

8. A lighting device, characterized in that, It includes the switching power supply and light-emitting component as described in claim 7, wherein the switching power supply is used to connect to AC power, and the light-emitting component is electrically connected to the switching power supply.

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