High-precision constant current control circuit, switching power supply, and lighting device

Abstract

The application discloses a high-precision constant current control circuit, a switching power supply and a lighting device, wherein the high-precision constant current control circuit comprises an error sampling circuit, a first input end of the error sampling circuit being connected with an output end of a switching tube, a second input end of the error sampling circuit being used for connecting a first reference power supply, the error sampling circuit being used for collecting an average current flowing through the inductor and outputting a corresponding error detection signal according to a deviation between the average current and the first reference power supply; and a shutdown time length modulation circuit, the shutdown time length modulation circuit being used for adjusting a shutdown time length of the switching tube in each working period according to the error detection signal, so as to adjust the average current value flowing through the inductor to a preset current value; and the technical scheme is aimed at solving the problem that when the switching power supply is affected by input and output voltages, an output current fluctuates, and the constant current precision of the switching power supply is poor.

Description

Technical Field

[0001] This invention relates to the field of constant current dimming technology, and in particular to a high-precision constant current control circuit, a switching power supply, and a lighting device. Background Technology

[0002] Currently, the input voltage of switching power supplies is usually supplied by the AC mains, batteries, etc. These power supplies are often impure, which causes the voltage connected to the switching power supply to change greatly due to fluctuations in the power supply. This affects the output voltage of the switching power supply. In addition, when the load LED changes or when there is a disturbance inside the system, the system output voltage will also change accordingly and will not remain constant. This will cause fluctuations in the output current, resulting in poor constant current accuracy of the switching power supply. Summary of the Invention

[0003] The main objective of this invention is to provide a high-precision constant current control circuit, a switching power supply, and a lighting device, aiming to solve the problem that when the switching power supply is affected by the input and output voltages, the output current fluctuates, resulting in poor constant current accuracy of the switching power supply.

[0004] To achieve the above objectives, the present invention proposes a high-precision constant current control circuit for use in a switching power supply. The switching power supply includes an inductor, a switching transistor, and a driving module. The inductor and the switching transistor are connected in series between the DC power supply and ground. The driving module is connected to the controlled terminal of the switching transistor. The high-precision constant current control circuit 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 first 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 first reference power supply.

[0006] The off-duration modulation circuit has its first input terminal connected to the output terminal of the switching transistor, its third input terminal connected to the output terminal of the error sampling circuit, and its output terminal connected to the driving module. The off-duration modulation circuit is used to adjust the off-duration of the switching transistor in each working cycle according to the error detection signal, so as to adjust the average current value flowing through the inductor to a preset current value.

[0007] Optionally, the off-duration modulation circuit includes:

[0008] A voltage-to-current conversion circuit, whose input terminal is connected to the output terminal of the error sampling circuit, is used to process the input error detection signal into voltage and current and output the corresponding error current.

[0009] The regulating circuit has a first input terminal connected to the output terminal of the voltage-to-current conversion circuit, and a second input terminal for receiving a conduction control signal. The regulating circuit is used to discharge stored electrical energy when it receives the conduction control signal, and to charge according to the error current when it does not receive the conduction control signal.

[0010] The comparator has a positive input terminal for connecting to a first reference voltage and a negative input terminal for being electrically connected to the adjustment circuit. The comparator is also used to output a conduction trigger signal to the drive module when it detects that the terminal voltage of the adjustment circuit reaches the first reference voltage.

[0011] Optionally, the off-duration modulation circuit includes:

[0012] A current mirror is electrically connected to the output terminal of the voltage-to-current conversion circuit and is used to mirror the error current and output the corresponding mirror current.

[0013] The first capacitor is connected in series between the negative phase output terminal of the comparator and ground, and is used to store electrical energy when the error current is received, and to discharge electrical energy when the mirror current is not received.

[0014] A charge / discharge control circuit is provided, which is electrically connected to the current mirror, the first capacitor, and the comparator. Its controlled terminal is used to receive a conduction control signal. The charge / discharge control circuit is also used to control the first capacitor to discharge and ground the negative phase input terminal of the comparator when the conduction control signal is received, and to control the first capacitor to charge when the conduction control signal is not received.

[0015] Optionally, the adjustment circuit includes a first MOSFET and a second MOSFET;

[0016] The drain of the first MOSFET is connected to the output terminal of the current mirror. The gate of the first MOSFET is used to receive the turn-on control signal and is connected to the gate of the second MOSFET. The source of the first MOSFET is connected to the source of the second MOSFET, the first terminal of the first capacitor, and the negative input terminal of the comparator. The source of the second MOSFET is grounded.

[0017] Optionally, the first reference power supply specifically includes a second reference voltage, and the error sampling circuit includes:

[0018] A current sampling resistor is connected in series between the output terminal of the switching transistor and ground to output the corresponding sampling voltage.

[0019] A digital low-pass filter has its first input terminal electrically connected to the current sampling resistor, its second terminal connected to the second reference voltage, and its output terminal connected to the input terminal of the turn-off duration modulation circuit. The low-pass filter is used to compare the sampled voltage with the second reference voltage and output a corresponding error detection signal.

[0020] Optionally, the error detection signal is specifically an error voltage, and the digital low-pass filter includes:

[0021] The modulator has a first input terminal electrically connected to the current sampling resistor and a second input terminal for receiving the second reference voltage. The modulator is also used to perform signal processing on the second reference voltage and the sampling voltage, and output a corresponding error digital signal.

[0022] A counter, the input of which is connected to the output of the modulator, is used to count the received error digital signal and output the corresponding counting error digital signal.

[0023] The digital-to-analog converter module has its input terminal connected to the output terminal of the counter and its output terminal connected to the input terminal of the off-duration modulation circuit. It is used to perform digital-to-analog conversion processing on the input counting error digital signal and output the corresponding analog voltage value error detection signal.

[0024] Optionally, the high-precision constant current control circuit further includes:

[0025] A reference voltage modulation circuit is provided, wherein the input terminal of the reference voltage modulation circuit is used to connect to a constant voltage source, the controlled terminal of the reference voltage modulation circuit is used to connect to a voltage regulation control signal, the output terminal of the reference voltage modulation circuit is connected to the second input terminal of the error sampling circuit, and the reference voltage modulation circuit is used to perform signal processing on the first reference power supply according to the received voltage regulation control signal to output a first reference power supply with a corresponding voltage value.

[0026] Optionally, the high-precision constant current control circuit further includes:

[0027] The current peak control circuit has a first input terminal connected to the output terminal of the switching transistor, a second input terminal for connecting to a second reference power supply, and an output terminal electrically connected to the drive module. The current peak control circuit is also used to collect the current flowing through the inductor and output a shutdown control signal when the current flowing through the inductor is greater than the current value represented by the second reference power supply.

[0028] The present invention also proposes a switching power supply, which includes a BUCK circuit and the high-precision constant current control circuit described above.

[0029] The BUCK circuit is used to connect to AC power and is electrically connected to the high-precision constant current control circuit; it is used to output a stable constant current source under the control of the high-precision constant current control circuit.

[0030] The present invention also proposes a lighting device, including an LED and the aforementioned switching power supply.

[0031] The technical solution of this invention sets up a turn-off duration modulation circuit. When the output voltage of the switching power supply changes, it outputs a corresponding turn-off duration adjustment signal based on the received error detection signal. The drive module controls the turn-off duration of the switching transistor in the current working cycle and subsequent working cycles. By adjusting the dead time, the product of the output voltage and the dead time remains constant, so that the peak-to-valley difference of the inductor current remains constant, thereby keeping the average current flowing through the inductor constant, that is, keeping the output current of the switching power supply constant. Therefore, it avoids the problem of poor constant current accuracy of the switching power supply caused by output voltage fluctuations. Attached Figure Description

[0032] 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.

[0033] Figure 1 This is a schematic diagram of an embodiment of the high-precision constant current control circuit of the present invention;

[0034] Figure 2 This is a schematic diagram of another embodiment of the high-precision constant current control circuit of the present invention;

[0035] Figure 3 This is a schematic diagram of another embodiment of the high-precision constant current control circuit of the present invention;

[0036] Figure 4 This is a schematic diagram of another embodiment of the high-precision constant current control circuit of the present invention;

[0037] Figure 5 This is a schematic diagram of another embodiment of the high-precision constant current control circuit of the present invention;

[0038] Figure 6 This is a schematic diagram of yet another embodiment of the high-precision constant current control circuit of the present invention;

[0039] Figure 7 This is a current waveform diagram of the high-precision constant current control circuit of the present invention.

[0040] Explanation of icon numbers:

[0041]

[0042]

[0043] 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

[0044] 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.

[0045] 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.

[0046] This invention proposes a high-precision constant current control circuit for use in switching power supplies.

[0047] Reference Figure 1 In one embodiment, the switching power supply includes an inductor, a switching transistor, and a driving module. The inductor and the switching transistor are connected in series between the DC power supply and ground. The driving module is connected to the controlled terminal of the switching transistor M. The high-precision constant current control circuit includes:

[0048] The error sampling circuit 100 has its first input terminal connected to the output terminal of the switching transistor M, its second input terminal connected to the first reference power supply, and outputs a corresponding error detection signal based on the deviation between the average current and the first reference power supply.

[0049] The off-duration modulation circuit 200 has its first input terminal connected to the output terminal of the switching transistor M, its third input terminal connected to the output terminal of the error sampling circuit 100, and its output terminal used to connect to the driving module. The off-duration modulation circuit 200 is also used to adjust the off-duration of the switching transistor M in each working cycle according to the error detection signal, so as to adjust the average current value flowing through the inductor to a preset current value.

[0050] Understandably, existing switching power supplies, during normal operation, perform PWM chopping on the input DC power according to the needs of the electrical equipment, adjusting the output current by regulating the duty cycle of the PWM signal. The output current of the switching power supply can be determined using the formula... (I average I is the average current flowing through the inductor, which is also the actual output current of the switching power supply. pk ΔI is the peak current flowing through the inductor. L (The peak-to-valley difference of the inductor current) indicates that at the peak current I pk When fixed, when the peak-to-valley difference ΔI of the inductor current L To maintain stability, thereby ensuring the output current I of the switching power supply average Constant. Specifically, a peak current control circuit is installed inside the switching power supply. During normal operation, once the current flowing through the inductor reaches a preset peak value, the switching transistor M is turned off, stopping the current flowing through the inductor from rising. Therefore, the peak current flowing through the inductor remains constant, i.e., I. pk Since this is a constant, it can be concluded that the average current flowing through the inductor is only related to the peak-to-valley difference ΔI of the inductor current. L related.

[0051] Among them, the peak-to-valley difference of inductor current ΔI L According to the formula (V IN V is the input voltage of the switching power supply. OUT Where L is the output voltage of the switching power supply, and T is the inductance value of the inductor. ON For the conduction time, T OFF (Assuming the turn-off time is used), when the input and output voltages are stable, fixing the on-time or off-time can effectively minimize the peak-to-valley difference ΔI in the inductor current. L The output current I of the switching power supply remains constant, thus maintaining the constant output current I. average Constant.

[0052] In this embodiment, the error sampling circuit 100 includes two parts: sampling and error detection. Sampling can use a current sampling resistor, and error detection can use a transconductance amplifier 120, a comparator 230, or other operational amplifier devices. The error sampling circuit 100 obtains the average current during the conduction period of the switching transistor M by collecting and integrating the current during the conduction period of the current operating cycle. Figure 7 As shown, when the switching power supply is operating in CCM mode, the average current during its conduction period is the same as the average current during its turn-off period. Therefore, by obtaining the average current during the conduction period of this working cycle, the average current of this working cycle can be obtained, thereby obtaining the corresponding error value based on the first reference power supply, and outputting an error detection signal characterizing this error value; the turn-off duration modulation circuit 200 can be a composite circuit composed of multiple MOSFETs, capacitors and other devices.

[0053] It should be noted that the input voltage of a switching power supply is usually supplied by the AC mains, battery, etc., which are often impure. This causes the voltage connected to the switching power supply to fluctuate significantly due to power supply fluctuations, affecting the output voltage of the switching power supply. Furthermore, when the load LED changes or internal disturbances occur in the system, the system output voltage will also change accordingly. When the output voltage of the switching power supply changes, if the turn-off time T of the switching transistor M... OFF Keeping it constant will result in a peak-to-valley difference ΔI in the inductor current. L The changes were affected and occurred in I pk Assuming the value is constant, since This makes the output current I of the switching power supply average It was affected.

[0054] To prevent the output current of the switching power supply from being affected by the output voltage V of the switching power supply OUT Fluctuations due to changes require the output voltage V to be adjusted. OUT When the time T changes, the turn-off time T of the switching transistor M is adjusted. OFF To make adaptive adjustments, this invention includes a shutdown duration modulation circuit 200, which modulates the output voltage V of the switching power supply. OUT When a change occurs, based on the received error detection signal, a corresponding off-time adjustment signal is output. This signal, via the drive module, controls the off-time of the switching transistor M during the current and subsequent working cycles. Thus, by adjusting the off-time, V is maintained. OUT With T OFF The product of these two constants remains constant, causing the peak-to-valley difference ΔI in the inductor current to remain constant. L Keep it constant, and thus keep the average current I flowing through the inductor constant. averageThis means that the output current of the switching power supply remains constant. Therefore, by adjusting the turn-off time of the switching transistor M through the turn-off time modulation circuit 200, the problem of poor constant current accuracy of the switching power supply caused by output voltage fluctuations can be avoided.

[0055] When the constant current circuit is operating normally, the error sampling circuit 100 collects the average current flowing through it during the conduction period. If the output voltage fluctuates due to power supply fluctuations or sudden changes in the internal resistance of the load device, the error sampling circuit 100 detects that the average current during the conduction period will also change, and outputs a corresponding error detection signal to the turn-off time control circuit 200. The turn-off duration modulation circuit 200 determines the error between the average current during the conduction period and the first reference power supply based on the error detection signal, and outputs a corresponding turn-off duration adjustment signal based on the error, so as to maintain V by adjusting the turn-off duration of the switching transistor M. OUT With T OFF The product remains unchanged.

[0056] For example, when the shutdown duration modulation circuit 200 determines that the average current is too high based on the error detection signal, it indicates that the output voltage V is at this time. OUT Due to fluctuations, the off-time modulation circuit 200 outputs an off-time adjustment signal representing an extension of the off-time to the drive circuit, so that the drive circuit increases the off-time T of the switch M in each operating cycle. OFF To maintain the output voltage V OUT With shutdown duration T OFF The product remains unchanged, thus 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 turn-off duration modulation circuit 200 outputs a turn-off duration adjustment signal representing a shortened turn-off duration to the drive circuit, so that the drive circuit reduces the turn-off duration T of the switching transistor M in each operating cycle. OFF To maintain the output voltage V OUT With shutdown duration T OFF The product remains constant, increasing the output current. By fixing V... OUT With T OFF The product of and thus fixes ΔI. L This improves current accuracy.

[0057] This invention modulates the off-time by setting a circuit 200, which modulates the output voltage V of the switching power supply. OUT When changes occur, based on the received error detection signal, a corresponding shutdown duration adjustment signal is output. This signal, via the drive module, controls the shutdown duration of the switching transistor M in the current and subsequent working cycles. By adjusting the dead time, V is maintained. OUT With T OFFThe product remains constant, thus controlling the peak-to-valley difference ΔI in the inductor current. L Keep the average current I flowing through the inductor constant. averape The constant current means that the output current of the switching power supply remains constant, thus avoiding the problem of poor constant current accuracy caused by fluctuations in the output current due to fluctuations in the output voltage.

[0058] Reference Figures 1 to 2 In one embodiment, the off-duration modulation circuit 200 includes:

[0059] The voltage-to-current conversion circuit 210 has its input terminal connected to the output terminal of the error sampling circuit 100, and is used to perform voltage-to-current processing on the input error detection signal and output the corresponding error current.

[0060] The regulating circuit 220 has its first input terminal connected to the output terminal of the voltage-to-current conversion circuit 210, and its second input terminal used to receive a conduction control signal. The regulating circuit 220 is used to discharge stored electrical energy when it receives the conduction control signal, and to charge according to the error current when it does not receive the conduction control signal.

[0061] The comparator 230 has a positive input terminal for connecting to a first reference voltage and a negative input terminal for being electrically connected to the first capacitor. The comparator 230 is also used to output a conduction trigger signal to the drive module when it detects that the terminal voltage of the adjustment circuit 220 reaches the first reference voltage.

[0062] In this embodiment, when the switching power supply is working normally, the error detection signal output by the error sampling circuit 100 is input to the voltage-to-current conversion circuit 210. Since the error detection signal is a voltage signal, after voltage-to-current conversion by the voltage-to-current conversion circuit 210, the corresponding error current can be output as the charging current of the adjustment circuit 220. The current value of the error current is positively correlated with the error represented by the error detection signal, and the magnitude of the error represented by the error detection signal will automatically adjust the magnitude of the error current.

[0063] When the regulating circuit 220 receives the conduction control signal, it indicates that the switching transistor M is in the conduction period. At this time, the regulating circuit 220 discharges the stored electrical energy and controls the negative input terminal of the comparator 230 to be grounded, so that the terminal voltage of the negative input terminal of the comparator 230 is always lower than the terminal voltage of the positive input terminal of the comparator 230, and outputs 1. It should be noted that the comparator 230 is only valid when its output is 0. That is to say, when the output of the comparator 230 is 1, it will not have any impact on the current working state of the switching transistor M.

[0064] When the regulating circuit 220 stops receiving the turn-on control signal, it indicates that the switching transistor M has entered the turn-off period and begins to store the received error current. During this process, the voltage at the negative input terminal of the comparator 230 is lower than the voltage at the positive input terminal of the comparator 230, and the output is still 1, keeping the switching transistor M in the off state until the voltage value output by the regulating circuit 220 reaches the first reference voltage again. When the voltage at the negative input terminal of the comparator 230 reaches the voltage at the positive input terminal of the comparator 230, the output is a 0 signal representing the turn-on trigger signal, triggering the power transistor to turn on again, completing one cycle of power transistor control.

[0065] Reference Figures 1 to 6 In one embodiment, the adjustment circuit 220 includes:

[0066] A current mirror is electrically connected to the output terminal of the voltage-to-current conversion circuit 210, and is used to mirror the error current and output the corresponding mirror current.

[0067] The first capacitor is connected in series between the negative output terminal of the comparator 230 and ground, and is used to store electrical energy when the mirror current is received, and to discharge electrical energy when the mirror current is not received.

[0068] A charge / discharge control circuit is provided, which is electrically connected to the current mirror, the first capacitor, and the comparator 230. Its controlled terminal is used to receive a conduction control signal. The charge / discharge control circuit is also used to control the first capacitor to discharge and ground the negative phase input terminal of the comparator 230 when the conduction control signal is received, and to control the first capacitor to charge when the conduction control signal is not received.

[0069] In this embodiment, when the switching power supply is operating normally, the error current output by the voltage-to-current conversion circuit 210 is received by the current mirror and mirrored. According to the design requirements, the error current is replicated in a 1:N ratio, where N is a non-zero positive number. The current mirror outputs the mirrored error current as the charging current.

[0070] When the switching transistor M is in the on-time period, the charge-discharge control circuit receives the on-time control signal. At this time, the charge-discharge control circuit disconnects the connection between the output terminal of the current mirror and the first capacitor, and grounds the negative input terminal of the comparator 230. The voltage at the negative input terminal of the comparator 230 is always lower than the voltage at the positive input terminal of the comparator 230, and outputs 1. When the switching transistor M begins to enter the off-time period, the charge-discharge control circuit stops receiving the on-time control signal, connects the output terminal of the current mirror to the first capacitor, so that the first capacitor begins to store energy from the received mirror current until the voltage value of the first capacitor reaches the first reference voltage again, and the voltage at the negative input terminal of the comparator 230 reaches the voltage at the positive input terminal of the comparator 230. The circuit outputs a 0 signal representing the on-time trigger signal, triggering the power transistor to turn on again, completing one cycle of power transistor control.

[0071] Reference Figures 1 to 6 In one embodiment, the adjustment circuit 220 includes a first MOSFET Q1 and a second MOSFET Q2;

[0072] The drain of the first MOSFET Q1 is connected to the output terminal of the current mirror. The gate of the first MOSFET Q1 is used to receive the turn-on control signal and is connected to the gate of the second MOSFET Q2. The source of the first MOSFET Q1 is connected to the source of the second MOSFET Q2, the first terminal of the first capacitor C1, and the negative input terminal of the comparator 230. The source of the second MOSFET Q2 is grounded.

[0073] In this embodiment, the first MOS transistor Q1 is a PMOS transistor, and the second MOS transistor Q2 is an NMOS transistor.

[0074] When switch M is in the on-time period, the gates of the first MOSFET Q1 and the second MOSFET Q2 receive a high-level turn-on control signal. At this time, the first MOSFET Q1 is turned off, and the second MOSFET Q2 is turned on, disconnecting the output terminal of the current mirror from the first capacitor and grounding the negative input terminal of the comparator 230. When switch M begins to enter the off-time period, the gates of the first MOSFET Q1 and the second MOSFET Q2 receive a low-level signal. At this time, the first MOSFET Q1 is turned on, and the second MOSFET is turned off, connecting the output terminal of the current mirror to the first capacitor C1, and disconnecting the negative input terminal of the comparator 230 from ground.

[0075] It should be noted that when a switching power supply is used for constant current dimming, fluctuations in the output voltage can cause noticeable flickering in the LEDs, a phenomenon known as stroboscopic flicker. Existing solutions typically use RC filter circuits to filter out voltage fluctuations. However, because the ripple interference frequency generated by the AC mains is generally very low when the switching power supply is connected to an AC power source, ranging from a few Hz to tens of Hz, ordinary filters cannot effectively filter out the interference signal, resulting in stroboscopic flickering in the circuit's output current.

[0076] Reference Figures 1 to 3 In one embodiment, the first reference power supply specifically includes a second reference voltage, and the error sampling circuit 100 includes:

[0077] A current sampling resistor is connected in series between the output terminal of the switching transistor M and ground to output the corresponding sampling voltage.

[0078] A digital low-pass filter 110 has its first input terminal electrically connected to the current sampling resistor, its second terminal connected to the second reference voltage, and its output terminal connected to the input terminal of the turn-off duration modulation circuit 200. The low-pass filter is used to compare the sampled voltage with the second reference voltage and output a corresponding error detection signal.

[0079] In this embodiment, the filtering frequency band of the digital low-pass filter 110 is below 50 Hz, which can effectively filter out low-frequency interference carried by the AC power grid.

[0080] Specifically, when the switching transistor M is turned on, the current flowing through the inductor is output to the current sampling resistor via the switching transistor M. The current sampling resistor converts the received current into a sampled voltage output. The digital low-pass filter 110 performs low-pass filtering on the received sampled voltage and then integrates it to obtain the voltage signal corresponding to the average current. The voltage signal is then compared with the second reference voltage to obtain the error voltage between the two, which is output as the corresponding error detection signal to the turn-off duration modulation circuit 200.

[0081] Reference Figures 1 to 4 In one embodiment, the error detection signal is specifically an error voltage, and the digital low-pass filter 110 includes:

[0082] The modulator 111 has a first input terminal electrically connected to the current sampling resistor, and a second input terminal used to connect to the second reference voltage. The modulator 111 is also used to perform signal processing on the second reference voltage and the sampling voltage, and output a corresponding error digital signal.

[0083] Counter 112, whose input terminal is connected to the output terminal of modulator 111, is used to count the received error digital signal and output the corresponding counting error digital signal;

[0084] The digital-to-analog converter module 113 has its input terminal connected to the output terminal of the counter 112 and its output terminal connected to the input terminal of the off-duration modulation circuit 200. It is used to perform digital-to-analog conversion processing on the input counting error digital signal and output the corresponding analog voltage value error detection signal.

[0085] In this embodiment, the modulator 111 processes the sampled signal Vcs and the second reference voltage to obtain PDM code (pulse density modulation). The counter counts the PDM code sampled multiple times and takes the average value as the current valid value. Finally, the value of the counter 112 is converted into an error detection signal represented by an analog error voltage by the digital-to-analog converter module 113. When the digital low-pass filter 110 is working, it can effectively overcome the fluctuation interference caused by random factors by taking the average value of multiple samples, and realize the filtering function of the measured parameters such as temperature and liquid level that change slowly. Thus, the output current is not affected by the input power frequency ripple and PWM signal ripple, solving the flicker problem and improving the constant current accuracy.

[0086] Reference Figures 1 to 4 In one embodiment, the high-precision constant current control circuit further includes:

[0087] A reference voltage modulation circuit 300 is provided, wherein the input terminal of the reference voltage modulation circuit 300 is used to connect to a constant voltage source, the controlled terminal of the reference voltage modulation circuit 300 is used to connect to a voltage regulation control signal, and the output terminal of the reference voltage modulation circuit 300 is connected to the second input terminal of the error sampling circuit 100. The reference voltage modulation circuit 300 is used to process the constant voltage source according to the received voltage regulation control signal to output a first reference power supply with a corresponding voltage value.

[0088] In this embodiment, the reference voltage modulation circuit 300 may include switching devices such as switching transistors and power transistors.

[0089] When the output voltage of the switching power supply is controlled by interactive components such as buttons, the reference voltage modulation circuit 300 receives the corresponding voltage regulation signal. By performing PWM chopping on the constant voltage source, the constant voltage source is processed into a first reference voltage output with different voltage values ​​according to the different duty cycles represented by the voltage regulation signal.

[0090] Reference Figures 1 to 5 In one embodiment, the high-precision constant current control circuit further includes:

[0091] The current peak control circuit 400 has a first input terminal connected to the output terminal of the switching transistor M, a second input terminal for connecting to a second reference power supply, and an output terminal electrically connected to the drive module. The current peak control circuit 400 is also used to collect the current flowing through the inductor and output a shutdown control signal when the current flowing through the inductor is greater than the current value represented by the second reference power supply.

[0092] In this embodiment, the current peak control circuit 400 can be a comparator 230, or a differential circuit or other circuit with comparison function.

[0093] When the switching power supply is operating normally, if the switching transistor M is in the on-state, the inductor current rises linearly. The current peak control circuit 400 begins to collect the current flowing through the inductor. Once it detects that the current flowing through the inductor has reached a preset peak value, it controls the switching transistor M to turn off, thus stopping the current flowing through the inductor from rising. Therefore, the peak value of the current flowing through the inductor is always a constant, i.e., I. pk It is a constant value.

[0094] This invention also proposes a switching power supply, including a BUCK circuit and the aforementioned high-precision constant current control circuit; the BUCK circuit is used to connect to AC power, and the BUCK circuit is electrically connected to the high-precision constant current control circuit; it is used to output a stable constant current source under the control of the high-precision constant current control circuit. The specific structure of the high-precision constant current control circuit 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 about by the technical solutions of the above embodiments, which will not be elaborated here.

[0095] The present invention also proposes a lighting device, including an LED and the aforementioned switching power supply. The specific structure of the switching power supply is as described in the above embodiments. Since this lighting device adopts all the technical solutions of all the above embodiments, it possesses at least all the beneficial effects brought about by the technical solutions of the above embodiments, which will not be elaborated upon here.

[0096] The above description is merely an optional embodiment of the present invention and does not limit the patent scope of the present invention. All 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 high-precision constant current control circuit, applied to a switching power supply, characterized in that, The switching power supply includes an inductor, a switching transistor, and a driving module. The inductor and the switching transistor are connected in series between the DC power supply and ground. The driving module is connected to the controlled terminal of the switching transistor. The high-precision constant current control circuit 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 first 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 first reference power supply. The off-duration modulation circuit has its first input terminal connected to the output terminal of the switching transistor, its third input terminal connected to the output terminal of the error sampling circuit, and its output terminal connected to the driving module. The off-duration modulation circuit is used to adjust the off-duration of the switching transistor in each working cycle according to the error detection signal, so as to adjust the average current value flowing through the inductor to a preset current value. The first reference power supply specifically includes a second reference voltage, and 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 digital low-pass filter has its first input terminal electrically connected to the current sampling resistor, its second terminal connected to the second reference voltage, and its output terminal connected to the input terminal of the turn-off duration modulation circuit. The low-pass filter is used to compare the sampled voltage with the second reference voltage and output a corresponding error detection signal. The error detection signal is specifically an error voltage, and the digital low-pass filter includes: The modulator has a first input terminal electrically connected to the current sampling resistor and a second input terminal for receiving the second reference voltage. The modulator is also used to perform signal processing on the second reference voltage and the sampling voltage, and output a corresponding error digital signal. A counter, the input of which is connected to the output of the modulator, is used to count the received error digital signal and output the corresponding count error digital signal. The digital-to-analog converter module has its input terminal connected to the output terminal of the counter and its output terminal connected to the input terminal of the off-duration modulation circuit. It is used to perform digital-to-analog conversion processing on the input counting error digital signal and output the corresponding analog voltage value error detection signal.

2. The high-precision constant current control circuit as described in claim 1, characterized in that, The off-duration modulation circuit includes: A voltage-to-current 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 into voltage and current and output the corresponding error current. The regulating circuit has a first input terminal connected to the output terminal of the voltage-to-current conversion circuit, and a second input terminal for receiving a conduction control signal. The regulating circuit is used to discharge stored electrical energy when it receives the conduction control signal, and to charge according to the error current when it does not receive the conduction control signal. The comparator has a positive input terminal for connecting to a first reference voltage and a negative input terminal for being electrically connected to the adjustment circuit. The comparator is also used to output a conduction trigger signal to the drive module when it detects that the terminal voltage of the adjustment circuit has reached the first reference voltage.

3. The high-precision constant current control circuit as described in claim 2, characterized in that, The regulating circuit includes: A current mirror is electrically connected to the output terminal of the voltage-to-current conversion circuit and is used to mirror the error current and output the corresponding mirror current. The first capacitor is connected in series between the negative phase output terminal of the comparator and ground, and is used to store electrical energy when the error current is received, and to discharge electrical energy when the mirror current is not received. A charge / discharge control circuit is provided, which is electrically connected to the current mirror, the first capacitor, and the comparator. Its controlled terminal is used to receive a conduction control signal. The charge / discharge control circuit is also used to control the first capacitor to discharge and ground the negative phase input terminal of the comparator when the conduction control signal is received, and to control the first capacitor to charge when the conduction control signal is not received.

4. The high-precision constant current control circuit as described in claim 3, characterized in that, The charge / discharge control circuit includes a first MOSFET and a second MOSFET; The drain of the first MOSFET is connected to the output terminal of the current mirror. The gate of the first MOSFET is used to receive the turn-on control signal and is connected to the gate of the second MOSFET. The source of the first MOSFET is connected to the source of the second MOSFET, the first terminal of the first capacitor, and the negative input terminal of the comparator. The source of the second MOSFET is grounded.

5. The high-precision constant current control circuit as described in claim 1, characterized in that, The high-precision constant current control circuit also includes: A reference voltage modulation circuit is provided, wherein the input terminal of the reference voltage modulation circuit is used to connect to a constant voltage source, the controlled terminal of the reference voltage modulation circuit is used to connect to a voltage regulation control signal, the output terminal of the reference voltage modulation circuit is connected to the second input terminal of the error sampling circuit, and the reference voltage modulation circuit is used to perform signal processing on the first reference power supply according to the received voltage regulation control signal to output a first reference power supply with a corresponding voltage value.

6. The high-precision constant current control circuit as described in claim 1, characterized in that, The high-precision constant current control circuit also includes: The current peak control circuit has a first input terminal connected to the output terminal of the switching transistor, a second input terminal for connecting to a second reference power supply, and an output terminal electrically connected to the drive module. The current peak control circuit is also used to collect the current flowing through the inductor and output a shutdown control signal when the current flowing through the inductor is greater than the current value represented by the second reference power supply.

7. A switching power supply, characterized in that, The switching power supply includes a BUCK circuit and a high-precision constant current control circuit as described in claims 1-6; The BUCK circuit is used to connect to AC power and is electrically connected to the high-precision constant current control circuit; it is used to output a stable constant current source under the control of the high-precision constant current control circuit.

8. A lighting device, characterized in that, Includes LEDs and the switching power supply as described in claim 7.

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