Constant current control circuit, system and method

Abstract

The present invention provides a constant current control circuit, system, and method, including: a sampling feedback module that generates a sampling feedback voltage; a reference module; an analog dimming module that generates a floating upper reference and a floating lower reference; when the analog dimming signal is less than the analog dimming upper limit reference, the floating upper reference and the floating lower reference are respectively proportional to the analog dimming signal; when the analog dimming signal is greater than or equal to the analog dimming upper limit reference, the floating upper reference is set to the maximum upper reference threshold, and the floating lower reference is set to the maximum lower reference threshold; a comparison module that compares the floating upper reference or the floating lower reference with the comparison sampling feedback voltage; and a logic drive module that generates a discontinuous conduction mode drive control signal when the analog dimming signal is less than a preset value; and generates a continuous conduction mode drive control signal when the analog dimming signal is greater than or equal to the preset value. The present invention has a maximum adjustable range, which greatly meets the customer's demand for a wider analog dimming range.

Description

Technical Field

[0001] The present invention relates to the field of integrated circuits, and in particular to a constant current control circuit, system and method. Background Art

[0002] In the low-end sampling circuit of a constant current control system, the source terminal of the power device is grounded through a sampling resistor. This causes voltage fluctuations at the source terminal of the power device, which can cause large errors in the input sampling feedback signal. However, the high-end sampling circuit does not affect the operating state of the power device, and the output current is more accurate.

[0003] Traditional constant current control systems using high-end sampling require continuous conduction mode to ensure output accuracy. Reducing the voltage on the analog dimming pin can reduce the system's output inductor current. However, due to the system's requirement to operate in continuous conduction mode, the minimum adjustable inductor current is not a sufficiently small percentage of the maximum inductor current, resulting in a narrow adjustable range and unable to meet the wider dimming range requirements of demanding customers.

[0004] Therefore, how to meet the demand for a wider dimming range has become one of the problems that those skilled in the art need to solve urgently. Summary of the Invention

[0005] In view of the above-mentioned shortcomings of the prior art, an object of the present invention is to provide a constant current control circuit, system and method for solving the problem of narrow dimming range in the prior art.

[0006] To achieve the above-mentioned and other related objectives, the present invention provides a constant current control circuit, which comprises at least:

[0007] The sampling feedback module obtains the sampling signal of the output current and converts it into a sampling feedback voltage;

[0008] A reference module is used to provide a maximum upper reference threshold, a maximum lower reference threshold and an upper limit reference for analog dimming;

[0009] an analog dimming module connected to the output terminal of the reference module and receiving an analog dimming signal, for generating a floating upper reference and a floating lower reference; when the analog dimming signal is less than the analog dimming upper limit reference, the floating upper reference and the floating lower reference are respectively proportional to the analog dimming signal; when the analog dimming signal is greater than or equal to the analog dimming upper limit reference, the floating upper reference is set to a maximum upper reference threshold, and the floating lower reference is set to a maximum lower reference threshold;

[0010] a comparison module, wherein a first input end is connected to the sampling feedback module and is configured to receive the sampled feedback voltage, and a second input end is configured to receive the floating upper reference and the floating lower reference output by the analog dimming module through switch switching, respectively. The comparison module compares the sampled feedback voltage with the floating upper reference and the floating lower reference, respectively, and outputs a comparison result;

[0011] a logic driving module connected to the output end of the comparison module, and generating a driving control signal for the discontinuous conduction mode based on the comparison result when the analog dimming signal is less than a preset value; and generating a driving control signal for the continuous conduction mode based on the comparison result when the analog dimming signal is greater than or equal to the preset value.

[0012] Optionally, the sampling feedback module includes a transconductance operational amplifier and a first resistor; the input end of the transconductance operational amplifier is connected to both ends of an external output current sampling resistor; one end of the first resistor is connected to the output end of the transconductance operational amplifier, and the other end is grounded.

[0013] Optionally, the analog dimming module includes an operational amplifier, a transistor unit, a second resistor, a third resistor, a fourth resistor, a control unit, a first selection unit, and a second selection unit;

[0014] The transistor unit, the second resistor, the third resistor and the fourth resistor are sequentially connected in series between a power source and a ground;

[0015] The operational amplifier has a non-inverting input terminal receiving the analog dimming signal, an inverting input terminal connected to a connection node between the transistor unit and the second resistor, and an output terminal connected to a control terminal of the transistor unit;

[0016] The control unit has a first input terminal connected to a connection node between the transistor unit and the second resistor, a second input terminal receiving the analog dimming upper limit reference, compares a voltage of the connection node with the analog dimming upper limit reference, and outputs a control signal based on the comparison result;

[0017] The first input terminal of the first selection unit is connected to the connection node between the second resistor and the third resistor, the second input terminal receives the maximum upper reference threshold, and the control terminal is connected to the output terminal of the control unit to output the floating upper reference;

[0018] The first input terminal of the second selection unit is connected to the connection node of the third resistor and the fourth resistor, the second input terminal receives the maximum lower reference threshold, and the control terminal is connected to the output terminal of the control unit; and outputs the floating lower reference.

[0019] Optionally, the logic drive module includes a turn-off time setting unit and a drive unit; the turn-off time setting unit receives the comparison result, and sets the turn-off time of the power switch tube based on the analog dimming signal when the power switch tube is in the turn-off state; the drive unit generates a drive control signal based on the comparison result.

[0020] More optionally, the off-time setting unit includes a current source, a charging unit and a Schmitt trigger; the current source is controlled by the analog dimming signal to generate a charging current; the charging unit is connected to the output end of the current source and charges based on the charging current; the input end of the Schmitt trigger is connected to the output end of the charging unit, and the control end is connected to the comparison result. When the power switch tube is in the off state and the voltage in the charging unit is greater than the set value, the off state is ended.

[0021] To achieve the above-mentioned and other related purposes, the present invention provides a constant current control system, which comprises at least:

[0022] Constant current circuit and the above constant current control circuit;

[0023] The constant current circuit receives a control signal from the power switch tube so as to keep the current of the output load constant;

[0024] The constant current control circuit obtains a sampling feedback signal of the output current in the constant current circuit, and controls the on and off of the power switch tube in the constant current circuit based on the sampling feedback signal and the analog dimming signal to achieve constant current output of the constant current circuit.

[0025] More optionally, the sampling resistor in the constant current circuit is a high-end sampling structure.

[0026] To achieve the above-mentioned and other related purposes, the present invention provides a constant current control method, which at least includes:

[0027] Collect output current and convert it into sampling feedback signal;

[0028] generating a floating upper reference and a floating lower reference according to an analog dimming signal, wherein when the analog dimming signal is less than the analog dimming upper limit reference, the floating upper reference and the floating lower reference are respectively proportional to the analog dimming signal; and when the analog dimming signal is greater than or equal to the analog dimming upper limit reference, the floating upper reference is a maximum upper reference threshold, and the floating lower reference is a maximum lower reference threshold;

[0029] The sampled feedback signal is compared with the floating upper reference and the floating lower reference switched by the switch, and when the analog dimming signal is less than a preset value, a drive control signal of the discontinuous conduction mode is generated based on the comparison result; when the analog dimming signal is greater than or equal to the preset value, a drive control signal of the continuous conduction mode is generated based on the comparison result.

[0030] Optionally, when the analog dimming signal is less than the analog dimming upper limit reference, the floating upper reference is in a first positive proportional relationship with the analog dimming signal, and the floating lower reference is in a second positive proportional relationship with the analog dimming signal, wherein the first positive proportional coefficient is greater than the second positive proportional coefficient, and at the same time, it is ensured that the average value of the floating upper reference and the floating lower reference added changes linearly with the change of the analog dimming signal.

[0031] Optionally, when the power switch tube is turned on, the sampled feedback signal is compared with the floating upper reference; when the power switch tube is turned off, the sampled feedback signal is compared with the floating lower reference.

[0032] More optionally, in the discontinuous conduction mode, the turn-off time is set based on the size of the analog dimming signal; wherein, when the analog dimming signal is zero, the turn-off time is set to the maximum turn-off time; when the analog dimming signal is greater than zero and less than a preset value, the turn-off time is inversely proportional to the analog dimming signal; when the analog dimming signal is greater than the preset value, the turn-off time is set to the minimum turn-off time.

[0033] As described above, the constant current control circuit, system and method of the present invention have the following beneficial effects:

[0034] The constant current control circuit, system, and method of the present invention automatically switch between continuous conduction mode and discontinuous conduction mode. When the analog dimming signal voltage is low, the circuit enters discontinuous conduction mode, and the percentage of the adjustable minimum inductor current corresponding to the maximum inductor current can be almost zero, maximizing the adjustable range. This greatly meets customer needs for a wider analog dimming range. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 Shown is a structural diagram of a switching buck-type LED control system using a high-end sampling resistor.

[0036] Figure 2 Shown is a structural schematic diagram of a constant current control circuit.

[0037] Figure 3 Display as Figure 2 Timing diagram of the constant current control circuit when there is no analog dimming signal.

[0038] Figure 4Display as Figure 2 The constant current control circuit has a timing diagram when simulating a dimming signal.

[0039] Figure 5 Display as Figure 2 Schematic diagram of the dimming principle of the constant current control circuit.

[0040] Figure 6 Shown is a structural schematic diagram of the constant current control circuit of the present invention.

[0041] Figure 7 It is a schematic structural diagram of the analog dimming module of the present invention.

[0042] Figure 8 It is a schematic diagram showing the principle of the analog dimming module of the present invention.

[0043] Figure 9 Shown is a structural schematic diagram of the off time setting unit of the present invention.

[0044] Figure 10 It is a schematic diagram showing the working principle of the constant current control method of the present invention in the discontinuous conduction mode.

[0045] Figure 11 It is a schematic diagram showing the relationship between the turn-off time and the analog dimming signal of the present invention.

[0046] Figure 12 It is a schematic diagram showing the working principle of the constant current control method of the present invention in the continuous conduction mode.

[0047] Figure 13 Shown is a structural schematic diagram of the constant current control system of the present invention.

[0048] Component number description

[0049] 1 Constant current control circuit

[0050] 11. First transconductance amplifier module

[0051] 12. Second transconductance amplifier module

[0052] 13 Benchmark Module

[0053] 14 PWM comparator module

[0054] 15 Logic and driver modules

[0055] 2 Constant current control circuit

[0056] 21 Sampling Feedback Module

[0057] 211 Transconductance Operational Amplifier

[0058] 22 Benchmark Module

[0059] 23 Analog dimming module

[0060] 231 Operational Amplifier

[0061] 232 control unit

[0062] 232a Comparator

[0063] 232b Inverter

[0064] 233 First Selection Unit

[0065] 234 Second Selection Unit

[0066] 24 Comparison Module

[0067] 25 Logic driver module

[0068] 251 Off time setting unit

[0069] 251a Current Source

[0070] 251b Charging Unit

[0071] 251c Schmitt trigger

[0072] 3 Constant current circuit DETAILED DESCRIPTION

[0073] The following describes the embodiments of the present invention through specific examples. Those skilled in the art will readily understand the other advantages and benefits of the present invention from the disclosure herein. The present invention may also be implemented or applied through various other specific embodiments, and the details in this specification may be modified or altered based on different viewpoints and applications without departing from the spirit of the present invention.

[0074] See also Figures 1 to 13 It should be noted that the diagrams provided in this embodiment are merely schematic illustrations of the basic concept of the present invention. Therefore, the diagrams only show components related to the present invention and are not drawn according to the number, shape, and size of components in actual implementation. In actual implementation, the type, quantity, and proportion of each component may be changed arbitrarily, and the component layout may also be more complex.

[0075] like Figure 1The figure shows a switching buck LED control system using a high-end sampling resistor, Rsense. It includes a constant current control circuit, a switching buck constant current circuit (power device Q, sampling resistor Rsense, freewheeling diode D, and inductor L), and an LED light module, LED. The input is a medium- or high-voltage DC power supply, Vin; the output voltage is the voltage drop across the LED light module, VLED. The external power device, Q, is periodically turned on and off. The sampling resistor, Rsense, is connected between the DC power supply, Vin, and the positive terminal of the LED light module, representing high-end sampling. The analog dimming pin, DIM, functions as a PWM or analog dimming terminal. When the sampling resistor, Rsense, is fixed, the output inductor current, IL, can be varied by changing the voltage on the DIM pin.

[0076] like Figure 2 As shown, the constant current control circuit 1 includes: a first transconductance operational amplifier module 11, a second transconductance operational amplifier module 12, a reference module 13, an operational amplifier output resistance module Rcs, a PWM comparator module 14, and a logic and drive module 15. The external pins are the input power pin VIN, the ground signal pin GND, the current sampling pin CSN, the analog dimming pin DIM, and the drive pin DRV. Among them:

[0077] The voltage difference across the sampling resistor Rsense reflects the voltage difference between the input power pin VIN and the current sampling pin CSN. This voltage difference generates an output current Ics through the first transconductance amplifier module 11. The transconductance gain of the first transconductance amplifier module 11 is set to GM1, then Ics = GM1*(Vin-V CSN ), where Vin is the voltage on the input power pin, V CSN is the voltage on the current sensing pin.

[0078] Analog dimming pin DIM voltage V DIM The voltage difference between the two is compared with the analog dimming upper limit reference VREF1 (fixed level) generated by the reference module 13. The second transconductance amplifier module 12 generates another output transconductance current Idim. The transconductance gain of the second transconductance amplifier module 12 is set to GM2, then Idim=GM2*(VREF1-V DIM ). When V DIM ≥ VREF1, Idim=0, at this time the output inductor current IL corresponds to the maximum output current, the sampling feedback signal Vcs=Ics*Rcs=GM1*(Vin-V CSN )*Rcs, from which the voltage difference between the input power pin VIN and the current sensing pin CSN can be inferred

[0079] The two output currents Ics and Idim both flow through the operational amplifier output resistance module Rcs, generating a sampling feedback signal VCS, where the sampling feedback signal Vcs = (Ics + Idim) * Rcs.

[0080] The sampling feedback signal VCS and the upper reference VREF_UP or the lower reference VREF_DOWN selected by the gating switch Switch are sent to the input of the PWM comparator module 14 for comparison, generating a comparison result COMPOUT. As Figure 3 shown, the average value VCSavg of the sampling feedback signal is stabilized at a fixed level, satisfying the following relationship:

[0081] VCS avg = (VREF_UP + VREF_DOWN) / 2,

[0082] thus ensuring the average value of VIN - CSN

[0083] Through the logic and drive module 15, the period and duty cycle D of the output signal COMPOUT of the PWM comparator module 14 correspond to the period of the final drive control signal VG (the output signal of the drive pin DRV) and the on - duty cycle of the power device Q (the duty cycle D of the output signal COMPOUT of the PWM comparator module 14 and the on - duty cycle of the power device Q also reflect the input - output voltage ratio, i.e., D = V LED / Vin), and the average value of the output inductor current IL is maintained at: to achieve the purpose of constant current.

[0084] When V DIM < VREF1, at this time, the analog dimming current Idim will generate leakage, which is superimposed on the sampling feedback signal VCS, and the actual sampling feedback signal VCS’ will decrease, and the system output inductor current IL will decrease. However, the duty cycle D of the output signal COMPOUT of the PWM comparator module 14 remains unchanged, as Figure 4 shown.

[0085] When V DIM changes from low to high, the output leakage current Idim of the second transconductance operational amplifier module 12 changes from large to small, and the current value of the output inductor current IL also changes from low to high, realizing the analog dimming function, as Figure 5 shown. Since the levels of the upper reference VREF_UP and the lower reference VREF_DOWN are fixed, therefore, the current ripple △IL of the output inductor current IL also remains unchanged. But when V DIM is very low and close to zero level, the actual sampling feedback signal VCS’ after conversion may become a negative voltage, as Figure 5As shown in the oval dotted box. However, the system requires operation in continuous conduction mode, so negative voltage is not allowed. It is imperative to ensure that the voltage of the analog dimming pin DIM is higher than the dimming start threshold VSHUT to ensure normal system operation and output current accuracy. This also limits the lower limit of the analog dimming percentage.

[0086] Based on the above reasons, the present invention provides a high-end sampling constant current control circuit with analog dimming, which can enter the discontinuous conduction mode when the voltage of the analog dimming pin DIM is low. The percentage of the adjustable minimum inductor current corresponding to its maximum inductor current can be almost zero; the adjustable range can be maximized, which greatly meets the customer's demand for a wider analog dimming range or even a full 100% dimming range.

[0087] Example 1

[0088] like Figure 6 As shown, this embodiment provides a constant current control circuit 2, and the constant current control circuit 2 includes:

[0089] Sampling feedback module 21 , reference module 22 , analog dimming module 23 , comparison module 24 and logic driving module 25 .

[0090] like Figure 6 As shown, the sampling feedback module 21 obtains the sampling signal of the output current and converts it into a sampling feedback voltage VCS.

[0091] Specifically, in this embodiment, the sampling feedback module 21 includes a transconductance operational amplifier 211 and a first resistor R1. The input of the transconductance operational amplifier 211 is connected to both ends of the external output current sampling resistor Rsense. As an example, the non-inverting input of the transconductance operational amplifier 211 is connected to the high potential node of the sampling resistor Rsense, and the inverting input is connected to the low potential node of the sampling resistor Rsense. One end of the first resistor R1 is connected to the output of the transconductance operational amplifier 211, and the other end is grounded.

[0092] It should be noted that the correspondence between the polarity of the input terminal of the transconductance operational amplifier 211 and the input signal can be adjusted as needed. The same logical relationship can be obtained by using an inverter, and this is not limited to this embodiment. Furthermore, any circuit structure that can convert the output current sampling signal into a sampled feedback voltage is applicable to the present invention.

[0093] like Figure 6 As shown, the reference module 22 is used to provide a maximum upper reference threshold REFmax, a maximum lower reference threshold REFmin, and an analog dimming upper limit reference VREF1, wherein the maximum upper reference threshold REFmax is greater than the maximum lower reference threshold REFmin.

[0094] Specifically, any circuit structure that can generate a reference voltage or current is applicable to the present invention, including but not limited to a bandgap reference circuit, which will not be described in detail here.

[0095] like Figure 6 As shown, the analog dimming module 23 is connected to the output end of the reference module 22 and receives the analog dimming signal V DIM , used to generate the floating upper reference VREF_UP and the floating lower reference VREF_DOWN. When the analog dimming signal V DIM When the analog dimming signal V DIM When the analog dimming signal V DIM When it is greater than or equal to the analog dimming upper limit reference VREF1, the floating upper reference VREF_UP is the maximum upper reference threshold REFmax, and the floating lower reference VREF_DOWN is the maximum lower reference threshold REFmin.

[0096] Specifically, if Figure 7 As shown, as an example, the analog dimming module 23 includes an operational amplifier 231, a transistor unit M1, a second resistor R2, a third resistor R3, a fourth resistor R4, a control unit 232, a first selection unit 233, and a second selection unit 234. In this example, the transistor unit M1 is implemented using an NMOS transistor, the drain of which is connected to the internal power supply VDD, the gate of which is connected to the output terminal of the operational amplifier 231, and the drain of which is grounded via the second resistor R2, the third resistor R3, and the fourth resistor R4 in sequence. The non-inverting input terminal of the operational amplifier 231 receives the analog dimming signal V DIM, the inverting input terminal is connected to the drain of the NMOS tube (the connection node with the second resistor). The first input terminal of the control unit 232 is connected to the connection node between the NMOS tube and the second resistor R2, and the second input terminal receives the analog dimming upper limit reference VREF1, compares the voltage of the connection node with the analog dimming upper limit reference VREF1, and outputs a control signal based on the comparison result. As an example, the control unit 232 includes a comparator 232a and an inverter 232b, the inverting input terminal of the comparator 232a is connected to the drain of the NMOS tube, the non-inverting input terminal is connected to the analog dimming upper limit reference VREF1, and outputs a control signal EN; the inverter 232b is connected to the output terminal of the comparator 232a, and is used to obtain the inverse signal ENINV of the control signal. In actual use, the corresponding relationship between the input polarity of the comparator 232a and the input signal can be adjusted as needed, which is not described here one by one. The first selection unit 233 has a first input connected to the connection node between the second resistor R2 and the third resistor R3, a second input receiving the maximum upper reference threshold REFmax, a control terminal connected to the output terminal of the control unit 232, and outputting the floating upper reference VREF_UP. For example, the first selection unit 233 includes a first switch and a second switch, wherein the first terminal of the first switch is connected to the connection node between the second resistor R2 and the third resistor R3, the second terminal is an output terminal, and the control terminal is connected to the control signal EN. The first terminal of the second switch receives the maximum upper reference threshold REFmax, the second terminal is connected to the second terminal of the second switch, and the control terminal is connected to the inverse signal ENINV of the control signal. The second selection unit 234 has a first input connected to the connection node between the third resistor R3 and the fourth resistor R4, a second input receiving the maximum lower reference threshold REFmin, a control terminal connected to the output terminal of the control unit 232, and outputting the floating lower reference VREF_DOWN. Its structure is the same as that of the first selection unit 233 and is not further described here.

[0097] The operational amplifier 231 is adjusted so that the drain voltage of the transistor unit M1 is equal to the analog dimming signal V DIM The source current IR flowing through the transistor unit M1, the second resistor R2, the third resistor R3 and the fourth resistor R4 satisfies: IR=V DIM / Rtotal=V DIM / (R2+R3+R4). Since the source current IR changes with the analog dimming signal V DIM Therefore, the node voltage VR1 on the fourth resistor R4 and the node voltage VR2 on the third resistor R3 are changed with the analog dimming signal V DIMincreases with the increase of the voltage, and the voltage drop of the third resistor R3 reflects the pressure difference between the node voltage VR1 and the node voltage VR2, and this pressure difference also increases with the increase of the source current IR. When V DIM < VREF1, the control signal EN is at a high level. At this time, the node voltage VR1 is selected as the floating upper reference VREF_UP, and the node voltage VR2 is selected as the floating lower reference VREF_DOWN; as Figure 8 shown, it can be found that: the floating upper reference VREF_UP and the analog dimming signal V DIM are in a first direct proportional relationship, and the floating lower reference VREF_DOWN and the analog dimming signal V DIM are in a second direct proportional relationship. Among them, the first proportional coefficient is greater than the second proportional coefficient. Affected by the source current IR, while ensuring that the average value after the floating upper reference VREF_UP and the floating lower reference VREF_DOWN are added changes linearly with the analog dimming signal. When V DIM ≥ VREF1, the control signal EN is at a low level. At this time, the maximum upper reference threshold REFmax is selected as the floating upper reference VREF_UP, and the maximum lower reference threshold REFmin is selected as the floating lower reference VREF_DOWN.

[0098] As Figure 6 shown, the first input end of the comparison module 24 is connected to the sampling feedback module 21 for receiving the sampling feedback voltage VCS. The second input end receives the floating upper reference VREF_UP and the floating lower reference VREF_DOWN output by the analog dimming module 23 through switch switching respectively. The comparison module compares the sampling feedback voltage VCS with the floating upper reference VREF_UP and the floating lower reference VREF_DOWN respectively and outputs a comparison result COMPOUT.

[0099] Specifically, in this embodiment, the positive input end of the comparison module 24 receives the floating upper reference VREF_UP and the floating lower reference VREF_DOWN respectively through a switch, and switches the input signals of the positive input end of the comparison module 24 through the switch; the negative input end is connected to the input end of the sampling feedback module 21; in actual use, the corresponding relationship between the input end polarity of the comparison module 24 and the input signal can be adjusted, as long as the logic of the present invention can be realized, and it is not limited to this embodiment.

[0100] As Figure 6 shown, the logic driving module 25 is connected to the output end of the comparison module 24. When the analog dimming signal V DIM is less than the preset value V DIM_th, a driving control signal of a discontinuous conduction mode is generated based on the comparison result COMPOUT; when the analog dimming signal V DIM Greater than or equal to the preset value V DIM_ th, a driving control signal of a continuous conduction mode is generated based on the comparison result COMPOUT.

[0101] It should be noted that, in the analog dimming signal V DIM When the switching frequency is high, it is easy to cause noise. Therefore, the discontinuous conduction mode can be used for driving at this stage. As an example, the preset value V DIM_ th is set to 0.5V. In actual use, the preset value V DIM_ th can be set according to actual device parameters, dimming requirements, etc., as long as it does not affect the final dimming effect, and is not limited to this embodiment.

[0102] Specifically, in this embodiment, the logic driving module 25 includes an off-time setting unit 251 and a driving unit (not shown in the figure). The off-time setting unit 251 receives the comparison result COMPOUT, and when the power switch tube is in the off state (COMPOUT is low, the inductor current enters the OFF state), the analog dimming signal V DIM The drive unit generates a drive control signal based on the comparison result COMPOUT.

[0103] More specifically, if Figure 9 As shown, as an example, the off time setting unit 251 includes a current source 251a, a charging unit 251b and a Schmitt trigger 251c. The current source 251a is driven by the analog dimming signal V DIM The control generates a charging current Ileak; the charging unit 251b is connected to the output end of the current source 251a, and is charged based on the charging current Ileak. As an example, the charging unit 251b includes a fifth resistor R5 and an energy storage capacitor C to form an RC delay structure; the input end of the Schmitt trigger 251c is connected to the output end of the charging unit 251b, and the control end is connected to the comparison result COMPOUT. When the power switch tube is in the off state and the voltage in the charging unit 251b is greater than the threshold of the Schmitt trigger, the off state is ended. The charging current Ileak changes with the analog dimming signal V DIM changes; when the analog dimming signal V DIM When the analog dimming signal V DIM Greater than zero and less than the preset value VDIM_ th, the charging current Ileak and the analog dimming signal V DIM The charging and discharging time is proportional to the analog dimming signal V DIM is inversely proportional to the analog dimming signal V DIM When the analog dimming signal V DIM Greater than the preset value V DIM_ At th, the charging current Ileak reaches its maximum value, the charge-discharge time is shortest, and the corresponding minimum off-time Toffmin is obtained, which no longer affects the discharge time of the output inductor current IL. The off-time setting unit 251 feeds the off-time Toff back to the comparison module 24, and during the off-time, sets the output signal of the comparison module 24 to the level corresponding to the power switch off (in this example, the power switch is turned off when the comparison result COMPOUT is low).

[0104] It should be noted that the off time Toff can be based on the analog dimming signal V DIM The analog dimming signal V in this embodiment is not limited to the analog dimming signal V in this embodiment. DIM The implementation of setting the off time Toff is not limited to the one listed in this embodiment, including but not limited to using the response delay of the comparator, which is not detailed here.

[0105] More specifically, the driving unit generates the driving control signal VG based on the comparison result COMPOUT, and the period and duty cycle D of the comparison result COMPOUT correspond to the period of the final driving control signal VG and the on-duty cycle of the power device.

[0106] Example 2

[0107] This embodiment provides a constant current control method. In this embodiment, the constant current control circuit 2 of the first embodiment is implemented. In actual use, any hardware or software that can implement the present invention is applicable. The constant current control method at least includes:

[0108] 1) Collect the output current and convert it into a sampling feedback signal VCS.

[0109] Specifically, in this embodiment, the output current is sampled through the sampling resistor Rsense, and a corresponding sampling feedback signal VCS is obtained.

[0110] 2) generating a floating upper reference and a floating lower reference according to an analog dimming signal, wherein, when the analog dimming signal is less than the analog dimming upper limit reference, the floating upper reference and the floating lower reference are respectively proportional to the analog dimming signal; when the analog dimming signal is greater than or equal to the analog dimming upper limit reference, the floating upper reference is a maximum upper reference threshold, and the floating lower reference is a maximum lower reference threshold.

[0111] Specifically, in this embodiment, when the analog dimming signal V DIM When the floating upper reference VREF_UP is less than the analog dimming upper limit reference VREF1, the floating upper reference VREF_UP and the analog dimming signal V DIM In a first direct proportional relationship, the floating lower reference VREF_DOWN and the analog dimming signal V DIM A second direct proportional relationship is formed, wherein the first direct proportional coefficient is greater than the second direct proportional coefficient. Figure 8 As shown, when the analog dimming signal V DIM When changing linearly from low to high, the floating upper reference VREF_UP and the floating lower reference VREF_DOWN gradually increase linearly, and the difference between VREF_UP and VREF_DOWN also gradually increases. It is known that the calculation formula of the output inductor current IL is: It can be found that the output inductor current IL is also gradually increasing linearly, and the ripple △IL of the output inductor current IL is also increasing accordingly, so that the voltage value of the analog dimming pin DIM can be lower and the system can still maintain the continuous conduction mode. DIM After the output inductor current IL reaches the maximum value when it is equal to the analog dimming upper limit reference VREF1, the analog dimming function is realized.

[0112] It should be noted that the order of step 1) and step 2) is not limited. Step 1) can be performed first and then step 2), or they can be performed simultaneously, which is not limited to this embodiment.

[0113] 3) Comparing the sampled feedback signal with the floating upper reference and floating lower reference switched by the switch, and generating a discontinuous conduction mode drive control signal based on the comparison result when the analog dimming signal is less than a preset value; and generating a continuous conduction mode drive control signal based on the comparison result when the analog dimming signal is greater than or equal to the preset value.

[0114] Specifically, if Figure 8 As shown, when the analog dimming signal V DIM Less than the preset value V DIM_ th enters the discontinuous conduction mode, when the analog dimming signal V DIM Greater than or equal to the preset value V DIM_th enters continuous conduction mode.

[0115] like Figure 10 As shown, the analog dimming signal V DIM Less than the preset value V DIM_ At th, since the set output inductor current IL is already very small, when the output inductor current IL rises, the sampling feedback signal VCS will quickly touch the floating upper reference VREF_UP and then enter the OFF state (shutdown state). The output inductor current IL will quickly discharge to zero. The sampling feedback signal VCS is lower than the floating lower reference VREF_DOWN. At this time, the logic drive module sets the off time Toff through the RC unit. This Toff time will increase as the DIM voltage decreases. After the output inductor current IL drops to zero, the output inductor current IL remains at zero before the off time Toff ends. At this time, the discontinuous conduction mode is entered. Among them, the conduction time is determined by the comparison result of the sampling feedback signal VCS and the floating upper reference VREF_UP; the off time Toff is determined by the analog dimming signal V DIM As an example, in this embodiment, the output signal of the comparison module 24 is set to a low level by setting the off time Toff to realize the control of the discontinuous conduction mode. Figure 11 As shown, when the analog dimming signal V DIM When the analog dimming signal is greater than zero and less than the preset value V DIM_ th, the off time Toff and the analog dimming signal V DIM becomes smaller in inverse proportion; when the analog dimming signal V DIM Greater than the preset value V DIM_ th, the off-time Toff is set to the minimum off-time Toffmin.

[0116] It should be noted that the off time Toff can be based on the analog dimming signal V DIM The analog dimming signal V in this embodiment is not limited to the analog dimming signal V in this embodiment. DIM I won’t go into details about them here.

[0117] like Figure 12 As shown, the analog dimming signal V DIM Greater than or equal to the preset value V DIM_ At th, the sampling feedback signal VCS switches between the floating upper reference VREF_UP and the floating lower reference VREF_DOWN in a triangle wave manner, and enters the continuous conduction mode.

[0118] like Figure 10 and Figure 12 As shown, the floating upper reference VREF_UP or the floating lower reference VREF_DOWN is connected to the non-inverting input terminal of the comparison module 24 through the switch switching signal switch, and is compared with the sampling feedback signal VCS; as an example, when the power switch tube is turned on (the comparison result COMPOUT is a high level), the sampling feedback signal VCS is compared with the floating upper reference VREF_UP; when the power switch tube is turned off (the comparison result COMPOUT is a low level), the sampling feedback signal VCS is compared with the floating lower reference VREF_DOWN.

[0119] In the present invention, in the discontinuous conduction mode, since the period varies with the analog dimming signal V DIM As the voltage increases, the average value of the output inductor current IL also gradually increases. The coexistence of discontinuous conduction mode and continuous conduction mode enables the maximum analog adjustment range to be from 0% to 100%.

[0120] Example 3

[0121] like Figure 13 As shown, this embodiment provides a constant current control system, which includes:

[0122] The constant current circuit 3 and the constant current control circuit 2 of the first embodiment.

[0123] like Figure 13 As shown, the constant current circuit 3 receives the driving control signal of the power switch tube, so that the current of the output load is constant.

[0124] Specifically, as an example, the sampling resistor in the constant current circuit 3 is a high-end sampling structure. The constant current circuit 3 can be Figure 1 The structure can also be a constant current circuit of any structure, which will not be described here one by one.

[0125] like Figure 13 As shown, the constant current control circuit 2 obtains a sampling feedback signal of the output current in the constant current circuit 3, and controls the on and off of the power switch tube in the constant current circuit 3 based on the sampling feedback signal and the analog dimming signal to achieve a constant current output of the constant current circuit 3.

[0126] Specifically, the structure and principle of the constant current control circuit 2 are as described above and will not be described in detail here.

[0127] In summary, the present invention provides a constant current control circuit, system and method, including: a sampling feedback module, which obtains a sampling signal of the output current and converts it into a sampling feedback voltage; a reference module, which is used to provide a maximum upper reference threshold, a maximum lower reference threshold and an analog dimming upper limit reference; an analog dimming module, which is connected to the output end of the reference module and receives an analog dimming signal, and is used to generate a floating upper reference and a floating lower reference; when the analog dimming signal is less than the analog dimming upper limit reference, the floating upper reference and the floating lower reference are respectively proportional to the analog dimming signal; when the analog dimming signal is greater than or equal to the analog dimming upper limit reference, the floating upper reference and the floating lower reference are respectively proportional to the analog dimming signal. On time, the floating upper reference is set to the maximum upper reference threshold, and the floating lower reference is set to the maximum lower reference threshold; the comparison module, the first input end is connected to the sampling feedback module, and the second input end receives the floating upper reference and floating lower reference output by the analog dimming module through switch switching, and outputs the comparison result; the logic drive module is connected to the output end of the comparison module, and when the analog dimming signal is less than the preset value, the drive control signal of the discontinuous conduction mode is generated based on the comparison result; when the analog dimming signal is greater than or equal to the preset value, the drive control signal of the continuous conduction mode is generated based on the comparison result. The constant current control circuit, system and method of the present invention automatically switch between continuous conduction mode and discontinuous conduction mode; when the DIM voltage is low, the discontinuous conduction mode is entered, and the percentage of the adjustable minimum inductor current corresponding to its maximum inductor current can be almost zero, and the adjustable range can be maximized, which greatly meets the customer's demand for a wider analog dimming range. Therefore, the present invention effectively overcomes the various shortcomings of the existing technology and has high industrial utilization value.

[0128] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the present invention. Anyone skilled in the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by one of ordinary skill in the art without departing from the spirit and technical principles disclosed herein are intended to be covered by the claims of the present invention.

Claims

1. A constant current control circuit, characterized in that: The constant current control circuit at least includes: The sampling feedback module obtains the sampling signal of the output current and converts it into a sampling feedback voltage; A reference module, configured to provide a maximum upper reference threshold, a maximum lower reference threshold, and an upper limit reference for analog dimming, wherein the reference module is a bandgap reference circuit; an analog dimming module connected to the output terminal of the reference module and receiving an analog dimming signal, for generating a floating upper reference and a floating lower reference; when the analog dimming signal is less than the analog dimming upper limit reference, the floating upper reference and the floating lower reference are respectively proportional to the analog dimming signal; when the analog dimming signal is greater than or equal to the analog dimming upper limit reference, the floating upper reference is set to a maximum upper reference threshold, and the floating lower reference is set to a maximum lower reference threshold; a comparison module, wherein a first input end is connected to the sampling feedback module and is configured to receive the sampled feedback voltage, and a second input end is configured to receive the floating upper reference and the floating lower reference output by the analog dimming module through switch switching, respectively. The comparison module compares the sampled feedback voltage with the floating upper reference and the floating lower reference, respectively, and outputs a comparison result; a logic driving module connected to the output end of the comparison module, and generating a driving control signal for the discontinuous conduction mode based on the comparison result when the analog dimming signal is less than a preset value; and generating a driving control signal for the continuous conduction mode based on the comparison result when the analog dimming signal is greater than or equal to the preset value.

2. The constant current control circuit according to claim 1, wherein: The sampling feedback module includes a transconductance operational amplifier and a first resistor; the input end of the transconductance operational amplifier is connected to the two ends of the external output current sampling resistor; one end of the first resistor is connected to the output end of the transconductance operational amplifier, and the other end is grounded.

3. The constant current control circuit according to claim 1, wherein: The analog dimming module includes an operational amplifier, a transistor unit, a second resistor, a third resistor, a fourth resistor, a control unit, a first selection unit, and a second selection unit; The transistor unit, the second resistor, the third resistor and the fourth resistor are sequentially connected in series between a power source and a ground; The operational amplifier has a non-inverting input terminal receiving the analog dimming signal, an inverting input terminal connected to a connection node between the transistor unit and the second resistor, and an output terminal connected to a control terminal of the transistor unit; The control unit has a first input terminal connected to a connection node between the transistor unit and the second resistor, a second input terminal receiving the analog dimming upper limit reference, compares a voltage of the connection node with the analog dimming upper limit reference, and outputs a control signal based on the comparison result; The first input terminal of the first selection unit is connected to the connection node between the second resistor and the third resistor, the second input terminal receives the maximum upper reference threshold, and the control terminal is connected to the output terminal of the control unit to output the floating upper reference; The first input terminal of the second selection unit is connected to the connection node of the third resistor and the fourth resistor, the second input terminal receives the maximum lower reference threshold, and the control terminal is connected to the output terminal of the control unit; and outputs the floating lower reference.

4. The constant current control circuit according to claim 1, wherein: The logic drive module includes a turn-off time setting unit and a drive unit; the turn-off time setting unit receives the comparison result and sets the turn-off time of the power switch tube based on the analog dimming signal when the power switch tube controlled by the drive control signal is in the turn-off state; the drive unit generates a drive control signal based on the comparison result.

5. The constant current control circuit according to claim 4, wherein: The off-time setting unit includes a current source, a charging unit and a Schmitt trigger; the current source is controlled by the analog dimming signal to generate a charging current; the charging unit is connected to the output end of the current source and charges based on the charging current; the input end of the Schmitt trigger is connected to the output end of the charging unit, and the control end is connected to the comparison result. When the power switch tube is in the off state and the voltage in the charging unit is greater than the set value, the off state is ended.

6. A constant current control system, characterized in that: The constant current control system at least includes: A constant current circuit and a constant current control circuit as claimed in any one of claims 1 to 5; The constant current circuit receives a driving control signal from the power switch tube, so that the current of the output load is constant; The constant current control circuit obtains a sampling feedback signal of the output current in the constant current circuit, and controls the on and off of the power switch tube in the constant current circuit based on the sampling feedback signal and the analog dimming signal to achieve constant current output of the constant current circuit.

7. The constant current control system according to claim 6, characterized in that: The sampling resistor in the constant current circuit is a high-end sampling structure.

8. A constant current control method, characterized in that: The constant current control method at least includes: Collect output current and convert it into sampling feedback signal; generating a floating upper reference and a floating lower reference according to an analog dimming signal, wherein when the analog dimming signal is less than an analog dimming upper limit reference, the floating upper reference and the floating lower reference are respectively proportional to the analog dimming signal; and when the analog dimming signal is greater than or equal to the analog dimming upper limit reference, the floating upper reference is a maximum upper reference threshold, and the floating lower reference is a maximum lower reference threshold; The sampled feedback signal is compared with the floating upper reference and the floating lower reference switched by the switch, and when the analog dimming signal is less than a preset value, a drive control signal of the discontinuous conduction mode is generated based on the comparison result; when the analog dimming signal is greater than or equal to the preset value, a drive control signal of the continuous conduction mode is generated based on the comparison result.

9. The constant current control method according to claim 8, wherein: When the analog dimming signal is less than the analog dimming upper limit reference, the floating upper reference is in a first proportional relationship with the analog dimming signal, and the floating lower reference is in a second proportional relationship with the analog dimming signal, wherein the first proportional coefficient is greater than the second proportional coefficient, and at the same time, it is ensured that the average value of the floating upper reference and the floating lower reference added changes linearly with the change of the analog dimming signal.

10. The constant current control method according to claim 8, wherein: When the power switch tube controlled by the drive control signal is turned on, the sampled feedback signal is compared with the floating upper reference; when the power switch tube is turned off, the sampled feedback signal is compared with the floating lower reference.

11. The constant current control method according to claim 8 or 10, characterized in that: In discontinuous conduction mode, the off time is set based on the size of the analog dimming signal; when the analog dimming signal is zero, the off time is set to the maximum off time; when the analog dimming signal is greater than zero and less than a preset value, the off time is inversely proportional to the analog dimming signal; when the analog dimming signal is greater than the preset value, the off time is set to the minimum off time.

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