A high-performance multi-channel constant-current driving circuit

Abstract

This invention discloses a high-efficiency multi-channel constant current driving circuit in the field of LED driving. The circuit includes a constant current module consisting of a step-down constant current driving chip and its peripheral components; a switching module composed of two NPN transistors and two PMOS transistors for selectively conducting either the infrared or white light source branch; and a reverse-blocking module composed of two diodes for isolating the two control signals and sharing the PWM dimming pin of the constant current chip. This invention uses only one constant current module to drive two light sources, saving cost and space, and supports independent stepless dimming for each channel. It can be expanded to multi-channel control and adapts to the supplementary lighting needs of security camera modules.

Description

Technical Field

[0001] This invention relates to the field of LED driving, specifically a high-efficiency multi-channel constant current driving circuit. Background Technology

[0002] In recent years, the security monitoring industry has developed rapidly, with continuously increasing demands for image quality, which has also created new requirements for supplementary lighting systems. To adapt to various application scenarios, supplementary lighting sources need to have multiple operating modes. Specifically, when people appear in the monitoring screen, it is necessary to switch to color image mode and activate visible light (white light) supplementary lighting; when there are no dynamic changes in the image, it should switch to infrared light supplementary lighting mode to achieve covert nighttime monitoring.

[0003] With the increasing demand for supplementary lighting sources, even the minimum configuration of existing security cameras needs to be equipped with dual light sources (infrared light source and white light source). However, in traditional designs, each light source needs to be equipped with an independent constant current drive module.

[0004] Figure 2 This is a block diagram of a traditional dual-path drive scheme. As shown in the diagram, in the traditional approach, the infrared drive module and the white light drive module are two completely independent sets of constant current drive modules. When the white light is on and the infrared light is off, the infrared drive module is idle; when the infrared light is on and the white light is off, the white light drive module is idle. Since enabling infrared in color mode will cause image color distortion in security cameras, the infrared is not enabled when white light is on, and vice versa. Only one set of constant current modules is always working, while the other is completely idle, resulting in serious resource waste.

[0005] Figure 3 This is the circuit schematic of a traditional dual-path drive scheme. As shown in the diagram, the traditional scheme includes two independent constant current modules. Each constant current module is equipped with complete driver chips U1 and U2, power inductors L1 and L2, freewheeling diodes D1 and D2, sampling resistors R1 and R2, and input / output capacitors, among other peripheral components. Each constant current module controls one light source independently, resulting in a single-control lamp per group. While this design is mature and simple to control, it suffers from the following prominent problems:

[0006] First, the cost is high. Two sets of constant current drive modules mean double the cost of the drive chip and double the cost of peripheral components such as inductors, capacitors, and diodes, significantly increasing the overall BOM cost of the product.

[0007] Secondly, it occupies a large space. Security cameras have limited internal space, and two independent constant current drive modules require a larger light panel area, which is not conducive to the miniaturization design of the product.

[0008] Third, resource waste. Because the two light sources operate in a time-sharing manner, the other constant current module remains idle when one light source is working, resulting in a double waste of resources and energy.

[0009] Therefore, those skilled in the art have provided a high-efficiency multi-path constant current drive circuit to solve the problems mentioned in the background art. Summary of the Invention

[0010] The purpose of this invention is to provide a high-efficiency multi-path constant current drive circuit to solve the problems mentioned in the background art.

[0011] To achieve the above objectives, the present invention provides the following technical solution:

[0012] A high-efficiency multi-path constant current drive circuit includes a constant current module, a first switching unit, a second switching unit, and a reverse protection module;

[0013] The constant current module includes a step-down LED constant current driver chip U1, an inductor L1, a freewheeling diode D3, a current sampling resistor Rcs, and an input filter capacitor. Chip bypass capacitor and output filter capacitor The driver chip U1 has Pins, SW pin, CS pin, GND pin, and PWM pin; Pin connected to the positive terminal of the input power supply +, and through the chip bypass capacitor Grounded, the positive terminal of the input power supply +Also through the input filter capacitor Grounded; the SW pin is connected to the first terminal of the inductor L1 and the anode of the freewheeling diode D3, and the second terminal of the inductor L1 is connected to the output LED terminal of the constant current module. The cathode of the freewheeling diode D3 The CS pin is connected to the output LED+ terminal of the constant current module through the current sampling resistor Rcs. The GND pin is grounded; the PWM pin serves as the PWM / EN control terminal of the constant current module; the output filter capacitor... Connected to the output terminal of the constant current module Between CS and LED+ terminals;

[0014] The first switching unit includes a first NPN transistor Q1 and a first PMOS transistor Q2; the base of the first NPN transistor Q1 is connected to the first control signal input terminal through a first current-limiting resistor R1. The emitter of the first NPN transistor Q1 is grounded, the collector of the first NPN transistor Q1 is connected to the gate of the first PMOS transistor Q2, and is connected to the output terminal of the constant current module through the first pull-up resistor R4. The drain (D) of the first PMOS transistor Q2 is connected to the output terminal of the constant current module. The source (S) terminal of the first PMOS transistor Q2 is connected to the positive terminal of the IRLED+ of the first light source branch;

[0015] The second switching unit includes a second NPN transistor Q3 and a second PMOS transistor Q4; the base of the second NPN transistor Q3 is connected to the second control signal input terminal through a second current-limiting resistor R5. The emitter of the second NPN transistor Q3 is grounded, the collector of the second NPN transistor Q3 is connected to the gate of the second PMOS transistor Q4, and is connected to the output terminal of the constant current module through the second pull-up resistor R8. The drain of the second PMOS transistor Q4 is connected to the output terminal of the constant current module. The source (S) terminal of the second PMOS transistor Q4 is connected to the positive terminal of WLED+ of the second light source branch; the negative terminals of LED- of the first light source branch and LED- of the second light source branch are connected to the module LED-.

[0016] The anti-reverse module includes a first diode D1 and a second diode D2; the anode of the first diode D1 is connected to the input terminal of the first PWM dimming signal. The cathode of the first diode D1 is connected to the PWM / EN pin of the driver chip U1 through two resistors R9 and R10; the anode of the second diode D2 is connected to the second PWM dimming signal input terminal. The cathode of the second diode D2 is also connected to the PWM / EN pin of the driver chip U1 through two resistors R9 and R10;

[0017] When the first control signal The second control signal is high. When the signal is low, the first NPN transistor Q1 and the first PMOS transistor Q2 are turned on, the first light source branch is connected, and the first PWM dimming signal is transmitted to the PWM pin via the first diode D1 to achieve dimming of the first light source; when the second control signal is low... The first control signal is high. When the signal is low, the second NPN transistor Q3 and the second PMOS transistor Q4 are turned on, the second light source branch is turned on, and the second PWM dimming signal is transmitted to the PWM pin through the second diode D2 to realize the dimming of the second light source; when both the first control signal and the second control signal are low, both light sources are turned off.

[0018] As a further aspect of the present invention: the output current of the constant current module is determined by the resistance value of the current sampling resistor Rcs, and the output current formula is as follows:

[0019]

[0020] in: This refers to the output current of the constant current module. The resistance value of the current sampling resistor is specified; the driver chip U1 has a 0.1V reference voltage source and an error amplifier inside, and the voltage detected by the CS pin is compared with the 0.1V reference to control the output current to be constant.

[0021] As a further aspect of the present invention: the inductance value of the inductor L1 determines the switching frequency, wherein: It is the DC resistance value of inductor L1. It is the voltage drop of the LED light source branch. It is the on-resistance of the power MOSFET inside the driver chip. For current sampling resistor, The drive circuit receives a DC input voltage. , The voltage drop across the freewheeling diode D3. Duration of the inductor charging phase. The switching frequency is calculated using the following formula to determine the duration of the inductor freewheeling discharge phase:

[0022]

[0023]

[0024]

[0025] The larger the inductance value, the slower the output current switches; when selecting an inductor, the peak current should not exceed the inductor's rated saturation current.

[0026] As a further aspect of the present invention: the freewheeling diode D3 is a Schottky diode, whose rated average current is greater than the average current flowing through the diode. The formula for calculating the average current is as follows:

[0027]

[0028] The reverse rated voltage of the diode is greater than .

[0029] > 2

[0030] As a further aspect of the present invention: the first light source branch is an infrared LED branch, and the second light source branch is a white LED branch; the voltage of the infrared LED and the voltage of the white LED satisfy the following relationship:

[0031] Furthermore, the operating current of the infrared LED is equal to that of the white LED, that is:

[0032]

[0033] As a further aspect of the present invention: the frequencies of the first PWM dimming signal and the second PWM dimming signal are both 100Hz to 20kHz, and the amplitude range is both 1.2V to 5V; the PWM / EN pin of the driver chip U1 can respond to PWM signals with a pulse width of less than 60ns, thereby realizing stepless dimming with an ultra-small duty cycle; when the PWM signal is low, the output is off, when the PWM signal is high, the output is on, and when the high impedance is floating, the port is high by default.

[0034] As a further aspect of the present invention: the input filter capacitor The capacitor is a 10μF / 50V bypass capacitor for the chip. It is a 0.1μF / 50V ceramic capacitor and is in close contact with the above. The output filter capacitor is arranged between the pins and ground. It is a 1μF / 50V ceramic capacitor.

[0035] As a further aspect of the present invention: the resistance values ​​of the first current-limiting resistor R1, the second current-limiting resistor R5, the first pull-up resistor R4, and the second pull-up resistor R8 satisfy the following: when the first control signal or the second control signal is at a high level, the corresponding NPN transistor is saturated and turned on, and the corresponding PMOS transistor is also saturated and turned on.

[0036] As a further embodiment of the present invention: the constant current module, the first switching unit, the second switching unit and the anti-reverse module constitute a basic driving unit; when it is necessary to drive 2N light sources, N basic driving units are set up, and the first light source branch and the second light source branch in each basic driving unit are respectively connected to different light sources, thereby realizing independent control of N groups of constant current modules driving 2N light sources, where N is a positive integer.

[0037] As a further embodiment of the present invention: the driving circuit adopts a common negative terminal connection method, with the negative terminals of the first light source branch and the second light source branch commonly connected to the LED; as a variation, it can also be extended to a constant current positive output method, that is, the positive terminal of the light source is commonly connected to the LED. The switching unit is connected between the negative electrode of the light source and the IRLED- and WLED- groups to achieve on / off control.

[0038] Compared with the prior art, the beneficial effects of the present invention are:

[0039] 1. Significantly reduced costs: Eliminating a complete constant current module (chip, inductor, capacitor, diode, etc.) significantly reduces costs, taking dual light sources as an example.

[0040] 2. Space saving: Reduced number of components and smaller light panel area facilitate miniaturization of security cameras.

[0041] 3. Full functionality: Both channels support PWM stepless dimming, with good light sensitivity and fast response.

[0042] 4. Reliable isolation: The anti-reverse diode ensures that the two PWM signals do not interfere with each other, ensuring dimming accuracy.

[0043] 5. Easy to expand: Modular design, multiple channels can be achieved by copying, without the need for redesign.

[0044] 6. High adaptability: It can be flexibly configured as common negative or common positive output to adapt to different LED connection methods. Attached Figure Description

[0045] Figure 1 This is a block diagram illustrating the principle of a single constant current module driving two light sources according to the present invention.

[0046] Figure 2 This is a block diagram of a traditional dual-path drive scheme (two independent constant current modules).

[0047] Figure 3 This is the circuit schematic of a traditional dual-path drive scheme (two independent constant current modules).

[0048] Figure 4 This is a circuit schematic diagram of the dual-path driving scheme of the present invention;

[0049] Figure 5 A comparison diagram of the connection methods for four-wire grouped drive and three-wire combined drive;

[0050] Figure 6 This is a circuit schematic diagram of the switching module of the present invention;

[0051] Figure 7 This is an internal block diagram of the constant current module of the present invention;

[0052] Figure 8 A typical application circuit diagram for a constant current module with 12V input and 1A output;

[0053] Figure 9 A typical application circuit diagram for a constant current module with 24V input and 1A output;

[0054] Figure 10 This is a steady-state operating waveform diagram of the constant current module of the present invention;

[0055] Figure 11 This is a typical characteristic curve of the constant current module of the present invention. Detailed Implementation

[0056] 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 some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0057] (I) Overall Circuit Structure

[0058] Figure 1 This is a block diagram illustrating the principle of a single constant current module driving two light sources according to the present invention. As shown in the figure, the present invention includes a constant current module, a first switching unit, a second switching unit, and a reverse-current blocking module. The constant current module outputs a constant current; the switching unit selects to turn on one of the light sources according to the control signal; the reverse-current blocking module enables the two PWM dimming signals to share the same PWM pin of the constant current chip without interfering with each other.

[0059] Figure 4 This is a schematic diagram of the dual-path drive scheme of the present invention. Figure 4 This is a circuit schematic diagram of the dual-path drive scheme of the present invention. The following is in conjunction with... Figure 4 and Figure 4 The specific connection relationships of each module are explained in detail.

[0060] (II) Specific connection relationships and working principles of each module

[0061] 1. Constant Current Module

[0062] The constant current module uses the U1 step-down LED constant current driver chip, which is a continuous current mode step-down LED constant current driver with a simple external circuit. When the input voltage is higher than the LED voltage, it can effectively drive one or more LEDs connected in series. The output current is adjustable, up to a maximum of 1.2A, and is suitable for non-isolated constant current LED driving applications with a voltage range of 5V to 40V. It incorporates a high-voltage, high-power switch and a high-side current detection circuit. Figure 7 This is an internal block diagram of the constant current module.

[0063] Chip startup conditions: After the constant current module is powered on, it passes... The pin supplies power to the chip when The chip circuitry begins to operate once the voltage exceeds 5V. This is to ensure better chip stability. A 0.1μF bypass capacitor should be connected in parallel to the chip ground pin.

[0064] Its peripheral components are connected as follows:

[0065] U1 Pin connected to the positive terminal of the input power supply +, and simultaneously through a 0.1μF chip bypass capacitor. Grounding is used to filter out high-frequency noise. Positive input power supply. It also uses a large-capacity input filter capacitor. (A 10μF capacitor is recommended) Ground it to smooth the input voltage.

[0066] The SW pin of U1 is connected to one end of inductor L1 and the anode of freewheeling diode D3 (Schottky diode). The other end of L1 is connected to the output terminal LED-. The cathode of D3 is... When the internal switch of SW is turned off, the inductor current freewheels through D3.

[0067] The CS pin of U1 is connected to LED+ through a current sampling resistor Rcs. CS detects the voltage drop across Rcs caused by the output current and compares it with an internal 0.1V reference to achieve constant current control.

[0068] The GND pin of U1 is grounded.

[0069] The PWM pin of U1 serves as the dimming and enable control terminal, receiving PWM signals. The PWM port supports PWM dimming with ultra-small duty cycles and can respond to PWM pulse width waveforms of less than 60ns.

[0070] Output filter capacitor Connected to the output terminal of the constant current module Between LED-, it is used to smooth the output current waveform and reduce current ripple when driving LED.

[0071] Output current setting: Precise current control is achieved by sampling the current at the CS port. The output current is sampled by the chip's internal error amplifier and compared with the internal 0.1V, and then amplified to achieve constant current control of the system. The output current formula is as follows:

[0072]

[0073] Inductor Selection and Switching Frequency: Due to the chip's inherent design, different inductor values ​​will affect the switching frequency of the drive. The inductor value determines the rise and fall slope of the output current during switching, and the current slope determines the time it takes for the current to rise from a trough to a peak and from a peak to a trough during FET switching. It is the DC resistance value of inductor L1. It is the voltage drop of the LED light source branch. It is the on-resistance of the power MOSFET inside the driver chip. For current sampling resistor, The drive circuit receives a DC input voltage. , The voltage drop across the freewheeling diode D3. Duration of the inductor charging phase. The switching frequency is calculated using the following formula to determine the duration of the inductor freewheeling discharge phase:

[0074]

[0075]

[0076]

[0077] A larger inductance value results in a slower switching of the output current. Because the CS detects a propagation delay between the MOSFET switches, there is a slight difference between the expected and actual ripple current. When selecting an inductor, the peak current should not exceed the inductor's rated saturation current.

[0078] Selection of freewheeling diode: The rated average current of the freewheeling diode should be greater than the average current flowing through the diode. The formula for calculating the average current is as follows:

[0079]

[0080] The diode should be able to withstand reverse peak voltage; it is recommended to select one with a reverse rated voltage greater than [value missing]. For diodes, fast recovery Schottky diodes are recommended to improve efficiency.

[0081] 2. Switching Unit

[0082] Figure 5 A comparison diagram of the connection methods for conventional four-wire grouped drives and three-wire combined drives. Figure 6 This is the circuit schematic of the reversing module. The switching unit consists of two identical branches, each controlling one of the two light sources.

[0083] First switching unit: When infrared illumination is required, the switching module uses an NPN transistor and a PMOS transistor to switch the light on and off. A high level turns the light on, and a low level turns it off. Specifically, the base of NPN transistor Q1 is connected to the first control signal via resistor R1. The emitter is grounded; the collector is connected to the gate (G) of PMOS transistor Q2, and simultaneously connected to the gate via pull-up resistor R2. The drain of PMOS transistor Q2 is connected to... The S terminal is connected to the positive terminal of the first light source WLED+. The negative terminal is connected to the constant current module output LED-.

[0084] Second switching unit: When white light is needed, the switching module switches the light on and off via another NPN transistor and another PMOS transistor. A high level turns the light on, and a low level turns it off. Specifically, the base of NPN transistor Q3 is connected to the second control signal via resistor R3. The emitter is grounded; the collector is connected to the gate (G) of PMOS transistor Q4, and simultaneously connected to the gate via pull-up resistor R4. The drain of PMOS transistor Q4 is also connected to... The S-terminal is connected to the positive terminal of the second light source IRLED+. The negative terminal of IRLED- is also connected to the common output terminal LED- of the constant current module.

[0085] When the control signal is high, the NPN transistor is turned on, its collector is pulled low, which pulls the gate (G) of the PMOS transistor low, turning the PMOS transistor on (because the drain (D) is connected to the common terminal of the constant current module, LED+, the gate (G) is lower than the source (S), thus turning on the light source. Conversely, it is turned off when the control signal is low.

[0086] 3. Anti-reverse module

[0087] Figure 7 This is the circuit schematic of the anti-reverse module. Because the PWM / EN chip only has a single input port, an anti-reverse function is added here to handle the synchronous PWM dimming function of both groups. The anti-reverse module consists of two diodes, D1 and D2.

[0088] The anode of D1 is connected to the first PWM signal input terminal PWM_IR, and the cathode is connected to the PWM pin of U1.

[0089] The anode of D2 is connected to the second PWM signal input terminal PWM_W, and the cathode is connected to the PWM pin of U1.

[0090] When a PWM_IR signal arrives, it passes through D1 to the chip's PWM pin. Because the reverse current cannot flow through D2, it will not flow back to the white light switching signal, thus providing isolation. When a PWM_W signal arrives, it passes through D2 to the chip's PWM pin. Because the reverse current cannot flow through D1, it will not flow back to the infrared signal switching signal, thus providing isolation. This allows two PWM signals to share the same dimming pin without interfering with each other.

[0091] (III) Work Process

[0092] When the module receives a PWM / EN signal, the infrared control IO goes high and the white light control IO goes low, turning on the infrared light; when the module receives a PWM / EN signal, the infrared control IO goes low and the white light control IO goes high, turning on the white light; when the module receives a PWM / EN signal, the infrared control IO goes low and the white light control IO goes low, turning off all lights.

[0093] Specifically:

[0094] Infrared mode: high, Low. Q1 and Q2 are turned on, and the first light source branch (infrared) is lit. At the same time, the PWM_IR input PWM wave is transmitted through D1 to the PWM pin of U1, adjusting the output current to achieve stepless infrared dimming.

[0095] White light mode: high, Low. Q3 and Q4 are turned on, and the second light source branch (white light) is lit. At the same time, the PWM_W input PWM wave is sent to the PWM pin of U1 via D2 to adjust the output current and achieve stepless dimming of the white light.

[0096] Shutdown mode: When both I / O pins are low, all light sources are turned off.

[0097] (iv) Light source matching design

[0098] Because both sets share a constant current drive, the output current supplied to both types of lamps is equal. To solve the problem of matching the operating voltage and current of infrared and white light, this invention needs to be implemented by combining lamp strings in parallel circuits when selecting light sources.

[0099] The voltage specifications for infrared lamps range from 1.2V to 1.8V. The current ratings for various chips are summarized in the table below:

[0100] Voltage range (V) 1.4-1.8 1.4-1.8 1.4-1.8 1.4-1.8 1.4-1.8 Application current (mA) 60 150 350 700 1000

[0101] The standard voltage for incandescent lamps is between 3V and 3.4V. The current ratings for various lamps are summarized in the table below:

[0102] Voltage range (V) 3-3.4 3-3.4 3-3.4 3-3.4 3-3.4 Application current (mA) 60 150 350 700 1000

[0103] When the two lamps mentioned above share a common output, the circuit design must be based on the table above. For example, infrared lamps have a voltage of 1.2V-1.8V, and white light lamps have a voltage of 3-3.4V. Taking the midpoint values, infrared is approximately 1.5V and white light is approximately 3.2V, which corresponds to a 2:1 ratio. The circuit design should follow this voltage relationship as follows:

[0104]

[0105] Since the constant current output is the same current, the following conditions are met:

[0106]

[0107] When applying this invention, use it as described above, as illustrated in the above figure for a sufficient explanation of its application principle.

[0108] (v) Extension Scheme

[0109] The aforementioned basic drive unit (including a set of constant current modules, two switching units, and one anti-reverse module) can be copied N times to achieve independent control of 2N light sources. Each channel can be dimmed individually.

[0110] (vi) Modified Implementation Methods

[0111] A common positive electrode method can be adopted: connect the positive electrodes of the two light sources to LED+, and connect the switching unit to the negative electrode of the light source and the negative electrode of the constant current module to control the on / off state.

[0112] The control signal can be active low; simply adjust the NPN / PNP polarity or add an inverter accordingly.

[0113] Example 1: Dual-Light Source Security Camera Driver Circuit

[0114] This embodiment selects a continuous current mode step-down LED constant current driver chip U1 with a simple peripheral circuit. The chip has a built-in high-voltage high-power switch and high-end current detection circuit, with an input voltage range of 5V to 40V and a maximum output current of 1.2A.

[0115] Figure 8 This is a typical application circuit diagram for 12V input / 1A output. Figure 9 This is a typical application circuit diagram for 24V input / 1A output. The following explanation, in conjunction with the attached diagram, illustrates component parameter selection:

[0116] Component parameter selection:

[0117] Input voltage +=12V, output current set to 350mA (for driving 0.5W white light or 16mil infrared).

[0118] The sampling resistor Rcs = 0.1V / 0.35A ≈ 0.286Ω, so a 0.3Ω standard resistor is selected.

[0119] The inductor L1 is selected as a 47μH / 1A power inductor.

[0120] The freewheeling diode D3 is an SS34 (40V / 3A) Schottky diode.

[0121] Input filter capacitor It is a 10μF / 25V capacitor.

[0122] Chip bypass capacitor It is a 0.1μF / 50V ceramic capacitor, closely attached to U1. With the GND pin.

[0123] Output filter capacitor It is a 1μF / 50V ceramic capacitor, connected to Between and the earth.

[0124] NPN transistors Q1 and Q3 are selected from MMBT3904, and PMOS transistors Q2 and Q4 are selected from CJ2302.

[0125] Diodes D1 and D2 are selected as 1N5819 diodes.

[0126] The current-limiting resistors R1 and R3 are 1kΩ, and the pull-up resistors R2 and R4 are 10kΩ.

[0127] LED configuration and formula matching verification:

[0128] Infrared branch: Two 16mil infrared LEDs are connected in series (refer to the infrared LED specification table; the application current of a 16mil chip is 350mA, and the voltage is 1.4-1.8V). By combining the two in series, the total operating current is kept below 350mA (close to 350mA), and the total voltage is approximately 3.3V.

[0129] White light branch: Use two 0.5W white LEDs connected in parallel (refer to the white light specification table; two 0.5W chips connected in parallel require a current of 350mA and a voltage of 3-3.4V). The center voltage is approximately 3.2V.

[0130] Verification of voltage compliance: The center voltage of the infrared LED is approximately 1.5V; a single 1.6V LED is selected, and two LEDs connected in series produce 3.2V; the center voltage of the white LED is 3.2V. This basically meets the requirements. Regarding the current, the series-parallel connection structure was adjusted to ensure that the actual operating current of both circuits matched the 350mA setting of the constant current module, thus meeting the requirements. conditions.

[0131] Connection verification:

[0132] according to Figure 4 The circuit schematic shown is used to solder the circuit board. During testing, [the circuit is then]... High level (3.3V). When the signal is low, a 20kHz PWM signal with a 50% duty cycle is input to the PWM_IR input. The infrared LED lights up at 50% brightness. Measuring the waveform on the PWM pin of U1 shows a synchronous PWM signal, proving that the reverse protection is effective. High level, Low PWM_W input signal, white light dimming normally. No delay or crosstalk during switching between two channels. Oscilloscope observation. Waveform, output filter capacitor It effectively smooths the sawtooth wave into a relatively flat DC current. Figure 10 This is the steady-state operating waveform diagram. Figure 11 This is a typical characteristic curve graph.

[0133] Example 2: Four-way light source expansion

[0134] The two basic drive units are combined: constant current module A drives light source 1 (infrared) and light source 2 (white light), and constant current module B drives light source 3 (infrared) and light source 4 (white light). Each module independently controls two channels, achieving a total of four independent dimming channels. This is suitable for monitoring scenarios requiring multi-angle supplemental lighting.

[0135] Example 3: Common Positive Output Deformation

[0136] Connect the positive terminals of both the infrared LED and the white LED to... The PMOS transistor in the switching unit is replaced with an NMOS transistor connected between the negative terminal of the light source and the constant current output LED, and the control signal logic is adjusted accordingly (high level conduction). At this time, the configuration of the freewheeling, sampling, and input / output capacitors remains unchanged, and the single constant current drive dual-channel switching is still achieved.

[0137] This invention features a clear circuit structure and uses common, low-cost components, making it easy to manufacture and debug. By employing a single constant current module, it solves the problem of two outputs while achieving the same function as two separate constant current modules, thus saving the cost of one additional module and achieving cost reduction while maintaining the same functionality. It can be widely applied in security monitoring, smart homes, machine vision, and other fields requiring multi-channel LED supplemental lighting and demanding cost-sensitive applications, possessing significant industrial application value.

[0138] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A high-efficiency multi-path constant current drive circuit, characterized in that: It includes a constant current module, a first switching unit, a second switching unit, and a reverse protection module; The constant current module includes a step-down LED constant current driver chip U1, an inductor L1, a freewheeling diode D3, a current sampling resistor Rcs, and an input filter capacitor. Chip bypass capacitor and output filter capacitor The driver chip U1 has Pins, SW pin, CS pin, GND pin, and PWM pin; Pin connected to the positive terminal of the input power supply +, and through the chip bypass capacitor Grounded, the positive terminal of the input power supply +Also through the input filter capacitor Grounded; the SW pin is connected to the first terminal of the inductor L1 and the anode of the freewheeling diode D3, and the second terminal of the inductor L1 is connected to the output terminal of the constant current module. The cathode of the freewheeling diode D3 is VDD; the CS pin is connected to the output terminal of the constant current module through the current sampling resistor Rcs. The GND pin is grounded; the PWM pin serves as the PWM / EN control terminal of the constant current module; the output filter capacitor... Connected to the output terminal of the constant current module Between and LED; The first switching unit includes a first NPN transistor Q1 and a first PMOS transistor Q2; the base of the first NPN transistor Q1 is connected to the first control signal input terminal through a first current-limiting resistor R1. The emitter of the first NPN transistor Q1 is grounded, the collector of the first NPN transistor Q1 is connected to the gate of the first PMOS transistor Q2, and is connected to the output terminal of the constant current module through the first pull-up resistor R4. The drain (D) of the first PMOS transistor Q2 is connected to the output terminal of the constant current module. The source (S) terminal of the first PMOS transistor Q2 is connected to the positive terminal IRLED+ of the first light source branch; The second switching unit includes a second NPN transistor Q3 and a second PMOS transistor Q4; the base of the second NPN transistor Q3 is connected to the second control signal input terminal through a second current-limiting resistor R5. The emitter of the second NPN transistor Q3 is grounded, the collector of the second NPN transistor Q3 is connected to the gate of the second PMOS transistor Q4, and is connected to the output terminal of the constant current module through the second pull-up resistor R8. The drain of the second PMOS transistor Q4 is connected to the output terminal of the constant current module. The source (S) terminal of the second PMOS transistor Q4 is connected to the positive terminal WLED+ of the second light source branch; the negative terminals of the first light source branch and the second light source branch are connected to LED-. The anti-reverse module includes a first diode D1 and a second diode D2; the anode of the first diode D1 is connected to the input terminal of the first PWM dimming signal. The cathode of the first diode D1 is connected to the PWM pin of the driver chip U1; the anode of the second diode D2 is connected to the second PWM dimming signal input terminal. The cathode of the second diode D2 is connected to the PWM pin of the driver chip U1; When the first control signal The second control signal is high. When the signal is low, the first NPN transistor Q1 and the first PMOS transistor Q2 are turned on, the first light source branch is connected, and the first PWM dimming signal is transmitted to the PWM pin via the first diode D1 to achieve dimming of the first light source; when the second control signal is low... The first control signal is high. When the signal is low, the second NPN transistor Q3 and the second PMOS transistor Q4 are turned on, the second light source branch is turned on, and the second PWM dimming signal is transmitted to the PWM pin through the second diode D2 to realize the dimming of the second light source; when both the first control signal and the second control signal are low, both light sources are turned off.

2. The high-efficiency multi-path constant current drive circuit according to claim 1, characterized in that: The output current of the constant current module is determined by the resistance value of the current sampling resistor Rcs, and the formula for the output current is as follows: ;in: This refers to the output current of the constant current module. The resistance value of the current sampling resistor is specified; the driver chip U1 has a 0.1V reference voltage source and an error amplifier inside, and the voltage detected by the CS pin is compared with the 0.1V reference to control the output current to be constant.

3. The high-efficiency multi-path constant current drive circuit according to claim 1, characterized in that: The inductance value of the inductor L1 determines the switching frequency, wherein: It is the DC resistance value of inductor L1. It is the voltage drop of the LED light source branch. It is the on-resistance of the power MOSFET inside the driver chip. For current sampling resistor, The drive circuit receives a DC input voltage. , The voltage drop across the freewheeling diode D3, Duration of the inductor charging phase. The switching frequency is calculated using the following formula to determine the duration of the inductor freewheeling discharge phase: The larger the inductance value, the slower the output current switches; when selecting an inductor, the peak current should not exceed the inductor's rated saturation current.

4. The high-efficiency multi-path constant current drive circuit according to claim 1, characterized in that: The freewheeling diode D3 is a Schottky diode, whose rated average current is greater than the average current flowing through the diode. The formula for calculating the average current is as follows: The reverse rated voltage of the diode is greater than It is recommended to select a device with a reverse rated voltage greater than [value missing]. For improved efficiency, a fast recovery Schottky diode is recommended. DVrrm> *2。 5. The high-efficiency multi-path constant current drive circuit according to claim 1, characterized in that: The first light source branch is an infrared LED branch, and the second light source branch is a white LED branch; the voltage of the infrared LED and the voltage of the white LED satisfy the following relationship: Furthermore, the operating current of the infrared LED is equal to that of the white LED, that is: 。 6. The high-efficiency multi-path constant current drive circuit according to claim 1, characterized in that: The frequencies of the first PWM dimming signal and the second PWM dimming signal are both 100Hz to 20kHz, and the amplitudes are both 1.5V to 5V. The PWM pin of the driver chip U1 can respond to PWM signals with a pulse width of less than 60ns, thereby realizing stepless dimming with an ultra-small duty cycle. When the PWM signal is low, the output is off; when the PWM signal is high, the output is on. When the high impedance is floating, the port is at a high level by default.

7. The high-efficiency multi-path constant current drive circuit according to claim 1, characterized in that: The input filter capacitor The capacitor is a 10μF / 50V bypass capacitor for the chip. It is a 0.1μF / 50V ceramic capacitor and is in close contact with the above. The output filter capacitor is arranged between the pins and ground. It is a 1μF / 50V ceramic capacitor.

8. The high-efficiency multi-path constant current drive circuit according to claim 1, characterized in that: The resistance values ​​of the first current-limiting resistor R1, the second current-limiting resistor R5, the first pull-up resistor R4, and the second pull-up resistor R8 satisfy the following: when the first control signal or the second control signal is high, the corresponding NPN transistor is saturated and turned on, and the corresponding PMOS transistor is also saturated and turned on.

9. The high-efficiency multi-path constant current drive circuit according to claim 1, characterized in that: The constant current module, the first switching unit, the second switching unit, and the anti-reverse module constitute a basic driving unit. When it is necessary to drive 2N light sources, N basic driving units are set up. The first light source branch and the second light source branch in each basic driving unit are respectively connected to different light sources, thereby realizing the independent control of N groups of constant current modules driving 2N light sources, where N is a positive integer.

10. The high-efficiency multi-path constant current drive circuit according to claim 1, characterized in that: The driving circuit adopts a common negative terminal connection method, where the negative terminals of the first light source branch and the second light source branch are connected to the LED- output. As a variation, it can also be extended to a constant current positive output method, where the positive terminal of the light source is connected to the LED+ terminal, and the switching unit is connected between the negative terminal of the light source and the LED- to realize on / off control.

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