Isolated direct current constant current source circuit

Abstract

The invention provides an isolated direct-current constant-current source circuit, and the circuit comprises an isolation module which isolates an external input from an internal circuit, and converts a first power voltage of the external input into a second power voltage based on a pulse control signal; the rectifying module is used for converting the second power supply voltage into third power supply voltage; the filtering module is used for filtering the third power supply voltage to obtain fourth power supply voltage; the BUCK constant current module is used for converting the fourth power supply voltage into a constant direct current source so as to supply power to a load; the voltage sampling module is used for sampling the voltage signal of the filtering module so as to generate a voltage feedback signal; the current sampling module is used for sampling the current signal of the filtering module so as to generate a current feedback signal; and the PWM control module provides the pulse control signal and adjusts the duty ratio of the pulse control signal based on the voltage feedback signal and the current feedback signal. The precision of the constant current source can be improved.

Description

Technical Field

[0001] The invention relates to the technical field of power electronics, and in particular to an isolated direct current constant current source circuit. Background Art

[0002] The main function of the constant current source circuit is to convert the input voltage into a constant output current. The common output range is from a few milliamperes to tens of amperes. It is widely used in various power electronic equipment, such as motor drive circuits, LED drive circuits, insensitive ignition circuits, etc. According to the input and output conditions, the constant current source can be divided into four types: DC-AC type (DV-AC), DC-DC type (DV-DC), AC-AC type (AV-AC), AC-DC type (AV-DC). The DV-AC type constant current source can convert the DC input voltage into a constant AC output current, the DV-DC type constant current source can convert the DC input voltage into a constant DC output current, the AV-AC type constant current source can convert the AC input voltage into a constant AC output current, and the AV-DC type constant current source can convert the AC input voltage into a constant DC output current.

[0003] With the advancement of electronic technology, the requirements for high integration, small size, and high reliability of constant current source circuits are getting higher and higher. Traditional AV-DC and DV-DC constant current source circuits use the method of controlling the junction resistance of field effect tubes to achieve constant current. Since the junction resistance of field effect tubes is greatly affected by factors such as gate-source voltage and ambient temperature, there are disadvantages such as large circuit volume, low working efficiency, and poor output current accuracy. Summary of the invention

[0004] In view of the above problems existing in the prior art, the present invention proposes an isolated DC constant current source circuit, which mainly solves the problems of poor output current accuracy, large size and low working efficiency of the existing constant current source circuit.

[0005] In order to achieve the above purpose and other purposes, the technical solution adopted by the present invention is as follows.

[0006] The present application provides an isolated DC constant current source circuit, comprising: an isolation module, which isolates an external input from an internal circuit, and converts a first power supply voltage of the external input into a second power supply voltage based on a pulse control signal; wherein the first power supply voltage is a DC voltage and the second power supply voltage is an AC voltage; a rectifier module, which converts the second power supply voltage into a third power supply voltage, wherein the third power supply voltage is a pulsed DC voltage; a filter module, which filters the third power supply voltage to obtain a fourth power supply voltage; a BUCK constant current module, which converts the fourth power supply voltage into a constant DC source to power a load; a voltage sampling module, which samples the voltage signal of the filter module during the shutdown phase of the isolation module to generate a voltage feedback signal; a current sampling module, which samples the current signal of the filter module during the conduction phase of the isolation module to generate a current feedback signal; and a PWM control module, which provides the pulse control signal and adjusts the duty cycle of the pulse control signal based on the voltage feedback signal and the current feedback signal to stabilize the fourth power supply voltage.

[0007] In one embodiment of the present application, the isolation module includes: a first transformer, a first NMOS tube and an eleventh capacitor; one end of the primary winding of the first transformer is connected to the first power supply voltage, and the other end is connected to the drain of the first NMOS tube; one end of the secondary winding of the first transformer is connected to the input end of the rectifier module to output the second power supply voltage, and the other end is connected to the secondary ground; the source of the first NMOS tube is connected to the primary ground, and the gate is connected to the output end of the PWM control module to receive the pulse control signal; one end of the eleventh capacitor is connected to the drain of the first NMOS tube, and the other end is connected to the source of the first NMOS tube.

[0008] In one embodiment of the present application, the rectifier module includes: a first diode, a second diode, a first resistor and a first capacitor; one end of the first resistor is connected to the anode of the first diode as the input end of the rectifier module, and the other end is connected to one end of the first capacitor; the other end of the first capacitor is respectively connected to the cathode of the first diode and the cathode of the second diode as the output end of the rectifier module; the anode of the second diode is connected to the secondary ground.

[0009] In one embodiment of the present application, the filtering module includes: a second transformer, a third transformer, a second capacitor and a second resistor; one end of the primary winding of the second transformer serves as the input end of the filtering module to receive the third power supply voltage, and the other end is connected to one end of the primary winding of the third transformer; the other end of the primary winding of the third transformer is respectively connected to one end of the second capacitor and one end of the second resistor as the output end of the filtering module; the other ends of the second capacitor and the second resistor are both connected to the secondary ground; the secondary winding of the second transformer is connected to the input end of the voltage sampling module, and the secondary winding of the third transformer is connected to the input end of the current sampling module.

[0010] In an embodiment of the present application, the voltage sampling module includes a fourth diode, a seventh capacitor, an eighth capacitor, a ninth capacitor, a tenth capacitor, a third resistor, a fourth resistor, a fifth resistor, a sixth resistor, and a seventh resistor;

[0011] The anode of the fourth diode is respectively connected to one end of the third resistor and one end of the seventh resistor as the first end of the voltage sampling module, and the other end of the third resistor is connected to the primary ground as the second end of the voltage sampling module, wherein the first end and the second end together constitute the input end of the voltage sampling module; the cathode of the fourth diode is connected to one end of the ninth capacitor, and the other end of the ninth capacitor is connected to the primary ground; the other end of the seventh resistor is connected to one end of the eighth capacitor, and the other end of the eighth capacitor is respectively connected to the cathode of the fourth diode, one end of the fourth resistor and one end of the ninth capacitor, and the other end of the fourth resistor is respectively connected to the fifth resistor, one end of the sixth resistor and the tenth capacitor C 10 one end of the fifth resistor, and the other end of the fifth resistor is connected to the primary ground; the connection end of the sixth resistor and the fifth resistor is connected to one end of the tenth capacitor as the output end of the voltage sampling module, and is also connected to the feedback voltage input terminal FB pin of the PWM control module; the other end of the sixth resistor is connected to one end of the seventh capacitor; the other end of the seventh capacitor is connected to the internal operational amplifier output terminal COMP pin of the PWM control module; the other end of the tenth capacitor is connected to the primary ground.

[0012] In an embodiment of the present application, the current sampling module includes a third diode, a fourth capacitor, a fifth capacitor, a sixth capacitor, an eighth resistor, a ninth resistor, a tenth resistor, and an eleventh resistor; the anode of the third diode is respectively connected to one end of the eleventh resistor and one end of the tenth resistor as the fourth end of the current sampling module; the other end of the tenth resistor is connected to the primary ground as the third end of the current sampling module, wherein the third end and the fourth end are jointly used as the input end of the current sampling module; the other end of the eleventh resistor is connected to one end of the fifth capacitor, and the other end of the fifth capacitor is respectively connected to the cathode of the third diode, one end of the fourth capacitor and one end of the eighth resistor, and the other end of the fourth capacitor is connected to the primary ground; the other end of the eighth resistor is respectively connected to one end of the sixth capacitor and one end of the ninth resistor as the output end of the current sampling module to output the current feedback signal, and is also connected to the IS pin of the PWM control module; the other ends of the sixth capacitor and the ninth resistor are both connected to the primary ground.

[0013] In one embodiment of the present application, the BUCK constant current module includes: a BUCK controller, a second NMOS tube, a third NMOS tube, a first inductor, a twelfth resistor, a thirteenth resistor, and a third capacitor; the drain of the second NMOS tube is connected to the output end of the filter module, the source is connected to the drain of the third NMOS tube, and the gate is connected to the HG pin of the BUCK controller; the source of the third NMOS tube is connected to the secondary ground, and the gate is connected to the LG pin of the BUCK controller; one end of the first inductor is connected to the source of the second NMOS tube, and the other end is connected to one end of the twelfth resistor, and the other end of the twelfth resistor is respectively connected to one end of the third capacitor and the positive electrode of the load; the other end of the third capacitor is connected to the secondary ground; one end of the thirteenth resistor is connected to the negative electrode of the load, and the other end is connected to the secondary ground; The thirteenth resistor converts the output current signal into a voltage sampling signal to feed back to the FB1 pin of the BUCK controller; the BUCK controller samples the current at both ends of the twelfth resistor through the CS+ pin and the CS- pin to obtain a corresponding current sampling signal; wherein, the HG pin in the BUCK controller is a high-side drive signal output pin, the LG pin is a low-side drive signal output pin, the CS+ pin is a current sampling signal positive input pin, the CS- pin is a current sampling signal negative input pin, and the FB1 pin is a voltage sampling signal input pin; the current and voltage in the BUCK constant current module are sampled through the CS+ pin, the CS- pin and the FB1 pin, so that the BUCK controller adjusts the output of the HG pin and the LG pin based on the corresponding sampling signal.

[0014] In an embodiment of the present application, an external resistor is provided in parallel with the thirteenth resistor to adjust the voltage sampling signal.

[0015] In an embodiment of the present application, the primary winding inductance of the second transformer is higher than the primary winding inductance of the third transformer.

[0016] In one embodiment of the present application, the PWM control module includes a feedback voltage error operational amplifier, a current comparator, a logic judgment circuit and a totem pole circuit. The FB pin of the PWM control module is the negative input terminal of the feedback voltage error operational amplifier, and the COMP pin of the PWM control module is the output terminal of the feedback voltage error operational amplifier. The output signal of the voltage sampling module is amplified by the feedback voltage error operational amplifier, and then compared with the output signal of the current sampling module detected by the current comparator. After the logic circuit performs logic judgment, a base control signal of the totem pole circuit is generated. The output terminal of the totem pole circuit is the OUTPUT pin of the PWM control module, wherein the totem pole circuit is composed of a PNP transistor and an NPN transistor.

[0017] As described above, the isolated DC constant current source circuit proposed in the present application has the following beneficial effects.

[0018] The present application realizes the isolation of internal and external voltages through an isolation module, controls the on-off time ratio of the isolation module through current sampling and voltage sampling, converts the DC voltage into an isolated DC voltage, and provides the DC voltage to the BUCK constant current module after rectification and filtering, so that the output current is accurately controlled and kept stable, which can effectively improve the accuracy, stability and reliability of the constant current source. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Schematic diagram of the structure of an isolated DC constant current source circuit in one embodiment of the present application.

[0020] Figure 2 Schematic diagram of the circuit structure of an isolated DC constant current source circuit in one embodiment of the present application.

[0021] Figure 3 1 is a simulated waveform diagram of the output voltage of the front-stage circuit under different input voltages in one embodiment of the present application.

[0022] Figure 4 This is a simulated waveform diagram of the output voltage of the isolated DC constant current source circuit under different load resistance values ​​in one embodiment of the present application.

[0023] Description of Figure Numbers:

[0024] Q1-first NMOS tube; Q2-second NMOS tube; Q3-third NMOS tube; R1-first resistor; R2-second resistor; R3-third resistor; R4-fourth resistor; R5-fifth resistor; R6-sixth resistor; R7-seventh resistor; R8-eighth resistor; R9-ninth resistor; R 10 - Tenth resistor; R 11 - Eleventh resistor; R 12 - 12th resistor; R 13 - Thirteenth resistor; R L -Load; R TRIM - external adjustment resistor; C1-first capacitor; C2-second capacitor; C3-third capacitor; C4-fourth capacitor; C5-fifth capacitor; C6-sixth capacitor; C7-seventh capacitor; C8-eighth capacitor; C9-ninth capacitor; C 10 - tenth capacitor; D1 - first diode; D2 - second diode; D3 - third diode; D4 - fourth diode; T1 - first transformer; T2 - second transformer; T3 - third transformer; L1 - first inductor. DETAILED DESCRIPTION

[0025] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the following embodiments and features in the embodiments can be combined with each other without conflict.

[0026] It should be noted that the illustrations provided in the following embodiments are only schematic illustrations of the basic concept of the present invention, and thus the drawings only show components related to the present invention rather than being 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 complicated.

[0027] The inventors have found that:

[0028] The main function of the constant current source circuit is to convert the input voltage into a constant output current. The common output range is from a few milliamperes to tens of amperes. It is widely used in various power electronic equipment, such as motor drive circuits, LED drive circuits, insensitive ignition circuits, etc. With the advancement of electronic technology, the requirements for high integration, small size, and high reliability of constant current source circuits are getting higher and higher.

[0029] Traditional AV-DC and DV-DC constant current source circuits use the method of controlling the junction resistance of the field effect tube to achieve the purpose of constant current. Since the junction resistance of the field effect tube is greatly affected by factors such as gate-source voltage and ambient temperature, especially in isolation, there are disadvantages such as large circuit size, low working efficiency, and poor output current accuracy.

[0030] Based on the above problems existing in the prior art, the present application proposes an isolated DC constant current source circuit. The technical solution of the present application is described in detail below in conjunction with specific embodiments.

[0031] The isolated DC constant current source circuit provided in the embodiment of the present application includes: an isolation module, which isolates the external input from the internal circuit, and converts the first power supply voltage of the external input into a second power supply voltage based on a pulse control signal; wherein the first power supply voltage is a DC voltage and the second power supply voltage is an AC voltage; a rectifier module, which converts the second power supply voltage into a third power supply voltage, wherein the third power supply voltage is a pulsed DC voltage; a filter module, which filters the third power supply voltage to obtain a fourth power supply voltage; a BUCK constant current module, which converts the fourth power supply voltage into a constant DC source to power the load RL; a voltage sampling module, which samples the voltage signal of the filter module during the shutdown phase of the isolation module to generate a voltage feedback signal; a current sampling module, which samples the current signal of the filter module during the conduction phase of the isolation module to generate a current feedback signal; and a PWM control module, which provides the pulse control signal and adjusts the duty cycle of the pulse control signal based on the voltage feedback signal and the current feedback signal to stabilize the fourth power supply voltage. Specifically, please refer to Figure 1 , Figure 1 Schematic diagram of the architecture of an isolated DC constant current source circuit in one embodiment of the present application. The isolation module is connected to the first power supply voltage V1, and based on the fifth control signal P5 (i.e., the pulse control signal), the first power supply voltage V1 is converted into a second power supply voltage V2. The rectifier module rectifies the second power supply voltage V2 and converts it into a third power supply voltage V3. The filter module filters the third power supply voltage V3 and outputs a fourth power supply voltage V4. The BUCK constant current module converts the fourth power supply voltage V4 into a constant DC I LOAD , provided to the load R L. The voltage sampling module samples the voltage signal from the filter module, and uses the sampled voltage signal as the first control signal P1, and generates a fourth control signal P4 (i.e., a voltage feedback signal) under the action of the first control signal P1. The current sampling module samples the current signal from the filter module, and uses the sampled current signal as the second control signal P2, and generates a third control signal P3 under the action of the second control signal P2. The PWM control module processes the third control signal P3 and the fourth control signal P4 to generate the fifth control signal P5.

[0032] In one embodiment, an isolation module, a rectification module, a filtering module, a voltage sampling module, a current sampling module, and a PWM control module constitute a front-stage circuit. A forward switching power supply working mode is adopted, and the first voltage V1 at the input end is mainly converted into a relatively stable DC output fourth voltage V4. The voltage sampling module and the current sampling module sample the voltage and current signals respectively in the secondary circuit, and obtain corresponding feedback control signals P4 and P3, which are respectively provided to the PWM controller to adjust the duty cycle of the switch tube Q1 in the isolation module. The fourth voltage V4 enters the BUCK constant current module, and after the current signal is sampled, it is converted into a precise and stable output DC I LOAD If an external trim resistor is connected to the TRIM port, the BUCK constant current module can adjust the output current I LOAD Make adjustments.

[0033] See also Figure 2 , Figure 2 Schematic diagram of the circuit structure of an isolated DC constant current source circuit in an embodiment of the present application. The isolation module includes: a first transformer T1, a first NMOS transistor Q1 and an eleventh capacitor C 11 ; One end of the primary winding of the first transformer T1 is connected to the first power supply voltage V1, and the other end is connected to the drain of the first NMOS tube Q1; the second voltage is generated at the secondary winding of the first transformer T1; one end of the secondary winding of the first transformer T1 is connected to the input end of the rectifier module to generate the third power supply voltage, and the other end is connected to the secondary ground; the source of the first NMOS tube Q1 is connected to the primary ground, and the gate is connected to the output end of the PWM control module to receive the pulse control signal; the eleventh capacitor C 11 One end is connected to the drain of the first NMOS tube Q1 , and the other end is connected to the source of the first NMOS tube Q1 .

[0034] In one embodiment, the first NMOS transistor Q1 can be turned on and off according to the OUTPUT pin signal (ie, the pulse control signal) of the PWM control module. 11It is one of the key components for the first transformer T1 to achieve forward resonance reset. The turns ratio of the first transformer T1 is determined according to the range of the first power supply voltage V1, the range of the output fourth power supply voltage V4 and other specific conditions, and is not limited here.

[0035] In one embodiment, the rectifier module includes: a first diode D1, a second diode D2, a first resistor R1 and a first capacitor C1; one end of the first resistor R1 is connected to the anode of the first diode D1 as the input end of the rectifier module, and the other end is connected to one end of the first capacitor C1; the other end of the first capacitor C1 is respectively connected to the cathode of the first diode D1 and the cathode of the second diode D2 as the output end of the rectifier module; the anode of the second diode D2 is connected to the secondary ground.

[0036] In one embodiment, the first capacitor C1 is one of the key components for resonant reset of the first transformer T1; the rectifier module is not limited to the above structure, and other rectifier topologies may be used to rectify the second power supply voltage V2, such as a synchronous rectifier structure.

[0037] In one embodiment, the filtering module includes: a second transformer T2, a third transformer T3, a second capacitor C2 and a second resistor R2; one end of the primary winding of the second transformer T2 serves as an input end of the filtering module to receive the third power supply voltage V3, and the other end is connected to one end of the primary winding of the third transformer T3; the other end of the primary winding of the third transformer T3 is respectively connected to one end of the second capacitor C2 and one end of the second resistor R2 as an output end of the filtering module; the other ends of the second capacitor C2 and the second resistor R2 are both connected to the secondary ground; the secondary winding of the second transformer T2 is connected to the input end of the voltage sampling module, and the secondary winding of the third transformer T3 is connected to the input end of the current sampling module.

[0038] In one embodiment, the resistance of the second resistor R2 is generally in the kΩ level; the second transformer T2 and the third transformer T3 constitute a filter circuit and also respectively play the role of voltage and current sampling, the difference is that the primary winding inductance of the second transformer T2 is in the μH level, and the primary winding inductance of the third transformer T3 is in the nH level.

[0039] In one embodiment, the voltage sampling module includes a fourth diode D4, a seventh capacitor C7, an eighth capacitor C8, a ninth capacitor C9, a tenth capacitor C 10, a third resistor R3, a fourth resistor R4, a fifth resistor R5, a sixth resistor R6, and a seventh resistor R7; the anode of the fourth diode D4 is respectively connected to one end of the third resistor R3 and one end of the seventh resistor R7 as the first end of the voltage sampling module, and the other end of the third resistor R3 is connected to the primary ground as the second end of the voltage sampling module, wherein the first end and the second end together constitute the input end of the voltage sampling module; the cathode of the fourth diode D4 is connected to one end of the ninth capacitor C9, and the other end of the ninth capacitor C9 is connected to the primary ground; the other end of the seventh resistor R7 is connected to one end of the eighth capacitor C8, and the other end of the eighth capacitor C8 is respectively connected to the cathode of the fourth diode D4, one end of the fourth resistor R4 and one end of the ninth capacitor C9, and the other end of the fourth resistor R4 is respectively connected to the fifth resistor R5, one end of the sixth resistor R6 and the tenth capacitor C 10 The connecting end of the sixth resistor R6 and the fifth resistor R5 is connected to the tenth capacitor C 10 As the output end of the voltage sampling module, one end is connected to the feedback voltage input terminal FB pin of the PWM control module; the other end of the sixth resistor R6 is connected to one end of the seventh capacitor C7; the other end of the seventh capacitor C7 is connected to the internal operational amplifier output terminal COMP pin of the PWM control module; the tenth capacitor C 10 The other end of the voltage sampling module is connected to the primary ground. Specifically, the first end of the voltage sampling module can be connected to one end of the secondary winding of the second transformer T2, and the second end can be connected to the other end of the secondary winding of the second transformer T2.

[0040] In one embodiment, the voltage sampling module samples the voltage when the first NMOS transistor Q1 is turned off. Figure 1 The voltage at point A is then converted into a voltage feedback signal and sent to the FB pin of the PWM controller. The RC network composed of the seventh resistor R7 and the eighth capacitor C8 plays a role in improving the sampling signal.

[0041] In one embodiment, the current sampling module includes a third diode D3, a fourth capacitor C4, a fifth capacitor C5, a sixth capacitor C6, an eighth resistor R8, a ninth resistor R9, a tenth resistor R 10 11th resistor R 11 The anode of the third diode D3 is connected to the eleventh resistor R 11 One end and the tenth resistor R 10 as the fourth end of the current sampling module; the tenth resistor R 10 The other end of the resistor R is connected to the primary ground as the third end of the current sampling module, wherein the third end and the fourth end are used together as the input end of the current sampling module; the eleventh resistor R 11The other end of the current sampling module is connected to one end of the fifth capacitor C5, and the other end of the fifth capacitor C5 is respectively connected to the cathode of the third diode D3, one end of the fourth capacitor C4 and one end of the eighth resistor R8, and the other end of the fourth capacitor C4 is connected to the primary ground; the other end of the eighth resistor R8 is respectively connected to one end of the sixth capacitor C6 and one end of the ninth resistor R9 as the output end of the current sampling module to output the current feedback signal; and is connected to the IS pin of the PWM control module; the other ends of the sixth capacitor C6 and the ninth resistor R9 are both connected to the primary ground. Specifically, the third end of the current sampling module is connected to one end of the secondary winding of the third transformer T3, and the fourth end is connected to the other end of the secondary winding of the third transformer T3.

[0042] In one embodiment, the turns ratios of the primary winding and the secondary winding of the second transformer T2 and the third transformer T3 are 1:NT2 and 1:NT3 respectively, the value range of NT2 is several to several tens, and the value range of NT3 is several tens to several hundred. The inductance of the primary and secondary windings of the second transformer T2 is μH level, and the inductance of the primary winding of the third transformer T3 is nH level and the inductance of the secondary winding is mH level. The second transformer T2 samples the output voltage during the off period of the first NMOS tube Q1, and generates a feedback voltage signal after conditioning. The third transformer T3 samples the current during the on period of the first NMOS tube Q1, and generates a current feedback signal after conditioning. The conditioned voltage feedback signal and current feedback signal are sent to the PWM controller for processing to generate a reasonable drive signal (i.e., a pulse control signal), thereby controlling the output voltage of the previous circuit. The voltage sampling module and the current sampling module have simple structures, and both can realize isolated sampling, which is conducive to reducing circuit costs.

[0043] In one embodiment, the BUCK constant current module includes: a BUCK controller, a second NMOS transistor Q2, a third NMOS transistor Q3, a first inductor L1, a twelfth resistor R 12 、Thirteenth resistor R 13 , a third capacitor C3; the drain of the second NMOS tube Q2 is connected to the output end of the filter module, the source is connected to the drain of the third NMOS tube Q3, and the gate is connected to the HG pin of the BUCK controller; the source of the third NMOS tube Q3 is connected to the secondary ground, and the gate is connected to the LG pin of the BUCK controller; one end of the first inductor is connected to the source of the second NMOS tube Q2, and the other end is connected to the twelfth resistor R 12 One end of the twelfth resistor R 12 The other end of the thirteenth resistor R 13 One end is connected to the negative electrode of the load, and the other end is connected to the secondary ground; the thirteenth resistor R 13The output current signal is converted into a voltage sampling signal to be fed back to the FB1 pin of the BUCK controller; the BUCK controller controls the twelfth resistor R through the CS+ pin and the CS- pin. 12 The current at both ends is sampled to obtain the corresponding current sampling signal; wherein, the HG pin in the BUCK controller is the high-side drive signal output pin, the LG pin is the low-side drive signal output pin, the CS+ pin is the current sampling signal positive input pin, the CS- pin is the current sampling signal negative input pin, and the FB1 pin is the voltage sampling signal input pin; the current and voltage in the BUCK constant current module are sampled through the CS+ pin, the CS- pin and the FB1 pin, so that the BUCK controller adjusts the output of the HG pin and the LG pin based on the corresponding sampling signal. After sampling the current signal in the BUCK constant current module through the CS+ pin, the CS- pin and the FB1 pin, the BUCK controller can generate reasonable high-side drive signals and low-side drive signals.

[0044] In one embodiment, the output current I LOAD Maximum not more than 10A, load R L The twelfth resistor R 12 、Thirteenth resistor R 13 They are all in the mΩ level, and the voltage drop they can withstand is from tens of mV to hundreds of mV. The greater the output current, the smaller the resistance.

[0045] In one embodiment, the PWM control module includes a feedback voltage error operational amplifier, a limiter circuit, a current comparator, a logic judgment circuit and a totem pole circuit. The FB pin of the PWM control module is the negative input terminal of the feedback voltage error operational amplifier, and the COMP pin of the PWM control module is the output terminal of the feedback voltage error operational amplifier. The output signal of the voltage sampling module is amplified by the feedback voltage error operational amplifier, limited by the limiter circuit, and compared with the output signal of the current sampling module detected by the current comparator. After the logic circuit performs logic judgment, the base control signal of the totem pole circuit is generated. The output terminal of the totem pole circuit is the OUTPUT pin of the PWM control module, and the pulse control signal is generated through the OUTPUT pin. The totem pole circuit is composed of a PNP transistor and an NPN transistor.

[0046] See also Figure 3 , Figure 3 : This is a simulation waveform diagram of the output voltage of the front-stage circuit under different input voltages in one embodiment of the present application. The output voltage of the front-stage circuit is Figure 2 The voltage at point A is respectively for input V1 = 16V / 28V / 40V and load R L The voltage at point A is simulated under three conditions: =6Ω.

[0047] like Figure 3 As shown, as the input voltage V1 increases, the voltage rise time at point A decreases and finally stabilizes at about 45 V. The voltage at point A can be adjusted by resistors R4, R5 and the primary-to-secondary turns ratio of the second transformer T2.

[0048] See also Figure 4 , Figure 4 The output voltage simulation waveform of the isolated DC constant current source circuit under different load resistance values ​​in one embodiment of the present application is shown in FIG. The output voltage of the isolated DC constant current source circuit is Figure 2 The voltage between points B and C is respectively L The voltage between points B and C was simulated under three conditions: =1Ω / 3Ω / 5Ω and input V1=28V.

[0049] like Figure 4 As shown, R L =1Ω, the voltage between points B and C is about 6V; R L =3Ω, the voltage between points B and C is about 18V; R L =5Ω, the voltage between points B and C is about 30V. It can be seen that the output current I O It is 6A, and the waveform stability is good and the accuracy is high.

[0050] Based on the technical solution of the above embodiment of the present application, the DC input voltage can be converted into a constant DC output current, and the input stage is isolated from the output stage circuit. The circuit of the present application has high reliability and simple structure, and the circuit includes: an isolation module, a rectifier module, a filter module, a BUCK constant current module, a current sampling module, a voltage sampling module, and a PWM control module. The isolation module converts the primary DC voltage into an AC voltage and isolates the secondary circuit. The rectifier module rectifies the AC voltage into a DC voltage. The voltage sampling module and the current sampling module sample the rectified DC voltage and current signals respectively. The PWM control module adjusts the conduction duty cycle of the field effect tube in the isolation module in real time according to the received voltage and current sampling signals, thereby controlling the output voltage of the front-stage circuit. The filter module filters the rectified DC voltage to obtain a stable DC voltage, and the module shares the inductive device with the voltage sampling module and the current sampling module. The BUCK constant current module converts the output voltage of the front-stage circuit into a constant DC output, and an external resistor can be connected to the TRIM port as needed to adjust the output current. In the present application, the voltage sampling module and the current sampling module use the transformer winding to sample the rectified voltage and current, which can play the role of isolated sampling, and use the BUCK circuit to achieve constant current, which has the advantages of high working efficiency, high current output accuracy, and strong environmental adaptability.

[0051] 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 familiar with 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 a person of ordinary skill in the art without departing from the spirit and technical ideas disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. An isolated DC constant current source circuit, characterized in that: include: an isolation module, which isolates the external input from the internal circuit and converts a first power supply voltage of the external input into a second power supply voltage based on a pulse control signal; The first power supply voltage is a DC voltage, and the second power supply voltage is an AC voltage; a rectifier module, which converts the second power supply voltage into a third power supply voltage, wherein the third power supply voltage is a pulsed DC voltage; a filtering module, configured to filter the third power supply voltage to obtain a fourth power supply voltage; A BUCK constant current module, which converts the fourth power supply voltage into a constant direct current source to supply power to a load; A voltage sampling module, which samples the voltage signal of the filtering module when the isolation module is turned off to generate a voltage feedback signal; A current sampling module, which samples the current signal of the filtering module during the conduction phase of the isolation module to generate a current feedback signal; as well as, The PWM control module provides the pulse control signal and adjusts the duty cycle of the pulse control signal based on the voltage feedback signal and the current feedback signal to stabilize the fourth power supply voltage.

2. The isolated DC constant current source circuit according to claim 1, characterized in that: The isolation module includes: a first transformer, a first NMOS tube and an eleventh capacitor; one end of the primary winding of the first transformer is connected to the first power supply voltage, and the other end is connected to the drain of the first NMOS tube; one end of the secondary winding of the first transformer is connected to the input end of the rectifier module to output the second power supply voltage, and the other end is connected to the secondary ground; the source of the first NMOS tube is connected to the primary ground, and the gate is connected to the output end of the PWM control module to receive the pulse control signal; one end of the eleventh capacitor is connected to the drain of the first NMOS tube, and the other end is connected to the source of the first NMOS tube.

3. The isolated DC constant current source circuit according to claim 1, characterized in that: The rectifier module includes: a first diode, a second diode, a first resistor and a first capacitor; one end of the first resistor is connected to the anode of the first diode as the input end of the rectifier module, and the other end is connected to one end of the first capacitor; the other end of the first capacitor is respectively connected to the cathode of the first diode and the cathode of the second diode as the output end of the rectifier module; the anode of the second diode is connected to the secondary ground.

4. The isolated DC constant current source circuit according to claim 1, characterized in that: The filtering module includes: a second transformer, a third transformer, a second capacitor and a second resistor; one end of the primary winding of the second transformer serves as the input end of the filtering module to receive the third power supply voltage, and the other end is connected to one end of the primary winding of the third transformer; the other end of the primary winding of the third transformer is respectively connected to one end of the second capacitor and one end of the second resistor as the output end of the filtering module; the other ends of the second capacitor and the second resistor are both connected to the secondary ground; the secondary winding of the second transformer is connected to the input end of the voltage sampling module, and the secondary winding of the third transformer is connected to the input end of the current sampling module.

5. The isolated DC constant current source circuit according to claim 1, characterized in that: The voltage sampling module includes a fourth diode, a seventh capacitor, an eighth capacitor, a ninth capacitor, a tenth capacitor, a third resistor, a fourth resistor, a fifth resistor, a sixth resistor, and a seventh resistor; the anode of the fourth diode is respectively connected to one end of the third resistor and one end of the seventh resistor as the first end of the voltage sampling module, and the other end of the third resistor is connected to the primary ground as the second end of the voltage sampling module, wherein the first end and the second end together constitute the input end of the voltage sampling module; the cathode of the fourth diode is connected to one end of the ninth capacitor, and the other end of the ninth capacitor is connected to the primary ground; the other end of the seventh resistor is connected to one end of the eighth capacitor, and the other end of the eighth capacitor is connected to the primary ground. The cathode of the fourth diode, one end of the fourth resistor and one end of the ninth capacitor are respectively connected, the other end of the fourth resistor is respectively connected to the fifth resistor, one end of the sixth resistor and one end of the tenth capacitor, and the other end of the fifth resistor is connected to the primary ground; the connection end of the sixth resistor and the fifth resistor is connected to one end of the tenth capacitor as the output end of the voltage sampling module, and is also connected to the feedback voltage input terminal FB pin of the PWM control module; the other end of the sixth resistor is connected to one end of the seventh capacitor; the other end of the seventh capacitor is connected to the internal operational amplifier output terminal COMP pin of the PWM control module; the other end of the tenth capacitor is connected to the primary ground.

6. The isolated DC constant current source circuit according to claim 1, characterized in that: The current sampling module includes a third diode, a fourth capacitor, a fifth capacitor, a sixth capacitor, an eighth resistor, a ninth resistor, a tenth resistor, and an eleventh resistor; the anode of the third diode is respectively connected to one end of the eleventh resistor and one end of the tenth resistor as the fourth end of the current sampling module; the other end of the tenth resistor is connected to the primary ground as the third end of the current sampling module, wherein the third end and the fourth end are jointly used as the input end of the current sampling module; the other end of the eleventh resistor is connected to one end of the fifth capacitor, the other end of the fifth capacitor is respectively connected to the cathode of the third diode, one end of the fourth capacitor and one end of the eighth resistor, and the other end of the fourth capacitor is connected to the primary ground; the other end of the eighth resistor is respectively connected to one end of the sixth capacitor and one end of the ninth resistor as the output end of the current sampling module to output the current feedback signal, and is connected to the IS pin of the PWM control module; the other ends of the sixth capacitor and the ninth resistor are both connected to the primary ground.

7. The isolated DC constant current source circuit according to claim 1, characterized in that: The BUCK constant current module includes: a BUCK controller, a second NMOS tube, a third NMOS tube, a first inductor, a twelfth resistor, a thirteenth resistor, and a third capacitor; the drain of the second NMOS tube is connected to the output end of the filter module, the source is connected to the drain of the third NMOS tube, and the gate is connected to the HG pin of the BUCK controller; the source of the third NMOS tube is connected to the secondary ground, and the gate is connected to the LG pin of the BUCK controller; one end of the first inductor is connected to the source of the second NMOS tube, and the other end is connected to one end of the twelfth resistor, and the other end of the twelfth resistor is respectively connected to one end of the third capacitor and the positive electrode of the load; the other end of the third capacitor is connected to the secondary ground; one end of the thirteenth resistor is connected to the negative electrode of the load, and the other end is connected to the secondary ground; The resistor converts the output current signal into a voltage sampling signal to feed back to the FB1 pin of the BUCK controller; the BUCK controller samples the current at both ends of the twelfth resistor through the CS+ pin and the CS- pin to obtain a corresponding current sampling signal; wherein, the HG pin in the BUCK controller is a high-side drive signal output pin, the LG pin is a low-side drive signal output pin, the CS+ pin is a current sampling signal positive input pin, the CS- pin is a current sampling signal negative input pin, and the FB1 pin is a voltage sampling signal input pin; the current and voltage in the BUCK constant current module are sampled through the CS+ pin, the CS- pin and the FB1 pin, so that the BUCK controller adjusts the output of the HG pin and the LG pin based on the corresponding sampling signal.

8. The isolated DC constant current source circuit according to claim 7, characterized in that: An external resistor is provided in parallel with the thirteenth resistor to adjust the voltage sampling signal.

9. The isolated DC constant current source circuit according to claim 5, characterized in that: The inductance of the primary winding of the second transformer is higher than the inductance of the primary winding of the third transformer.

10. The isolated DC constant current source circuit according to claim 2, characterized in that: The PWM control module includes a feedback voltage error operational amplifier, a current comparator, a logic judgment circuit and a totem pole circuit. The FB pin of the PWM control module is the negative input terminal of the feedback voltage error operational amplifier, and the COMP pin of the PWM control module is the output terminal of the feedback voltage error operational amplifier. The output signal of the voltage sampling module is amplified by the feedback voltage error operational amplifier, and then compared with the output signal of the current sampling module detected by the current comparator. After the logic circuit performs logic judgment, a base control signal of the totem pole circuit is generated. The output terminal of the totem pole circuit is the OUTPUT pin of the PWM control module, wherein the totem pole circuit is composed of a PNP transistor and an NPN transistor.

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