A low-cost analog signal isolation conversion circuit

Abstract

This utility model discloses a high-precision and low-cost analog signal isolation and conversion circuit, comprising: a resistor voltage divider circuit, a voltage follower circuit, a signal transmission modulation circuit, a first transformer, a signal coupling demodulation circuit, a signal output circuit, a Schmitt oscillator circuit, a DC / AC conversion circuit, and a second transformer; the input terminal of the resistor voltage divider circuit is connected to the signal input terminal, the output terminal of the resistor voltage divider circuit is electrically connected to the input terminal of the voltage follower circuit, the output terminal of the voltage follower circuit is electrically connected to the input terminal of the signal transmission modulation circuit, the output terminal of the signal transmission modulation circuit is electrically connected to the primary winding terminal of the first transformer, the secondary winding terminal of the first transformer is electrically connected to the input terminal of the signal coupling demodulation circuit, the output terminal of the signal coupling demodulation circuit is electrically connected to the input terminal of the signal output circuit, and the output terminal of the signal output circuit is connected to the signal output terminal.

Description

Technical Field

[0001] This utility model relates to the field of electronic circuit technology, specifically to a low-cost analog signal isolation and conversion circuit. Background Technology

[0002] Common analog signal isolation methods include capacitive isolation, opto-isolation, and electromagnetic isolation. Capacitive isolation is represented by isolation amplifiers, which offer excellent accuracy but are very expensive. Opto-isolation is represented by optocouplers, which come in linear and nonlinear types. Linear optocouplers guarantee high linearity but also suffer from high cost. Nonlinear optocouplers use PWM conversion and require an MCU for operation. They offer high accuracy and low cost, but the digital response time is longer than the analog response time, making them unsuitable for applications requiring rapid response. Electromagnetic isolation is represented by transformers, which are commonly used for current coupling applications. This method offers high accuracy and low cost, but suffers from high power consumption in multi-channel analog signal isolation and conversion applications. Utility Model Content

[0003] The purpose of this invention is to overcome the defects in the existing technology and provide a high-precision and low-cost analog signal isolation and conversion circuit.

[0004] To achieve the above objectives, the technical solution of this utility model is to design a low-cost analog signal isolation and conversion circuit, comprising: Resistor voltage divider circuit, voltage follower circuit, signal transmission modulation circuit, first transformer, signal coupling demodulation circuit, signal output circuit, Schmitt oscillator circuit, DC / AC conversion circuit and second transformer; The input terminal of the resistor voltage divider circuit is connected to the signal input terminal. The output terminal of the resistor voltage divider circuit is electrically connected to the input terminal of the voltage follower circuit. The output terminal of the voltage follower circuit is electrically connected to the input terminal of the signal transmission modulation circuit. The output terminal of the signal transmission modulation circuit is electrically connected to the primary winding terminal of the first transformer. The secondary winding terminal of the first transformer is electrically connected to the input terminal of the signal coupling demodulation circuit. The output terminal of the signal coupling demodulation circuit is electrically connected to the input terminal of the signal output circuit. The output terminal of the signal output circuit is connected to the signal output terminal. The power supply terminal of the Schmitt oscillator circuit is electrically connected to the first power supply VCC. The output terminal of the Schmitt oscillator circuit is electrically connected to the driving terminal of the signal coupling demodulation circuit and the driving terminal of the DC / AC conversion circuit. The input terminal of the DC / AC conversion circuit is electrically connected to the first power supply VCC. The output terminal of the DC / AC conversion circuit is electrically connected to the primary winding terminal of the second transformer. The secondary winding terminal of the second transformer is electrically connected to the driving terminal of the signal transmission modulation circuit.

[0005] Furthermore, the resistor voltage divider circuit includes a first resistor, a second resistor, a third resistor, a fourth resistor, and a first capacitor; The first end of the third resistor is connected to the signal input terminal. The second end of the third resistor is electrically connected to the first end of the second resistor. The second end of the second resistor is electrically connected to the first end of the first resistor. The first end of the fourth resistor is connected in parallel between the second resistor and the first resistor. The second end of the fourth resistor is electrically connected to the input terminal of the voltage follower circuit. The first end of the first capacitor is connected in parallel between the fourth resistor and the input terminal of the voltage follower circuit. The second ends of the first resistor and the second ends of the first capacitor are grounded.

[0006] Furthermore, the voltage follower circuit includes a first operational amplifier; The non-inverting input of the first operational amplifier is electrically connected to the output of the resistor divider circuit, the output of the first operational amplifier is electrically connected to the input of the signal transmission modulation circuit, and the inverting input of the first operational amplifier is connected in parallel to the output of the first operational amplifier.

[0007] Furthermore, the signal transmission modulation circuit includes a fifth resistor, a sixth resistor, a first NMOS transistor, and a second capacitor; The first terminal of the second capacitor is electrically connected to the output terminal of the voltage follower circuit, the second terminal of the second capacitor is electrically connected to the drain of the first NMOS transistor, the source of the first NMOS transistor is grounded, the gate of the first NMOS transistor is electrically connected to the first terminal of the fifth resistor, the second terminal of the fifth resistor is electrically connected to the secondary winding terminal of the second transformer, the sixth resistor is connected in parallel between the source and gate of the first NMOS transistor, and the two ends of the primary winding of the first transformer are connected in parallel between the two ends of the second capacitor.

[0008] Furthermore, the signal coupling demodulation circuit includes a third capacitor, a second NMOS transistor, a seventh resistor, and an eighth resistor; The two ends of the secondary winding of the first transformer are connected in parallel to the two ends of the third capacitor. The first end of the third capacitor is electrically connected to the input terminal of the signal output circuit. The second end of the third capacitor is electrically connected to the drain of the second NMOS transistor. The source of the second NMOS transistor is grounded. The gate of the second NMOS transistor is electrically connected to the first end of the eighth resistor. The second end of the eighth resistor is electrically connected to the output terminal of the Schmitt trigger oscillator circuit. The seventh resistor is connected in parallel between the source and gate of the second NMOS transistor.

[0009] Furthermore, the signal output circuit includes a ninth resistor, a tenth resistor, an adjustable resistor, a second operational amplifier, an eleventh resistor, and a twelfth resistor; The first end of the ninth resistor is electrically connected to the output terminal of the signal coupling demodulation circuit. The second end of the ninth resistor is electrically connected to the first end of the adjustable resistor. The second end of the adjustable resistor is electrically connected to the first end of the tenth resistor. The control terminal of the adjustable resistor is electrically connected to the non-inverting input terminal of the second operational amplifier. The output terminal of the second operational amplifier is connected to the signal output terminal. The eleventh resistor is connected in parallel between the inverting input terminal and the output terminal of the second operational amplifier. The first end of the twelfth resistor is connected in parallel between the inverting input terminal of the second operational amplifier and the eleventh resistor. The second end of the twelfth resistor and the second end of the tenth resistor are grounded. The power supply terminal of the second operational amplifier is electrically connected to the first power supply.

[0010] Furthermore, the Schmitt oscillator circuit includes a thirteenth resistor, a Zener diode, a fourth capacitor, a logic gate chip, a fifth capacitor, and a fourteenth resistor; The first end of the thirteenth resistor is electrically connected to the first power supply, the second end of the thirteenth resistor is electrically connected to the power supply pin of the logic gate chip, the cathode of the Zener diode is connected in parallel between the second end of the thirteenth resistor and the power supply pin of the logic gate chip, the first end of the fourth capacitor is connected in parallel between the cathode of the Zener diode and the power supply pin of the logic gate chip, the anode of the Zener diode, the second end of the fourth capacitor, and the ground pin of the logic gate chip are connected in parallel to ground, the output pin of the logic gate chip is electrically connected to the first end of the fifth capacitor, the input pin of the logic gate chip is electrically connected to the first end of the fourteenth resistor, the second end of the fifth capacitor is connected in parallel between the fourteenth resistor and the input pin of the logic gate chip, and the second end of the fourteenth resistor is electrically connected to the driving terminal of the signal coupling demodulation circuit and the driving terminal of the DC / AC conversion circuit.

[0011] Furthermore, the DC / AC conversion circuit includes a fifteenth resistor, a sixth capacitor, a seventh capacitor, a PNP transistor, an NPN transistor, an eighth capacitor, and a ninth capacitor. The first end of the fifteenth resistor is electrically connected to the output terminal of the Schmitt trigger circuit. The first end of the sixth capacitor C9 is connected in parallel with the first end of the seventh capacitor to the second end of the fifteenth resistor. The second end of the sixth capacitor is electrically connected to the base of the PNP transistor. The second end of the seventh capacitor is electrically connected to the base of the NPN transistor. The emitter of the PNP transistor is connected in parallel with the first end of the eighth capacitor to the first power supply. The second end of the eighth capacitor is connected in parallel with the first end of the ninth capacitor to the first end of the primary winding of the second transformer. The collector of the PNP transistor is connected in parallel with the collector of the NPN transistor to the second end of the primary winding of the second transformer. The emitter of the NPN transistor is connected in parallel with the second end of the ninth capacitor to ground.

[0012] Furthermore, the low-cost analog signal isolation conversion circuit also includes an AC / DC conversion circuit. The input terminal of the AC / DC conversion circuit is electrically connected to the secondary winding terminal of the second transformer, and the output terminal of the AC / DC conversion circuit outputs a second power supply to power the power supply terminal of the voltage follower circuit.

[0013] Furthermore, the AC / DC conversion circuit includes dual diodes, a tenth capacitor, and an eleventh capacitor; The common terminal of the dual diodes is electrically connected to the first terminal of the secondary winding of the transformer. The parallel output terminal of the cathode of the dual diodes and the first terminal of the eleventh capacitor serves as the positive output terminal of the second power supply. The parallel output terminal of the anode of the dual diodes and the first terminal of the tenth capacitor serves as the negative output terminal of the second power supply. The second terminal of the eleventh capacitor and the second terminal of the tenth capacitor are connected to ground in parallel with the second terminal of the secondary winding of the transformer.

[0014] The advantages and beneficial effects of this invention are as follows: the resistor voltage divider circuit preprocesses the input signal, and the voltage follower circuit ensures signal anti-interference capability and impedance matching, laying the foundation for improved accuracy; the signal transmission modulation circuit, the first transformer T1, and the signal coupling demodulation circuit work together to complete signal isolation transmission and accurate demodulation, avoiding interference affecting accuracy; the signal output circuit can be adjusted to adapt to requirements, further improving accuracy. Simultaneously, the Schmitt trigger oscillator circuit provides unified drive for the signal coupling demodulation circuit and the DC / AC conversion circuit, reducing additional driving devices; the DC / AC conversion circuit utilizes the first power supply VCC and the second transformer T2 to achieve drive signal coupling, eliminating the need for an additional power supply module. Furthermore, all circuit modules use conventional components, without high-cost components such as high-cost isolation amplifiers, reducing overall cost and achieving low-cost, high-precision analog signal isolation conversion. In addition, this invention uses voltage coupling, ensuring accuracy while avoiding the problem of excessive power consumption associated with current coupling. Attached Figure Description

[0015] Figure 1 This is a diagram of the low-cost analog signal isolation and conversion circuit architecture of this utility model; Figure 2 This is another low-cost analog signal isolation and conversion circuit architecture diagram of this utility model; Figure 3 This is a low-cost analog signal isolation and conversion circuit diagram of this utility model.

[0016] In the diagram: T1, first transformer; T2, second transformer; R1, first resistor; R2, second resistor; R3, third resistor; R4, fourth resistor; C2, first capacitor; U1A, first operational amplifier; R5, fifth resistor; R6, sixth resistor; Q1, first NMOS transistor; C4, second capacitor; C7, third capacitor; Q2, second NMOS transistor; R7, seventh resistor; R8, eighth resistor; R12, ninth resistor; R11, tenth resistor; RP1, adjustable resistor; U3A, Second Operational Amplifier; R15, Eleventh Resistor; R14, Twelfth Resistor; R13, Thirteenth Resistor; D2, Zener Diode; C11, Fourth Capacitor; U2, Logic Gate Chip; C10, Fifth Capacitor; R10, Fourteenth Resistor; R9, Fifteenth Resistor; C9, Sixth Capacitor; C8, Seventh Capacitor; Q4, PNP Transistor; Q3, NPN Transistor; C6, Eighth Capacitor; Ninth Capacitor C5; D2, Dual Diode; C3, Tenth Capacitor; C1, Eleventh Capacitor. Detailed Implementation

[0017] The specific embodiments of this utility model will be further described below with reference to the accompanying drawings and examples. The following examples are only used to more clearly illustrate the technical solution of this utility model and should not be construed as limiting the scope of protection of this utility model.

[0018] according to Figures 1-3 As shown, this utility model is a low-cost analog signal isolation and conversion circuit, including: a resistor voltage divider circuit, a voltage follower circuit, a signal transmission modulation circuit, a first transformer T1, a signal coupling demodulation circuit, a signal output circuit, a Schmitt oscillator circuit, a DC / AC conversion circuit, and a second transformer T2.

[0019] The resistor voltage divider circuit has its input terminal connected to the signal input terminal. Its output terminal is electrically connected to the input terminal of the voltage follower circuit. The output terminal of the voltage follower circuit is electrically connected to the input terminal of the signal transmission modulation circuit. The output terminal of the signal transmission modulation circuit is electrically connected to the primary winding terminal of the first transformer T1. The secondary winding terminal of the first transformer T1 is electrically connected to the input terminal of the signal coupling demodulation circuit. The output terminal of the signal coupling demodulation circuit is electrically connected to the input terminal of the signal output circuit. The output terminal of the signal output circuit is connected to the signal output terminal. The power supply terminal of the Schmitt trigger circuit is electrically connected to the first power supply VCC. The output terminal of the Schmitt trigger circuit is electrically connected to the drive terminal of both the signal coupling demodulation circuit and the DC / AC conversion circuit. The input terminal of the DC / AC conversion circuit is electrically connected to the first power supply VCC. The output terminal of the DC / AC conversion circuit is electrically connected to the primary winding terminal of the second transformer T2. The secondary winding terminal of the second transformer T2 is electrically connected to the drive terminal of the signal transmission modulation circuit. The first transformer T1 is a signal coupling transformer.

[0020] In this invention, a resistor divider circuit preprocesses the input signal, and a voltage follower circuit ensures signal anti-interference capability and impedance matching, laying the foundation for improved accuracy. The signal transmission modulation circuit, the first transformer T1, and the signal coupling demodulation circuit work together to complete signal isolation transmission and accurate demodulation, avoiding interference affecting accuracy. The signal output circuit can be adjusted to meet output requirements, further improving accuracy. Simultaneously, a Schmitt trigger oscillator circuit provides unified drive for the signal coupling demodulation circuit and the DC / AC conversion circuit, reducing the need for additional driving devices. The DC / AC conversion circuit utilizes the first power supply VCC and the second transformer T2 to achieve signal coupling, eliminating the need for an additional power supply module. Furthermore, all circuit modules use conventional components, avoiding high-cost components such as isolation amplifiers, thus reducing overall cost and achieving low-cost, high-precision analog signal isolation conversion. In addition, this invention uses voltage coupling, ensuring accuracy while avoiding the problem of excessive power consumption associated with current coupling.

[0021] To convert a high-voltage raw input signal into a suitable voltage signal for subsequent processing while maintaining low circuit cost, the preferred embodiment of this utility model is that the resistor voltage divider circuit includes a first resistor R1, a second resistor R2, a third resistor R3, a fourth resistor R4, and a first capacitor C2; the first end of the third resistor R3 is connected to the signal input terminal, the second end of the third resistor R3 is electrically connected to the first end of the second resistor R2, the second end of the second resistor R2 is electrically connected to the first end of the first resistor R1, the first end of the fourth resistor R4 is connected in parallel between the second resistor R2 and the first resistor, the second end of the fourth resistor R4 is electrically connected to the input terminal of the voltage follower circuit, the first end of the first capacitor C2 is connected in parallel between the fourth resistor R4 and the input terminal of the voltage follower circuit, and the second ends of the first resistor R1 and the second end of the first capacitor C2 are grounded.

[0022] The DC voltage Input at the signal input terminal is divided by resistors R1, R2, and R3, and then low-pass filtered by resistor R4 and capacitor C2 to convert the input DC voltage into a suitable voltage V1.

[0023] To improve the anti-interference capability of the circuit, the preferred embodiment of this utility model is that the voltage follower circuit includes a first operational amplifier U1A; the non-inverting input terminal of the first operational amplifier U1A is electrically connected to the output terminal of the resistor voltage divider circuit, the output terminal of the first operational amplifier U1A is electrically connected to the input terminal of the signal transmission modulation circuit, and the inverting input terminal of the first operational amplifier U1A is connected in parallel to the output terminal of the first operational amplifier U1A.

[0024] The voltage follower circuit uses operational amplifier U1A to follow the output of voltage V1. The voltage follower output makes the impedance of voltage V1 lower and the output capability stronger, thus ensuring the anti-interference capability of voltage V1.

[0025] To reduce circuit costs, minimize interference, and improve accuracy, the preferred embodiment of this utility model is that the signal transmission modulation circuit includes a fifth resistor R5, a sixth resistor R6, a first NMOS transistor Q1, and a second capacitor C4; the first terminal of the second capacitor C4 is electrically connected to the output terminal of the voltage follower circuit, the second terminal of the second capacitor C4 is electrically connected to the drain of the first NMOS transistor Q1, the source of the first NMOS transistor Q1 is grounded, the gate of the first NMOS transistor Q1 is electrically connected to the first terminal of the fifth resistor R5, the second terminal of the fifth resistor R5 is electrically connected to the secondary winding terminal of the second transformer T2, the sixth resistor R6 is connected in parallel between the source and gate of the first NMOS transistor Q1, and the two ends of the primary winding of the first transformer T1 are connected in parallel between the two ends of the second capacitor C4.

[0026] The signal transmission modulation circuit consists of capacitor C4, MOSFET Q1, capacitor bank R5, and resistor R6. Resistor R5 is the drive resistor, used to limit the drive current. Resistor R6 is the pull-down resistor. Capacitor C4 is used for filtering. MOSFET Q1 is used for modulation, converting the DC signal into an AC signal. Transformer T1 is a coupling transformer, isolating and coupling the voltage signal V1 from the primary winding side to the secondary winding side.

[0027] To reduce circuit costs, minimize interference, and improve accuracy, the preferred embodiment of this utility model is that the signal coupling and demodulation circuit includes a third capacitor C7, a second NMOS transistor Q2, a seventh resistor R7, and an eighth resistor R8; the two ends of the secondary winding of the first transformer T1 are connected in parallel to the two ends of the third capacitor C7; the first end of the third capacitor C7 is electrically connected to the input terminal of the signal output circuit; the second end of the third capacitor C7 is electrically connected to the drain of the second NMOS transistor Q2; the source of the second NMOS transistor Q2 is grounded; the gate of the second NMOS transistor Q2 is electrically connected to the first end of the eighth resistor R8; the second end of the eighth resistor R8 is electrically connected to the output terminal of the Schmitt trigger oscillator circuit; and the seventh resistor R7 is connected in parallel between the source and gate of the second NMOS transistor Q2.

[0028] The signal coupling and demodulation circuit consists of capacitor C7, MOSFET Q2, resistor R7, and resistor R8. MOSFET Q2 and capacitor C7 are used to demodulate the coupled AC signal into a DC signal, and resistors R7 and R8 are the pull-down resistor and current-limiting resistor for MOSFET Q2, respectively.

[0029] In the modulation and demodulation circuit module consisting of the signal transmission modulation circuit, signal coupling transformer T1, and signal coupling demodulation circuit described above, transformer T1 achieves electrical isolation between the input and output sides through voltage coupling, blocking interference caused by power supply and ground fluctuations during equipment startup, shutdown, or switching. Simultaneously, the signal transmission modulation circuit converts DC signals to AC, and the signal coupling demodulation circuit restores AC signals to DC, further reducing interference during signal transmission. The switching characteristics of the MOSFET ensure the timing accuracy of signal modulation and demodulation, while the parameter matching of RC components reduces signal distortion. Combined with the stable coupling of transformer T1, this ultimately achieves high-precision isolation and conversion of analog signals. To achieve adjustable output, adapt to different needs, and further improve accuracy, the preferred embodiment of this utility model is as follows: the signal output circuit includes a ninth resistor R12, a tenth resistor R11, an adjustable resistor RP1, a second operational amplifier U3A, an eleventh resistor R15, and a twelfth resistor R14; the first end of the ninth resistor R12 is electrically connected to the output end of the signal coupling demodulation circuit, the second end of the ninth resistor R12 is electrically connected to the first end of the adjustable resistor RP1, the second end of the adjustable resistor RP1 is electrically connected to the first end of the tenth resistor R11, the control end of the adjustable resistor RP1 is electrically connected to the non-inverting input end of the second operational amplifier U3A, the output end of the second operational amplifier U3A is connected to the signal output end, the eleventh resistor R15 is connected in parallel between the inverting input end and the output end of the second operational amplifier U3A, the first end of the twelfth resistor R14 is connected in parallel between the inverting input end of the second operational amplifier U3A and the eleventh resistor R15, the second end of the twelfth resistor R14 and the second end of the tenth resistor R11 are grounded, and the power supply end of the second operational amplifier U3A is electrically connected to the first power supply VCC.

[0030] The signal output circuit consists of resistor R12, adjustable resistor RP1, resistor R11, operational amplifier U3A, resistor R14, and resistor R15. The demodulated output DC voltage signal V2 is divided by resistors R12, RP1, and R11 to set and adjust the voltage appropriately. It then passes through the non-inverting proportional amplifier circuit formed by operational amplifier U3A and resistors R14 and R15, and is output from the power supply VCC. The relationship between the input voltage (Input) and the output voltage (Output) can be adjusted using adjustable resistor RP1, thus achieving isolated conversion of the input signal.

[0031] To reduce additional driving devices, provide unified driving, and lower costs, the preferred embodiment of this utility model is that the Schmitt trigger oscillator circuit includes a thirteenth resistor R13, a Zener diode D2, a fourth capacitor C11, a logic gate chip U2, a fifth capacitor C10, and a fourteenth resistor R10. The first terminal of the thirteenth resistor R13 is electrically connected to the first power supply VCC, and the second terminal of the thirteenth resistor R13 is electrically connected to the power supply pin VCC of the logic gate chip U2. The cathode of the Zener diode D2 is connected in parallel between the second terminal of the thirteenth resistor R13 and the power supply pin VCC of the logic gate chip U2. The first terminal of the fourth capacitor C11 is connected in parallel to the Zener diode... The cathode of D2 is connected to the power supply pin VCC of the logic gate chip U2. The anode of the Zener diode D2 and the second end of the fourth capacitor C11 are connected in parallel to the ground pin GND of the logic gate chip U2. The output pin Y of the logic gate chip U2 is electrically connected to the first end of the fifth capacitor C10. The input pin A of the logic gate chip U2 is electrically connected to the first end of the fourteenth resistor R10. The second end of the fifth capacitor C10 is connected in parallel between the fourteenth resistor R10 and the input pin A of the logic gate chip U2. The second end of the fourteenth resistor R10 is electrically connected to the driving end of the signal coupling demodulation circuit and the driving end of the DC / AC conversion circuit, respectively.

[0032] The Schmitt trigger oscillator circuit consists of logic gate chip U2, resistor R13, capacitor C11, Zener diode D2, capacitor C10, and resistor R10. Resistor R13, capacitor C11, and Zener diode D2 form the power supply for logic gate chip U2; capacitor C10 and resistor R10 are used to set the switching frequency of the control. The Schmitt trigger oscillator circuit outputs a drive signal PWM1, which is used to drive the signal coupling and demodulation circuit.

[0033] To achieve adjustable output to adapt to different needs and further improve accuracy, the preferred embodiment of this utility model is that the DC / AC conversion circuit includes a fifteenth resistor R9, a sixth capacitor C9, a seventh capacitor C8, a PNP transistor Q4, an NPN transistor Q3, an eighth capacitor C6, and a ninth capacitor C5; the first end of the fifteenth resistor R9 is electrically connected to the output terminal of the Schmitt trigger circuit; the first end of the sixth capacitor C9 and the first end of the seventh capacitor C8 are connected in parallel to the second end of the fifteenth resistor R9; the second end of the sixth capacitor C9 is connected in parallel to the output terminal of the PNP transistor Q4, an NPN transistor Q3, an eighth capacitor C6, and a ninth capacitor C5. The base of transistor Q4 is electrically connected. The second terminal of the seventh capacitor C8 is electrically connected to the base of NPN transistor Q3. The emitter of PNP transistor Q4 is connected in parallel with the first terminal of the eighth capacitor C6 and connected to the first power supply VCC. The second terminal of the eighth capacitor C6 is connected in parallel with the first terminal of the ninth capacitor C5 and connected to the first terminal of the primary winding of the second transformer T2. The collector of PNP transistor Q4 is connected in parallel with the collector of NPN transistor Q3 and connected to the second terminal of the primary winding of the second transformer T2. The emitter of NPN transistor Q3 is connected in parallel with the second terminal of the ninth capacitor C5 and connected to ground.

[0034] The DC / AC conversion circuit consists of capacitor C5, capacitor C6, transistors Q3 and Q4, capacitor C8, capacitor C9, and resistor R9. Capacitors C5 and C6 form a series voltage divider for the power supply VCC. Since capacitors C5 and C6 are of the same specification, the voltage at the connection point of capacitors C5 and C6 is 1 / 2 VCC. Transistors Q3 and Q4 form a push-pull configuration. Capacitors C8 and C9, along with resistor R9, drive transistors Q3 and Q4. Resistor R9 limits the current during the drive, while capacitors C8 and C9 ensure fast and reliable operation.

[0035] Since the DC / AC conversion circuit is driven by the drive signal PWM1 output from the Schmitt trigger circuit, the output of the DC / AC conversion circuit is coupled to the 1 / 2VCC power supply through transformer T2. With a suitable ratio between the primary and secondary windings of transformer T2, a suitable square wave voltage PWM2 can be obtained on the secondary winding side of the transformer. Its driving frequency and voltage are consistent with those on the primary winding side of transformer T2; that is, PWM2 and PWM1 have the same switching frequency. The square wave voltage PWM2 is also a drive signal used to drive the signal transmission modulation circuit.

[0036] To reduce the need for external power and further lower costs, a preferred embodiment of this invention is that the low-cost analog signal isolation conversion circuit further includes an AC / DC conversion circuit. The input terminal of the AC / DC conversion circuit is electrically connected to the secondary winding terminal of the second transformer T2, and the output terminal of the AC / DC conversion circuit outputs a second power supply VCC1 to power the power supply terminal of the voltage follower circuit.

[0037] The AC / DC conversion circuit includes two diodes D2, a tenth capacitor C3, and an eleventh capacitor C1. The common terminal of the two diodes D2 is electrically connected to the first terminal of the secondary winding of transformer T2. The parallel output terminal of the cathode of the two diodes D2 and the first terminal of the eleventh capacitor C1 serves as the positive output terminal VCC1+ of the second power supply VCC1. The parallel output terminal of the anode of the two diodes D2 and the first terminal of the tenth capacitor C3 serves as the negative output terminal VCC1- of the second power supply VCC1. The second terminals of the eleventh capacitor C1 and the tenth capacitor C3 are connected to ground in parallel with the second terminal of the secondary winding of transformer T2.

[0038] The AC / DC conversion circuit consists of dual diodes D1, capacitors C1 and C3. The square wave voltage PWM2 passes through the AC / DC conversion circuit and is rectified to output power supply VCC1, which includes a positive power supply VCC1+, a negative power supply VCC1-, and a reference ground GND1. This power supply VCC1 is used to power operational amplifier U1A.

[0039] The above description is only a preferred embodiment of the present utility model. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present utility model, and these improvements and modifications should also be considered within the protection scope of the present utility model.

Claims

1. A low cost analog signal isolation conversion circuit, characterized by, include: Resistor voltage divider circuit, voltage follower circuit, signal transmission modulation circuit, first transformer, signal coupling demodulation circuit, signal output circuit, Schmitt oscillator circuit, DC / AC conversion circuit and second transformer; The input terminal of the resistor voltage divider circuit is connected to the signal input terminal. The output terminal of the resistor voltage divider circuit is electrically connected to the input terminal of the voltage follower circuit. The output terminal of the voltage follower circuit is electrically connected to the input terminal of the signal transmission modulation circuit. The output terminal of the signal transmission modulation circuit is electrically connected to the primary winding terminal of the first transformer. The secondary winding terminal of the first transformer is electrically connected to the input terminal of the signal coupling demodulation circuit. The output terminal of the signal coupling demodulation circuit is electrically connected to the input terminal of the signal output circuit. The output terminal of the signal output circuit is connected to the signal output terminal. The power supply terminal of the Schmitt oscillator circuit is electrically connected to the first power supply VCC. The output terminal of the Schmitt oscillator circuit is electrically connected to the driving terminal of the signal coupling demodulation circuit and the driving terminal of the DC / AC conversion circuit. The input terminal of the DC / AC conversion circuit is electrically connected to the first power supply VCC. The output terminal of the DC / AC conversion circuit is electrically connected to the primary winding terminal of the second transformer. The secondary winding terminal of the second transformer is electrically connected to the driving terminal of the signal transmission modulation circuit.

2. The low cost analog signal isolation conversion circuit of claim 1, wherein, The resistor voltage divider circuit includes a first resistor, a second resistor, a third resistor, a fourth resistor, and a first capacitor; The first end of the third resistor is connected to the signal input terminal. The second end of the third resistor is electrically connected to the first end of the second resistor. The second end of the second resistor is electrically connected to the first end of the first resistor. The first end of the fourth resistor is connected in parallel between the second resistor and the first resistor. The second end of the fourth resistor is electrically connected to the input terminal of the voltage follower circuit. The first end of the first capacitor is connected in parallel between the fourth resistor and the input terminal of the voltage follower circuit. The second ends of the first resistor and the second ends of the first capacitor are grounded.

3. The low cost analog signal isolation conversion circuit of claim 1, wherein, The voltage follower circuit includes a first operational amplifier; The non-inverting input of the first operational amplifier is electrically connected to the output of the resistor divider circuit, the output of the first operational amplifier is electrically connected to the input of the signal transmission modulation circuit, and the inverting input of the first operational amplifier is connected in parallel to the output of the first operational amplifier.

4. The low cost analog signal isolation conversion circuit of claim 1, wherein, The signal transmission modulation circuit includes a fifth resistor, a sixth resistor, a first NMOS transistor, and a second capacitor; The first terminal of the second capacitor is electrically connected to the output terminal of the voltage follower circuit, the second terminal of the second capacitor is electrically connected to the drain of the first NMOS transistor, the source of the first NMOS transistor is grounded, the gate of the first NMOS transistor is electrically connected to the first terminal of the fifth resistor, the second terminal of the fifth resistor is electrically connected to the secondary winding terminal of the second transformer, the sixth resistor is connected in parallel between the source and gate of the first NMOS transistor, and the two ends of the primary winding of the first transformer are connected in parallel between the two ends of the second capacitor.

5. The low cost analog signal isolation conversion circuit of claim 1, wherein, The signal coupling and demodulation circuit includes a third capacitor, a second NMOS transistor, a seventh resistor, and an eighth resistor; The two ends of the secondary winding of the first transformer are connected in parallel to the two ends of the third capacitor. The first end of the third capacitor is electrically connected to the input terminal of the signal output circuit. The second end of the third capacitor is electrically connected to the drain of the second NMOS transistor. The source of the second NMOS transistor is grounded. The gate of the second NMOS transistor is electrically connected to the first end of the eighth resistor. The second end of the eighth resistor is electrically connected to the output terminal of the Schmitt trigger oscillator circuit. The seventh resistor is connected in parallel between the source and gate of the second NMOS transistor.

6. The low cost analog signal isolation conversion circuit of claim 1, wherein, The signal output circuit includes a ninth resistor, a tenth resistor, an adjustable resistor, a second operational amplifier, an eleventh resistor, and a twelfth resistor; The first end of the ninth resistor is electrically connected to the output terminal of the signal coupling demodulation circuit. The second end of the ninth resistor is electrically connected to the first end of the adjustable resistor. The second end of the adjustable resistor is electrically connected to the first end of the tenth resistor. The control terminal of the adjustable resistor is electrically connected to the non-inverting input terminal of the second operational amplifier. The output terminal of the second operational amplifier is connected to the signal output terminal. The eleventh resistor is connected in parallel between the inverting input terminal and the output terminal of the second operational amplifier. The first end of the twelfth resistor is connected in parallel between the inverting input terminal of the second operational amplifier and the eleventh resistor. The second end of the twelfth resistor and the second end of the tenth resistor are grounded. The power supply terminal of the second operational amplifier is electrically connected to the first power supply.

7. The low cost analog signal isolation translation circuit of claim 1, wherein, The Schmitt oscillator circuit includes a thirteenth resistor, a Zener diode, a fourth capacitor, a logic gate chip, a fifth capacitor, and a fourteenth resistor; The first end of the thirteenth resistor is electrically connected to the first power supply, the second end of the thirteenth resistor is electrically connected to the power supply pin of the logic gate chip, the cathode of the Zener diode is connected in parallel between the second end of the thirteenth resistor and the power supply pin of the logic gate chip, the first end of the fourth capacitor is connected in parallel between the cathode of the Zener diode and the power supply pin of the logic gate chip, the anode of the Zener diode, the second end of the fourth capacitor, and the ground pin of the logic gate chip are connected in parallel to ground, the output pin of the logic gate chip is electrically connected to the first end of the fifth capacitor, the input pin of the logic gate chip is electrically connected to the first end of the fourteenth resistor, the second end of the fifth capacitor is connected in parallel between the fourteenth resistor and the input pin of the logic gate chip, and the second end of the fourteenth resistor is electrically connected to the driving terminal of the signal coupling demodulation circuit and the driving terminal of the DC / AC conversion circuit.

8. The low cost analog signal isolation translation circuit of claim 1, wherein, The DC / AC conversion circuit includes a fifteenth resistor, a sixth capacitor, a seventh capacitor, a PNP transistor, an NPN transistor, an eighth capacitor, and a ninth capacitor. The first end of the fifteenth resistor is electrically connected to the output terminal of the Schmitt trigger circuit. The first end of the sixth capacitor C9 is connected in parallel with the first end of the seventh capacitor to the second end of the fifteenth resistor. The second end of the sixth capacitor is electrically connected to the base of the PNP transistor. The second end of the seventh capacitor is electrically connected to the base of the NPN transistor. The emitter of the PNP transistor is connected in parallel with the first end of the eighth capacitor to the first power supply. The second end of the eighth capacitor is connected in parallel with the first end of the ninth capacitor to the first end of the primary winding of the second transformer. The collector of the PNP transistor is connected in parallel with the collector of the NPN transistor to the second end of the primary winding of the second transformer. The emitter of the NPN transistor is connected in parallel with the second end of the ninth capacitor to ground.

9. The low cost analog signal isolation translation circuit of claim 1, wherein, The low-cost analog signal isolation conversion circuit also includes an AC / DC conversion circuit. The input terminal of the AC / DC conversion circuit is electrically connected to the secondary winding terminal of the second transformer, and the output terminal of the AC / DC conversion circuit outputs a second power supply to power the power supply terminal of the voltage follower circuit.

10. The low cost analog signal isolation conversion circuit of claim 9, wherein, The AC / DC conversion circuit includes dual diodes, a tenth capacitor, and an eleventh capacitor; The common terminal of the dual diodes is electrically connected to the first terminal of the secondary winding of the transformer. The parallel output terminal of the cathode of the dual diodes and the first terminal of the eleventh capacitor serves as the positive output terminal of the second power supply. The parallel output terminal of the anode of the dual diodes and the first terminal of the tenth capacitor serves as the negative output terminal of the second power supply. The second terminal of the eleventh capacitor and the second terminal of the tenth capacitor are connected to ground in parallel with the second terminal of the secondary winding of the transformer.

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