Digital isolation circuit adaptable to different input voltages

Abstract

The embodiment of the invention provides a digital isolation circuit capable of adapting to different input voltages, which comprises an input filter circuit, an optocoupler current adjusting circuit, a photoelectric coupler and an optocoupler output adjusting circuit, and is characterized in that the input filter circuit is configured to receive an input signal and filter the input signal; the optocoupler current adjusting circuit is configured to adjust optocoupler current to keep the optocoupler current constant when the input signals are different input voltages, and the optocoupler current is current which is generated according to the input signals and flows through the input end of the photoelectric coupler; the photoelectric coupler is configured to receive the optocoupler current to drive a light emitting diode in the photoelectric coupler and output an optocoupler output signal according to the photoelectric effect of the light receiver; and the optocoupler output adjusting circuit is configured to perform shaping and filtering on the optocoupler output signal. The problem that when the input voltage of an existing digital isolation circuit is changed, normal work of an optocoupler is affected or the optocoupler is damaged is solved.

Description

Technical Field

[0001] Embodiments of the present disclosure relate to the technical field of integrated circuits, and in particular, to a digital isolation circuit that can adapt to different input voltages. Background Art

[0002] In integrated circuit applications, in order to prevent the direct connection of signals with different reference grounds from damaging the chip, digital isolation circuits are usually used for isolation. Digital isolation circuits generally use photoelectric coupling isolators (also called optocouplers). A commonly used digital coupling circuit in the prior art is to limit the current only with resistors. The optocoupler can be turned on and off by selecting an appropriate resistor according to the optocoupler current.

[0003] like Figure 1 FIG. 1 is an exemplary circuit diagram of a commonly used digital coupling circuit in the prior art. Figure 1 In the figure, resistor R95 is a current limiting resistor, which determines the current limiting size of the optocoupler. However, the inventors found that this circuit can only support a certain fixed voltage input. If the input voltage is greater than the fixed voltage, the optocoupler current will increase, and eventually the optocoupler will burn out due to overcurrent; if the input voltage is less than the fixed voltage, the optocoupler current will decrease, which will eventually affect the normal operation of the optocoupler, resulting in the optocoupler current being too small to turn on the optocoupler, and the input state being invalid; or the current being too small to turn on the optocoupler, but the response speed is slow, etc.

[0004] In summary, when the input voltage of the existing digital isolation circuit changes, the normal operation of the optocoupler will be affected, or the optocoupler may be damaged. Summary of the invention

[0005] The embodiments described herein provide a digital isolation circuit that can adapt to different input voltages, in order to solve the problem that when the input voltage of the existing digital isolation circuit changes, the normal operation of the optocoupler will be affected, or the optocoupler will be damaged.

[0006] According to the first aspect of the present disclosure, there is provided a digital isolation circuit comprising: an input filtering circuit, an optocoupler current regulating circuit, a photoelectric coupler, and an optocoupler output adjusting circuit, wherein the input filtering circuit is configured to receive an input signal and filter the input signal according to a magnetic bead and a first capacitor; the optocoupler current regulating circuit is coupled to the input end of the optocoupler, and the optocoupler current regulating circuit is configured to regulate the optocoupler current through a first resistor, a first transistor, and a second transistor when the input signal has different input voltages, so that the optocoupler current remains constant, and the optocoupler current is a current flowing through the input end of the optocoupler generated according to the input signal; the optocoupler is configured to receive the optocoupler current to drive a light-emitting diode in the optocoupler, and output an optocoupler output signal according to the photoelectric effect of a light receiver in the optocoupler; the optocoupler output adjusting circuit is configured to obtain a final optocoupler output signal after shaping and filtering the optocoupler output signal.

[0007] Optionally, the input signal is a differential input signal. After the optocoupler current regulation circuit receives the signal of the positive electrode of the filtered input signal, it passes through the light-emitting diode, the first transistor, the first resistor in sequence and then returns to the negative electrode of the input signal. The current flowing through the light-emitting diode is the optocoupler current. When the input signal is a different input voltage, the optocoupler current is regulated through the first resistor, the first transistor, and the second transistor, including: when the optocoupler current changes positively correlated with the input signal, the collector voltage of the second transistor is regulated by the change of the voltage across the first resistor, and then the base voltage and collector current of the first third transistor are adjusted, and finally the reverse regulation of the optocoupler current is realized to keep the optocoupler current constant. The second transistor is coupled to the first resistor and the first transistor respectively.

[0008] Optionally, the optocoupler current regulation circuit includes: the first resistor, the first transistor, the second transistor, the second resistor, and the third resistor, wherein the collector of the first transistor and one end of the third resistor are both coupled to the cathode of the light-emitting diode, and the emitter of the first transistor and the other end of the third resistor are respectively coupled to the base of the second transistor and one end of the first resistor; the base of the first transistor is respectively coupled to the collector of the second transistor and one end of the second resistor; the emitter of the second transistor is respectively coupled to the other end of the first resistor and the cathode of the input signal; and the other end of the second resistor is respectively coupled to the anode of the light-emitting diode and the anode of the filtered input signal.

[0009] Optionally, the input filter circuit includes: the magnetic bead and the first capacitor, wherein one end of the magnetic bead is coupled to the positive pole of the input signal, the other end of the magnetic bead is respectively coupled to one end of the first capacitor and the optocoupler current regulation circuit, and the other end of the first capacitor is coupled to the negative pole of the input signal.

[0010] Optionally, the optocoupler output adjustment circuit includes: a first output filtering module, a shaping module, and a second output filtering module, wherein the first output filtering module is configured to perform a first interference filtering on the optocoupler output signal output by the photocoupler based on a PI-type filter; the shaping module is configured to perform waveform shaping on the optocoupler output signal after interference filtering; and the second output filtering module is configured to perform a second interference filtering on the optocoupler output signal after waveform shaping to obtain the final optocoupler output signal.

[0011] Optionally, the first output filtering module includes: a second capacitor, a third capacitor, and a fourth resistor, wherein one end of the second capacitor is respectively coupled to the output end of the optocoupler and one end of the fourth resistor, and the other end of the second capacitor is coupled to the ground; the other end of the fourth resistor is respectively coupled to one end of the third capacitor and the shaping module; and the other end of the third capacitor is coupled to the ground.

[0012] Optionally, the shaping module includes: a Schmitt trigger and a fifth resistor, wherein the input end of the Schmitt trigger is coupled to the first output filter module, the output end of the Schmitt trigger is respectively coupled to one end of the fifth resistor and the second output filter module, the power supply end of the Schmitt trigger is coupled to the power supply voltage; the other end of the fifth resistor is coupled to the power supply voltage.

[0013] Optionally, the second output filtering module includes: a sixth resistor and a fourth capacitor, wherein one end of the sixth resistor is coupled to the shaping module, the other end of the sixth resistor is coupled to one end of the fourth capacitor, the other end of the fourth capacitor is coupled to the ground end, and the other end of the sixth resistor also outputs the final optocoupler output signal.

[0014] Optionally, the digital isolation circuit further includes an anti-reverse diode, wherein the anti-reverse diode is coupled between the input signal and the input filter circuit.

[0015] Optionally, the current value when the optocoupler current is constant is determined according to the following formula: Ioc=VBEset / R1, wherein Ioc is the optocoupler current, VBEset is the voltage between the base and the emitter when the second transistor is turned on, and R1 is the resistance value of the first resistor.

[0016] Optionally, the digital isolation circuit further includes a seventh resistor, one end of the seventh resistor is coupled to the output end of the photocoupler, and the other end of the seventh resistor is coupled to the power supply voltage.

[0017] The digital isolation circuit that can adapt to different input voltages in the embodiments of the present disclosure includes an input filtering circuit, an optocoupler current regulating circuit, a photoelectric coupler, and an optocoupler output adjusting circuit, wherein the input filtering circuit is configured to receive an input signal and filter the input signal according to a magnetic bead and a first capacitor; the optocoupler current regulating circuit is coupled to the input end of the optocoupler, and the optocoupler current regulating circuit is configured to regulate the optocoupler current through a first resistor, a first transistor, and a second transistor when the input signal is a different input voltage, so that the optocoupler current remains constant, and the optocoupler current is a current flowing through the input end of the optocoupler generated according to the input signal; the optocoupler is configured to receive the optocoupler current to drive a light-emitting diode in the optocoupler, and output an optocoupler output signal according to the photoelectric effect of a light receiver in the optocoupler; the optocoupler output adjusting circuit is configured to obtain a final optocoupler output signal after shaping and filtering the optocoupler output signal. It can be seen that in the digital isolation circuit that can adapt to different input voltages in the embodiment of the present invention, the optocoupler current regulation circuit can adjust the optocoupler current through the first resistor, the first transistor, and the second transistor when the input signal is a different input voltage, so that the optocoupler current remains constant. Compared with the prior art, the optocoupler current does not change with the change of the input signal, and the current remains constant, which is equivalent to adding a constant current circuit to the input end of the photocoupler, and can effectively avoid the phenomenon in the prior art that the optocoupler cannot work normally or is damaged due to changes in the input voltage. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions of the embodiments of the present disclosure, the drawings of the embodiments will be briefly described below. It should be noted that the drawings described below only relate to some embodiments of the present disclosure, but are not intended to limit the present disclosure, wherein:

[0019] Figure 1 An exemplary circuit diagram of a commonly used digital coupling circuit in the prior art is shown;

[0020] Figure 2 A schematic block diagram of a digital isolation circuit that can adapt to different input voltages according to an embodiment of the present disclosure is shown;

[0021] Figure 3 An exemplary circuit diagram showing an optocoupler current regulating circuit and an input filtering circuit of a digital isolation circuit that can adapt to different input voltages according to an embodiment of the present disclosure;

[0022] Figure 4An exemplary circuit diagram of an optocoupler output adjustment circuit of a digital isolation circuit that can adapt to different input voltages according to an embodiment of the present disclosure is shown;

[0023] Figure 5 A schematic block diagram of another digital isolation circuit that can adapt to different input voltages according to an embodiment of the present disclosure is shown;

[0024] Figure 6 A schematic block diagram of a digital isolation circuit capable of adapting to different input voltages corresponding to a dual-path optical coupler according to an embodiment of the present disclosure is shown;

[0025] The elements in the drawings are schematic and not drawn to scale. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solution and advantages of the embodiments of the present disclosure clearer, the technical solution of the embodiments of the present disclosure will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present disclosure, rather than all of the embodiments. Based on the described embodiments of the present disclosure, all other embodiments obtained by those skilled in the art without creative work also fall within the scope of protection of the present disclosure.

[0027] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by a person skilled in the art to which the subject matter of the present disclosure belongs. It will be further understood that terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the specification and the relevant art, and will not be interpreted in an idealized or overly formal form unless otherwise explicitly defined herein. As used herein, a statement that two or more parts are "connected" or "coupled" together shall mean that the parts are joined together directly or through one or more intermediate components.

[0028] In all embodiments of the present disclosure, terms such as “first” and “second” are used only to distinguish one component (or a part of a component) from another component (or another part of a component).

[0029] In order to solve the problem that the existing digital isolation circuit will affect the normal operation of the optocoupler or cause damage to the optocoupler when the input voltage changes, a new digital isolation circuit that can adapt to different input voltages is proposed. The digital isolation circuit that can adapt to different input voltages of the embodiment of the present disclosure can achieve that when the input voltage changes, the optocoupler current can be kept constant by adjusting the resistor and the transistor, so that the digital isolation circuit can be normally used under different input voltages, and the speed is not affected. The digital isolation circuit 100 that can adapt to different input voltages of the present disclosure is described in detail below.

[0030] Figure 2 FIG. 1 is a schematic block diagram of a digital isolation circuit 100 that can adapt to different input voltages according to an embodiment of the present disclosure. Figure 2 As shown, the digital isolation circuit 100 that can adapt to different input voltages includes: an input filter circuit 110, an optocoupler current regulation circuit 120, a photocoupler 130, and an optocoupler output adjustment circuit 140.

[0031] The input filter circuit 110 is configured to receive an input signal (V1+, V1-) and filter the input signal according to the magnetic bead FB ( Figure 2 ) and the first capacitor C1 ( Figure 2 The input signal (V1+, V1-) is filtered by the first capacitor (not shown). The input signal (V1+, V1-) is a differential voltage signal. The magnetic bead FB and the first capacitor C1 are used to filter the interference and jitter that may exist in the input signal (V1+, V1-) to ensure the accuracy and stability of the input signal (V1+, V1-).

[0032] The optocoupler current regulating circuit 120 is coupled to the input end of the photocoupler 130. The optocoupler current regulating circuit 120 is configured to, when the input signals (V1+, V1-) are of different input voltages, Figure 2 Not shown), the first transistor Q1 ( Figure 2 Not shown), the second transistor Q2 ( Figure 2 (not shown) adjusts the optocoupler current Ioc to keep the optocoupler current Ioc constant. The optocoupler current Ioc is the current flowing through the input end of the optocoupler 130 generated according to the input signal (V1+, V1-).

[0033] The optocoupler current regulating circuit 120 in the embodiment of the present disclosure is coupled between the input signal (V1+, V1-) and the optocoupler 130 in order to regulate the optocoupler current Ioc generated by the input signal (V1+, V1-) so that it does not change with the change of the input voltage, thereby ensuring the stability of the optocoupler current Ioc. Specifically, the input signal (V1+, V1-) is a differential input signal (V1+, V1-), and the optocoupler current regulating circuit 120 receives the signal V1+ of the positive electrode of the filtered input signal (V1+, V1-), and then passes through the light-emitting diode at the input end of the optocoupler 130, the first transistor Q1, and the first resistor R1 in sequence, and then returns to the negative electrode V1- of the input signal (V1+, V1-) (it should be noted that the embodiment of the present disclosure The positive electrode V1+ and the negative electrode V1- of the input signal can be regarded as a differential input as a whole. For example, the positive electrode of the input signal (V1+, V1-) is 105V and the negative electrode is 100V, then the actual differential input is 5V. The subsequent calculation of the optocoupler current Ioc is also based on the actual differential input voltage value). The second transistor Q2 is coupled to the first resistor R1 and the first transistor Q1 respectively, and the current flowing through the light-emitting diode is the optocoupler current Ioc.

[0034] In the embodiment of the present disclosure, when the input signal (V1+, V1-) is a different input voltage, the optocoupler current regulating circuit 120 regulates the optocoupler current Ioc through the first resistor R1, the first transistor Q1, and the second transistor Q2. The principle is as follows: when the optocoupler current Ioc changes positively with the input signal (V1+, V1-) (here refers to the instantaneous change), the collector voltage of the second transistor Q2 is regulated by the change of the voltage across the first resistor R1, that is, when the optocoupler current Ioc changes (increases or decreases), the voltage across the first resistor R1 changes (increases or decreases); the first resistor R1 is coupled to the second transistor Q2, and the first resistor R1 can be used to adjust the collector voltage of the second transistor Q2. The voltage across R1 changes (increases or decreases) to change the working state of the second transistor Q2, thereby changing the collector voltage of the second transistor Q2 (decreases or increases), and the second transistor Q2 and the first transistor Q1 are also coupled, so the base voltage and collector current of the first transistor can be adjusted (decreased or increased) by changing the collector voltage of the second transistor Q2, and finally the reverse regulation of the optocoupler current Ioc is achieved (that is, when the optocoupler current Ioc increases instantaneously due to the increase of the input voltage, it can be reduced, and when the optocoupler current Ioc decreases instantaneously due to the decrease of the input voltage, it can be increased), so that the optocoupler current Ioc remains constant.

[0035] The photocoupler 130 is configured to receive the photocoupler current Ioc to drive the light emitting diode in the photocoupler 130, and output a photocoupler output signal according to the photoelectric effect of the photoreceiver in the photocoupler 130. The photocoupler 130 in the embodiment of the present disclosure is an optical integrated circuit type photocoupler, and its structural principle is the same as that of the existing optical integrated circuit type. In addition, Figure 2 The power terminal of the optocoupler 130 is also coupled to the power voltage VCC.

[0036] The optocoupler output adjustment circuit 140 is configured to perform shaping and filtering on the optocoupler output signal output by the optocoupler 130 to obtain the final optocoupler output signal E1. The digital isolation circuit 100 that can adapt to different input voltages in the disclosed embodiment is to isolate signals of the same state (high level or low level) but with different reference grounds (i.e., the isolated input signal (V1+, V1-) and the final optocoupler output signal E1). The final optocoupler output signal E1 is usually used for detection by a microcontroller unit (MCU). In order to ensure the consistency and accuracy of the detection, it is necessary to perform shaping and filtering on the optocoupler output signal directly output from the optocoupler 130. Shaping and filtering can be achieved by commonly used waveform shaping circuits and filtering circuits. For example, the shaping circuit can be an op amp circuit (which is converted into a voltage of the required size through an op amp, then passes through a voltage follower, and then passes through a voltage zero-crossing comparison circuit to output a square wave signal), a comparator, a Schmitt trigger, etc.; the filtering circuit can be an RC filter, etc.

[0037] From the above description, it can be seen that the digital isolation circuit that can adapt to different input voltages in the embodiment of the present disclosure can adjust the optocoupler current Ioc through the first resistor R1, the first transistor Q1, and the second transistor Q2 when the input signal (V1+, V1-) is a different input voltage, so that the optocoupler current Ioc remains constant. Compared with the prior art, the optocoupler current Ioc will not change with the change of the input signal (V1+, V1-), and remains constant, which is equivalent to adding a constant current circuit to the input end of the photocoupler 130. Therefore, it can effectively avoid the phenomenon in the prior art that the optocoupler cannot work normally or is damaged due to changes in the input voltage.

[0038] Further, such as Figure 3As shown, the optocoupler current regulation circuit 120 includes: the first resistor R1, the first transistor Q1, the second transistor Q2, the second resistor R2, and the third resistor R3, wherein the collector of the first transistor Q1 and one end of the third resistor R3 are both coupled to the cathode of the light-emitting diode, the emitter of the first transistor Q1 and the other end of the third resistor R3 are respectively coupled to the base of the second transistor Q2 and one end of the first resistor R1; the base of the first transistor Q1 is respectively coupled to the collector of the second transistor Q2 and one end of the second resistor R2; the emitter of the second transistor Q2 is respectively coupled to the other end of the first resistor R1 and the cathode V1- of the input signal (V1+, V1-); the other end of the second resistor R2 is respectively coupled to the anode of the light-emitting diode and the anode of the filtered input signal (V1+, V1-). Among them, the resistance value of the first resistor R1 can be calculated based on the value of the optocoupler current Ioc when actually required and the voltage VBEset (usually 0.7V) between the base and the emitter when the second transistor Q2 is turned on. R1 is usually a small resistor, such as tens of ohms. The first resistor R1 is used to adjust the optocoupler current Ioc, and the second resistor R2 is to provide the base current to the first transistor Q1 so that the first transistor Q1 can be turned on. In practical applications, the minimum value of the second resistor R2 can be calculated based on the maximum value of the optocoupler current Ioc. Specifically, the collector current Ic of the first transistor Q1 is taken as the maximum value of the optocoupler current Ioc, and then the base current Ib of the first transistor Q1 is calculated according to the amplification ratio of the first transistor Q1, and then the minimum value of the second resistor R2 is determined based on the calculated Ib. R2 is generally a large resistor, such as several thousand ohms. The third resistor R3 is mainly used to shunt the first transistor Q1. When the voltage across the first transistor Q1 is less than VCEset (usually 0.2V), only the third resistor R3 has current, and the first transistor Q1 has no current. In this case, the circuit can still work normally. When the voltage across the first transistor Q1 is greater than VCEset, both the first transistor Q1 and the third resistor R3 have current. After shunting, the collector current Ic of the first transistor Q1 is smaller, and the heat is also smaller, which better protects the first transistor Q1.

[0039] Further, such as Figure 3As shown, the input filter circuit 110 includes: the magnetic bead FB, the first capacitor C1, wherein one end of the magnetic bead FB is coupled to the positive electrode V1+ of the input signal (V1+, V1-), the other end of the magnetic bead FB is respectively coupled to one end of the first capacitor C1 and the optocoupler current regulation circuit 120 (specifically coupled to the other end of the second resistor R2 in the optocoupler current regulation circuit 120), and the other end of the first capacitor C1 is coupled to the negative electrode V1- of the input signal (V1+, V1-).

[0040] Further, such as Figure 4 As shown, the optocoupler output adjustment circuit 140 includes: a first output filtering module 141, a shaping module 142, and a second output filtering module 143, wherein the first output filtering module 141 is configured to perform a first interference filtering on the optocoupler output signal output by the photoelectric coupler 130 based on a PI-type filter; the shaping module 142 is configured to perform waveform shaping on the optocoupler output signal after interference filtering; and the second output filtering module 143 is configured to perform a second interference filtering on the optocoupler output signal after waveform shaping to obtain the final optocoupler output signal E1.

[0041] Further, such as Figure 4 As shown, the first output filtering module 141 includes: a second capacitor C2, a third capacitor C3, and a fourth resistor R4, wherein one end of the second capacitor C2 is respectively coupled to the output end VO of the optocoupler 130 and one end of the fourth resistor R4, and the other end of the second capacitor C2 is coupled to the ground; the other end of the fourth resistor R4 is respectively coupled to one end of the third capacitor C3 and the shaping module 142; the other end of the third capacitor C3 is coupled to the ground. Figure 4 The second capacitor C2, the third capacitor C3, and the fourth resistor R4 in the first output filter module 141 constitute a PI filter, which can filter out the interference of the optical coupling part (photoelectric coupler 130). Figure 4 As shown, a seventh resistor R7 is also coupled to the first output filter module 141, one end of the seventh resistor R7 is coupled to the output end VO of the optocoupler 130, and the other end of the seventh resistor R7 is coupled to the power supply voltage VCC. Here, the seventh resistor R7 serves as a pull-up resistor of the optocoupler 130. Because the optocoupler 130 is an open-collector output, it needs to be pulled up by a pull-up resistor.

[0042] like Figure 4As shown, the shaping module 142 includes: a Schmitt trigger 1421, a fifth resistor R5, wherein the input terminal A of the Schmitt trigger 1421 is coupled to the first output filter module 141, the output terminal Y of the Schmitt trigger 1421 is respectively coupled to one end of the fifth resistor R5 and the second output filter module 143, the power supply terminal VCC of the Schmitt trigger 1421 is coupled to the power supply voltage VCC; the other end of the fifth resistor R5 is coupled to the power supply voltage VCC. Figure 4 As shown, the NC terminal and the GND terminal of the Schmitt trigger 1421 are both coupled to the ground terminal. In addition, the fifth resistor R5 also acts as a pull-up resistor to improve the stability output capability of the Schmitt trigger 1421. In the disclosed embodiment, the Schmitt trigger 1421 converts the optocoupler output signal with a low slope or a sinusoidal waveform (possibly in the middle state between 0 and 1) into a square wave (only 0 and 1 states).

[0043] like Figure 4 As shown, the second output filter module 143 includes: a sixth resistor R6 and a fourth capacitor C4, wherein one end of the sixth resistor R6 is coupled to the shaping module 142, the other end of the sixth resistor R6 is coupled to one end of the fourth capacitor C4, the other end of the fourth capacitor C4 is coupled to the ground terminal, and the other end of the sixth resistor R6 also outputs the final optical coupler output signal E1. The sixth resistor R6 and the fourth capacitor C4 in the second output filter module 143 constitute a common RC filter circuit, so that the final optical coupler output signal E1 obtained is a stable output signal.

[0044] Combination Figure 2-4 The working principle of the digital isolation circuit 100 that can adapt to different input voltages in the embodiment of the present disclosure is explained: after the circuit is turned on, Q1 is in the open state because of R2 by default (the input signal (V1+, V1-) provides Q1 with a base current Ib that can turn on Q1 through R2), and Q2 is in the closed state because of R1 (the voltage across R1 is very small initially, so Q2's VBE is also very small, and Q2 cannot be turned on. When the R1 voltage is greater than the Q2 input VBEset voltage (usually 0.7V), Q2 turns on), the positive signal V1+ of the input signal (V1+, V1-) is filtered through FB6 and C1, and the optocoupler current Ioc passes through the input end (light-emitting diode) of the optocoupler 130, and then to Q1 and R3, and finally returns to the negative pole V1- of the input signal (V1+, V1-) through R1. In a stable state, the current value when the optocoupler current Ioc is constant can be determined according to the following formula:

[0045] Ioc=VBEset / R1,

[0046] Wherein, Ioc is the optocoupler current Ioc, VBEset is the voltage between the base and the emitter when the second transistor Q2 is turned on, and R1 is the resistance value of the first resistor R1.

[0047] When the input signal increases and the optocoupler current Ioc increases (greater than the constant optocoupler current Ioc value during stability), the currents of Q1 and R3 will also increase instantaneously, the current flowing through R1 will also increase, and the voltage across R1 will also increase. The increase in voltage across R1 will increase Q2's VB, and then Q2's collector voltage VC will decrease, thereby pulling Q1's VB down, and at this time, Q1's collector current Ic will decrease, thereby reducing the optocoupler current Ioc. On the contrary, if the input signal decreases and the current decreases (less than the constant optocoupler current Ioc value during stability), the voltage across R1 decreases, Q2's VBE decreases, and Q2's VC increases, causing Q1's VB to increase, and then Q1's Ic to increase, thereby increasing the optocoupler current Ioc.

[0048] From the above analysis, we can see that the minimum voltage Vmin of the input signal (V1+, V1-) is VR1+VQ2+VF1, where VR1 is the voltage across R1 when stable, VQ2 is the conduction voltage of Q2 when stable, and VF1 is the forward voltage of the input end of the optocoupler 130 (the forward voltage of the light-emitting diode). In theory, as long as the input signal (V1+, V1-) is greater than the minimum voltage Vmin, the optocoupler current Ioc is a constant value and does not increase with the increase of voltage. At this time, the output of the optocoupler 130 is a stable state with the same state as the input signal (high level or low level). Then, the interference of the optocoupler isolation part is filtered out by R2, C2, and C3, and then shaped by the Schmitt trigger 1421, and finally filtered by R6 and C4 to obtain a stable and accurate final optocoupler output signal E1 for MCU detection.

[0049] Further, such as Figure 5 As shown, the digital isolation circuit further includes an anti-reverse diode D1, wherein the anti-reverse diode D1 is coupled between the input signal (V1+, V1-) and the input filter circuit 110. The anti-reverse diode D1 prevents the signal from flowing back to the input terminal. It should be noted that, Figure 5 Vmin also needs to be in Figure 4 Add the forward voltage VF2 of D1 to the Vmin, that is, Figure 5 Where Vmin=VR1+VQ2+VF1+VF2.

[0050] In addition, it should be noted that Figure 2The photocoupler 130 shown in the figure is a single-channel photocoupler. In practical applications, it can also be a photocoupler 130 with multiple input terminals, such as a TLP2168 dual-channel photocoupler. If it is a multi-channel photocoupler, multiple input filter circuits 110, multiple photocoupler current adjustment circuits 120, multiple photocoupler output adjustment circuits 140, and multiple anti-reverse diodes D1 are required. Figure 6 As shown, a schematic block diagram of a digital isolation circuit 200 that can adapt to different input voltages corresponding to the dual-channel optocoupler TLP2168 is given. In order to distinguish, the input signal of the first channel is represented as V1+, V1-, and the corresponding final optocoupler output signal of the first channel is E1; the input signal of the second channel is represented as V2+, V2-, and the corresponding final optocoupler output signal of the second channel is E2.

[0051] In summary, the digital isolation circuit that can adapt to different input voltages in the embodiment of the present invention can keep the optocoupler current constant by adjusting the resistor and the transistor when different voltages are input. The optocoupler current will not be too small to trigger the optocoupler action, nor will the optocoupler be damaged due to excessive input voltage. The signals after isolation are the same and the speed is not affected.

[0052] Unless the context clearly indicates otherwise, the singular form of the words used herein and in the appended claims includes the plural and vice versa. Thus, when referring to the singular, the plural form of the corresponding term is generally included. Similarly, the words "comprise" and "include" are to be interpreted as inclusive rather than exclusive. Likewise, the terms "include" and "or" should be interpreted as inclusive, unless such interpretation is expressly prohibited herein. Where the term "example" is used herein, particularly when it is placed after a group of terms, "example" is merely exemplary and illustrative and should not be considered exclusive or comprehensive.

[0053] Further aspects and scopes of adaptability become apparent from the description provided herein. It should be understood that various aspects of the present disclosure can be implemented individually or in combination with one or more other aspects. It should also be understood that the description and specific embodiments herein are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.

[0054] Several embodiments of the present disclosure are described in detail above, but it is obvious that those skilled in the art can make various modifications and variations to the embodiments of the present disclosure without departing from the spirit and scope of the present disclosure. The protection scope of the present disclosure is defined by the attached claims.

Claims

1. A digital isolation circuit that can adapt to different input voltages, characterized in that: The digital isolation circuit includes: an input filter circuit, an optocoupler current regulation circuit, a photoelectric coupler, and an optocoupler output adjustment circuit. Wherein, the input filter circuit is configured to receive an input signal and filter the input signal according to the magnetic bead and the first capacitor; The optocoupler current regulating circuit is coupled to the input end of the photocoupler, and the optocoupler current regulating circuit is configured to regulate the optocoupler current through the first resistor, the first transistor, and the second transistor when the input signal has different input voltages, so that the optocoupler current remains constant, and the optocoupler current is the current flowing through the input end of the photocoupler generated according to the input signal; The photocoupler is configured to receive the photocoupler current to drive a light emitting diode in the photocoupler, and output a photocoupler output signal according to a photoelectric effect of a light receiver in the photocoupler; The optocoupler output adjustment circuit is configured to perform shaping and filtering on the optocoupler output signal to obtain a final optocoupler output signal.

2. The digital isolation circuit capable of adapting to different input voltages according to claim 1, characterized in that: The input signal is a differential input signal. After the optocoupler current regulating circuit receives the signal of the positive electrode of the filtered input signal, it passes through the light-emitting diode, the first transistor, and the first resistor in sequence and then returns to the negative electrode of the input signal. The current flowing through the light-emitting diode is the optocoupler current. When the input signal is a different input voltage, the optocoupler current is regulated by the first resistor, the first transistor, and the second transistor, including: When the optocoupler current changes positively with the input signal, the collector voltage of the second transistor is adjusted by changing the voltage across the first resistor, thereby adjusting the base voltage and collector current of the first transistor, and finally achieving reverse regulation of the optocoupler current to keep the optocoupler current constant. The second transistor is coupled to the first resistor and the first transistor respectively.

3. The digital isolation circuit capable of adapting to different input voltages according to claim 2, characterized in that: The optocoupler current regulating circuit includes: the first resistor, the first transistor, the second transistor, the second resistor, and the third resistor. Wherein, the collector of the first transistor and one end of the third resistor are coupled to the cathode of the light-emitting diode, and the emitter of the first transistor and the other end of the third resistor are coupled to the base of the second transistor and one end of the first resistor respectively; The base of the first transistor is respectively coupled to the collector of the second transistor and one end of the second resistor; The emitter of the second transistor is respectively coupled to the other end of the first resistor and the negative electrode of the input signal; The other end of the second resistor is respectively coupled to the anode of the light emitting diode and the anode of the filtered input signal.

4. The digital isolation circuit capable of adapting to different input voltages according to claim 2, characterized in that: The input filter circuit includes: the magnetic bead, the first capacitor, Among them, one end of the magnetic bead is coupled to the positive pole of the input signal, the other end of the magnetic bead is coupled to one end of the first capacitor and the optocoupler current regulation circuit respectively, and the other end of the first capacitor is coupled to the negative pole of the input signal.

5. The digital isolation circuit capable of adapting to different input voltages according to claim 2, characterized in that: The optocoupler output adjustment circuit includes: a first output filter module, a shaping module, and a second output filter module. Wherein, the first output filtering module is configured to perform a first interference filtering on the optocoupler output signal output by the optocoupler based on a PI filter; The shaping module is configured to perform waveform shaping on the optocoupler output signal after interference filtering; The second output filtering module is configured to perform a second interference filtering on the optocoupler output signal after waveform shaping to obtain the final optocoupler output signal.

6. The digital isolation circuit capable of adapting to different input voltages according to claim 5, characterized in that: The first output filter module includes: a second capacitor, a third capacitor, and a fourth resistor. Wherein, one end of the second capacitor is coupled to the output end of the photoelectric coupler and one end of the fourth resistor respectively, and the other end of the second capacitor is coupled to the ground end; The other end of the fourth resistor is respectively coupled to one end of the third capacitor and the shaping module; The other end of the third capacitor is coupled to the ground.

7. The digital isolation circuit capable of adapting to different input voltages according to claim 6, characterized in that: The shaping module includes: a Schmitt trigger, a fifth resistor, The input end of the Schmitt trigger is coupled to the first output filter module, the output end of the Schmitt trigger is respectively coupled to one end of the fifth resistor and the second output filter module, and the power supply end of the Schmitt trigger is coupled to the power supply voltage; The other end of the fifth resistor is coupled to the power voltage.

8. The digital isolation circuit capable of adapting to different input voltages according to claim 7, characterized in that: The second output filter module includes: a sixth resistor, a fourth capacitor, Among them, one end of the sixth resistor is coupled to the shaping module, the other end of the sixth resistor is coupled to one end of the fourth capacitor, the other end of the fourth capacitor is coupled to the ground end, and the other end of the sixth resistor also outputs the final optocoupler output signal.

9. The digital isolation circuit capable of adapting to different input voltages according to claim 1, characterized in that: The digital isolation circuit also includes an anti-reverse diode. The anti-reverse diode is coupled between the input signal and the input filter circuit.

10. The digital isolation circuit capable of adapting to different input voltages according to claim 3, characterized in that: The current value when the optocoupler current is constant is determined according to the following formula: Ioc=VBEset / R1, Wherein, Ioc is the optocoupler current, VBEset is the voltage between the base and the emitter when the second transistor is turned on, and R1 is the resistance value of the first resistor.

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