An isolated level detection circuit

Abstract

The present invention provides an isolated level detection circuit, which includes an input terminal, a control circuit, a first switching transistor, a second switching transistor, an isolation device and an output terminal. When a normal voltage is applied to the input terminal, the control circuit controls the first switching transistor to conduct, and the second switching transistor to cut off, so that the isolation device cuts off, and the output terminal outputs a high level; when the voltage applied to the input terminal is lower than the required voltage, the control circuit controls the first switch to cut off, and the second switching transistor to conduct, so that the isolation device conducts, and the output terminal outputs a low level. It realizes that the output logic is the same as the level of the input voltage, and the power consumption of the circuit is relatively small.

Description

Technical Field

[0001] The present invention relates to the technical field of power management, and particularly to an isolated level detection circuit. Background Art

[0002] In the existing isolated level detection circuit, the input signal and the output signal are isolated by an optocoupler. When the input level is higher than the threshold level, the optocoupler conducts and the output is a low level; when the input level is lower than the threshold level, the optocoupler cuts off and the output is a high level. For such an isolated level detection circuit, when the input level is higher than the threshold level, it needs to consume several milliamperes of current, resulting in relatively high power consumption, which is not very suitable for low-power circuits and circuits sensitive to heat.

[0003] In view of this, our company has designed an isolated level detection circuit, which consumes less current when the level is normal, that is, when the input level is higher than the threshold level, and is thus more suitable for low-power circuits and circuits sensitive to heat. Summary of the Invention

[0004] To solve the above problems, the present invention is realized through the following technical solutions:

[0005] An isolated level detection circuit includes an input terminal, a control circuit, a first switching tube, a second switching tube, an isolation device, and an output terminal;

[0006] The input terminal is used for inputting a voltage; the control circuit is disposed between the positive and negative electrodes of the input terminal; the first switching tube is connected to the control circuit; the second switching tube is respectively connected to the first switching tube and one side of the isolation device; the other side of the isolation device is connected to the output terminal; the positive electrode of the output terminal is connected to a first power supply;

[0007] When the input terminal accesses a normal voltage, the control circuit controls the first switching tube to conduct, and the second switching tube to cut off, so that the isolation device cuts off and the output terminal outputs a high level; when the voltage accessed by the input terminal is lower than the required voltage, the control circuit controls the first switching tube to cut off, and the second switching tube to conduct, so that the isolation device conducts and the output terminal outputs a low level.

[0008] Further, the control circuit includes a switching element and a second resistor connected in series between the positive and negative electrodes of the input terminal, a third resistor and a fifth resistor connected in series and then connected in parallel across the two ends of the second resistor; the first switching tube is connected to the common terminal of the third resistor and the fifth resistor, wherein one end of the fifth resistor far from the third resistor is connected to the common terminal of the second resistor and the switching element.

[0009] Further, the first switching transistor is a PNP type triode. The base of the first switching transistor is connected to the common terminal of the third resistor and the fifth resistor. The collector of the first switching transistor is connected to the negative pole of the input terminal through the seventh resistor, and the emitter of the first switching transistor is connected to the positive pole of the input terminal.

[0010] Further, the fifth resistor and the third resistor satisfy: R5 / R3 < 0.3.

[0011] Further, (V CC -U Z ) / R2 + (Vcc - 0.7V - U Z ) / R5 + V CC / R7 is less than 1 mA, where the V CC is the input voltage of the input terminal, and the U Z is the conduction voltage of the switching device.

[0012] Further, the second switching transistor is a PNP type triode. The emitter of the second switch is connected to the positive pole of the input terminal. The base of the second switching transistor is connected to the common terminal of the collector of the first switching transistor and the seventh resistor. The collector of the first switching transistor is connected to one side of the isolation device, and one end of the side of the isolation device away from the second switching transistor is connected to the negative pole of the input terminal.

[0013] Further, a fourth resistor is connected between the emitter and the base of the second switching transistor, and a sixth resistor is connected between the base of the second switching transistor and the collector of the first switching transistor. R4 / (R6 + R7) > 0.25.

[0014] Further, the isolation device is an optocoupler. The light emitter of the isolation component is connected to the second switching transistor and the negative pole of the input terminal. The positive pole of the photoreceiver of the isolation device is connected to the first power supply through the eighth resistor.

[0015] Further, the switching device is a diode whose anode is connected to the negative pole of the input terminal.

[0016] Further, a first resistor is connected between the light emitter of the isolation device and the collector of the second switching transistor, and a first capacitor is connected in parallel at both ends of the light emitter of the isolation device.

[0017] Compared with the prior art, the technical solution and its beneficial effects of the present invention are as follows:

[0018] (1) For the level detection circuit of the present invention, the output logic level is the same as the level of the input voltage, where the level of the voltage refers to the comparison with the set threshold.

[0019] (2) By reasonably selecting the resistors in the present invention, when the normal input voltage value is applied, the current consumption of the circuit is less than 1 mA. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 FIG. is a circuit schematic diagram of an isolated level detection circuit provided by an embodiment of the present invention;

[0021] Illustration:

[0022] Input terminal - 100; control circuit - 200; output terminal - 300. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0023] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Apparently, the described embodiments are some, but not all, of the embodiments of the present invention. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0024] Refer to Figure 1 , an isolated level detection circuit, including an input terminal 100, a control circuit 200, a first switching transistor Q1, a second switching transistor Q2, an isolation device U1 and an output terminal 300. The input terminal 100 is used to input a voltage. The control circuit 200 is disposed between the positive and negative poles of the input terminal 100. The first switching transistor Q1 is connected to the control circuit 200. The second switching transistor Q2 is respectively connected to the first switching transistor Q1 and one side of the isolation device U1. The other side of the isolation device U1 is connected to the output terminal 300. The positive pole of the output terminal 300 is connected to a first power supply.

[0025] When the input terminal 100 is connected to a normal voltage, the control circuit 200 controls the first switching transistor Q1 to conduct, and the second switching transistor Q2 is cut off, so that the isolation device U1 is cut off, and the output terminal 300 outputs a high level. When the voltage connected to the input terminal 100 is lower than the required voltage, the control circuit 200 controls the first switch Q1 to be cut off, and the second switching transistor Q2 conducts, so that the isolation device U1 conducts, and the output terminal 300 outputs a low level. Thus, when the detected level is lower than the threshold level or the detected level is normal, the same logic level is output.

[0026] The control circuit 200 includes a switching device and a second resistor R2 connected in series between the positive and negative terminals of the input end, a third resistor R3 and a fifth resistor R5 connected in series and then connected in parallel across the two ends of the second resistor R2; a first switching transistor Q1 is connected to the common terminal of the third resistor R3 and the fifth resistor R5. In this embodiment, the switching device is a diode D1, the anode of the diode D1 is connected to the negative terminal of the input end 100, that is, the diode D1 is reversely connected. The first switching transistor Q1 is a PNP type triode, the base of the first switching transistor Q1 is connected to the common terminal of the third resistor R3 and the fifth resistor R5, the collector of the first switching transistor Q1 is connected to the negative terminal of the input end through a seventh resistor R7, and the emitter of the first switching transistor Q1 is connected to the positive terminal of the input end 100.

[0027] When the voltage input at the input end 100 is the normal required voltage, the voltage V input at the input end 100 CC = U Z + V R2 , U Z is the conduction voltage of the diode D1, and V R2 is the voltage across the second resistor R2. When the voltage V R3 across the third resistor R3 is greater than or equal to 0.7V, the first switching transistor Q1 conducts. At this time, V R2 = V R3 + V R5 , that is, when V R3 is equal to 0.7V, V R5 is equal to 0.7V * (R5 / R3).

[0028] In this embodiment, the resistance value relationship between the fifth resistor and the third resistor is set to satisfy: R5 / R3 < 0.3, that is, 0.7 * (1 + R5 / R3) < 1. For example, when the required input voltage is 16V or higher, a diode with a reverse conduction voltage of 15V is selected, so that V R2 is greater than or equal to 1V, and further satisfies that the voltage across V R3 is greater than or equal to 0.7V, so that the first switching transistor Q1 conducts. When the required input voltage is 15V or lower, at this time the input voltage is less than the conduction voltage U Z of the diode D1, the voltage V R2 across R2 is close to 0V, and V R3 is also close to 0V, so the first switching transistor Q1 is cut off.

[0029] It is not difficult to see that the setting of the normal voltage threshold can be achieved by selecting diodes with different reverse conduction voltages.

[0030] Continue to refer to Figure 1, the second switching transistor Q2 is a PNP type triode. The emitter of the second switch Q2 is connected to the positive pole of the input terminal 100. The base of the second switching transistor Q2 is connected to the common terminal of the collector of the first switching transistor Q1 and the seventh resistor R7. The collector of the first switching transistor Q1 is connected to one side of the isolation device U1. One end of the isolation device U1 away from the second switching transistor Q2 is connected to the negative pole of the input terminal 100.

[0031] A fourth resistor R4 is connected between the emitter and the base of the second switching transistor Q2, and a sixth resistor R6 is connected between the base of the second switching transistor Q2 and the collector of the first switching transistor Q1.

[0032] The isolation device U1 is selected as an optocoupler. One side of the isolation device U1 is a light emitter, and the other side of the isolation device U1 is a light receiver. The output terminal of the light receiver is connected to the first power supply through an eighth resistor R8, and the first power supply is 3.3V.

[0033] When the input voltage is higher than the threshold voltage, that is, when the voltage input is normal, the first switching transistor Q1 conducts, the second switching transistor Q2 cuts off, no current passes through both ends of the light emitter of the optocoupler, the optocoupler cuts off, and its output terminal is pulled up to 3.3V by the eighth resistor R8. Therefore, the output terminal 300 outputs a high level of 3.3V. That is, when the normal voltage range is input, the first switching transistor Q1 conducts, the second switching transistor Q2 cuts off, the isolation device U1 cuts off, and a high level is output.

[0034] When the input voltage is lower than the threshold voltage, the first switching transistor Q1 cuts off, satisfying V CC *R4 / (R4 + R6 + R7) is greater than 0.7V, the second switching transistor Q2 conducts, current passes through both ends of the light emitter of the optocoupler, the optocoupler conducts, the positive pole of the output terminal 300 is pulled down to 0V by the optocoupler. Therefore, the output terminal 300 outputs a low level of 0V. That is, when the input is lower than the threshold voltage range, the first switching transistor Q1 cuts off, the second switching transistor Q2 conducts, the isolation device U1 conducts, and a low level is output.

[0035] Next, specific values are set to further elaborate on the principle of this application. The required normal voltage range value is 16V to 32V, and the voltage range lower than the threshold voltage is 5V to 15V. The diode D1 is selected with a conduction voltage U Z Of 15V. The second resistor R2 is selected as 51KΩ, the fifth resistor R5 is selected as 51KΩ, the third resistor R3 is selected as 51KΩ, the seventh resistor R7 is selected as 150KΩ, the sixth resistor R6 is selected as 10KΩ, and the fourth resistor R4 is selected as 324KΩ.

[0036] When the input voltage is 16 - 32V, which is greater than the conduction voltage of diode D1, the voltage across both ends of diode D1 is clamped to 15V, and the voltage across R2 is 1 - 17V. Since R5 / R3 < 0.3, the voltage across the third resistor R3 is greater than 0.7, the first switching transistor Q1 conducts, the second switching transistor Q2 cuts off, the optocoupler U1 cuts off, and the positive pole of the output terminal 300 is pulled up to 3.3V by the eighth resistor R8, outputting a high level.

[0037] When the input voltage is 5V - 15V, which is less than the conduction voltage of diode D1, which is 15V, the first switching transistor Q1 cuts off, V CC *R4 / (R4 + R6 + R7) is greater than 0.7V, the second switching transistor Q2 conducts, so the optocoupler U1 conducts, and the output terminal 300 outputs a low level.

[0038] At the same time, when the input voltage is 16 - 32V, that is, when the voltage is normally output, no current passes through the optocoupler, and the current consumption of the detection circuit is: I = I R2 +I R5 +I R7 , it can be simply judged that when the input voltage is 32V, the current consumed by the circuit reaches the maximum. At this time: I R2 =V R2 / R2 = 17V / 51KΩ = 0.33mA, I R5 =V R5 / R5 = (17V - 0.7V) / 51KΩ = 0.32mA, I R7 =V R7 / R7 = 32V / 150KΩ = 0.21mA. Therefore, I = 0.33mA + 0.32mA + 0.21mA = 0.86mA. Therefore, when the normal input voltage is 16 - 32V, the current consumption of the circuit is less than 1mA.

[0039] The isolation - type level detection circuit of the present invention realizes that when the input voltage is 16 - 32V, a high level is output and the current consumption of the circuit is less than 1mA, and when the input voltage is 5V - 15V, a low level is output. The output logic of the present invention is the same as the level of the input voltage, and the circuit power consumption is small.

[0040] The above description shows and describes the preferred embodiments of the present invention. It should be understood that the present invention is not limited to the forms disclosed herein, should not be regarded as excluding other embodiments, but can be used in various other combinations, modifications and environments, and can be changed within the scope of the inventive concept herein through the above teachings or the technology or knowledge in related fields. And the changes and modifications made by those skilled in the art that do not depart from the spirit and scope of the present invention should all be within the protection scope of the appended claims of the present invention.

Claims

1. An isolated level detection circuit, characterized in that, It includes an input terminal, a control circuit, a first switching transistor, a second switching transistor, an isolation device, and an output terminal; The input terminal is used for inputting a voltage; the control circuit is disposed between the positive and negative electrodes of the input terminal; the first switching transistor is connected to the control circuit; the second switching transistor is respectively connected to the first switching transistor and one side of the isolation device; the other side of the isolation device is connected to the output terminal; a first power supply is connected to the positive electrode of the output terminal; When the input terminal accesses a normal voltage, the control circuit controls the first switching transistor to conduct, and the second switching transistor to cut off, so that the isolation device cuts off, and the output terminal outputs a high level; when the voltage accessed by the input terminal is lower than the required voltage, the control circuit controls the first switching transistor to cut off, and the second switching transistor to conduct, so that the isolation device conducts, and the output terminal outputs a low level; The control circuit includes a switching element and a second resistor connected in series between the positive and negative electrodes of the input terminal, a third resistor and a fifth resistor connected in series and then connected in parallel across the two ends of the second resistor, and one end of the fifth resistor far from the third resistor is connected to the common terminal of the second resistor and the switching element; the first switching transistor is a PNP type triode, and the base of the first switching transistor is connected to the common terminal of the third resistor and the fifth resistor. Wherein, the collector of the first switching transistor is connected to the negative electrode of the input terminal through a seventh resistor, and the emitter of the first switching transistor is connected to the positive electrode of the input terminal; The second switching transistor is a PNP type triode, the emitter of the second switching transistor is connected to the positive electrode of the input terminal, the base of the second switching transistor is connected to the common terminal of the collector of the first switching transistor and the seventh resistor, the collector of the first switching transistor is connected to one side of the isolation device, and one end of the isolation device far from the second switching transistor is connected to the negative electrode of the input terminal.

2. The isolation type level detection circuit according to claim 1, characterized in that, The fifth resistor and the third resistor satisfy: R5 / R3 < 0.3, where R5 is the resistance value of the fifth resistor and R3 is the resistance value of the third resistor.

3. The isolation type level detection circuit according to claim 1, wherein (V CC - U Z ) / R2+(Vcc - 0.7V - U Z ) / R5+V CC / R7 is less than 1 mA, where the V CC is the input voltage of the input terminal, the U Z is the conduction voltage of the switching device, R2 is the resistance value of the second resistor, and R7 is the resistance value of the seventh resistor.

4. The isolation type level detection circuit according to claim 1, wherein A fourth resistor is connected between the emitter and the base of the second switching transistor, and a sixth resistor is connected between the base of the second switching transistor and the collector of the first switching transistor. R4 / (R6 + R7) > 0.25, where R4 is the resistance value of the fourth resistor, R6 is the resistance value of the sixth resistor, and R7 is the resistance value of the seventh resistor.

5. An isolated level detection circuit according to claim 1, characterized in that, The isolation device is an optocoupler. The light emitter of the isolation device is connected to the second switching transistor and the negative electrode of the input terminal, and the positive electrode of the light receiver of the isolation device is connected to the first power supply through an eighth resistor.

6. The isolated level detection circuit according to claim 2, wherein The switching element is a diode with its anode connected to the negative electrode of the input terminal.

7. An isolated level detection circuit according to claim 5, characterized in that, A first resistor is connected between the light emitter of the isolation device and the collector of the second switching transistor, and a first capacitor is connected in parallel across the two ends of the light emitter of the isolation device.

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