Isolation push-pull circuit

Abstract

The utility model relates to an isolation push-pull circuit. Comprising a first photoelectric coupling module, a second photoelectric coupling module, a first triode and a second triode, the input end of the first photoelectric coupling module and the input end of the second photoelectric coupling module are jointly connected with a first connection point, and the first connection point is used for being connected with the output end of a single-chip microcomputer; the output end of the first photoelectric coupling module and the output end of the second photoelectric coupling module are both connected with the second connecting point, the first end of the first triode is connected with the second connecting point, the second end of the first triode is used for being connected with a first power supply, the first end of the second triode is connected with the second connecting point, and the second end of the second triode is used for being grounded; the third end of the first triode and the third end of the second triode are connected with a third connection point, and the third connection point serves as the output end of the isolation push-pull circuit. The circuit can control high-low level conversion of the output end of the isolation push-pull circuit through the single-chip microcomputer, and reduces electromagnetic interference through the photoelectric coupling module.

Description

Technical Field

[0001] This application relates to the field of circuits, and in particular to an isolated push-pull circuit. Background Technology

[0002] An isolated push-pull circuit is a switching power supply circuit based on a push-pull topology and using a transformer to achieve electrical isolation between input and output. It is widely used in low-to-medium power applications requiring high reliability and electrical isolation. Its core feature is that by alternately turning on two switching transistors, an alternating voltage is generated on the primary winding of the transformer. This voltage is then coupled to the secondary winding, rectified, and filtered to output the target voltage.

[0003] Most existing isolation push-pull circuits on the market adopt the push-pull + transformer form, but this form may generate electromagnetic interference during operation, and reasonable circuit design and shielding measures are needed to reduce the impact on other equipment. Utility Model Content

[0004] Therefore, it is necessary to provide an isolated push-pull circuit to prevent electromagnetic interference.

[0005] An isolated push-pull circuit includes a first optocoupler module, a second optocoupler module, a first transistor, and a second transistor, wherein:

[0006] The input terminals of the first and second optocouplers are both connected to a first connection point, which is used to connect to the output terminal of the microcontroller. The output terminals of both the first and second optocouplers are connected to a second connection point. The first terminal of the first transistor is connected to the second connection point, and the second terminal of the first transistor is used to connect to a first power supply. The first terminal of the second transistor is connected to the second connection point, and the second terminal of the second transistor is used to ground. The third terminals of both the first and second transistors are connected to a third connection point, which serves as the output terminal of the isolation push-pull circuit.

[0007] When the output terminal of the microcontroller outputs a low level, the first optocoupler module is turned off, the second optocoupler module is turned on, the output terminal of the second optocoupler module outputs a low level through the second connection point, the second transistor is turned off, the first transistor is turned on, and the third terminal of the first transistor outputs a high level through the third connection point.

[0008] When the output terminal of the microcontroller is floating, the second optocoupler module is turned off, the first optocoupler module is turned on, the output terminal of the first optocoupler module outputs a high level through the second connection point, the first transistor is turned off, the second transistor is turned on, and the third terminal of the second transistor outputs a low level through the third connection point.

[0009] In one embodiment, the first optocoupler module includes a first optocoupler and a switching diode, wherein:

[0010] The first end of the first optocoupler is used to connect to the second power supply, and the first end of the first optocoupler is also connected to the anode of the switching diode. The cathode of the switching diode serves as the input terminal of the first optocoupler module. The second end of the first optocoupler is used to ground, the third end of the first optocoupler serves as the output terminal of the first optocoupler module, and the fourth end of the first optocoupler is used to connect to the first power supply.

[0011] In one embodiment, the first optocoupler module further includes a first resistor, a first end of the first optocoupler is connected to a first end of the first resistor, and a second end of the first resistor is used to connect to a second power supply.

[0012] In one embodiment, the second optocoupler module includes a second optocoupler, wherein:

[0013] The first end of the second optocoupler is used to connect to the second power supply, and the second end of the second optocoupler serves as the input end of the second optocoupler module; the third end of the second optocoupler is used to ground, and the fourth end of the second optocoupler serves as the output end of the second optocoupler module.

[0014] In one embodiment, the second optocoupler module further includes a second resistor, with a first end of the second optocoupler connected to a first end of the second resistor, and a second end of the second resistor used to connect to a second power supply.

[0015] In one embodiment, the isolated push-pull circuit further includes a light-emitting diode and a third resistor, wherein:

[0016] The anode of the light-emitting diode is connected to the first end of the third resistor, the second end of the third resistor is used to connect to the second power supply, and the cathode of the light-emitting diode is connected to the first connection point.

[0017] In one embodiment, the isolation push-pull circuit further includes a fuse, the first end of which is connected to the third connection point, and the second end of which serves as the output terminal of the isolation push-pull circuit.

[0018] In one embodiment, the isolation push-pull circuit further includes a freewheeling diode, the anode of which is grounded and the cathode of which is connected to the second end of the fuse.

[0019] In one embodiment, the first transistor is an NPN transistor.

[0020] In one embodiment, the second transistor is a PNP transistor.

[0021] Compared to the push-pull circuit that combines a push-pull circuit with a transformer, the aforementioned isolated push-pull circuit achieves electrical isolation from the push-pull circuit (first transistor and second transistor) through a first optocoupler module and a second optocoupler module, thereby reducing electromagnetic interference during operation. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of this application or the conventional technology, the drawings used in the description of the embodiments or the conventional technology will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 An isolated push-pull circuit as one embodiment;

[0024] Figure 2 This is an example of an isolated push-pull circuit. Detailed Implementation

[0025] To facilitate understanding of this application, a more complete description will be provided below with reference to the accompanying drawings, which illustrate embodiments of the present application. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that the disclosure of this application will be more thorough and complete.

[0026] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of this application.

[0027] It is understood that the terms "first," "second," etc., used herein may be used to describe various elements, but these elements are not limited by these terms. These terms are only used to distinguish one element from another. For example, without departing from the scope of this application, a first resistor may be referred to as a second resistor, and similarly, a second resistor may be referred to as a first resistor. Both the first resistor and the second resistor are resistors, but they are not the same resistor.

[0028] It is understood that the term "connection" in the following embodiments should be understood as "electrical connection," "communication connection," etc., if the connected circuits, modules, units, etc., have electrical signal or data transmission with each other.

[0029] When used herein, the singular forms of “a,” “an,” and “the” may also include the plural forms unless the context clearly indicates otherwise. It should also be understood that the terms “comprising / including” or “having,” etc., specify the presence of the stated features, wholes, steps, operations, components, parts, or combinations thereof, but do not preclude the possibility of the presence or addition of one or more other features, wholes, steps, operations, components, parts, or combinations thereof. Meanwhile, the term “and / or” as used in this specification includes any and all combinations of the associated listed items.

[0030] Most existing push-pull isolation circuits on the market adopt a push-pull + transformer configuration. However, this configuration may generate electromagnetic interference during operation, requiring proper circuit design and shielding measures to reduce its impact on other devices and ensure stable system operation. Furthermore, because both switches are turned on simultaneously, the turn-on loss is approximately twice that of other topologies. It also cannot change the output level through programming without altering the circuit structure. The core structure of a push-pull circuit is two switches connected in parallel with the primary winding of a transformer with a center tap. The simultaneous turn-on of both switches is essentially a power supply short circuit caused by control logic failure; the core reason for its huge turn-on loss is the strong coupling between the instantaneous large current and voltage.

[0031] In one exemplary embodiment, such as Figure 1 As shown, an isolated push-pull circuit is provided, including a first optocoupler module 10, a second optocoupler module 20, a first transistor 30, and a second transistor 40, wherein:

[0032] The input terminals of the first optocoupler module 10 and the second optocoupler module 20 are both connected to the first connection point, which is used to connect to the output terminal of the microcontroller. The output terminals of the first optocoupler module 10 and the second optocoupler module 20 are both connected to the second connection point. The first end of the first transistor 30 is connected to the second connection point, and the second end of the first transistor 30 is used to connect to the first power supply VCC. The first end of the second transistor 40 is connected to the second connection point, and the second end of the second transistor 40 is used to ground. The third ends of the first transistor 30 and the second transistor 40 are both connected to the third connection point, which serves as the output terminal of the isolation push-pull circuit.

[0033] Among them, the optocoupler module can refer to a module composed of light-emitting diodes (LEDs) and photosensitive devices (such as phototransistors or photosensitive field-effect transistors) and other circuit elements (such as resistors, diodes, etc.), which achieves electrical isolation between input and output through optical signals.

[0034] Among them, the first transistor 30 and the second transistor 40 act as switches or amplifiers, controlling the conduction and cutoff according to the base signal (i.e. the signal received from the optocoupler module).

[0035] The first connection point can be the input node of the microcontroller signal, simultaneously driving the input terminals of two optocoupler modules. The second connection point can be the common node for the output signals of the two optocoupler modules, controlling the base level (signal) of the first transistor 30 and the second transistor. The third connection point can be the push-pull output node, outputting high / low levels through the alternating conduction of the two transistors.

[0036] Among them, the first power supply VCC can refer to the power supply of the voltage level required in actual application, such as 12V, 24V, etc., and the circuit is adjusted and connected according to the actual voltage requirements.

[0037] When the output terminal of the microcontroller is low, the first optocoupler module 10 is cut off, the second optocoupler module 20 is turned on, the output terminal of the second optocoupler module 20 outputs a low level through the second connection point, the second transistor 40 is cut off, the first transistor 30 is turned on, and the third terminal of the first transistor 30 outputs a high level through the third connection point.

[0038] Specifically, when the microcontroller outputs a low level (logic 0), the first optocoupler module 10 receives the low level, its LED has no current, the photosensitive end is cut off, and it outputs a high impedance state; the second optocoupler module 20 receives the low level, its LED is turned on, the photosensitive end is turned on, and it outputs a low level to the second connection point; the base of the second transistor 40 is at a low level, the second transistor 40 is cut off, and it cannot conduct to ground; the base of the first transistor 30 is at a low level, the first transistor 30 is turned on, and it transmits the voltage of the connected first power supply VCC to the third connection point, that is, it outputs a high level.

[0039] When the output terminal of the aforementioned microcontroller is left floating, the aforementioned second optocoupler module 20 is turned off, the aforementioned first optocoupler module 10 is turned on, the output terminal of the aforementioned first optocoupler module 10 outputs a high level through the aforementioned second connection point, the aforementioned first transistor 30 is turned off, the aforementioned second transistor 40 is turned on, and the third terminal of the aforementioned second transistor 40 outputs a low level through the aforementioned third connection point.

[0040] Specifically, when the microcontroller output is floating, the first optocoupler module 10 forms a high level through an internal or external pull-up resistor, its LED is turned on, the photosensitive end is turned on, and the output high level is sent to the second connection point; when the microcontroller output is floating, the second optocoupler module 20 has no current in its LED, the photosensitive end is cut off, and the output is in a high impedance state; the base of the first transistor 30 is at a high level, and the first transistor 30 is cut off; the base of the second transistor 40 is at a high level, and the second transistor 40 is turned on, grounding the third connection point, that is, outputting a low level.

[0041] In the aforementioned isolated push-pull circuit, compared to the isolated push-pull circuit combined with a transformer, this application achieves electrical isolation from the push-pull circuit (first transistor 30 and second transistor 40) through the first optocoupler module 10 and the second optocoupler module 20, thereby reducing electromagnetic interference during operation.

[0042] In one exemplary embodiment, such as Figure 2 As shown, the first optocoupler module 10 includes a first optocoupler U14 and a switching diode D27. The first end of the first optocoupler U14 is connected to a second power supply, and is also connected to the anode of the switching diode D27. The cathode of the switching diode D27 serves as the input terminal of the first optocoupler module 10. The second end of the first optocoupler U14 is grounded, the third end serves as the output terminal of the first optocoupler module 10, and the fourth end is connected to the first power supply. The second power supply can be a power supply with the required voltage level in actual application, such as 5V, and the circuit adjustment and connection are based on the actual voltage requirements.

[0043] In one exemplary embodiment, such as Figure 2 As shown, the first optocoupler module 10 further includes a first resistor R112. The first end (pin 1) of the first optocoupler U14 is connected to the first end of the first resistor R112, and the second end of the first resistor R112 is used to connect to the second power supply.

[0044] In one exemplary embodiment, such as Figure 2 As shown, the second optocoupler module 20 includes a second optocoupler U15, wherein:

[0045] The first end (pin 1) of the second optocoupler U15 is used to connect to the second power supply, the second end (pin 2) of the second optocoupler U15 is used as the input end of the second optocoupler module 20, the third end (pin 3) of the second optocoupler U15 is used to ground, and the fourth end (pin 4) of the second optocoupler U15 is used as the output end of the second optocoupler module 20.

[0046] In one exemplary embodiment, such as Figure 2 As shown, the second optocoupler module 20 further includes a second resistor R116. The first end (pin 1) of the second optocoupler U15 is connected to the first end of the second resistor R116, and the second end of the second resistor R116 is used to connect to the second power supply.

[0047] In one exemplary embodiment, such as Figure 2 As shown, the above-mentioned isolated push-pull circuit also includes a light-emitting diode D26 and a third resistor R111, wherein:

[0048] The anode of the aforementioned LED D26 is connected to the first terminal of the aforementioned third resistor R111, the second terminal of the aforementioned third resistor R111 is used to connect to the second power supply, and the cathode of the aforementioned LED D26 is connected to the aforementioned first connection point (DO_24_9). The aforementioned LED D26 is used to indicate the output level status of the aforementioned microcontroller. For example, when the microcontroller outputs a low level, the LED D26 is turned on, indicating that the microcontroller output is low; when the microcontroller outputs a high level, the LED D26 is turned off, the light is not turned on, indicating that the microcontroller output is floating.

[0049] In one exemplary embodiment, such as Figure 2 As shown, the aforementioned isolation push-pull circuit also includes a fuse F22. The first end (pin 2) of the fuse is connected to the third connection point, and the second end (pin 1) of the fuse F22 serves as the output terminal of the isolation push-pull circuit. Specifically, as... Figure 2As shown, pin 1 of fuse F22 is connected to point DO9_1, which serves as the output terminal of the isolated push-pull circuit. Specifically, fuse F22 is mainly used to prevent excessive voltage in the downstream circuit connected to the isolated push-pull circuit from causing reverse current and burning out the transistors in the push-pull circuit.

[0050] In one exemplary embodiment, such as Figure 2 As shown, the aforementioned isolation push-pull circuit also includes a freewheeling diode D156. The anode of the freewheeling diode D156 is grounded, and the cathode of the freewheeling diode D156 is connected to the second terminal (pin 1) of the fuse F22. Specifically, the freewheeling diode D156 can provide a freewheeling path: when the inductive load (such as a relay coil, motor winding, etc.) connected to the isolation push-pull circuit is de-energized, the inductor will generate a reverse electromotive force. At this time, the freewheeling diode D156 conducts, providing a low-impedance freewheeling path for the inductor current, allowing the current to decay smoothly and avoiding sudden current changes. It can also suppress voltage spikes: through freewheeling, the energy stored in the inductor is gradually dissipated in the form of heat, preventing the formation of high-voltage spikes from the reverse electromotive force, avoiding breakdown of switching transistors (such as MOSFETs) or other integrated circuits, and protecting circuit safety. It can also reduce electromagnetic interference: reduce high-frequency oscillations and electromagnetic interference caused by sudden current changes, and improve circuit stability and reliability.

[0051] In one exemplary embodiment, combined with Figure 1 as well as Figure 2 The first transistor 30 in the aforementioned push-pull isolation circuit, also known as transistor Q75, can be an NPN transistor. It is used to primarily perform the "push" function (outputting a high level) in the push-pull circuit.

[0052] In one exemplary embodiment, combined with Figure 1 as well as Figure 2 The second transistor 40 in the aforementioned push-pull isolation circuit, also known as transistor Q74, can be a PNP transistor. It is used to primarily achieve the "pull" function (outputting a low level) in the push-pull circuit.

[0053] The following combination Figure 2 The working process of the isolation push-pull circuit is explained in detail.

[0054] When point DO_24_9 is low (close to 0V), LED D26 illuminates, indicating that the microcontroller's output is low. Then, switching diode D27 conducts. Due to the diode characteristics of switching diode D27, a voltage drop occurs, causing the LED inside the first optocoupler U14 to turn off. The LED inside the second optocoupler U15 emits light as current flows through it. Its internal phototransistor, when illuminated, conducts current and outputs a low level. The NPN transistor Q75 then conducts, outputting a high level from the 24V power supply through fuse F22 to point D09-1. However, the forward voltage drop (approximately 0.7V) generated when switching diode D27 is on is insufficient, failing to meet the conduction and light-emitting conditions, thus causing the LED inside the first optocoupler U14 to turn off.

[0055] When the microcontroller output is floating, point DO_24_9 is at a high level, LED D26 is off, switching diode D27 is off, second optocoupler U15 is off, LED inside first optocoupler U14 emits light as current flows through it, and its internal phototransistor conducts current after being illuminated, outputting 24V power, PNP transistor Q74 conducts, and outputs a low level to point D09-1 through fuse F22.

[0056] The aforementioned isolated push-pull circuit uses optocoupler isolation to prevent common-ground interference, isolates circuits with different voltage levels, and boasts strong anti-interference capabilities, high reliability, a simple circuit structure, few components, and convenient maintenance. It eliminates the need for an output transformer, reducing cost and weight, and in some applications, it can save space. The high-low level conversion at the output of the isolated push-pull circuit is achieved by changing the output state of the microcontroller. The alternating conduction and cutoff of the two transistors reduces power loss caused by simultaneous conduction, enabling efficient power conversion and improving energy conversion efficiency. The alternating conduction and cutoff process is very fast, enabling rapid response and meeting the needs of applications requiring rapid adjustment. Furthermore, the emitters of the two power switches are connected together, and the two sets of drive circuits share a common terminal without the need for insulation, thus simplifying the drive circuit and broadening its application scenarios.

[0057] The aforementioned isolation push-pull circuit can be widely used in scenarios requiring electrical isolation and high reliability. For example, in industrial communication and interfaces, it can isolate communication interfaces: providing signal isolation power for communication protocols such as RS-485, RS-422, and CAN bus, ensuring safe isolation between high-voltage and low-voltage systems, and preventing noise interference and electrical faults; it can also be used in network equipment: in PoE (Power over Ethernet) applications, the push-pull circuit can provide high-power isolated power, ensuring stable power supply for network devices. Another example is its application in BMS (Battery Management System) in automotive electronics and new energy fields: the isolation push-pull circuit provides isolated power between the high-voltage battery pack and the low-voltage control circuit in electric vehicles, preventing the risk of high-voltage breakdown. Or in on-board inverters and charging systems: the push-pull circuit provides bias voltage to the drive MOSFETs through isolated power, while supporting safe high-voltage to low-voltage conversion. Furthermore, for medical instruments requiring strict electrical isolation, the aforementioned isolation push-pull circuit can serve as a safe, small-sized isolated power supply while reducing electromagnetic interference to the instrument. Similarly, it can be applied to industrial control systems, ensuring the electromagnetic interference resistance of industrial control systems in industrial environments. It can also be applied to synchronous motor drives, high-frequency switching power supplies, portable device power supplies, and low-voltage signal drives, among other applications.

[0058] In the description of this specification, references to terms such as "some embodiments," "other embodiments," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative descriptions of the above terms do not necessarily refer to the same embodiments or examples.

[0059] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0060] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of this application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these modifications and improvements all fall within the protection scope of this application. Therefore, the protection scope of this application should be determined by the appended claims.

Claims

1. An isolated push-pull circuit, characterized by It includes a first optocoupler module, a second optocoupler module, a first transistor, and a second transistor, wherein: The input terminals of the first and second optocouplers are both connected to a first connection point, which is used to connect to the output terminal of the microcontroller. The output terminals of both the first and second optocouplers are connected to a second connection point. The first terminal of the first transistor is connected to the second connection point, and the second terminal of the first transistor is used to connect to a first power supply. The first terminal of the second transistor is connected to the second connection point, and the second terminal of the second transistor is used to ground. The third terminals of both the first and second transistors are connected to a third connection point, which serves as the output terminal of the isolation push-pull circuit. When the output terminal of the microcontroller outputs a low level, the first optocoupler module is turned off, the second optocoupler module is turned on, the output terminal of the second optocoupler module outputs a low level through the second connection point, the second transistor is turned off, the first transistor is turned on, and the third terminal of the first transistor outputs a high level through the third connection point. When the output terminal of the microcontroller is floating, the second optocoupler module is turned off, the first optocoupler module is turned on, the output terminal of the first optocoupler module outputs a high level through the second connection point, the first transistor is turned off, the second transistor is turned on, and the third terminal of the second transistor outputs a low level through the third connection point.

2. The isolated push-pull circuit of claim 1, wherein, The first optocoupler module includes a first optocoupler and a switching diode, wherein: The first end of the first optocoupler is used to connect to the second power supply, and the first end of the first optocoupler is also connected to the anode of the switching diode. The cathode of the switching diode serves as the input terminal of the first optocoupler module. The second end of the first optocoupler is used to ground, the third end of the first optocoupler serves as the output terminal of the first optocoupler module, and the fourth end of the first optocoupler is used to connect to the first power supply.

3. The isolated push-pull circuit of claim 2, wherein, The first optocoupler module further includes a first resistor, a first end of the first optocoupler is connected to a first end of the first resistor, and a second end of the first resistor is used to connect to a second power supply.

4. The isolated push-pull circuit of claim 2, wherein, The second optocoupler module includes a second optocoupler, wherein: The first end of the second optocoupler is used to connect to the second power supply, and the second end of the second optocoupler serves as the input end of the second optocoupler module; the third end of the second optocoupler is used to ground, and the fourth end of the second optocoupler serves as the output end of the second optocoupler module.

5. The isolated push-pull circuit of claim 4, wherein, The second optocoupler module further includes a second resistor, with the first end of the second optocoupler connected to the first end of the second resistor, and the second end of the second resistor used to connect to a second power supply.

6. The isolated push-pull circuit according to any one of claims 1 to 5, characterized in that The isolated push-pull circuit also includes a light-emitting diode and a third resistor, wherein: The anode of the light-emitting diode is connected to the first end of the third resistor, the second end of the third resistor is used to connect to the second power supply, and the cathode of the light-emitting diode is connected to the first connection point.

7. The isolated push-pull circuit according to any one of claims 1 to 5, characterized in that, The isolation push-pull circuit also includes a fuse, the first end of which is connected to the third connection point, and the second end of which serves as the output terminal of the isolation push-pull circuit.

8. The isolated push-pull circuit of claim 7, wherein, The isolation push-pull circuit also includes a freewheeling diode, the anode of which is grounded and the cathode of which is connected to the second end of the fuse.

9. The isolated push-pull circuit of any one of claims 1 to 5, wherein, The first transistor is an NPN transistor.

10. The isolated push-pull circuit of claim 9, wherein, The second transistor is a PNP type transistor.

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