CN218352491U - Push-pull type tri-state output circuit - Google Patents

Abstract

The utility model discloses a three state output circuit of push-pull, include: a signal input terminal receiving an input signal of one of a high level, a low level and a high impedance state; the push-pull output module comprises a first switching element connected with the first power supply and a second switching element connected with the ground terminal, wherein the first switching element is controlled to be switched on and switched off by a third switching element, and the second switching element is controlled to be switched on and switched off by a fourth switching element; and the path control module is connected with the signal input end and is connected with the control end of the third switching device and the control end of the fourth switching device. When the input signal is in a high-impedance state, the output of the path control module enables the third switching device and the fourth switching device to be turned off, so that the first switching device and the second switching device are turned off to output a high-impedance state signal. The utility model provides a three-state output circuit of push-pull has realized that three-state output just possesses protect function's effect to internal device, has extensive suitability to the specially adapted integrated circuit makes.

Description

Push-pull type tri-state output circuit

Technical Field

The utility model relates to a circuit field relates to push-pull circuit technical field especially for realize tristate logic output.

Background

In the field of circuit design, different signals have a problem of matching default states of the signals during communication, and particularly, when a signal of one device needs to drive a signal of another device, the default state of the signal between the two devices may be uncertain: may be pulled up to the power supply by default through a resistor, i.e., a high state, may be pulled down to GND by default through a resistor, i.e., a low state, or may be a high resistance state. Therefore, when signals between two devices are directly interconnected, if the front and rear signal states do not match, a situation where the signals are not recognized may occur. In addition, short circuits between signals of different devices may occur, thereby damaging the circuit.

In the prior art, when signal control and driving are performed, a push-pull circuit is often used in order to accelerate the control speed. Among them, the push-pull circuit generally can output only a high level and a low level state, but cannot output a high impedance state.

For example, the push-pull output circuit disclosed in chinese patent document CN109656298a is divided into two parts, i.e., a first module and a second module; inputting an input end Vin to the first module; the first module is used for separating the input signal of the input end Vin into two same signals and respectively inputting the two same signals to the second module; the second module is a push-pull output circuit and is used for realizing rail-to-rail output. In the above scheme, when the input signal is in the high impedance state, the output circuit cannot output the high impedance state. And the circuit also has no short-circuit protection function.

In addition, to the inventor's knowledge, there is no single integrated chip that implements the tri-state output function.

It is therefore advantageous to design a circuit that can implement a push-pull tri-state output function, and preferably provides the circuit with a short circuit protection function.

SUMMERY OF THE UTILITY MODEL

In order to solve at least one problem that exists among the above-mentioned prior art, the utility model provides a three-state output circuit of push-pull, include:

a signal input terminal receiving an input signal, the input signal being one of a high level, a low level and a high impedance state,

the push-pull output module comprises a first switching device connected with a first power supply and a second switching device connected with a ground terminal, wherein the first switching device is controlled to be switched on and switched off by a third switching device according to the high level or low level state of the input signal, the second switching device is controlled to be switched on and switched off by a fourth switching device according to the high level or low level state of the input signal, and therefore a high level or low level signal corresponding to the input signal is output, the push-pull output module comprises a first switching device connected with the first power supply and a second switching device connected with the ground terminal

And the path control module is connected with the signal input end and is connected with the control end of the third switching device and the control end of the fourth switching device, and when the input signal is in a high-impedance state, the output of the path control module enables the third switching device and the fourth switching device to be turned off, so that the first switching device and the second switching device are turned off, and a high-impedance signal is output.

In some embodiments of the present invention, the path control module may include a first voltage divider circuit, the first voltage divider circuit includes a series resistor having one end connected to the second power supply and the other end grounded, wherein one end of the first resistor in the series resistor is connected to the control terminal and the signal input terminal of the fourth switching device, the other end is connected to the second power supply, one end of the third resistor is connected to the control terminal of the third switching device, the other end is grounded, the second resistor is connected between the first and third resistors, and the second resistor is connected to the signal input terminal with the connection end of the first resistor.

In some embodiments of the present invention, the third switching device may turn on the first switching device through a second voltage dividing circuit, and the fourth switching device may turn on the second switching device through a third voltage dividing circuit.

In some embodiments of the present invention, the second voltage dividing circuit may include a series resistor having one end connected to the first power supply and the other end grounded through the third switching device, wherein a connection end of two resistors in the series resistor is connected to the control end of the first switching device.

In some embodiments of the present invention, the third voltage dividing circuit may include a series resistor having one end connected to the third power supply through the fourth switching device and the other end grounded, wherein a connection end of two resistors in the series resistor is connected to the control end of the second switching device.

In some embodiments of the present invention, the second power supply and the third power supply may be the same power supply. This can reduce the power consumption of the entire system.

In some embodiments of the present invention, the circuit further comprises a first short circuit protection module connected to said first switching device, said first switching device being closed when a current flowing through said first switching device exceeds a preset value; and/or a second short-circuit protection module connected with the second switching device and used for closing the second switching device when the current flowing through the second switching device exceeds a preset value. Therefore, the utility model provides a circuit possesses the protect function to the output short circuit (power short circuit and GND short circuit).

In some embodiments of the present invention, the first short-circuit protection module may include a first protection device, a first current limiting resistor and a pull-up resistor, and the second short-circuit protection module may include a second protection device, a second current limiting resistor and a pull-down resistor.

In some embodiments of the present invention, the first protection device and the second protection device may use a triode.

In some embodiments of the present invention, the first switching device, the second switching device, the third switching device and the fourth switching device are selected from MOS field effect transistors or triodes.

In some embodiments of the present invention, the third switching device may employ an NPN transistor, and the fourth switching device may employ a PMOS field effect transistor. In this case, the emitter of the third switching device is grounded, and the collector is connected to the second voltage dividing circuit; the drain of the fourth switching device is connected to the third power supply source, and the source is connected to a fourth resistor of the series resistors of the third voltage dividing circuit.

In some embodiments of the present invention, the first protection device may adopt a PNP triode, and the first switching device may adopt a PMOS field effect transistor. In this case, a collector of the first protection device is connected to a gate of the first switching device, an emitter of the first protection device is connected to the first power supply, a base of the first protection device is connected to one end of a first current limiting resistor, and the other end of the first current limiting resistor is connected to a source of the first switching device and connected to the first power supply through a pull-up resistor; the second protection device may be an NPN transistor, and the second switching device is an NMOS field effect transistor. In this case, the collector of the second protection device is connected to the gate of the second switching device, the emitter of the second protection device is grounded, the base of the second protection device is connected to one end of the second current limiting resistor, and the other end of the second current limiting resistor is connected to the source of the second switching device and grounded via the pull-down resistor.

In some embodiments of the present invention, the push-pull output module may further include a diode, an anode of the diode is connected to the first switching device, and a cathode of the diode is connected to the second switching device. The embodiment can prevent the first power supply from being damaged when the signal output end is short-circuited with the outside.

The utility model provides a three-state output circuit of push-pull through specific circuit structure design, has still realized the output of high attitude on the basis of conventional push-pull output circuit's high level, low level output function for the output state and the input state of circuit are unanimous, can not receive external circuit's influence. Thus, the circuit implements a tri-state output.

Moreover, because the short-circuit protection function is designed for the high-level state output and the low-level state output of the push-pull output, the protection function is added for devices in the circuit, the circuit has wider applicability, and is particularly suitable for manufacturing integrated circuits.

Drawings

Fig. 1 is a schematic structural diagram of a push-pull tri-state output circuit according to an embodiment of the present invention.

Fig. 2 is a schematic structural diagram of a path control module according to an embodiment of the present invention.

Fig. 3 is a circuit diagram of a push-pull tri-state output circuit according to an embodiment of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention clearer, the present invention is described in further detail with reference to the accompanying drawings and specific embodiments. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be embodied in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concept of the invention to those skilled in the art.

Referring to fig. 1, a schematic structural diagram of a push-pull tri-state output circuit according to an embodiment of the present invention is shown. As shown in fig. 1, the push-pull tri-state output circuit provided by the present invention mainly includes a signal input terminal 10, a path control module 20, two switching devices 30 and 40, and a push-pull output module 50.

The signal input terminal 10 is used for receiving an input signal, and the state of the input signal may be a high level, a low level, or a high impedance state.

The push-pull output block 50 includes a first switching device 51 and a second switching device 52 for outputting signals of corresponding states according to the state (high level, low level or high impedance state) of an input signal. The first switching device 51 is connected to a first power supply 53, and the second switching device 52 is connected to a ground 54. The connection of the first switching device 51 to the second switching device 52 is connected to the signal output 60, and can output a signal in a push-pull operation.

In the push-pull type tri-state output circuit of the present embodiment, in order to control the outputs of the first switching device 51 and the second switching device 52, the push-pull type tri-state output circuit further includes a third switching device 30 and a fourth switching device 40 respectively connected to the control terminal of the first switching device 51 and the control terminal of the second switching device 52, and configured to respectively control on/off of the first switching device 51 and the second switching device 52 according to the states (high level and low level) of the input signal.

The path control module 20 has one end connected to the signal input terminal 10 and the other end connected to a control terminal of the third switching device 30 and a control terminal of the fourth switching device 40. The function of the path control module 20 is to output a level, which enables the first switching device 51 and the second switching device 52 to be turned off, to the control terminals of the third switching device 30 and the fourth switching device 40 respectively through the path control module 20 when the input signal is in a high impedance state.

Thus, when the signal input through the signal input terminal 10 is a high level signal, the third switching device 30 turns on the first switching device 51, and the fourth switching device 40 turns off the second switching device 52, so that the signal output terminal 60 connected to the push-pull output module 50 outputs the high level signal.

When the input signal is a low level signal, the third switching device 30 turns off the first switching device 51, and the fourth switching device 40 turns on the second switching device 52, so that the push-pull output module 50 outputs the low level signal through the signal output terminal 60.

When the input signal is a high impedance signal, in order to output the high impedance signal, the first switching device 51 and the second switching device 52 need to be turned off, so the path control module 20 is designed to output corresponding levels to the third switching device 30 and the fourth switching device 40 according to the input high impedance signal, so that the third switching device 30 and the fourth switching device 40 control the first switching device 51 and the second switching device 52 to be turned off, and the push-pull output module 50 finally outputs the high impedance signal through the signal output terminal 60.

The circuit structure can realize tri-state output with a push-pull function, and particularly when an input signal is in a high-impedance state, the circuit can also realize corresponding high-impedance state output.

One implementation of the path control module 20 may be a voltage divider circuit 21.

For example, referring to fig. 2, a schematic structural diagram of a path control module according to an embodiment of the present invention is shown. The voltage dividing circuit 21 (referred to as a first voltage dividing circuit) may include series resistors R1, R2, and R3 having one end connected to the second power supply VCC1 and the other end grounded. One end of a first resistor R1 in the series resistors is connected with the control end of the fourth switching device 40 and the signal input end 10, and the other end of the first resistor R1 is connected with a second power supply VCC 1; one end of a third resistor R3 in the series resistor is connected to the control end of the third switching device 30, and the other end is grounded. The second resistor R2 is connected between the first and third resistors, and the connection of the second resistor R2 to the first resistor R1 is connected to the signal input terminal.

Based on the above structure, the voltage dividing circuit can control the turn-off of the fourth switching device by the voltage division of the first resistor R1 in the series resistors in all the series resistors R1, R2, R3 when the input signal is in the high impedance state, and can control the turn-off of the third switching device by the voltage division of the third resistor R3 in the series resistors in all the series resistors R1, R2, R3. Therefore, when the input signal is in a high impedance state, the voltage division circuit outputs corresponding levels to the third switching device and the fourth switching device, so that the third switching device and the fourth switching device operate (for example, turn off), so that the first switching device and the second switching device in the push-pull output module are also turned off, and the output signal is also ensured to be in the high impedance state.

It should be understood by those skilled in the art that the path control module may also take other forms as long as it can control the operating states of the third switching device and the fourth switching device when the input is high impedance, so that the third switching device and the fourth switching device control both the first switching device and the second switching device to turn off to realize high impedance output. As for the on/off control of the first switching device 51 by the third switching device 30 and the on/off control of the second switching device 52 by the fourth switching device 40, depending on the types of the selected first and second switching devices (NMOS, PMOS, NPN, PNP, etc.), a person skilled in the art can select a corresponding appropriate device type and its output mode for the third switching device 30 and the fourth switching device 40, thereby selecting an output control mode of the path control module for the third switching device 30 and the fourth switching device 40 when the path control module is in the high impedance state. As will be exemplified below in connection with specific device types.

Further, the third switching device 30 and the fourth switching device 40 may also respectively turn on or off the first switching device 51 and the second switching device 52 through corresponding voltage dividing circuits, so as to implement a push-pull type tri-state output.

Specifically, the corresponding voltage dividing circuit (referred to as a second voltage dividing circuit) of the first switching device 51 is configured such that, when the third switching device 30 is turned on, the first switching device 51 is also turned on.

For example, the second voltage dividing circuit may include series resistors R6, R8 having one end connected to the first power supply 53 and the other end connected to the ground through the third switching device 30. Wherein the connection terminals of two resistors in the series resistor are connected to the control terminal of the first switching device 51. The specific circuit structure can refer to a circuit diagram provided by an embodiment of the present invention shown in fig. 3 hereinafter.

Specifically, the corresponding voltage dividing circuit (referred to as a third voltage dividing circuit) of the second switching device 52 is configured such that, when the fourth switching device 40 is turned on, the second switching device 52 is also turned on.

For example, the third voltage dividing circuit includes series resistors R4 and R5 having one end connected to the third power supply VCC2 through the fourth switching device 40 and the other end connected to the ground. Wherein the connection terminals of two resistors in the series resistor are connected to the control terminal of the second switching device 52. The specific circuit structure can refer to a circuit diagram provided by an embodiment of the present invention shown in fig. 3 hereinafter.

Further, it should be understood by those skilled in the art that the second voltage dividing circuit and the third voltage dividing circuit may also adopt other structures, as long as it is satisfied that the first switching device 51 is turned on when the third switching device 30 is turned on, and the second switching device 52 is turned on when the fourth switching device 40 is turned on.

In the above, the second power supply VCC1 and the third power supply VCC2 may be the same power supply, so as to reduce the power consumption of the system.

Furthermore, the utility model provides a circuit can also include the first short-circuit protection module to first switching device Q1 and/or the second short-circuit protection module to second switching device Q2 to realize the short-circuit protection function of external interface.

Optionally, the first/second short-circuit protection module may perform short-circuit protection on the circuit through a first/second protection device (preferably a triode to adjust the magnitude of the current limiting current), a first/second current limiting resistor, and a pull-up/pull-down resistor. The specific circuit structure can refer to a circuit diagram provided by an embodiment of the present invention shown in fig. 3 hereinafter.

Additionally, the utility model provides an in the circuit, first switching element and the second switching element of push-pull output module can be complementary, promptly, the two can be field effect transistor or the triode that polarity is different. The structure has high stability, strong anti-interference capability and lower static power consumption.

Specifically, the first switching device may be selected from one of a PMOS field effect transistor and an NMOS field effect transistor, and the second switching device may be selected from the other of the PMOS field effect transistor and the NMOS field effect transistor. In other words, when the first switching device is a PMOS transistor, the second switching device is an NMOS transistor; when the first switching device is an NMOS transistor, the second switching device is a PMOS transistor.

Alternatively, the first switching device is selected from one of a PNP transistor and an NPN transistor, and the second switching device is selected from the other.

Similarly, the third switching device and the fourth switching device may be MOS field effect transistors or triodes.

To the utility model provides an in the circuit selection of each switching device, the skilled person in the art can understand, the utility model provides a first, second, third, fourth switching device can be the MOS pipe, also can be the triode in place. These switching devices may be of the same type, for example all MOS transistors, or all transistors; alternatively, one part of the transistor can be a MOS transistor, and the other part of the transistor can be a triode. No matter what type of switching device each switching device is, those skilled in the art can adapt the corresponding structure of the above-described circuit according to the operating principle of the corresponding switching device.

Optionally, the push-pull output module 50 may further include a protection circuit formed by a diode, an anode of the diode is connected to the first switching device 51, and a cathode of the diode is connected to the second switching device 52. Therefore, unidirectional current circulation can be ensured, and the current is prevented from flowing backwards from the signal output end to damage the first power supply.

The circuit provided by an embodiment of the present invention is specifically described below by taking the first switch device 51 as the PMOS transistor Q1, the second switch device 52 as the NMOS transistor Q2, the third switch device 30 as the NPN transistor T1, the fourth switch device 40 as the PMOS transistor Q3, the first protection device as the PNP transistor T2, and the second protection device as the NPN transistor T3.

Referring to fig. 3, a specific embodiment of the push-pull tri-state output circuit of the present invention is shown. The circuit comprises resistors R1/R2/R3/R4/R5/R6/R7/R8/R9, a sampling resistor R10/R11, triodes T1, T2 and T3, a diode D1 and MOS (metal oxide semiconductor) tubes Q1, Q2 and Q3.

In the circuit, the signal input terminal 10 is an MCU-IO port, and the signal output terminal 60 is a Vout port. The path control module 20 is in the form of a voltage divider circuit, and includes series resistors R1, R2, and R3.

The third switching device 30 is an NPN transistor T1, and the second voltage dividing circuit coupled thereto includes resistors R6 and R8.

The fourth switching device 40 is a PMOS transistor Q3, and the third voltage dividing circuit includes resistors R4 and R5.

The first switching device 51 in the push-pull output module 50 is a PMOS transistor Q1, and the first power supply 53 connected thereto is VDD. The second switching device 52 is an NMOS transistor Q2, and is connected to the ground terminal 54 (GND).

In this embodiment, the second power supply VCC1 of the first voltage dividing circuit and the third power supply VCC2 connected to the fourth switching device Q3 share one power supply VCC.

As also shown in fig. 3, in one embodiment, the push-pull tri-state output circuit includes a first short protection module and a second short protection module. The first short-circuit protection module comprises a first protection device, namely a triode T2, a first current limiting resistor R7 and a pull-up resistor R10. The second short-circuit protection module comprises a second protection device, namely a triode T3, a second current limiting resistor R9 and a pull-down resistor R11.

The connection relationship and the corresponding function of each circuit device will be described in detail below.

One end of the resistor R1 is connected with the power source VCC and the drain electrode of the transistor Q3, and the other end is connected with the grid electrode of the PMOS transistor Q3, one end of the resistor R2 and the MCU-IO port of the signal input end. The function of R1 is two, namely, a reliable state is provided for the voltage difference Vgs of the grid electrode and the source electrode of Q3, and Q3 is ensured to be in a closed state. Secondly, when the MCU-IO port is in a high-impedance state, R1, R2 and R3 form a voltage division circuit for the VCC power supply, and at the moment, the resistance value matching relation of R1-R3 can be set according to the type selection of Q3 to ensure that the voltage division voltage on R1 is less than | Vgs (TH) | of Q3, thereby ensuring that Q3 is in a closed state.

Those skilled in the art will understand that: for an NMOS (N-channel metal oxide semiconductor) transistor, vg-Vs > Vgs (TH), vgs (TH) is a threshold voltage threshold of the MOS transistor, namely the voltage difference between a G pole (grid) and an S pole (source) is larger than a certain value, the MOS transistor is conducted, but the voltage difference cannot be too large, otherwise the MOS transistor is burnt out. The turn-on voltage and other parameters are referred to in the specification according to the specific device selected. Similarly, vg-Vs < Vgs (TH) for the PMOS transistor, namely the pressure difference between the G pole and the S pole is less than a certain value, the MOS transistor is conducted (Vgs (TH) is a negative value for the PMOS transistor). Likewise, specific parameters may be referred to in the specification for a particular device.

One end of the resistor R2 is connected with the base electrode of the triode T1 and one end of the resistor R3, and the other end of the resistor R2 is connected with one end of the MCU-IO and the resistor R1 and the grid electrode of the transistor Q3. The circuit has two functions, namely, when the MCU-IO outputs high level, the circuit provides base current limiting function for T1, and when the MCU-IO is in high resistance state, the circuit forms a voltage division circuit for a VCC power supply together with R1 and R3, thereby ensuring that T1/Q3 is in off state.

One end of the resistor R3 is connected with GND, and the other end of the resistor R3 is connected with the base electrode of the T1 and one end of the resistor R2, so that the effect of the resistor R is to ensure that the T1 is in a reliable closing state when the MCU-IO is in a high-resistance state.

The emitter of triode T1 links to each other with GND, and the base links to each other with the one end of resistance R1 and R2, and the collector links to each other with the one end of resistance R6, and its effect is when control signal MCU-IO is effective, through opening triode T1, makes R6 and R8 constitute bleeder circuit, satisfies Q1's the difference Vgs of grid voltage and source voltage < Vgs (TH) to open PMOS pipe Q1.

One end of the resistor R6 is connected with a collector of the triode T1, and the other end of the resistor R6 is connected with a collector of the triode T2, a grid of the Q1 and one end of the resistor R8, so that when a control signal MCU-IO is effective (high level), the collector and an emitter of the T1 are connected to GND, the grid of the Q1 is formed into a voltage division circuit by R6, R8 and R10, and the voltage value on the R8 is larger than Vgs (TH) of the Q1 by setting the resistance value of R6/R8, so that the Q1 is ensured to be opened; and secondly, the current limiting function is provided for preventing the T2 from burning out the T1 or the T2 when the T2 is started.

One end of the resistor R7 is connected with the base electrode of the triode T2, and the other end is connected with one end of the resistor R8, the source electrode of the Q1 and one end of the resistor R10, and the resistor R7 is used for providing current limiting for the base electrode of the T2. When the current passing through the R10 is too large and exceeds a certain value, so that the voltage drop on the R10 exceeds 0.7V, the emitter junction voltage Ube of the T2 is larger than 0.7V, the T2 is started according to the property of the triode, and the R7 can limit the base current of the T2 to prevent the T2 from being burnt by the too large current.

The base electrode of the triode T2 is connected with one end of the R7, the emitter electrode and one end of the sampling resistor R10 are connected to the power supply VDD, and the collector electrode is connected with one end of the R6, one end of the R8 and the grid electrode of the Q1. The effect of which is that when the voltage difference V on R10 is _R10 If the voltage is more than 0.7V, namely when the current flowing through the Q1 is too large, the T2 is started; the collector voltage of T2 is equal to VDD, namely the grid voltage of Q1 is equal to VDD, vgs =0 of Q1, and the PMOS tube Q1 is closed, so that the purpose of protecting Q1 is achieved.

One end of a current sampling resistor R10 is directly connected with an emitter of the T2 and VDD, one end of the current sampling resistor R10 is connected with one end of the R7, a source electrode of the Q1 and one end of the R8, and the current sampling resistor R10 is used for detecting a voltage value V generated when a load passes through the R10 in the short circuit process _R10 To set the magnitude of the short circuit current.

One end of a resistor R8 is connected with a source electrode of the Q1, one end of the R7 and one end of the R10, and the other end is connected with one end of the R6, a collector electrode of the T2 and a grid electrode of the Q1. The function is to form a partial pressure with R6 when the PMOS transistor Q1 is normally turned on. The function of the circuit is that when T1 is opened, R10/R8/R6 forms a voltage division circuit, the resistance value matching relation of R6, R8 and R10 is set according to the selection of Q1, and reliable grid starting voltage is provided for Q1.

The grid electrode of the PMOS tube Q1 is connected with one end of the R6, the collector electrode of the T2 and one end of the R8, the source electrode of the PMOS tube Q1 is connected with one end of the R7, one end of the R8 and one end of the R10, and the drain electrode of the PMOS tube Q1 is connected with the anode of the diode D1. The function of which is to provide a high level signal for the push-pull output circuit.

The anode of the diode D1 is connected with the drain of the PMOS tube Q1, and the cathode is directly connected with the drain of the NMOS tube Q2. Its function is to prevent the breakdown of the VDD power supply when Vout is shorted to other external power supplies, and this diode can be eliminated if VDD and external shorted power supplies are equal.

The grid electrode of the PMOS tube Q3 is connected with one end of the R1, one end of the MCU-IO port and one end of the R2, the source electrode and one end of the R1 are connected to a power supply VCC, the drain electrode is connected with one end of the R4, and the effect is that when the MCU-IO port outputs a low level, the Q3 is conducted to generate a grid electrode starting voltage signal of the NMOS tube Q2.

One end of the resistor R4 is connected with the drain electrode of the Q3, one end of the resistor R4 is connected with one end of the resistor R5, the grid electrode of the Q2 and the collector electrode of the T3, the effect of the resistor R4 is two, firstly, after the Q3 is opened, the resistor R3 and the resistor R5 form a voltage division circuit for VCC, and the voltage division value of the resistor R5 at the moment is larger than Vgs (TH) of the Q2, so that the Q2 can be reliably opened. Secondly, when the output is short-circuited, the current flowing through R11 is large, V _R11 If the voltage is more than 0.7V, T3 can be turned on according to the property of the triode, and R4 is an Ice current limiting resistor for providing a collector and an emitter of the T3.

One end of the resistor R5 is connected with one end of the R4, the collector of the T3 and the grid of the Q2, and the other end of the resistor R is directly connected with GND. The effect is to provide a reliable pull-down state for the gate of Q2 when MCU-IO is in a high impedance state.

The collector of the triode T3 is connected with one end of the R5, one end of the R4 and the grid of the Q2, the emitter of the T3 is directly connected with GND, and the base is connected with one end of the R9. The function is to turn on T3 when the current flowing through the sampling resistor R11 is too large and exceeds a certain value, then to make the grid of Q2 quickly change to low level, and to close the NMOS tube Q2.

One end of the resistor R9 is connected with the base electrode of the T3, the other end of the resistor R9 is connected with one end of the R11 and the source electrode of the Q2, and the resistor R is used for providing a current-limiting resistor for the base electrode of the T3.

One end of the sampling resistor R11 is connected with one end of the R9 and the source electrode of the Q2, and one end is directly connected with GND. The effect is that when the load current is too large, a large voltage drop V is generated on R11 _R11 When V is _R11 When the voltage is larger than a certain value (short-circuit current setting threshold value multiplied by resistance value of the sampling resistor R11), T3 is turned on, so that the grid voltage of Q2 is smaller than Vgs, and Q2 is turned off.

The drain electrode of the NMOS tube Q2 is connected with the cathode of the D1 and the output Vout, the source electrode is connected with one end of the R11 and one end of the R9, and the grid electrode is connected with one end of the R5, one end of the R4 and the collector electrode of the T3. The function of the low-level output circuit is to control the on and off of the negative pole of the push-pull output to realize the low-level output state.

The MOS tube used in the scheme can be replaced by a triode, such as Q1/Q2/Q3, and T1 can also be replaced by an MOS tube. In addition, the pull-up resistor R10 and the pull-down resistor R11 are added to increase the protection accuracy, and in practical application, the internal resistance Rds (on) of the MOS transistor Q1/Q2 may be used as a sampling resistor instead, and the circuit structure of the invention may be changed accordingly, but those skilled in the art will understand that the idea is unchanged, that is, the current passing through Rds (on) may generate a certain voltage drop, and the voltage drop may close the MOS transistor.

The specific operating principle of the circuit in this embodiment is as follows:

1. when the signal input end MCU-IO outputs a high level to a next stage (specifically, the MCU-IO high level should be equal to the VCC voltage value, or the difference between the two is small), the T1 triode is turned on, vgs of Q1 is smaller than a turn-on threshold Vgs (TH), Q1 is turned on, at this time, Q3 is in a turn-off state, Q2 is also in a turn-off state, vout output level is a high level, and Vout = VDD-0.7V.

2. When the signal input end MCU-IO outputs a low level to the next stage, T1 is not conducted, so Q1 is also in a closed state; at this time, the fourth switching device Q3 is in a conducting state, the gate signal of Q2 is enabled, so that Q2 is turned on, and the output terminal Vout =0V, that is, a low level is output.

3. When the signal input end MCU-IO outputs backward to be in a high-resistance state, the series resistors R1, R2 and R3 form a voltage division circuit for the VCC power supply, and at the moment, the voltage division voltage on the R1 is ensured to be smaller than | Vgs (TH) | of Q3, so that the Q3 can be ensured to be in a closed state, and the voltage of the R3 is smaller than 0.7V, so that the T1 is ensured to be in the closed state. Accordingly, both Q1 and Q2 are turned off and the output Vout is high.

The utility model provides a three state output circuit of push-pull type, owing to all made the short-circuit protection function to the high level of push-pull output and the state output of low level, and realized the output state of high resistant attitude for the state of output can not receive external circuit's influence. Therefore, the circuit realizes tri-state output and has the function of protecting internal devices, has wide applicability and is particularly suitable for manufacturing integrated circuits.

In the description herein, reference to the description of the terms "one embodiment," "some embodiments," "an example," "an embodiment," or "some examples," etc., means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the application. In this specification, the schematic representations of the terms used above are not necessarily intended to refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Moreover, various embodiments or examples and features of various embodiments or examples described in this specification can be combined and combined by one skilled in the art without being mutually inconsistent.

In the present invention, the terms "connected" and "connecting" should be interpreted broadly, for example, the term "connected" may be a fixed connection, a detachable connection, or an integrated connection; "coupled" may be direct or indirect through an intermediary. The specific meaning of the above terms in the present invention can be understood according to specific situations by those skilled in the art.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention and are not restrictive. Although the present invention has been described in detail with reference to the embodiments, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the appended claims.

Claims (10)

1. A push-pull tri-state output circuit, comprising:

a signal input terminal receiving an input signal, the input signal being one of a high level, a low level and a high impedance state,

the push-pull output module comprises a first switching device connected with a first power supply and a second switching device connected with a grounding terminal, wherein the first switching device is controlled to be switched on and switched off by a third switching device according to the high level or low level state of the input signal, the second switching device is controlled to be switched on and switched off by a fourth switching device according to the high level or low level state of the input signal, and therefore a high level or low level signal corresponding to the input signal is output, the push-pull output module comprises a first switching device connected with the first power supply and a second switching device connected with the grounding terminal

And the path control module is connected with the signal input end and is connected with the control end of the third switching device and the control end of the fourth switching device, when the input signal is in a high-impedance state, the output of the path control module enables the third switching device and the fourth switching device to be turned off, so that the first switching device and the second switching device are turned off to output a high-impedance signal.

2. A push-pull three-state output circuit as claimed in claim 1, wherein the path control module is a first voltage divider circuit comprising a series resistor having one end connected to the second power supply and the other end connected to ground, wherein a first resistor of the series resistor has one end connected to the control terminal of the fourth switching device and the signal input terminal, the other end connected to the second power supply, a third resistor has one end connected to the control terminal of the third switching device and the other end connected to ground, a second resistor is connected between the first and third resistors, and a connection end of the second resistor to the first resistor is connected to the signal input terminal.

3. A push-pull three-state output circuit as claimed in claim 2, wherein said third switching device renders said first switching device conductive through a second voltage dividing circuit, and said fourth switching device renders said second switching device conductive through a third voltage dividing circuit.

4. A push-pull three state output circuit as claimed in claim 3 wherein the second voltage divider circuit comprises a series resistor having one end connected to the first power supply and the other end connected to ground through a third switching device, wherein the connection of two resistors in the series resistor is connected to the control terminal of the first switching device; and/or

The third voltage division circuit comprises a series resistor with one end connected with a third power supply through a fourth switching device and the other end grounded, wherein the connection end of two resistors in the series resistor is connected with the control end of the second switching device.

5. The push-pull tri-state output circuit of claim 4, wherein the first, second, third and fourth switching devices are selected from MOS field effect transistors or triodes, wherein the first and second switching devices are complementary.

6. The push-pull tri-state output circuit of claim 5, wherein the third switching device is an NPN transistor and the fourth switching device is a PMOS field effect transistor, wherein the third switching device has an emitter connected to ground and a collector connected to the second voltage divider circuit; the drain of the fourth switching device is connected to the third power supply source, and the source is connected to a fourth resistor among the series resistors of the third voltage dividing circuit.

7. The push-pull tri-state output circuit of any of claims 1-6, further comprising:

the first short-circuit protection module is connected with the first switching device and is used for closing the first switching device when the current flowing through the first switching device exceeds a preset value; and/or

And the second short-circuit protection module is connected with the second switching device and is used for closing the second switching device when the current flowing through the second switching device exceeds a preset value.

8. The push-pull tri-state output circuit of claim 7, wherein the first short protection module comprises a first protection device, a first current limiting resistor and a pull-up resistor, and the second short protection module comprises a second protection device, a second current limiting resistor and a pull-down resistor, the first and second protection devices being selected from a triode.

9. The push-pull tri-state output circuit of claim 8, wherein the first protection device is a PNP transistor, the first switching device is a PMOS field effect transistor,

the collector of the first protection device is connected with the grid of the first switch device, the emitter of the first protection device is connected with the first power supply, the base of the first protection device is connected with one end of a first current-limiting resistor, and the other end of the first current-limiting resistor is connected with the source of the first switch device and is connected with the first power supply through a pull-up resistor; and/or

The second protection device is an NPN triode, the second switching device is an NMOS field effect transistor,

the collector of the second protection device is connected with the grid of the second switch device, the emitter of the second protection device is grounded, the base of the second protection device is connected with one end of a second current-limiting resistor, and the other end of the second current-limiting resistor is connected with the source of the second switch device and grounded through a pull-down resistor.

10. Push-pull tristate output circuit as claimed in any of claims 1 to 6 wherein said push-pull output module further comprises a diode, said diode having an anode connected to the first switching device and a cathode connected to the second switching device.

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