WO2017186104A1

WO2017186104A1 - Pwm generation circuit

Info

Publication number: WO2017186104A1
Application number: PCT/CN2017/081912
Authority: WO
Inventors: 万黎
Original assignee: 中兴通讯股份有限公司
Priority date: 2016-04-25
Filing date: 2017-04-25
Publication date: 2017-11-02
Also published as: CN107306126A

Abstract

A PWM generation circuit. The generation circuit comprises: a constant current source circuit, a sawtooth wave circuit, a comparison circuit and a controllable DC circuit, wherein the constant current source circuit is configured to supply a constant direct current to a capacitor C1 in the sawtooth circuit; the sawtooth circuit is connected to the constant current source circuit, and is configured to control the voltage of the capacitor C1, such that the capacitor C1 outputs a sawtooth output signal; the comparison circuit is connected to the sawtooth wave circuit and the controllable DC power source, respectively, and is configured to receive the sawtooth signal and a DC signal outputted by the controllable DC power source, to compare the sawtooth wave signal with the DC signal, and to output a PWM signal according to the comparison result.

Description

PWM generation circuit

Technical field

The present disclosure relates to the field of communications, for example to a PWM generating circuit.

Background technique

In the industrial measurement and control, the Pulse Width Modulation (PWM) generator can generally output the PWM wave by using the MCU output pin or the control special chip controlled by the MCU. In the field of testing, an additional design of the single-chip circuit is required, and an interface circuit for realizing communication between the single-chip microcomputer and the upper-level control machine is required. This additionally increases the complexity of the software and hardware design of the system. For example, the MCU needs to do additional software development, which extends the development cycle and increases the cost.

The output PWM wave requires additional microcontrollers, etc., which increases system complexity, long development cycle, and increased cost. No effective solution has been proposed.

Summary of the invention

The present disclosure provides a PWM generating circuit, which can solve the problem that the output PWM wave requires an additional single chip, which increases the complexity of the system, shortens the development cycle, and reduces the cost.

The embodiment provides a pulse width modulation PWM generating circuit, comprising: a constant current source circuit, a sawtooth wave circuit, a comparison circuit and a controllable DC power supply; the constant current source circuit is set to provide a constant capacitance C1 in the sawtooth wave circuit. a DC current; the sawtooth wave circuit is connected to the constant current source circuit, configured to control a voltage of the capacitor C1 such that the capacitor C1 outputs a sawtooth wave signal; and a comparison circuit respectively with the sawtooth wave circuit and The controllable DC power supply is connected to receive the sawtooth wave signal and the DC signal output by the controllable DC power supply, compare the sawtooth wave signal and the DC signal, and output a PWM signal according to the comparison result.

Optionally, the constant current source circuit may include a voltage reference chip, a resistor R1, an adjustable resistor RP1, and a PNP transistor Q1. The PNP transistor includes a base B, a collector C, and a source E, wherein the resistor R1 is connected between B-E of the PNP transistor, and the adjustable resistor RP1 and the voltage reference chip are connected between B-C of the PNP transistor.

Optionally, the adjustable resistor RP1 is configured to adjust a period of the sawtooth wave signal output by the capacitor C1 by adjusting a self resistance value.

Optionally, the controllable DC power source is configured to be connected to the controller, configured to receive a control command of the controller, and output a DC voltage signal corresponding to the control command.

Optionally, the comparison circuit may include: an operational amplifier and a voltage dividing resistor, the operational amplifier is electrically connected to the voltage dividing resistor; and the voltage dividing resistor is configured to divide the direct signal input by the controllable current source to form a voltage dividing signal; The operational amplifier includes a first signal input configured to receive the divided signal.

Optionally, the resistance of the voltage dividing resistor is determined according to a voltage value of a DC signal input by the controllable DC power source.

Optionally, the operational amplifier may further comprise a second signal input configured to receive the sawtooth signal.

Alternatively, the operational amplifier may be arranged to compare the sawtooth signal with the divided signal.

Optionally, the operational amplifier may further include a signal output end, configured to output a low level when the sawtooth wave signal is greater than the divided voltage signal, and output high when the sawtooth wave signal is smaller than the divided voltage signal a level in which the high level and the low level are used as PWM signals.

Optionally, the operational amplifier is an LM 2903 chip.

Optionally, the sawtooth wave circuit comprises: a timer, and the capacitor and the capacitor C1 are electrically connected.

Optionally, the timer is an ICM 7555 chip.

Optionally, the capacitor C1 is a COG ceramic capacitor or an NPO ceramic capacitor.

Through the constant current source circuit, the sawtooth wave circuit and the comparison circuit interaction process, the PWM signal can be conveniently generated, which can solve the problem of increasing system complexity, long development cycle and increasing cost caused by the output of the PWM wave requiring additional single-chip microcomputer. .

DRAWINGS

The drawings described herein are provided to provide an understanding of the following embodiments, which are set forth in the accompanying claims. In the drawing:

Fig. 1 is a block diagram showing the configuration of a PWM generating circuit of this embodiment.

2A is a block diagram showing the structure of a PWM generating circuit of the alternative example.

2B is a block diagram showing the structure of an internal comparator in the ICM 7555 chip in the alternative embodiment.

FIG. 3 is a structural block diagram of a controllable PWM wave generator circuit according to an alternative embodiment 1.

detailed description

Hereinafter, the technical solutions of the present disclosure will be described with reference to the accompanying drawings in conjunction with the embodiments. The features of the following embodiments and examples may be combined with each other without conflict.

It is to be noted that the terms "first", "second", and the like in the embodiments and the claims and the above drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or order.

In this embodiment, a PWM generating circuit is provided. FIG. 1 is a structural block diagram of a PWM generating circuit according to the embodiment. As shown in FIG. 1, the generating circuit may include: a constant current source circuit 10, and a sawtooth. Wave circuit 12 and comparison circuit 14.

The constant current source circuit 10 is arranged to supply a constant direct current to the capacitor C1 in the sawtooth circuit.

The sawtooth circuit 12 is arranged to control the voltage of the capacitor C1 such that the capacitor C1 outputs a sawtooth signal.

Optionally, the sawtooth wave circuit controls the signal output by the capacitor C1 to be a sawtooth wave signal.

The comparison circuit 14 is arranged to receive the sawtooth wave output signal, and output a PWM signal according to the comparison result according to the sawtooth wave output signal and the DC signal input by the controllable DC power source 16.

Optionally, the comparison circuit receives the sawtooth wave signal output by the sawtooth wave circuit through the capacitor C1, and further receives the DC signal output by the controllable DC power supply, compares the sawtooth wave signal with the DC signal, and outputs the PWM signal according to the comparison result.

Optionally, comparing the two signals, for example, at a time if the sawtooth signal is greater than The DC signal outputs a low level, and if the sawtooth signal is less than the DC signal, it outputs a high level.

Optionally, the constant current source circuit 10 supplies a constant direct current to the capacitor C1 in the sawtooth circuit, and the sawtooth circuit 12 controls the voltage of the capacitor C1 so that the capacitor C1 outputs a sawtooth output signal, and the comparison circuit 14 The sawtooth wave output signal is received, and the PWM signal is output according to the comparison result according to the sawtooth wave output signal and the DC signal input by the controllable DC power source 16. It can solve the problem of increasing system complexity, long development cycle and increasing cost caused by the output of PWM wave requiring additional single-chip microcomputer, etc., and thus does not need additional single-chip circuit, using separate device and controllable DC source in industrial control to realize one kind The simple and stable controllable PWM wave generator circuit makes the development cycle shorter and the cost is reduced.

2A and 2B are structural block diagrams of a PWM generating circuit according to the present alternative example. As shown in FIG. 2A and FIG. 2B, the constant current source circuit 10 may include: a voltage reference chip, a resistor R1, an adjustable resistor RP1, and a PNP. Transistor Q1. The voltage reference chip, the resistor R1, the adjustable resistor RP1, and the two P poles of the PNP transistor Q1 are connected in series, and the N pole of the PNP transistor Q1 is connected to the voltage reference chip and the resistor R1.

Optionally, the PNP transistor Q1 includes a base B, a collector C and a source E, wherein the resistor R1 is connected between the B-E of the PNP transistor, and the adjustable resistor RP1 and the voltage reference chip are connected between the B-C of the PNP transistor.

The sawtooth circuit 12 can also include an ICM7555 chip and a capacitor C1. The comparison circuit 14 can include an LM2903 chip and a voltage dividing resistor that can be configured to divide the voltage signal input by the controllable current source.

Optionally, the ICM7555 chip in the sawtooth circuit 12 is a timer. The ICM7555 chip is only an exemplary timer model. In this embodiment, other types of timers can also be used instead of the ICM 7555 chip. The function of the sawtooth circuit.

Optionally, the generating circuit may further include: a controllable DC power source 16, for example, embodied in FIG. 2A as a programmable DC voltage source 16, the controllable DC power source may be configured to receive a control command of the controller, and output and the control The voltage corresponding to the instruction.

Based on the schematic diagram of the circuit shown in FIG. 2A, in the embodiment, the adjustable resistor RP1 adjusts the period of the sawtooth wave by adjusting its own resistance value; the resistance value of the voltage dividing resistor passes through the DC input of the controllable DC power supply. The voltage value of the signal is determined.

Optionally, the comparison circuit may be further configured to compare the divided signal of the sawtooth wave output signal and the DC signal input by the controllable DC power source by the voltage dividing resistor. The comparison circuit outputs a low level when the sawtooth wave output signal is greater than the divided voltage signal, and outputs a high level when the sawtooth wave output signal is smaller than the divided voltage signal, wherein the high level is The low level is used as a PWM signal.

Alternatively, in order to make the voltage on the capacitor C1 stable, the capacitor C1 can select a COG ceramic capacitor, an NPO ceramic capacitor.

The above-described PWM generating circuit will be explained below in conjunction with an alternative embodiment.

Alternative embodiment 1

The optional embodiment 1 provides a simple high-stability linear remote controllable PWM wave generator circuit, and FIG. 3 is a structural block diagram of the controllable PWM wave generator circuit according to the first embodiment. The circuit can pass the following modules. The constant current source circuit module 30 (corresponding to the constant current source circuit 10 in FIG. 1), the sawtooth circuit module 32 (corresponding to the sawtooth circuit module 12 in FIG. 1), and the square wave circuit module 34 are embodied by the TL431. (corresponding to the comparison circuit 14 in FIG. 1) and the programmable DC source module 36 (corresponding to the controllable DC power source 16 in FIG. 1). The constant current source circuit module may also be referred to as a constant current source circuit, and the sawtooth wave circuit module may also be referred to as a sawtooth wave circuit. The square wave circuit module 34 may also be referred to as a square wave circuit, and the programmable DC source. The module can also be called a programmable DC source.

As shown in Figure 2A-2B and Figure 3, the constant current source circuit formed by TL431 can provide a constant current source to capacitor C1, and provide a constant current source for capacitor C1. This ensures that the charging voltage waveform on C1 is linear. Waveform. C1 and ICM7555 can form a sawtooth circuit. Because whenever the voltage of C1 rises linearly to 2/3VCC (supply voltage), the ICM7555 internally turns on the discharge loop, which instantly pulls the voltage of C1 down to 1/3VCC. Then the internal discharge circuit of the ICM7555 is turned off, so that the constant current source continues to charge C1. Repeatedly, on capacitor C1 (

ICM7555

2, 6, 7 tubes) The foot) forms a signal of a periodic sawtooth wave. In order to make the capacitance of the capacitor C1 unaffected by factors such as temperature and time, the capacitor C1 can use a ceramic capacitor of the COG/NPO type.

The square wave circuit can be a comparison circuit formed by an operational amplifier LM2903. When the positive input terminal of the op amp is INA+ (the control voltage sent from the programmable DC source passes through the resistor R3, the voltage divider signal of R4) is greater than the INA-voltage of the negative input terminal of the op amp (ie, the periodic sawtooth output of the sawtooth circuit) When the wave signal is), the output terminal OUT_A is high. When the voltage of the positive input terminal INA+ of the operational amplifier is less than the INA-voltage of the negative input terminal of the operational amplifier, the output terminal OUT_A of the operational amplifier is low. The output voltage of the programmable DC source causes the positive input voltage of the op amp to be within the voltage variation range of the capacitor C1 (1/3VCC-2/3VCC), so that a fixed-period square wave signal is formed at the output end, and the square wave signal is formed. The period is equal to the period of the sawtooth signal on capacitor C1. When the programmable DC source changes the voltage under the control of the host computer program, the duty cycle of the square wave signal also changes, so that the PWM signal can be formed. And this PWM signal can conveniently control some heating sources, speed control fans, etc., to achieve the integration of the control system.

By adopting the above technical solution provided by the optional embodiment 1, the single circuit and the software design are not needed, the progress of the control process is simplified, the same stable and controllable PWM effect is achieved, the cost is saved, and the efficiency of the entire control system is improved.

Alternative embodiment 2

As shown in FIG. 2A and FIG. 2B, the constant current source circuit may include U3-TL431, resistor R1, adjustable resistor RP1, and PNP transistor Q1. The TL431 is a 2.5V reference source device and the resistor R1 provides a bias current for the TL431 to operate stably. The PNP transistor Q1 uses a reverse connection mode. The pressure difference between the C and B poles of the PNP transistor is stable, so that there is a stable differential pressure at the 2 end of the RP1. Thus, after power-on, the E pole of Q1 outputs a constant current. Moreover, by adjusting the size of RP1, this current value can be adjusted to change the slope of C1 charging, thereby adjusting the period (or frequency) of the entire sawtooth and PWM waves.

The sawtooth circuit module 32 in FIG. 3 may be composed of an ICM7555, a charge and discharge capacitor C1 (to ensure the capacity stability of the C1 capacitor, the capacitor may be a COG or NPO ceramic capacitor) and a filter capacitor C2. The filter capacitor C2 can be electrically connected to the CONTROL_VOLRAGE pin of the ICM7555 chip to stabilize the voltage of the CONTROL_VOLRAGE pin. The ICM7555 has two built-in comparators. Pin 6Threshold and Pin 2trigger are connected to the positive input of one comparator and the negative input of another comparator. The voltage at the other end of the comparator connected to pin 6 is fixed at 2/3 VCC, and the fixed voltage at the other end of the comparator connected to pin 2 is 1/3 VCC. Optionally, FIG. 2B is a schematic structural diagram of an internal comparator of the ICM 7555 chip. As shown in FIG. 2B, the pin 6Threshold is connected to the positive input terminal of the comparator Comparator A, and the pin 2trigger is connected to the negative input of the comparator Comparator B. end. The pin CONTROL_VOLTAGE 5 is connected to the negative input of comparator Comparator A and is electrically connected to a fixed voltage of 2/3VCC. The positive input of the comparator Comparator B is electrically connected to a fixed voltage of 1/3 VCC.

After the circuit is powered up, the internal discharge loop of the 7Discharge pin of the ICM7555 is OFF. As the constant current source circuit starts to charge the capacitor C1 constant current, when the voltage of the capacitor C1 exceeds 2/3VCC, the pin 7Discharge is connected. The internal discharge loop state is reversed to the ON state, and then the internal discharge loop is pulled down to the ground, so that the charge stored in the capacitor C1 is quickly released until the voltage of the capacitor C1 is lower than 1/3 VCC, and the state of the internal discharge loop connected to the pin 7Discharge is switched to In the OFF state, the voltage of the capacitor C1 is linearly increased again in the constant current charging mode. Repeatedly, a periodic sawtooth output signal is formed on capacitor C1.

The square wave circuit module 34 includes a comparator LM2903 which, as shown in FIG. 2A, includes two input signal terminals INA+ and INA-. The input signal terminal INA- is connected to the periodic sawtooth signal on C1, and the input signal terminal INA+ is connected to the DC signal after the programmable voltage of the programmable DC source output is divided by the resistors R3 and R4. When the voltage division signal of the programmable DC source is greater than the sawtooth voltage on C1, the output terminal OUT_A of the LM2903 outputs a high level; when the voltage division signal of the programmable DC source is lower than the sawtooth voltage on C1, the output of the LM2903 OUT_A outputs a low level. This makes it possible to form a square wave signal with a fixed duty cycle. However, since the upper computer can remotely control the output voltage of the programmable DC source through a General Purpose Interface Bus (GPIB) or an RS232 interface, the square wave signal can be converted into a required PWM signal under program control. . And because of constant current charging Use, so that this adjustment can be linearly adjusted, which is convenient for the design of the program of the upper computer.

Optionally, the LM 2903 is an operational amplifier, and the LM 2903 chip is only an exemplary timer type. In this embodiment, other types of operational amplifiers can also implement the functions of the square wave circuit module instead of the LM 2903. .

In summary, the technical solution of the embodiment can solve the problem of increasing system complexity, long development cycle, and increased cost caused by the output of the PWM wave requiring an additional single-chip microcomputer, etc., thereby eliminating the need for a single-chip circuit, using separate devices, and The existing controllable DC source in industrial control realizes a simple and stable controllable PWM wave generator circuit, which shortens the development cycle and reduces the cost.

Industrial applicability

The present disclosure provides a PWM generating circuit, which can solve the problem of increasing the complexity of the system caused by the output of the PWM wave requiring an additional single chip microcomputer, etc., which can shorten the development cycle and reduce the development cost.

Claims

A pulse width modulation PWM generating circuit comprises: a constant current source circuit, a sawtooth wave circuit, a comparison circuit and a controllable DC power supply;

The constant current source circuit is configured to provide a constant direct current for the capacitor C1 in the sawtooth circuit;

The sawtooth wave circuit is connected to the constant current source circuit and configured to control a voltage of the capacitor C1 such that the capacitor C1 outputs a sawtooth wave signal;

The comparison circuit is respectively connected to the sawtooth wave circuit and the controllable DC power source, and configured to receive the sawtooth wave signal and the DC signal output by the controllable DC power source, compare the sawtooth wave signal with the The DC signal is output and the PWM signal is output according to the comparison result.
The generating circuit according to claim 1, wherein said constant current source circuit comprises a voltage reference chip, a resistor R1, an adjustable resistor RP1 and a PNP transistor Q1, said PNP transistor comprising a base B, a collector C and a source E, wherein the resistor R1 is connected between the BEs of the PNP transistors, and the adjustable resistor RP1 and the voltage reference chip are connected between the BCs of the PNP transistors.
The generating circuit according to claim 2, wherein the adjustable resistor RP1 is set to adjust a period of the sawtooth wave signal output by the capacitor C1 by adjusting a self resistance value.
The generating circuit of claim 1, wherein the controllable DC power source is configured to be coupled to the controller, configured to receive a control command from the controller, and output a DC voltage signal corresponding to the control command.
The generating circuit according to claim 1, wherein said comparison circuit comprises: an operational amplifier and a voltage dividing resistor, said operational amplifier being electrically connected to said voltage dividing resistor;

The voltage dividing resistor is configured to divide a DC signal input by the controllable current source to form a voltage dividing signal;

The operational amplifier includes a first signal input configured to receive the divided signal.
The generating circuit according to claim 5, wherein the resistance of the voltage dividing resistor is determined according to a voltage value of a direct current signal input from the controllable direct current power source.
The generating circuit of claim 5 wherein said operational amplifier further comprises a second signal input configured to receive said sawtooth signal.
The generating circuit of claim 7, wherein the operational amplifier is arranged to compare the sawtooth signal with the divided signal.
The generating circuit according to claim 8, wherein the operational amplifier further comprises a signal output end, and is further configured to output a low level when the sawtooth wave signal is greater than the divided voltage signal; and when the sawtooth wave signal is smaller than The divided signal outputs a high level, wherein the high level and the low level are used as PWM signals.
The generating circuit according to any one of claims 5-9, wherein the operational amplifier is an LM 2903 chip.
The generating circuit according to claim 1, wherein said sawtooth wave circuit further comprises: a timer; said timer being electrically connected to said capacitor C1.
The generation circuit of claim 11 wherein said timer is an I CM 7555 chip.
The generating circuit according to any one of claims 1 to 12, wherein the capacitor C1 is a COG ceramic capacitor or an NPO ceramic capacitor.