CN108599741B

CN108599741B - Square wave generator with controllable duty cycle

Info

Publication number: CN108599741B
Application number: CN201810459105.1A
Authority: CN
Inventors: 高玉琴
Original assignee: Individual
Current assignee: Individual
Priority date: 2018-05-15
Filing date: 2018-05-15
Publication date: 2023-08-25
Anticipated expiration: 2038-05-15
Also published as: CN108599741A

Abstract

A square wave generator with controllable duty ratio comprises a triode T1, a triode T2, a resistor R1, a resistor R2, a capacitor C1, a comparator A1, a resistor R3, a resistor R4, a resistor R5, a triode T3, a NOT gate F1, a resistor R5 triode T1 and a resistor R1, wherein a constant current circuit is formed to charge the capacitor C1; the triode T2 and the resistor R2 form a constant current circuit to discharge the capacitor C1, the comparator A1, the resistor R3, the resistor R4 and the resistor R5 form a comparison circuit, and the NOT gate F1 controls the charge and discharge of the capacitor C1 through the triode T3 according to the comparison result, so that square wave oscillation is formed. The square wave generator with controllable duty ratio is characterized in that the duty ratio of the square wave signal uo can be changed by changing the control voltage ui, and the oscillation period of the square wave signal uo is unchanged; can meet the requirement of automatic control.

Description

Square wave generator with controllable duty cycle

Technical Field

The invention relates to a square wave generator, in particular to a square wave generator with controllable duty ratio, wherein the duty ratio of square waves can be changed along with the change of control voltage.

Background

The duty ratio of the existing square wave generator is generally adjusted by a potentiometer, and in some automatic control occasions, the duty ratio is unchanged by adjusting the potentiometer, so that the square wave generator with controllable duty ratio is necessary to meet the automatic control requirement.

Disclosure of Invention

The invention aims to provide a square wave generator with controllable duty ratio, wherein the duty ratio of square waves can be changed along with the change of control voltage so as to meet the requirement of automatic control.

The square wave generator with controllable duty ratio comprises a triode T1, a triode T2, a triode T3 and a comparator A1, and is characterized in that an emitter of the triode T1 is connected with a power supply VDD through a resistor R1, a collector of the triode T1 is grounded through a capacitor C1, a collector of the triode T2 is connected with a collector of the triode T1, an emitter of the triode T2 is connected with an emitter of the triode T1 through a resistor R2, bases of the triode T1 and the triode T2 are connected with control voltage ui, an inverting input end of the comparator A1 is connected with a collector of the triode T1, an in-phase input end of the comparator A1 is connected with a power supply VDD through a resistor R3, an in-phase input end of the comparator A1 is grounded through a resistor R4, an output end of the comparator A1 is connected with an input end of a non-gate F1 through a resistor R6, an output end of the non-gate F1 is connected with a base of the triode T3, an inverting input end of the triode T3 is connected with an output end of the triode T1, and the output end of the triode T1 is of the triode T2 is of the type of the triode T1, and the triode T2 is of the type of the triode T3.

The square wave generator with controllable duty ratio is characterized in that the duty ratio of the square wave signal uo can be changed by changing the control voltage ui, and the oscillation period of the square wave signal uo is unchanged; can meet the requirement of automatic control.

Drawings

Fig. 1 is a schematic circuit diagram of the present invention.

Description of the embodiments

Specific embodiments of the present invention will now be described with reference to the accompanying drawings.

A square wave generator with controllable duty ratio comprises a triode T1, a triode T2, a resistor R1, a resistor R2, a capacitor C1, a comparator A1, a resistor R3, a resistor R4, a resistor R5, a triode T3, a NOT gate F1 and a resistor R5.

The triode T1 and the resistor R1 form a constant current circuit to charge the capacitor C1, and when the control voltage ui is increased, the charging current is reduced, and vice versa;

the triode T2 and the resistor R2 form a constant current circuit to discharge the capacitor C1, and when the control voltage ui is increased, the discharge flow is reduced, and vice versa.

The comparator A1, the resistor R3, the resistor R4 and the resistor R5 form a comparison circuit, and when the output of the comparator A1 is at a low level, the resistor R4 and the resistor R5 form parallel connection; when the output of the comparator A1 is at a high level, the resistor R3 and the resistor R5 are connected in parallel; when the resistance values of the resistor R3, the resistor R4 and the resistor R5 are equal, and the output of the comparator A1 is at a low level (i.e., the output voltage of the comparator A1 is close to 0), the voltage at the non-inverting input terminal of the comparator A1 is approximately ud (ud is the power supply voltage); when the output of the comparator A1 is high (i.e., the output voltage of the comparator A1 is close to ud), the voltage at the non-inverting input of the comparator A1 is about 2/3 ud.

The resistance values of the resistor R3, the resistor R4 and the resistor R5 are equal, so that the capacitance C1 can be changed within a proper range.

The NOT gate F1 inverts the output signal of the comparator A1 and then controls the triode T3, and the triode T3 controls the charge and discharge of the capacitor C1; when the comparator A1 outputs a high level, the triode T3 is cut off, the capacitor C1 is in a charging stage, when the comparator A1 outputs a low level, the triode T3 is conducted, and the capacitor C1 is in a discharging stage.

In the charging phase of the capacitor C1, when the voltage on the capacitor C1 rises to ud which is equal to or greater than 2/3, the output of the comparator A1 changes from high to low, at this time, the capacitor C1 enters the discharging phase, and when the voltage on the capacitor C1 falls below ud which is 1/3, the output of the comparator A1 changes from low to high, thereby cyclically forming an oscillating output square wave signal.

The duty cycle of a square wave signal is defined as:

duty cycle=tg/(tg+td); where tg is the high level duration of the square wave signal, td is the low level duration of the square wave signal, and tg+td is the oscillation period of the square wave signal.

When the control voltage ui increases, the charging current decreases, the discharging current increases, the duty ratio increases, and when the control voltage ui decreases, the charging current increases, the discharging current decreases, and the duty ratio decreases.

When the control voltage ui is close to ud, the triode T3 is cut off to stop charging the capacitor C1, the output of the comparator A1 is kept in a high level state, and the duty ratio is close to 1; when the control voltage ui is close to ud, the triode T1 stops charging the capacitor C1, the triode T1 is always conducted to discharge the capacitor C1, the output of the comparator A1 is kept in a high level state, and the duty ratio is close to 1; when the control voltage ui is close to 0, the transistor T1 is always turned on to charge the capacitor C1, and the transistor T1 is always turned off to stop discharging the capacitor C1, the output of the comparator A1 is kept in a low level state, and the duty ratio is close to 0.

The constant current charge and discharge can eliminate the influence of the change of the voltage of the capacitor C1 on the control voltage, and the constant current charge and discharge can keep the oscillation period of the square wave signal unchanged.

Claims

1. The utility model provides a controllable square wave generator of duty cycle, it includes triode T1, triode T2, triode T3, comparator A1, characterized by, triode T1's projecting pole connects power VDD through resistance R1, triode T1's collecting electrode passes through electric capacity C1 ground connection, triode T2's collecting electrode connects triode T1's collecting electrode, triode T2's projecting pole passes through resistance R2 and connects triode T1's projecting pole, triode T1 and triode T2's base connects control voltage ui, comparator A1's inverting input termination triode T1's collecting electrode, comparator A1's homophase input passes through resistance R3 and connects power VDD, comparator A1's homophase input passes through resistance R4 ground connection, there is resistance R5 between comparator A1's homophase input and output, comparator A1's output is connected NOT 3's base through resistance R6, triode T3's projecting pole connects triode T1's projecting pole, comparator A1's output is the output of PNP signal type, triode T2 type of triode T1 and triode T3.

2. The square wave generator as claimed in claim 1, wherein the resistances of the resistors R3, R4 and R5 are equal.