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Mono-stable multivibrator


Abstract -This article represents a novel monostable multivibrator circuit in which width and height of the pulse output can be independent electronically adjusted. In addition, the pulse width of output is not restricted to be wider or narrower than that of input pulse as conventionally employed. Namely, there is no restriction on the width of input and output pulse, the circuit's implementation is thus more convenient. The proposed circuit is composed of one MOSFET, Zener diodes, variable capacitors. The simplicity of the circuit makes it is suitable to be fabricated for integrated circuit. The results of circuit simulation is accordance well with theoretical analysis.

I. Introduction

MONOSTABLE multivibrator or one-shot timer is widely used in communication system, such as pulse position modulation, FM demodulation, clock recovery circuit. One of many conventional monostable multivibrator circuits that is typically employed for this purpose is the IC 555. It is composed of voltage comparator, timing resistor, timing capacitor and flip-flop. The basic operation of this circuit is RC series network. With the provided voltage source, the capacitor is charged and discharged where the voltage across capacitor rises and falls exponentially. When the charged voltage reaches an upper threshold level, it results in the changing of the flip-flop's state. The positive output pulse is then generated. The height of output pulse depends on the supply's voltage whereas the pulse width is directly proportional to the RC time constant. However, it is interesting to mention about some disadvantages of the conventional monostable circuits. Firstly, the input pulse width has an effect on the operation of the circuits. Namely, most circuits require the input pulse width to be either wider or narrower than the output pulse width. Secondly, the output pulse height of most circuits cannot be electronically adjusted which is important in some application.

In this project, a novel monostable multivibrator circuit is presented where its output pulse width and height can be electronically tuned. In addition, the circuit operation does not depend heavily on the input pulse width. In other words, there is no restriction between pulse width of input and output. The proposed circuit scheme is composed of resistors, zener diodes and an nmos . It is seen that the components of this circuit are fewer than that of proposed by [1]. The outline of this project will be arranged as follows. In section II, the circuit description and operation are discussed where the experimental and simulation results are given in section III. Finally the conclusion is presented in section IV

II. circuit principle

Variation in the output pulse width can be observed with the change in capacitance value. It can be made equal to the trigger width or even narrower. The height of the output pulse i.e., the pulse amplitude can be varied by varying the supply voltage level.

An equivalent circuit for 555 timer is made using a mosfet, Zener diodes. It can be used for making monostable multivibrator.

CIRCUIT DIAGRAM:

III. SIMULATION RESULTS

This circuit is designed by using zener diodes, resistors and an N-MOSFET. The standard values taken are

COMPONENTS

VALUES

RA

10K

R

10K

C

1U

C1

0.01U

C2

1U

C3

0.01U

VCC

5V

R1

500e9

R2

500e9

R3

75e3

R4

75e3

R5

75e3

R6

1e3

R7

1e3

R8

150e3

R9

500e9

R10

1e3

R11

1e3

R12

150e3

R13

150e3

R14

150e3

R15

150e3

R16

1e3

R17

150e3

R18

1e3

R19

500e9

E1

1000

E2

1000

E3

1000

E4

1000

E5

1000

E6

1000

M1

D1-D16

For these values, output of the monostable multivibrator is coming as an impulse with width of high less than the trigger input pulse width. The output waveform is:

When C = 1UF, C1 = 0.01U, C2 = 1UF, C3 = 0.1U,I.e., when C1 is reduced, the width of output pulse is reduced. The output wave form is:

C1
tp
0.01uf
20ms
0.1uf
50ms
CONCLUSION

The novel monostable multivibrator is presented in this project. The main advantage of this proposed scheme is that there is no restriction on the input's pulse width. Namely, it can be greater than that of the output's pulse width. The operation of this scheme only depends on the positive edge of the input signal. In addition, the proposed circuit can be applied for PWM, PPM, DM circuits. With the less compactness of the circuit structure, the proposed scheme can be built easily.