Practical application of the 555 series timer. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Application of microcircuits

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This material is borrowed from various foreign journals. Considering that each country has its own indexing system for chip types, the schemes given here will contain their various names: 555, B555. In essence, they are the same. All of them correspond to the domestic version of the integrated timer KR1006VI1 - a complete analog (electrical parameters, design, pin numbering). Information about this chip was given in "Radio" No. 7 for 1986 (p. 57, 58).

REGULATION OF DUTY OF PULSES

On fig. 1 shows a diagram of a multivibrator. The use of the B555 chip in this device made it possible to regulate the duty cycle of the pulses over a wide range. This is achieved by separating the charging and discharging circuits of the capacitor C1. At a high level at the output of the microcircuit (pin 3), transistors VT1 and VT2 are open. At this time, the capacitor C1 is charged through the transistor VT1, the resistor RA and the part R'A of the variable resistor RP1. When the voltage reaches the level of 0,66 Up on it, the multivibrator goes into a state with a low output signal level.

Ris.1

Now the capacitor C1 is discharged through the part Rg of the variable resistor RP1, the resistor Rg and the internal discharge circuit (pin 7) of the microcircuit. When the voltage level on it is 0,33 Up, the multivibrator goes into its original state with a high level at the output. Thus, the charging time (t1) and discharging time (t2) can be adjusted with a variable resistor. The duty cycle of the pulses is determined by the ratio of resistors

T/t1=(RA+RP1+RB)/(RA+R'A)

With the resistance values ​​indicated on the diagram, the duty cycle is regulated from 2 to 98 at a constant generation frequency.

"Radio, Fernsehen, Flektronik", 1988, No. 11

LINEAR FREQUENCY CONTROL OF THE MULTIVIBRATOR

On fig. 2 shows a modernized version of the classical circuit of a rectangular pulse generator with an integrated circuit of the 555 series. In this device, the charging and discharging of the timing capacitor C1 is carried out through the diode bridge VD1-VD4 and two current sources on transistors VT3 and VT4, which are controlled by the operation of the transistor VT2.

Ris.2

The oscillation frequency at the output is changed linearly by a variable resistor R2. With the values ​​\u2b\u1bof the elements indicated in the diagram, a twenty-fold change in frequency can be obtained, with the middle position of RXNUMX, the generation frequency is XNUMX kHz.

Instead of a variable resistor, the oscillation frequency can be controlled by applying an external constant voltage to the base of the transistor VT2. The emitter junction of the transistor VT1 provides the necessary thermal stabilization of the device.

If the linearity requirements are not very stringent, the device can be made with a hundredfold frequency change.

"Radio, television, electronic", 1989, No. 8

DIGITAL DISPLAY BRIGHTNESS ADJUSTMENT

Devices with luminescent indicators (stationary electronic clocks, information boards, etc.) are convenient to use only with a high contrast of luminous segments. For example, in a darkened room, a small current of the anode-segment is enough for its normal visual observation. But with high illumination of the room and the brightness of the glow of the indicator elements should be much higher.

Ris.3

"Radio, Fernsehen, Flektronik", 1986, No. 12

DEVICE FOR PERIODIC LOAD DISCONNECTING IN AC CIRCUITS

The device, the scheme of which is shown in Fig. 4, can be used to periodically connect and disconnect loads in the AC circuit, such as illuminated advertising, Christmas garland, buzzer, etc.

Ris.4

The load is switched on through a symmetric thyristor (triac) VS1, which is controlled through the transistor VT1 from the generator on the DD1 chip. The generator frequency is set by selecting the capacitor C2 and resistors R1, R2 and determines the intervals for switching on the load. The state of the load on can be judged by the operation of the LED indicator HL1, it also helps to control the frequency of the generator even when the load is off.

In the design it is possible to use a power transformer with a power of up to 5 watts.

The use of the device requires special attention, since the elements of the load and their connecting circuits are under the phase voltage of the AC supply network. Therefore, careful observance of safety measures is required, and the device itself should be placed in a plastic case.

"Haul Parleur", I988, No. 12

SLOW DOWN INTERIOR LIGHTS

The time relay device (Fig. 5) slows down by 10 ... 15 s the lighting in the car interior turns off after the doors are closed. During this time, the driver can safely look around the dashboard and insert the ignition key.

Ris.5

When the car doors are closed, the contacts SA1 are open and the lighting lamp EL1 does not light up. Capacitors C1 and C2 are charged respectively through the circuits VD1R3 and VD1R4. Maintaining the voltage on the capacitor C2 protects the timer from false alarms due to impulse noise when starting the engine and during its operation. After charging the capacitor C1 at pin 3 of the microcircuit, the voltage is close to zero and the transistors VT1-VT3 are closed. When the doors are opened, the contacts SA1 close, the lamp in the cabin lights up, the capacitor C1 is discharged through the VD2 R1 circuit.

Publication: N. Bolshakov, rf.atnn.ru

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