Running lights on a four-phase multivibrator. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Running lights on a four-phase multivibrator. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Color and music installations, garlands

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This machine allows you to control four garlands of lamps rated for a voltage of 220 V and a current of up to 0,2 A. The switching frequency of the garlands is approximately 0,5 Hz, but it is easy to change it by selecting the capacitors of the time-setting circuits to obtain the usual mode of alternate switching of the garlands.

(click to enlarge)

The machine is made on low-power transistors VT1-VT4, which control the trinistors VS1-VS4, and those, in turn, control the garlands of EL1-EL4 lamps.

Four-phase multivibrators are usually unstable in operation. In this case, diodes VD5-VD16 are introduced to increase stability. What is their role?

Suppose that after turning on the machine in the network, the transistor VT2 opened earlier than others. Then VT3, VT4, VT1 will turn out to be closed, since their bases through a discharged capacitor C2, diodes VD16, VD10 and an open transistor VT2 will be connected to a common wire - the plus of the multivibrator power source, and hence to the emitters. Over time, the capacitor C2 will charge, and the current flowing through the resistor R9, the emitter junction of the transistor VT3, will open this transistor. Then the transistor VT2 closes - its base through the diode VD11 and the open transistor VT3 will be connected to the emitter. Transistors VT4 and VT1 will also be closed. Soon the capacitor C3 will charge and the transistor VT4 will open. The rest of the transistors will turn off. So the cascades of the multivibrator will alternately switch.

Diodes VD5-VD8 are used as non-linear elements with a stable forward voltage (up to 0,6 V) on them, which ensures reliable closing of the multivibrator transistors.

Part of the collector current of an open transistor flows through the control electrode of the corresponding SCR and opens it. And he turns on "his" garland of lamps.

Garlands are powered from the mains through a full-wave rectifier on diodes VD1-VD4. To power the multivibrator, the simplest parametric stabilizer was used on a VD17 zener diode and series-connected ballast resistors R17, R18. Capacitor C5 filters the stabilized voltage.

The machine used resistors MLT-2 (R17, R18) and MLT-0,125 (the rest). All capacitors - K50-6. Diodes VD5-VD8 can be any of the D9 series; VD1-VD4 - any others that can withstand a reverse voltage of at least 300 V and a rectified current of more than 0,2 A. Instead of a D814V zener diode, D810 or any of the D818 series is suitable, and instead of KU101E-KU103V trinistors. Transistors can be any of the KT361, KT203 series, as well as MP40-MP42 (in this embodiment, the base resistors R3, R7, R11, R15 must be 2 kOhm). Under these details, a printed circuit board made of one-sided foil fiberglass is designed.

The machine does not require adjustment, but in the event of an unreliable inclusion of one or another garland, it may be necessary to select the appropriate trinistor.

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