Intermittent signaling on opposite-polar transistors. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Radio amateur designer
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This device, the description of which was published in the magazine "Funkamater" (GDR), is used in various control and measuring instruments or equipment where intermittent light or sound signaling is required. Moreover, the load can be connected both from the positive and negative poles of the power source.
(click to enlarge)
At the moment of switching on, capacitor C1 (Fig. 1) is discharged. The voltage at the emitter of transistor VT1 is greater than at the base. During the charging process C1, the potential on the emitter VT1 decreases and, when it becomes approximately 0,6 V below the base potential, this transistor opens, causing the semiconductor triode VT2 to turn on. A current flows through it, depending on the size of the load. Capacitor C1 is discharged through VT1, VT2 and R3. After its discharge, the transistors are turned off and the process repeats. The oscillation frequency is determined by the values C1 and R3. By changing resistance R3, the ratio of the duration of the on to off state is varied in the range from 1:1 to 1:100.
Figure 2 shows a diagram of a simple and reliable signaling device using LEDs or incandescent lamps with a current of up to 100 mA. Using resistor R4, the glow time is changed within small limits, but its resistance should not be too high, otherwise transistor VT2 will not be completely unlocked. The values of capacitor C1 and resistor R3 can also be changed within small limits.
As VT1, you can use any transistor of the KTZ15 series with a gain h219> 50, VT2 - an MP42 semiconductor triode with any letter index.
The switch, the diagram of which is shown in Figure 3, can serve as a direction indicator, for example on a moped. Transistors VT2 and VT3 are respectively types MP42 and P216, P217 of any letter indices, and VT3 does not need to be installed on the radiator. The requirements for VT1 are the same as in the previous scheme.
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