Designs on transistors of different structures. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Designs on transistors of different structures. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Beginner radio amateur

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There are many designs that use a generator or trigger, made on two transistors of the same structure. Of no less interest are similar devices in which transistors of different structures operate, especially since fewer parts are needed for them.

The first design - light pulse generator (Fig. 1). It works like this. At the initial moment, after applying the supply voltage, the capacitor C1 is discharged, the transistors are closed. Capacitor C1 will slowly charge through resistors R3, R4 and lamp EL1. When the voltage on it reaches 0,6 ... 0,7 V, the transistor VT1 starts to open, its collector current will increase. This will lead to an increase in the collector current of the transistor VT2, which means a decrease in the voltage on its collector. After some time, the capacitor will begin to charge through the resistor R4, the collector circuit of the transistor VT2 and the base transistor VT1. Both transistors will open, the lamp will light up.

Designs on transistors of different structures

In this state, the generator is until the capacitor is fully charged. Now the base current of the transistor VT1 will be determined only by the resistance of the resistor R3, and it will not be enough to keep both transistors in the open state. The transistors will start to close, and the voltage on the VT2 collector will increase. The voltage on the capacitor will be closing for the transistor VT1. Soon the transistors will close, the lamp will go out.

The device will stay in this state until the capacitor recharges, or rather, discharges to a voltage at which VT1 starts to open again, and the process repeats.

Since the charging and discharging of the capacitor occurs through circuits with different resistances, the duration of the lamp glow and pause will also be different - the lamp, like a beacon, will flash for a short time. The duration of its glow can be adjusted by selecting the capacitor C1 and resistor R4, and pauses - by selecting the same capacitor and resistor R3.

An incandescent lamp should be rated for a voltage of about 1 V less than the supply voltage. The lamp current is limited by the collector current of the VT2 transistor and can reach 8 A, but at a current of more than 1 A, the transistor should be installed on a radiator. In addition, the maximum collector current of the transistor should be approximately ten times higher than the rated current of the lamp - so many times the resistance of the filament in cold and heated states differs.

A drawing of a printed circuit board made of one-sided foil fiberglass for the option of installing the specified transistor without a radiator is shown in fig. 2. It is designed for the use of MLT-0,125 resistors and a K50-6 or K50-16 capacitor.

Designs on transistors of different structures

Next design - Sensor switch (Fig. 3). Here, the output stage is similar to the cascade of the previous device, and it is controlled by touch contacts E1, E2 and cascades on transistors VT1, VT2.

Designs on transistors of different structures

In the initial state, all transistors are closed, the incandescent lamp is off. If you touch the touch contacts E2, the base current of the transistor VT2 will appear and it will open. This will lead to the opening of transistors VT3, VT4 and ignition of the EL1 lamp.

To turn off the lamp, you need to touch the contacts E1. Transistor VT1 opens and shunts the emitter junction of transistor VT3. As a result, transistors VT3, VT4 will close, the lamp will go out.

As sensor contacts, it is permissible to use pieces of foil fiberglass with dimensions of approximately 20x20 mm with a cut (1 ... 2 mm wide) of metallization in the middle. One half of the metallization of the segment is connected to the corresponding resistor, and the other half to a common wire.

The power switched by the switch is the same as in the previous design, and the printed circuit board drawing is shown in fig. 4 (for mounting the VT4 transistor without a heatsink).

Designs on transistors of different structures

If the switch is planned to be installed in a room with a high level of interference and interference, capacitors with a capacitance of 10 ... 20 microfarads, connected between the right terminals of the resistors R1, R2 and the common wire, will help protect against them.

The third design is watchdog (Fig. 5). It uses contact sensors SF1, SF2, working for opening (mechanical or reed switches), as sensors. It is permissible to include in series with them a wired loop stretched along the perimeter of the protected area.

Designs on transistors of different structures

How does the device work? After the supply voltage is applied, the charging of the capacitor C1 will begin, and soon the transistor VT1 will open and shunt the emitter junction of the transistor VT2. Within a few tens of seconds, while the capacitor is charging, you need to leave the protected area. At the end of charging, the transistor VT1 closes, the watchdog comes into operation.

When the contacts open or the loop breaks, an opening voltage will be applied to the base of the transistor VT2 (through resistors R7, R6). As a result, the transistor VT3 will open and supply power to the alarm device connected to the conductors a, b. You can turn off the signaling device only by turning off the power source (the switch, of course, must be installed in a "hidden" place).

If it is necessary to increase the delay in switching the device into the watchdog mode, a larger capacitor C1 should be installed. Capacitor C2 increases the noise immunity of the device.

The alarm signaling device can be either a light (incandescent lamp) or a sound one - a generator assembled according to the diagram shown in fig. 6. The dynamic head in it - with a power of 2-4 W with a voice coil with a resistance of 4-8 ohms.

Designs on transistors of different structures

Generator parts are mounted on a printed circuit board (Fig. 7) made of foil material. If desired, both signaling devices are connected to the device.

Designs on transistors of different structures

In all designs, transistors KT361B can be replaced with KT208A-KT208I, KT209A-KT209I, KT3108A or similar. With a load current of more than 200 mA, instead of the KT829G transistors, you can use any other of the KT829 or KT973 series. If the load current is less, transistors of the KT603, KT608, KT3117 or similar series are applicable. The power supply is 6 ... 30 V and even more, but you will need the appropriate transistors and capacitors designed for this voltage. It is also necessary to adjust the device (by selecting parts marked with an asterisk in the diagrams) at this voltage.

Author: I. Nechaev, Kursk

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