Atypical use of stabilizers of the KR142EN8, KR142EN5 series. Scheme, description

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Atypical use of stabilizers of the KR142EN8, KR142EN5 series. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Surge Protectors

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Microcircuit fixed voltage DC stabilizers KR142EN8A - KR142EN8E, KR142EN5A...KR142EN5G were popular in amateur radio and industrial designs 10-25 years ago. Now these stabilizers are outdated, giving way to economical pulsed or linear ones with a low intrinsic voltage drop.

If a radio amateur has a lot of old stabilizers and not all of them are destined to be used for their intended purpose in the near future, then you can try to implement something different on them.

The figure shows, as an example, a circuit of a light pulse generator assembled on a KR142EN8B microcircuit. This stabilizer is designed for a fixed output voltage of 12 V and a load current of 1,5 A, maximum power dissipation is 9 W. As can be seen from the diagram, the generator is extremely simple. Oxide capacitor C2 is a frequency-setting capacitor, incandescent lamp EL1 serves as a stabilizer load. Capacitor C1 is a blocking capacitor in the power supply circuit; its role can be played by a capacitor installed at the output of the bridge rectifier in the network adapter, which is convenient to use as a generator power source.

Atypical use of stabilizers of the KR142EN8, KR142EN5 series

The generator operates with a frequency of about 0,8 Hz, duty cycle is about 5. The lamp shines in the mode - short pause, relatively long flash.

When the power is turned on, capacitor C2 begins to charge, the incandescent lamp shines at full intensity. When the voltage at its terminals reaches 10 V, the lamp goes out, the capacitor is discharged, after which the cycle repeats.

With a supply voltage of 12. V and a load current of 0,3, and the voltage on the lamp during a flash is 10,5 V, and during a pause it drops to 2 V. The fact that the lamp is not completely de-energized during a pause significantly increases its service life . The generator is operational when the supply voltage drops to 3 V.

To test the performance of generators built on microcircuit uncontrolled stabilizers for a fixed voltage, about fifty domestic and imported microcircuits of the KR142EN8, KR142EN5, 78, 78M series were tested. Almost all imported microcircuits refused to “generate” - after power was applied, the lamp suddenly turned on, and after a few seconds the output voltage dropped by 1,5...3 V and did not change any more. The KR142EN5A microcircuits produced after 1995 behaved in the same way. The KR142EN8 series stabilizers all worked in generator mode, with the caveat that microcircuits produced before 1991 had a smaller output voltage drop during generation.

Among the imported ones, there were only two microcircuits that turned out to be different from the rest. The first - OTI7805 - is a stabilizer for a fixed output voltage of 5 V. When it was turned on according to the considered circuit, it began to generate with a frequency of 5 Hz and a duty cycle of about 2. To reduce the oscillation frequency, you can choose a capacitor C2 of a larger capacity.

The second - TL780-05C - also for a fixed voltage of 5 V. When power was applied, the incandescent lamp turned on at full intensity, and after three seconds it went out completely, the voltage on the lamp dropped to 50 mV. Such a unique one-shot can be used, for example, as a power-on signal or as a zeroing unit for digital microcircuits.

I tested the operation of the generators with incandescent lamps with a current consumption of 0,06 to 1 A. If you use LEDs as a load, then the output of the stabilizer should be additionally loaded with a resistor with a resistance of 150 Ohms and a power of 1 W. In order for incandescent lamps to flash at full power, the generator supply voltage can be increased to 13,5...15 V.

References:

Radio 2011 №2

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