Launching ULF on points. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Launching ULF on points. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Transistor power amplifiers

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First you need to talk about protective resistors. The purpose of all resistors is to reduce current. Included at different points in the circuit, they create collector currents, input currents, bias currents, and others. Included in the break of the power wires, they reduce the current consumed by the circuit, or limit it.

Protective rectifier circuit:

(click to enlarge)

On contacts 2-3-7, the usual power supply is, so to speak, "±" (plus or minus). On contacts 1-3-8 the same power supply, only weakened in power. As a result, if the rectifier gives ± 30V at a current of 5A on contacts 2-3-7, then we will not remove a current greater than 1A from contacts 3-8-0,3. By testing the amplifier with such a current, you can check its performance, but if there are errors in the circuit, then in more than half of the cases it is possible to prevent burnout of parts, save time and money. If a newly assembled amplifier is tested immediately at full power, errors in the circuit will lead to various kinds of pyrotechnic effects, burning out transistors and even more problems.

Printed circuit board:

Launching ULF on points. PCB drawing of a protective rectifier

So, we connect our baby :) to protective power, and - let's go!

After power is applied, touch the input of the amplifier with any metal object (screwdriver). At the same time, hands must be isolated from the object and current-carrying parts of the circuit. A network background should be heard from the speakers.

If the background appears, disconnect the amplifier from the network, wait until the power capacitors are discharged and connect the signal source. We supply power and hear the sound from the speakers :) Oh, miracle! it worked!!! Drink beer early. We still have a lot of work ahead of us. Let's move on to point 7.

The background mixed with whistling tells us about the self-excitation of the amplifier. If so, go to point 6.

If the sound comes through but is distorted, the signal may be too strong or distorted before the amplifier. Turn down the volume. If the distortion has not passed, then the malfunction is on the board; go to point 6.

If there is no background, then there may be a malfunction on the board, in this form the amplifier may fail. It is advisable to immediately disconnect the amplifier from the network. We are in point 6.

We check the installation, the short circuits between the elements, between the tracks, the serviceability of the elements, the correctness of their installation on the board. We wash the board with alcohol, acetone. If the problem persists - either the circuit itself is not working, or we forgot to do something, or when assembling the circuit, someone walked by and sneezed. Self-excitation is observed by an oscilloscope, in the form of a noisy broadband signal at the output of the amplifier in the absence of a signal at the input.

If everything seems to work, the conders do not swell, the resistors do not fry and there is sound - we leave the amplifier to work for about 5 minutes at a low volume. The supply voltage at the amplifier itself should be the same as before the resistors, or thereabouts. If the difference is large, measure the current through the resistors. It must be the same as indicated in the description of the amplifier. If something is wrong, then you need to not forget about it and figure it out.

Well, it's the final test! The faint of heart, please leave the room! Do not conduct these tests without going through steps 1-7!!!

Switch the power to full power. Let's not forget about the fuses, otherwise we will either pick out fragments of transistors from ourselves, or we will run to the entrance to change traffic jams.

SLOW AND GRADUAL!!! add volume. Our organs of touch, smell and all the rest are working at the limit, as in the movie "Without Feelings". We are getting ready for the appearance of smell, smoke, hum, we keep our hand on the power switch, you never know if anything. We control the temperature of transistors, microcircuits.

If the radiators heat up to such a temperature that you can’t hold your hand, turn it off immediately, otherwise it’s booming. they need to be replaced with bigger ones.

If the capacitors swell, turn off immediately, otherwise the boom.

If the resistors get dark and start to stink, turn it off immediately, otherwise the boom.

Don't forget the rectifier. The diode bridge should not be hot, otherwise broads.

After 10-20 minutes of operation of the amplifier at full power, we can talk about its readiness for work for the benefit of the fatherland. Having tightened all the bolts, caps, we go for beer, call the girls and turn on the amplifier to its fullest for three hours.

Publication: radiokot.ru

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