Over the last 20 years a huge number of regional commercial television stations, broadcasting via very puny transmitters of dubious quality. To tolerably to take their signal, need complex steel antenna with the obligatory presence of the antenna amplifier and good coaxial cable reduction. For this reason, there is now a lot harder to meet individual TV antenna without amplifier. Chinese and partly domestic industry have responded promptly to the needs of the population, and buy a good quality antenna amplifier may be no problem at very low prices, sometimes cheaper than the cost of one microwave transistor for this amplifier. Unfortunately, the power supplies, which are equipped with television antennas with amplifiers, often made by the national Chinese traditions: a minimum of costs and reliability as it will.
Therefore, these power supplies often overheat and fail even if the rated voltage of the alternating current. Constantly hot power supply of antenna amplifier not only consumes from a network of excessively high current, but also can cause the occurrence of a fire, for example, the high voltage network. Given the fact that the antenna power supply normally operates around the clock and are often left unattended, was made of homemade power pack, which has both high reliability and security, and low power consumption.
The device is a modernization of industrial power supply of antenna amplifier. Modernization was carried out with the aim of improving the reliability, efficiency and safety of the device. As a step-down transformer T1 is used to import transformer industrial manufacturing with a small load current. The rectifier and voltage regulator +12 V is made on the basis of the module from your old power supply of antenna amplifier, which burned down transformer. Miniature PCB power supply were installed in the missing details "Chinese" is usually considered superfluous: the capacitors C1-C4 and the safety resistor R2. In addition, there was installed the capacitor C5 with the stock on the operating voltage and the capacitance of the capacitor C6 is increased from 0.01 µf to 1 µf. The resistor R3 is set by the resistance 4.7 Ohm instead of 1.5 ohms.
Chip voltage regulator type 78L12, made in a miniature package TO-92,when feeding of antenna amplifiers often fail. To resolve this phenomenon, to the body of the chip heat-conducting glue glued a small heatsink size 15x10 mm. With the same purpose set resistor R2, which reduces power dissipation by the chip power. Install inductors L1-L3 is optional, but the author when using this unit in conjunction with the internal computer TV tuner and personal external antenna managed to eliminate moiré when receiving signals on the channel meter of the TV band. The inductor L1 is mounted on the PCB stabilizer, and miniature inductors L2, L3 and capacitors C7,C8 - body antenna plug. Breaking resistor R1 reduces the voltage on the primary winding of the step-down transformer, and also performs the function of the fuse.
Details and design
As the transformer T1, the author used a ready-made transformer EASTAR 430-035 from faulty UPS. A distinctive feature of this transformer in a low power, idle current, which does not exceed 1.3 mA at a voltage of AC 220 V, which corresponds to the power consumption less than 0.3 watts. The transformer can withstand without overheating for a long period of increasing the voltage to 300 V and a short-term up to 380 V. With such a transformer power supply current when the load is switched off is 1.8 mA, with a load of 21...38 mA, which means that the unit consumes power from the mains power less than 1 watt when the load is connected. For comparison, the domestic industrial power unit IPS-5 for antenna amplifier consumes from the mains current of about 13 mA when working with same load similar "Chinese" - 20...40 mA. If you do not have such a cost-efficient transformers, the transformer low no-load current can be wound independently.
Transformer, made of W-shaped magnetic core with a square Central core of 1.3 cm2 contains: the primary winding of 12,000 turns of wire PEL-1 with a diameter of 0.05 mm, the secondary - 1000 turns of the wrapping wire diameter of 0.16 mm. If you used a larger magnetic circuit with a cross-sectional area of 2.25 cm2, the primary winding must contain 7100 turns wire diameter of 0.05...0.07 mm, and the secondary - 700 turns of wire with a diameter of 0.15...0.23 mm. Both versions of transformers are designed for continuous operation at mains voltage up to 320 V. As shown by years of practice, supply of consumers of electricity with voltage 280...320 instead of 220 In may last many hours, while voltage 380...420 V is usually present in the AC not more than a few minutes. The resistor R1 used imported bursting, you can apply domestic noncombustible P1-7-2. Other types of resistors MLT, S1-4,S2-23. The capacitor C5 and import analogue K50-35, the rest - ceramic K10-17, K10-50 or imported counterparts. Rectifier diodes with a load current up to 50 mA you can use any of 1N4148, KD521, KD522, and with a larger load current from any 1N4000 series-1N4007, CD, CD.
Chip low-power regulator 78L12 to improve the reliability mounted on a small heatsink. You can use a more powerful chip CREE, CROW, xxx-7805-H. Reliability of the stabilizer in this case will increase, but the efficiency will decrease. The inductor L1 consists of 7 turns double-folded mounting wire wound around a cylinder of ferrite with permeability of 400-N from the inverter circuit of the old Soviet transistor radio. Inductors L1, L2 can be used small industrial inductance 3...20 µh. You can use SMD inductors for surface mounting. As already mentioned, L2, L3, C7, C8 are located in the antenna plug. The presence of these chokes, in addition to protection against ordinary noise, also has a positive effect on the immunity of the antenna system from the powerful radiation of cell phones.
Some time ago the author was actively practicing the power of antenna amplifiers directly from radio and television reception. As it turned out, this method has its disadvantages, since it was necessary or Refine each connected to the antenna device, and/or to use a special adapter, so using a separate power supply for antenna amplifier proved to be more practical.
Author: A. L. Butov, S. CORBA, Yaroslavl region; Publication: www.cxem.net