Over the past 20 years, a huge number of regional commercial television companies have appeared, broadcasting through very frail transmitters of dubious quality. In order to receive their signal tolerably, complex antennas with the obligatory presence of an antenna amplifier and a good coaxial reduction cable began to be needed. For this reason, it is now much more difficult to find a personal television antenna without an amplifier. Chinese and partly domestic industry responded quite quickly to the needs of the population, and you can purchase a good quality antenna amplifier without any problems at a symbolic price, sometimes cheaper than the cost of one microwave transistor for such an amplifier. Unfortunately, the power supplies that accompany television antennas with amplifiers are often made according to national Chinese traditions: minimum costs, and reliability as it turns out. Therefore, such power supplies often overheat and fail even at the rated AC voltage. A constantly hot antenna amplifier power supply not only consumes excessive current from the network, but can also cause a fire, for example, when the network voltage is high. Taking into account the fact that the antenna power supply usually operates around the clock and is often left unattended, a homemade power supply was manufactured, which has both high reliability and safety, and low power consumption.
The device is a modernization of an industrial antenna amplifier power supply. The modernization was carried out to improve the reliability, efficiency and safety of the device. An imported industrial transformer with a low no-load current was used as a step-down transformer T1. The rectifier and +12 V voltage stabilizer are made on the basis of a module from an old antenna amplifier power supply, in which the step-down transformer burned out. The missing parts, which the “Chinese” usually consider unnecessary: capacitors C1-C4 and safety resistor R2, were installed on the miniature printed circuit board of the power supply. In addition, capacitor C5 was installed with a margin of operating voltage, and the capacitance of capacitor C6 was increased from 0.01 μF to 1 μF. Resistor R3 is set to 4.7 kOhm instead of 1.5 kOhm. Voltage stabilizer chips of type 78L12, made in a miniature TO-92 package, often fail when powering antenna amplifiers. To eliminate this phenomenon, a small heat sink measuring 15x10 mm is glued to the chip body with thermally conductive glue. For the same purpose, resistor R2 is installed, which reduces the power dissipated by the microcircuit. The installation of chokes L1-L3 is optional, but the author, using this power supply in conjunction with an internal computer TV tuner and an individual external antenna, was able to eliminate small moire when receiving signals on meter TV channels. Inductor L1 is mounted on the stabilizer printed circuit board, and miniature inductors L2, L3 and capacitors C7, C8 are in the antenna plug housing. Breaking resistor R1 reduces the voltage on the primary winding of the step-down transformer and also serves as a fuse.
Details and design. As transformer T1, the author used a ready-made transformer EASTAR 430-035 from a faulty uninterruptible power supply unit. A distinctive feature of this transformer is the low idle current consumption, which does not exceed 1.3 mA at an AC voltage of 220 V, which corresponds to a power consumption of less than 0.3 W. The transformer, without overheating, can withstand a long-term increase in network voltage up to 300 V and a short-term increase up to 380 V. With such a transformer, the current consumed by the power supply when the load is off is 1.8 mA, with a load of 21...38 mA, which means that the power supply consumes power from the network no more than 1 W with connected load. For comparison, the domestic industrial power supply IPS-5 for an antenna amplifier consumes a current of about 13 mA from the network when operating with the same load; similar “Chinese” ones are 20...40 mA. If you do not have such economical transformers, then you can wind the necessary transformer with a low no-load current yourself. A transformer made on a W-shaped magnetic core with a central core area of 1.3 cm2 contains: a primary winding of 12,000 turns with PEL-1 wire with a diameter of 0.05 mm, a secondary winding with 1,000 turns of winding wire with a diameter of 0.16 mm. If a larger magnetic core with a cross-sectional area of 2.25 cm2 is used, then the primary winding should contain 7100 turns of wire with a diameter of 0.05...0.07 mm, and the secondary winding should contain 700 turns of wire with a diameter of 0.15...0.23 mm. Both transformer options are designed for continuous operation at network voltages up to 320 V. As long-term practice shows, supplying electricity consumers with a network voltage of 280...320 V instead of 220 V can last for many hours, while a voltage of 380...420 V is usually present in an AC network current for no more than a few minutes. Resistor R1 uses an imported discontinuous one; the domestic non-flammable R1-7-2 can be used. The remaining resistors are types MLT, S1-4, S2-23. Capacitor C5 is an imported analogue of K50-35, the rest are ceramic K10-17, K10-50 or imported analogues. Rectifier diodes for load currents up to 50 mA can be used from any of the 1N4148, KD521, KD522 series, and for higher load currents, any of the 1N4000-1N4007, KD209, KD243 series. The 78L12 low-power stabilizer chip is installed on a small heat sink to increase reliability. You can also use more powerful microcircuits KR142EN5A, KR142EN5V, xxx-7805-x. In this case, the reliability of the stabilizer will increase, but the efficiency will decrease. Choke L1 consists of 7 turns of double-folded mounting wire wound on a cylinder of 400NN-1000NN ferrite from the IF circuit of an old domestic transistor radio. Chokes L1, L2 can be used with small-sized industrial ones with an inductance of 3...20 μH. You can also use SMD chokes 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 from normal interference, also has a positive effect on the noise immunity of the antenna system from powerful radiation from cell phones. Some time ago, the author actively practiced feeding antenna amplifiers directly from television and radio receivers. As it turned out later, this method is not without its drawbacks, since it was necessary to either modify each device connected to the antennas, and/or use special adapters, so using a separate power supply for the antenna amplifier turned out to be more practical.
A.L. Butov, s. Kurba, Yaroslavl region, Radioamator No. 5, 2008.
Over the past 20 years, a huge number of regional commercial television companies have appeared, broadcasting through very frail transmitters of dubious quality. In order to receive their signal tolerably, complex antennas with the obligatory presence of an antenna amplifier and a good coaxial reduction cable began to be needed. For this reason, it is now much more difficult to find a personal television antenna without an amplifier. Chinese and partly domestic industry responded quite quickly to the needs of the population, and you can purchase a good quality antenna amplifier without any problems at a symbolic price, sometimes cheaper than the cost of one microwave transistor for such an amplifier. Unfortunately, the power supplies that accompany television antennas with amplifiers are often made according to national Chinese traditions: minimum costs, and reliability as it turns out.
Therefore, such power supplies often overheat and fail even at the rated AC voltage. A constantly hot antenna amplifier power supply not only consumes excessive current from the network, but can also cause a fire, for example, when the network voltage is high. Taking into account the fact that the antenna power supply usually operates around the clock and is often left unattended, a homemade power supply was manufactured, which has both high reliability and safety, and low power consumption.
The device is a modernization of an industrial antenna amplifier power supply. The modernization was carried out to improve the reliability, efficiency and safety of the device. An imported industrial transformer with a low no-load current was used as a step-down transformer T1. The rectifier and +12 V voltage stabilizer are made on the basis of a module from an old antenna amplifier power supply, in which the step-down transformer burned out. The missing parts, which the “Chinese” usually consider superfluous, were installed on the miniature printed circuit board of the power supply: capacitors C1-C4 and safety resistor R2. In addition, capacitor C5 was installed with a margin of operating voltage, and the capacitance of capacitor C6 was increased from 0.01 μF to 1 μF. Resistor R3 is set to 4.7 kOhm instead of 1.5 kOhm.
Voltage stabilizer chips of type 78L12, made in a miniature TO-92 package, often fail when powering antenna amplifiers. To eliminate this phenomenon, a small heat sink measuring 15x10 mm is glued to the chip body with thermally conductive glue. For the same purpose, resistor R2 is installed, which reduces the power dissipated by the microcircuit. The installation of chokes L1-L3 is optional, but the author, using this power supply in conjunction with an internal computer TV tuner and an individual external antenna, was able to eliminate small moire when receiving signals on meter TV channels. Inductor L1 is mounted on the stabilizer printed circuit board, and miniature inductors L2, L3 and capacitors C7, C8 are in the antenna plug housing. Breaking resistor R1 reduces the voltage on the primary winding of the step-down transformer and also serves as a fuse.
Details and design
As transformer T1, the author used a ready-made transformer EASTAR 430-035 from a faulty uninterruptible power supply unit. A distinctive feature of this transformer is the low idle current consumption, which does not exceed 1.3 mA at an AC voltage of 220 V, which corresponds to a power consumption of less than 0.3 W. The transformer, without overheating, can withstand a long-term increase in network voltage up to 300 V and a short-term increase up to 380 V. With such a transformer, the current consumed by the power supply when the load is off is 1.8 mA, with a load of 21...38 mA, which means that the power supply consumes from network power no more than 1 W with connected load. For comparison, the domestic industrial power supply IPS-5 for an antenna amplifier consumes a current of about 13 mA from the network when operating with the same load, similar to the “Chinese” ones - 20...40 mA. If you do not have such economical transformers, then you can wind the necessary transformer with a low no-load current yourself.
A transformer made on a W-shaped magnetic core with a central core area of 1.3 cm2 contains: a primary winding of 12,000 turns with PEL-1 wire with a diameter of 0.05 mm, a secondary winding with 1,000 turns of winding wire with a diameter of 0.16 mm. If a larger magnetic core with a cross-sectional area of 2.25 cm2 is used, then the primary winding should contain 7100 turns of wire with a diameter of 0.05...0.07 mm, and the secondary winding should contain 700 turns of wire with a diameter of 0.15...0.23 mm . Both transformer options are designed for continuous operation at network voltages up to 320 V. As long-term practice shows, supplying electricity consumers with a network voltage of 280...320 V instead of 220 V can last for many hours, while a voltage of 380...420 V usually is present in the AC network for no more than a few minutes. Resistor R1 uses an imported discontinuous one; the domestic non-flammable R1-7-2 can be used. The remaining resistors are types MLT, S1-4, S2-23. Capacitor C5 is an imported analogue of K50-35, the rest are ceramic K10-17, K10-50 or imported analogues. Rectifier diodes for load currents up to 50 mA can be used from any of the 1N4148, KD521, KD522 series, and for higher load currents, any of the 1N4000-1N4007, KD209, KD243 series.
The 78L12 low-power stabilizer chip is installed on a small heat sink to increase reliability. You can also use more powerful microcircuits KR142EN5A, KR142EN5V, xxx-7805-x. In this case, the reliability of the stabilizer will increase, but the efficiency will decrease. Choke L1 consists of 7 turns of double-folded mounting wire wound on a cylinder of 400NN-1000NN ferrite from the IF circuit of an old domestic transistor radio. Chokes L1, L2 can be used with small-sized industrial ones with an inductance of 3...20 μH. You can also use SMD chokes 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 from normal interference, also has a positive effect on the noise immunity of the antenna system from powerful radiation from cell phones.
Some time ago, the author actively practiced feeding antenna amplifiers directly from television and radio receivers. As it turned out later, this method is not without its drawbacks, since it was necessary to either modify each device connected to the antennas, and/or use special adapters, so using a separate power supply for the antenna amplifier turned out to be more practical.
See other articles section.As a device for smoothing the output sinusoid, eliminating interference and inclusions. The idea was gleaned from one of the electronic magazines, but they asked for money for the full version of the article and diagrams. Therefore, only now is this idea being put into practice: refusal to pay led to the development of our own circuit and its practical assembly.
For implementation, two 430-2063D transformers from the APC BK 500EI UPS were selected. Primary: white+black thin wires - 220V, secondary: white+red - 14.6V, white+black thick - 7.1V, red+black - 7.1V, blue+brown - 17.7V.
Transformers may vary by model. You can connect 430W and 230W transformers and use loads up to 230W. But the same performance characteristics dictate the same sizes of transformers, which will help when installing them in a housing. If you have a datasheet for the transformer, that’s great, otherwise you’ll have to output the maximum currents yourself - which is what we had to do.
Every UPS lies about its power, expressing it in VA. Added to this is the name of the transformer, which in a 500VA UPS has “430” in the name - hinting at 430VA. But the transformer has an energy conversion efficiency, so this number needs to be reduced even more: I assumed a number equal to 400W. And I assembled the device in accordance with this figure (using various tricks):
UPS transformers are not designed for long-term operation; they critically need cooling both under load and when idle;
- the housing was made 1.5 years ago as a reserve for the RPA-01(RM) rheostat, but it was useful specifically in this device. A large number of holes, the ability to melt plastic, the strength and flexibility of plastic, the ability to install a lid on top, a handle for carrying, ease of drilling additional holes, does not burn without a fire source (melts, hisses, boils), price - these are its advantages in places where temperature may be high. The elements are installed directly into the holes without using glue or sealant (although I still pour it out of habit); broke - replaced by disconnecting the fixing terminals;
- a white round tablet with wires in the third picture - a 2A refractory fuse, filled with liquid sealant without adhesion in a plastic cup (full insulation 220V). The sealant can be torn off if it burns out, change the fuse in the terminals and refill it (or cut the wire and solder another one). However, the fuse between the transformers is more likely to burn out; the role is 2A only in the event of a short circuit in the primary winding in the first transformer;
- excess transformer terminals are crimped with heat shrink: required - you can carefully cut off the heat shrink with a blade. But, in an amicable way, these wires had to be cut off and insulated with drops of sealant;
- the use of refractory fuses is mandatory, because cylindrical ones will burn during peak current surges. You can use automotive ones by thinning the contacts with a file under the terminals of UPS transformers. This can be seen in the connection of the red wires - as a way to connect non-standard terminals. On transformers, thickened terminals - standard response terminals RPI-P 1.5-7-0.8 do not provide proper contact, and a current of 33A can cause heating of this connection;
- the connection of the fan can be realized with a separate 12V source, but why? The first UPS with a diode bridge and a capacitor perfectly acts as a power adapter for various DC voltages: 10V, 20V, 25V DC (depending on the pair of wires). Therefore, using a 17.7V branch and a rectifier, a voltage of 24.2V was generated, which was distributed between the series fan (14.1V) and the relay winding (10.1V). But a series connection to the relay winding is not good: increased heating due to a current of ~110mA. It comes to mind to connect identical fans on both sides of the case in series - and you will get 12.1V on each (and solder a relay in parallel to one of them);
- plywood acts as an excellent heat insulator (there was an experiment: on one side 240 degrees through the sealant, on the other 70), so the transformers are glued to it with a high-temperature sealant, and the plywood itself is glued to the plastic case with ordinary sealant with good adhesion. For redundant fixation of transformers, there are 3 bolt connections from below, and a metal plate can be glued to the top of the transformers. The device is carried on the handle of the case; but it’s heavy, your hands hurt - you should at least wrap the handle with electrical tape;
- “ground” is required for galvanic isolation, so the supply wire was divided into 2 parts - but maintaining an almost unbreakable “ground” wire. Almost - because it’s easier to cut it and solder it with heat shrink than to take care of its safety when cutting the supply wire;
- buying an extension cord with grounding: I am increasingly inclined to the version: it is cheaper, safer and more optimal to buy a block with grounding for 1-2 sockets and solder the power wire from the PC there. If you go even further (plug, wire and socket separately) - you can create an extension cord for equipment of any power. In practice, IEC-320 "10A" 0.75mm 2 power cables cannot withstand 8.4A for more than a minute (protection is triggered), so "16A" (1mm 2) is required, which is enough for a continuous 10A;
- a switch for the first transformer is required to prevent its heating and energy consumption when the device is idle.
Now comes the best part: the practice test. I turned on a 400W hairdryer - the voltage dropped to 146V/1.4A. Empirically, withstanding ±10% of the nominal 220V, I came to the conclusion that the power of this galvanic isolation is only 120W (198V/0.6A). How so?! And it’s very simple: the transformers in the APC BK 500EI UPS are cheap - and that says it all. The greater the current supplied, the greater the voltage drop, and here there are two such transformers in series. And I wondered why, when the power was turned off, the APC BK 350EI output voltage became 199V. The reason is the same: as long as there is a network, 220V goes bypassing the transformer; and as soon as power was supplied from the battery, the transformer absorbed 21V when converting voltage.
Bottom line: the rated power of galvanic isolation from transformers 430-2063D is 120 W. The maximum power, with a strong voltage drop and heating of the transformers, is 400W (it will work as 146V·1.4A=200W - which means that the maximum power without reducing it is still somewhere lower). The rated power of one individual transformer, using the same calculation method, is 240W.
Since the role of galvanic isolation is in filtering the input voltage, and consumers (like oscilloscopes) do not have high power consumption, galvanic isolation was created successfully.
However, the circuit itself had to be greatly simplified (since the current along the 14.6V line is a maximum of 10A, with some voltage drop):
- the KSD-85LC thermal fuse can be installed directly into the red wire, eliminating the need for a 40A fuse;
- as a result, there is no need for a relay and a diode bridge (the relay does not tolerate pulse voltage);
- the fan can be turned on through a regular diode, powered with a pulse voltage of 17.7V (successful test of a fan with 18V variable voltage through a 2D203A diode for 4 hours);
- just one fan is enough (the device worked for 4 hours without overheating, it didn’t even burn your fingers). In general, the big question is the need for a thermal fuse;
- cut off excess wires and solder many connections without using terminals;
- the input fuse can be set to 1A.
