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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Voltage converter for household equipment. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Voltage converters, rectifiers, inverters The life of a modern person is closely connected with the AC electrical network. Many people cannot do without televisions, telephones, computers and various household electrical appliances. Therefore, it is useful to have a backup source of electricity on the household, especially in rural areas, for example, an internal combustion engine with an electric generator - a gasoline-electric unit. But a constant power supply requires its continuous operation, which will lead to high gasoline consumption. At the same time, many modern electrical appliances (energy-saving lamps, televisions, computers) consume little power (no more than 100 W), so powering a house or apartment from a constantly running electric generator is too expensive. To power household electrical appliances, it is more advisable to use a 220 V DC-to-AC converter powered by a high-capacity battery. Such devices are usually expensive and, along with their advantages, have certain disadvantages. The most widely used converters operate on the principle of high-frequency conversion with a switching frequency of several tens of kilohertz. Their disadvantage is strong interference with radio and television reception; they are sensitive to short-term overloads that occur, for example, when turning on a refrigerator or a powerful incandescent lamp. In addition, the industry produces low-frequency voltage converters operating at a frequency of 50 Hz. But such converters are rare, expensive and full of automation, which makes their repair difficult. Therefore, radio amateurs independently design low-frequency converters according to descriptions published, for example, in [1-3]. But they do not provide automatic shutdown when the battery is severely discharged. In addition, they have low efficiency at low loads. For this reason, most published converters are designed for low power (up to 150 W). If you use a more powerful transformer, then even without a load the converter will quickly discharge the battery. To increase efficiency, the proposed converter contains two step-up transformers of different power. When the power consumed by the load is below a certain limit, a smaller power transformer is used, otherwise a more powerful one is used.
The circuit of the proposed converter is shown in the figure. The device contains two supply voltage control units on transistors VT7 and VT8, a voltage stabilizer on the DA1 chip, a generator of two pulse sequences with pauses between them on the DA2 chip, a push-pull output stage on transistors VT1-VT4 with a powerful transformer T2, a push-pull output stage on transistors VT5 and VT6 with transformer T1 ten times less powerful, a load current measuring unit on current transformer T3, diode VD3 and transistor VT9. To automatically turn off the converter when the supply battery is completely discharged, a unit on the VT7 transistor is used. If its voltage is more than 10,5 V, transistor VT7 is open, relay K1 is activated and, through its contacts K1.1, the supply voltage is supplied to the voltage stabilizer on the DA1 chip and then to the pulse generator on the DA2 chip. When the battery voltage decreases below 10,5 V, transistor VT7 closes, contacts K1.1 open and turn off the power to the pulse generator, as a result of which all switching transistors VT1-VT6 are closed and the converter is turned off. The shutdown voltage is regulated by trimming resistor R8. The characteristic of the node on transistor VT7 has a slight hysteresis (due to the fact that the turn-on voltage of the electromagnetic relay is greater than the turn-off voltage), which is sufficient for practical use. The supply voltage control unit is assembled on a VT8 transistor according to a similar circuit, but its response threshold is 13 V. It provides two-stage output voltage stabilization. If the supply voltage is less than 13 V, transistor VT8 is closed, relay winding K2 is de-energized, the load receives voltage from the full secondary winding of one of the output transformers T1 or T2 through relay contacts K2.1 or K2.2. Otherwise, transistor VT8 opens, relay K2 is activated and the load is connected to the outlet of the secondary winding of transformer T1 or T2. The output voltage of the converter changes by no more than 7,7% when the supply voltage changes within 11... 15 V. This allows it to operate from one of two power sources: a 10,5... 12 V battery or the vehicle’s on-board network 14 V. The device does not use inertia-free protection against excess load current at the FC input of the DA2 chip. A conventional fuse link FU1 is used, and switching transistors VT1 -VT6 are selected with a margin of maximum permissible current. In idle mode or at low current consumed by the load, the voltage on the motor of resistor R10 is not enough to open transistor VT9, the winding of relay K3 is de-energized. Through relay contacts K3.1 and KZ.2, pulses from the outputs of the DA2 microcircuit are supplied to the gates of transistors VT5 and VT6. The load is connected through the contacts of relay K3.3 to the secondary winding of transformer T1. In this case, the current consumed by the converter without load is an order of magnitude less than when operating transformer T2. If the load current exceeds a certain limit, regulated by trimming resistor R10, transistor VT9 opens and supplies voltage to the coil of relay K3. Through relay contacts K3.1 and KZ.2, pulses from the outputs of the DA2 microcircuit are supplied to the gates of transistors VT1-VT4. Relay contacts K3.3 connect the load to the secondary winding of the powerful transformer T2. The output voltage of the converter has the form of multi-polar pulses separated by pauses with an amplitude of approximately 250 V. Its effective value is about 190 V. These parameters fall within the permissible limits of the supply voltage not only for devices with switching power supplies, but also for household refrigerators. All parts of the converter are housed in a sheet aluminum housing. Transistors VT1-VT6 are fixed to the housing using insulating gaskets and heat-conducting paste. An air flow from a fan with an M1 electric motor with a power of 3 W is constantly blown through the housing to cool the parts. Transformers T1 and T2 must have a transformation ratio of 20, and the current transformer TZ - 100, while its primary winding with a maximum converter power of 1 kW must be designed for a current of 5 A. Transformer T1 is made from a TS-180 transformer from the power supply of a tube TV. All its secondary windings have been removed. The primary winding is left and used as the main section of the secondary winding (in the diagram from end to tap). An additional section of 90 turns of PEV-2 wire with a diameter of 0,5 mm (from the beginning to the outlet) was added to it. The new primary winding contains two sections of 40 turns of PEV-2 wire with a diameter of 1,2 mm, wound into two wires. Transformer T2 is wound on the stator of an asynchronous three-phase electric motor with a power of 7,5 kW. The primary winding (I) contains two sections of 15 turns and is wound with APV-10 aluminum wire into two wires to ensure symmetry. The secondary winding (II) is wound with mounting aluminum wire with a cross section of 2,5 mm2. It contains 345 turns with a tap from the 45th turn. Transformer T3 is made from the output transformer of an ultrasonic tube TV. Its anode winding is left and used as a secondary winding, and the other is removed. Instead, a primary winding is wound - 24 turns of PEV-2 wire with a diameter of 1,2 mm. When setting up the converter, it may be necessary to change the transformation ratio of transformers T1 and T2 within small limits. To do this, you should wind an additional winding of several turns and, taking into account the phase, connect it in series with the secondary winding of the transformer. If the windings are turned on in phase, the transformation ratio will increase, otherwise it will decrease. All relays must have an operating voltage of no more than 10 V. Relay K1 is low-current, it can even be a reed switch - the current switched by the contacts does not exceed 0,1 A at a voltage of no more than 15 V. The contacts of relay K2 and KZ must be designed for switching alternating voltage 220 V and current 5 A. The author’s copy uses relays K1 - RES-59 (version HP4.500.020), K2 - V23079-D1003-B301, K3 - HJQ-18F 12VDC-3Z. All tuning resistors SPZ-1 b. Before installing them, it is necessary to check the serviceability of the movable contact system. Before turning on the power for the first time, the slider of the trimming resistor R1 is set to any extreme position, the slider R8 is set to the top position according to the diagram, and the sliders of other trimmer resistors are set to the bottom. Instead of a battery, connect a laboratory power source with an adjustable output voltage of 10... 13 V and an output current of at least 10 A. Using the trimmer resistor R1, a voltage of 1...8 V is set at the output of the DA9 microcircuit. The connection of this resistor shown in the diagram, according to In the author’s opinion, it reduces the risk of excessive supply voltage to the DA2 microcircuit when the terminals of the fixed contacts of resistor R1 break. Next, by selecting resistor R2, the frequency of the alternating voltage at the output of the converter is set to 50 Hz. After this, the supply voltage is reduced to 10,5 V and the slider of the trimming resistor R8 is moved from top to bottom according to the circuit until relay K1 is turned off. Then the supply voltage is increased to 13 V and the variable resistor R9 slider is moved from bottom to top according to the circuit until relay K2 is activated. Finally, connect the primary winding of current transformer T3 to an alternating current source of 0,5...0,6 A and move the variable resistor R10 until relay K3 operates. Literature
Author: A. Sergeev
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