Pulse converter, 12/220 volts 100 watts. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Pulse converter, 12/220 volts 100 watts. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Voltage converters, rectifiers, inverters

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Sometimes, in the absence of network wiring, it becomes necessary to power household electrical appliances from the car's on-board network. The literature describes a lot of the simplest converters from 12 to 220 V, but operating at an increased frequency of the supply voltage. For a lighting lamp or an electronic fishing rod, this is still acceptable, but not all household appliances designed for a mains frequency of 50 Hz can operate at higher frequencies.

In addition, many of the published circuits do not have output overload protection. Any household appliances up to 100 W can be connected to this converter (when using a more powerful transformer, it can be increased). The proposed converter circuit (Fig. 4.43) operates at a frequency of 50 Hz and has overcurrent protection. In addition, this converter gives the output waveform closer to a sinusoid, which reduces the level of high-frequency harmonics (noise). The device is assembled on a 1114EU4 chip specially designed for switching power supplies (an imported analogue of TL494CN). This allows you to reduce the number of parts used and make the circuit quite simple.

(click to enlarge)

Inside the microcircuit there is an oscillator with a circuit for obtaining output pulses with pulse-width modulation, as well as a number of additional nodes that provide its advanced capabilities. The output keys of the microcircuit are designed for a current of not more than 200 mA, and in order to control more power, the output pulses are fed to the bases of the key transistors VT1, VT2. Diode VD1 prevents damage to the circuit if the power is connected in the wrong polarity (only the input fuse FU1 will blow). Current protection at 1 A is set by resistor R10. This prevents damage to the converter in the event of an output overload or short circuit, as the circuit begins to reduce the output voltage, switching to current stabilization mode. The converter does not have feedback on the output voltage, since the experience of practical operation shows that it changes slightly when the power of the connected load changes and does not go beyond the permissible range of 190...240 V.

The adjustment of the device begins with the transformer turned off by setting the frequency of the master oscillator to 100 Hz using a timing circuit of resistor R1 and capacitor C4. Since the microcircuit has a push-pull output, the output frequency is equal to half the frequency of the oscillator (50 Hz at outputs 8 and 11).

Resistor R7 adjusts the shape of the output pulses of the microcircuit in accordance with the diagram shown in fig. 4.44. After that, a transformer is connected, and at the supply voltage of the circuit from a 12-volt source, resistor R7 sets the nominal voltage in the secondary circuit to 220 V (measured with a dial gauge). This is done with a connected load with a power of 25 ... 60 watts. A circuit of resistor R12 and capacitor C9 may require selection of ratings in order to remove surges in the transformer along the signal fronts at the time of transients during current switching.

The converter consumes no more than 1 A at idle, and with a load, the current increases in proportion to the power.

Transistors are mounted on a radiator with a surface area of at least 300 cm2. Transformer T1 will have to be made independently. A magnetic circuit of the type PLM27x40-73 or similar was used. Windings I and II contain 14 turns of PEL-2 wire with a diameter of 2 mm; winding III contains 700 turns of wire with a diameter of 0,5 mm. Windings I and II must be symmetrical - this condition is easily met when they are wound simultaneously (with two wires at once). A 10 A fuse can be made from a copper wire with a diameter of 0,25 mm.

Author: Semyan A.P.

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