Voltage converter for cell phone chargers. Scheme, description

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Voltage converter for cell phone chargers. 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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Its use makes it possible to charge cell phone batteries from a 12 V DC source, for example, from a car's on-board network.

During a long trip by car or a countryside family vacation in nature, the problem of charging a cell phone battery often arises. It, of course, can be solved by acquiring a specialized memory that works from the car's on-board network. But in most cases, family members have different types of cell phones, so both the connectors for connecting the charger and the chargers themselves are different. It is difficult to find adapters for various types of connectors.

This problem can be solved in another way - to manufacture the proposed DC voltage converter 12 V to DC 300 V, which will allow you to charge cell phone batteries from standard chargers. True, the memory devices themselves must be with a transformerless input, that is, assembled according to the circuit of a pulsed voltage converter with a mains rectifier. The scheme of the proposed device is shown in the figure.

Voltage converter for cell phone chargers
Fig. 1

This is a single-cycle flyback voltage converter with external excitation. On the DA1 timer, a controlled generator of rectangular pulses is assembled, which are fed to the gate of a powerful switching field-effect transistor VT1. The voltage pulses on the secondary winding of the transformer are rectified by the diode VD1, the capacitor C5 is smoothing. The output voltage is stabilized by a unit consisting of zener diodes VD2, VD3 and a transistor VT2.

After the supply voltage is applied, the rectangular pulse generator starts to work. The generation frequency is determined by the parameters of the R1C2 circuit and is about 30 kHz. When the transistor VT1 opens, current flows through the primary winding of the step-up transformer T1 and energy accumulates in its magnetic field. After closing the transistor VT1, the energy from the secondary winding is transferred through the diode VD1 to the capacitor C5. When the output voltage exceeds the breakdown voltage of the zener diodes VD2 and VD3, a current will flow through the resistor R5 and the voltage across it will increase. This leads to the opening of the transistor VT2, it connects the input E of the DA1 timer to a common wire, which leads to a breakdown in generation and a decrease in the output voltage.

After that, the transistor VT2 closes, generation resumes and all processes are repeated cyclically. Therefore, the output voltage is determined mainly by the total stabilization voltage of the zener diodes VD2, VD3.

The device uses resistors MLT, S2-23, oxide capacitors are imported, the rest are K10-17. The transformer is wound on a SH12x14 ferrite magnetic circuit from the line-scan transformer of the UPIMCT TV, the primary contains 12 turns of PEV-2 wire, PEL with a diameter of 1 mm, the secondary contains 310 turns of PEV-2 wire with a diameter of 0,31 mm. The field-effect transistor IRFZ44N can be replaced with field-effect transistors IRFZ24N, IRFZ48N, IRFZ34N or bipolar KT825 with any letter index, in the latter case, the resistance of the resistor R4 should be increased to 1 kOhm. Instead of two 1N5383B Zener diodes, three 1N5378B or 1N4764 Zener diodes connected in series can be used.

It is also possible to replace a group of zener diodes with a rectifier diode KD212A. It is necessary to select an instance with a breakdown voltage of 300 ... 320 V. To do this, the zener diodes VD2, VD3 are replaced with one KD212A diode. Temporarily, in place of the capacitor C5, two capacitors K73-17 connected in series with a capacity of 0,47 μF for a voltage of 630 V are installed, and another one, the same, is connected in series with the VD1 diode. By changing the KD212A diodes, the required output voltage is set. According to the author's experiments, the breakdown voltage of these diodes is in the range of 280 ... 380 V. After selecting the diode, the temporarily installed elements are removed and regular ones are mounted. On this, the adjustment can be considered complete.

The parts of the transducer are mounted on a fiberglass printed circuit board using wired wiring. The board is placed in a plastic case measuring 85x50x45 mm, on the wall of which there is a socket for connecting the charger. The converter is connected to the vehicle's electrical system to the cigarette lighter using a special plug in which a FU1 fusible insert is installed. When operating the converter, it should be borne in mind that in some chargers the mains rectifier is made according to a half-wave circuit. Therefore, if charging is not performed after connecting the charger, it is necessary to turn its plug 180 °, thereby changing the polarity of the voltage supplied to it. The two-year operation of the device showed its high reliability and demand.

Author: K. Moroz, Nadym, Yamalo-Nenets Autonomous Okrug; Publication: radioradar.net

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