Encyclopedia of radio electronics and electrical engineering / Civil radio communications

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In many VHF or CB radios with a battery voltage of 12,5...13,5 V (10 NiCd elements), a transistor current stabilizer or a current limiter on resistors and an LED indicator are installed. These devices charge the battery through an external power supply socket. For their normal operation, the power source must have an output voltage of 16... 18 V. When used in conjunction with the vehicle’s on-board network, a full charge is impossible.

The proposed device allows us to solve these problems. It contains a step-up voltage converter and a filter that suppresses interference from the car's ignition system.

The scheme of the device is shown in fig. one.

A powerful operational amplifier DA1 is used to create a rectangular pulse generator with a repetition rate of 1...2 kHz. Diodes VD1 VD2 and capacitors C5, C6 - a rectifier with voltage doubling. Inductor L1 and capacitors C6-C9 form an interference suppression filter. LEDs HL1, HL2 provide indication of device operating modes.

It works like this. The input of the device is connected to the car battery. In the "Operation" switch position SA1, the voltage from the car's on-board network through filter L1, C7 C9 is supplied directly to the output of the device to power the radio station, and the pulse generator does not work. At the same time, the indicator HL1 "Work" is on.

When switch SA1 is moved to the “Charge” position, the HL2 (“Charge”) indicator lights up, the supply voltage is supplied to the op-amp, the generator begins to operate and an increased voltage is supplied to the output of the device. With an input voltage of 12 V, the output of the device will be 18 V at a load current of 50 mA and 16 V at a current of 100 mA. This is enough for charging. The radio itself must be turned off at this time.

Most of the device parts are placed on a printed circuit board made of one-sided foil fiberglass 1,5 mm thick. A sketch of the board is shown in Fig. 2.

It is advisable to use a metal body of the device and use a shielded cable as connecting wires. The switch and LEDs are installed on the device body. The following parts can be used in the device: LEDs - any with an operating current of 10... 20 mA, diodes - KD247, KD248, KD257, KD258 with any letter indices. Oxide capacitors - K50-16 K50-35 or similar imported, non-polar K10 17, resistors - MLT, S2-33. Inductor L1 is wound on a ring ferrite magnetic core (M2000NM) of standard size K12x8x3 mm. Its winding contains one layer of wire PEV-2 0,5...0,6 or MGTF 0,3...0 4. To reduce the magnetization effect, the ring is broken in half before winding, and then the ends are glued together through thin paper spacers.

With an output current of more than 80 mA, the microcircuit can become noticeably warm, so it must be equipped with a small heatsink.

Setting up the device comes down to checking the functionality of the generator at maximum load and setting, if necessary, its frequency by selecting the capacitance of the capacitor C3z. If interference from the car's ignition system does not interfere with the operation of the radio station, then the housing can be made of plastic, and elements L1, C8, C9 can be excluded from the circuit.

When charging the battery separately from the radio station, a current-limiting resistor or incandescent lamp must be installed at the output of the device. In this case, you can exclude from the circuit the switch, capacitors C1, C6, C8, C9, the inductor and one of the LEDs with a resistor. Rectifier diodes can be replaced with KD103A, V or KD106A.

Author: I. Nechaev (UA3WIA), Kursk

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