Voltage converter 5/9 volts for powering radios. Encyclopedia of radio electronics and electrical engineering

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

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Domestic transistor radios manufactured in the second half of the last century, as a rule, were designed to be powered by a voltage of 9 V from chemical current sources. Many of them have survived to this day, but it is expensive to power them from galvanic batteries ... At the same time, today many people have a personal computer, laptop, DVD player, modern TV or charger with a USB connector in which there is voltage at home. 5 VDC. The problem of powering old transistor receivers in this case can be solved quite simply - it is enough to make a step-up voltage converter.

A diagram of a possible variant of such a converter is shown in fig. 1. It is designed to connect to the USB connector of the above devices and provides a stabilized voltage of 9 V at the output at a load current of up to 500 mA. Small-sized transistor radios at maximum volume usually consume current up to 100.150 mA, relatively large portable radios and radio receivers - up to 300.500 mA.

Rice. 1 (click to enlarge)

A voltage of 5 V is supplied to the input of the converter through LC filters C1L1C2 and L2C3C4, which suppress interference both coming into the device from the current source and in the opposite direction. The step-up voltage converter is assembled on the popular MC34063AP1 (DA1) chip. Its output is powered by a bipolar transistor VT1, which improves the load characteristics of the voltage regulator and significantly increases the reliability of the device. The output voltage depends on the ratio of the resistances of the resistors R5/R3. Choke L3 - storage. Resistor R1 sets the operation current of the overload protection built into the microcircuit. With its resistance indicated in the diagram and an input voltage of 5 V, it begins to operate at a load current of about 0,6 ... 0,7 A. The output voltage is supplied to the load through the C7C8L4C9C10 and L5C11C12C13 noise suppression filters. LED HL1 glows when there is an output voltage.

With an input voltage of 5 V and a load current of 500 mA, the device consumes a current of 1,4 A, the operating frequency of the converter is about 43 kHz, the ripple amplitude on the capacitors C7, C8 is 200 mV, and at the output of the stabilizer - only 6 mV at the conversion frequency. With a decrease in load current to 200 mA, the current consumed by the device decreases to 0,44 A, and the conversion frequency is reduced to 34 kHz. In the absence of load, the device consumes a current of 12 mA. With an input voltage of 3 V, it provides an output voltage of 9 V at a load current of up to 20 mA.

Fig. 2

All parts, except for the LED, are placed on a board with dimensions of 80x50 mm (Fig. 2) from the UM1-4 APCG module (used in domestic UPIMCT TVs), from which all parts and printed conductors were previously removed. Hanging installation. The mounted board is placed in a metal screen 85x54x30 mm in size, which is the case of the named module. You can also use metal screen cases from the UM1-2 UPCHZ television module, SKD-24, SK-D-30-3, SK-M-30-3 channel selectors, BRK-1S block or solder a box of the same dimensions from tin, for example, from a can of instant coffee. The screen is connected to the board at only one point - with the negative terminal of the capacitor C12. This is a prerequisite, otherwise the screen will not suppress interference, but radiate it.

Any small-sized resistors (C1-4, C1-14, MLT and the like) can be used in the device. Resistor R4 is soldered directly to the terminals of the transistor VT1. Capacitor C6 - small-sized film, C4, C7, C10, C12 - oxide aluminum or tantalum, for example, K50-68, K53-19 or analogues. The remaining capacitors are multilayer ceramic for surface mounting (SMD): C5 is soldered directly to the pins of the DA1 chip, C3, C8, C9, C11 - to the pins of the corresponding oxide capacitors, C13 is installed in the XP2 power plug. Pin 4 of the DA1 microcircuit, the pins of the inductor L1, the emitter VT1, the capacitor C7 and the connection point of the pins of the capacitor C6 with the resistor R3 are connected to the negative pin of the capacitor C4 with separate wires - this is also a prerequisite, on which the quality of work and reliability of the design depend. Fuse FU1 - polymer self-healing.

Possible replacement chip MC34063AP1 - MC34063AP, MC33063AP1, MC33063AVP (heat resistant), KA34063A, IP33063N, IP34063N. Schottky diode 1 N5822 replace with SR306, SR360, MBRS340T3, MBR340, 30BQ040, 30BQ060, 31DQ06. Instead of the red LED RL513-SR113, you can use any other continuous glow, for example, the KIPD21, KIPD40, KIPD66 series.

Of the different types of transistors tested in the device with suitable parameters, 2SC3747 showed the best results (possible replacement - 2SC3748, 2SC3746). It is produced in an insulated TO-220ML case. The transistor is mounted on a duralumin heat sink with a cooling surface of about 4 cm2. If a transistor with an uninsulated heat sink flange is used, then it must be isolated from the heat sink. The length of the connecting wires going to the terminals of the transistor should be as short as possible. The same requirement applies to the resistor R1.

Two-winding inductor L1 is used ready-made, from a computer power supply. With self-production, it can be wound with PEV-2 wire with a diameter of at least 0,65 mm (before filling) on ​​a ferrite (M2000NM) ring of size K16x10x5. Chokes L2, L4 have the same magnetic core, containing 15 turns of stranded mounting wire with a copper diameter of 0,65 mm. The L3 inductor winding consists of 30 turns of a bundle of four PEV-2 0,23 wires folded together and twisted, wound in one layer on a K20x12x6 ring made of M2000NM ferrite with a non-magnetic gap (for this it is filed, broken into two approximately equal parts, then glued with BF or Quintol glue and dried for two days at room temperature). The L5 inductor is wound on a ferrite (2000NM) ring of size K10x6x4,5 and contains eight turns of a mounting wire folded in half with a diameter (for copper) of 0,5 mm. Before winding, the rings are wrapped with a strip of varnished cloth or PVC electrical tape, the winding of the finished inductor is impregnated with zaponlak.

To connect the device to the USB connector, a home-made two-wire cable with a USB plug is made (commercially available ready-made USB cables for working with the described device are not suitable due to the rather high resistance of the power wires). The cross section of its cores must be at least 0,75 mm2, length - no more than 1 m. The load is connected to the converter with a two-wire cable with a cross section of 0,5 mm2 and a length of 1,5 ... 2,5 m.

If the device is supposed to be connected to a desktop computer, then if there is a "+5V/+5VSB" jumper on its system board, it is advisable to put the latter in the "+5V" position. An option similar in purpose (instead of a jumper) can be found in the BIOS settings of the computer. In modern motherboards, switching of external ports from + 5VSB to + 5V power supply can occur automatically when the computer is switched from standby to working mode.

After checking the performance and testing the voltage converter, put the upper and lower metal covers of the case in place, wrap it in four layers with sticky aluminum foil, then with the same number of layers of adhesive tape and, finally, glue it with a self-adhesive decorative PVC film.

The device made by the author does not interfere with radio reception in any broadcasting range, even if the receiver is installed directly on its body. If the voltage converter is connected to the USB port of the computer, and the radio receiver powered by it must be connected to the input of the sound card (for example, to record radio broadcasts), then the signal from the receiver output should be fed through an isolating transformer or an optoelectronic decoupling unit.

In addition to radio receivers, any other devices with a nominal supply voltage of 9 V at a load current of up to 0,5 A can be powered from the converter, for example, children's toys, measuring instruments, etc.

Since the current consumed by the converter exceeds the load current by 2,5...2,8 times, when connecting a load with a current consumption of more than 200 mA, the power line of the USB port may be overloaded. Therefore, before connecting the converter, you should make sure that the current drawn by it for the power line of the USB port will be acceptable.

Author: A. Butov

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