On the power supply of low-power household equipment. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Power Supplies

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Battery poweredV. Our market is overflowing with products from far-abroad countries. Small-sized receivers are very convenient, but galvanic cells "sit down" very quickly.

For example, the IB-202 receiver draws more than 50 mA. A set of AA batteries is enough for only a few days of operation. Batteries of a similar size have insufficient voltage, and their cost is such that for this money you can buy the radio itself. It is much cheaper to purchase three disk batteries of the type D0,26D, D-0,55 or similar. By connecting these batteries in series, we get a voltage of 4,2 V (after charging).

To ensure a long service life of these batteries, the discharge current should not exceed 0,1-0,3C, where C is the nominal capacity of the battery (Ah). For D-0,26D - 0,26 Ah, therefore, the discharge current should not exceed 70 mA.

To avoid problems with bad contacts, the batteries need to be connected with wires and soldered. You need to solder quickly with low-melting solder and a soldering iron with a power of 60 ... 100 watts. In this case, 1...2 s is sufficient for a solder joint.

Only one copy of D-0,26D is freely placed in the compartment of standard batteries. By removing the springs (and they are removed very easily), you can place two batteries. The third battery can be placed by cutting a D25 mm hole in the back cover of the receiver with a jigsaw. After installing the battery in this hole, it can be sealed from the outside with adhesive tape.

The price of a D-0,26D battery is comparable to the price of good AA batteries. With careful operation of these batteries, several hundred charge-discharge cycles are easily achieved.

If there are no strict requirements for small size, then three-volt equipment can be connected to a miner's flashlight. I used 3SHNK-10-05. Its capacity is solid - 10 Ah. It is only necessary to install a detachable connector, there is plenty of space for this in the flashlight. It is advisable to change the electrolyte in the flashlight battery every six months. Such a battery is enough to operate the above receiver for almost a whole month with 8-hour daily operation. No circuits are needed to reduce the voltage, since the voltage of this battery is in the range of 3,5 ... 4,2 V.

Mains powered. Do not buy Asian adapters: throw your money away. If this already happened, then you need to monitor the heating of the network transformer. Usually it is hot and will not work for a long time, because the primary winding is unwound. There are two ways out: wind up the primary winding or turn on the ballast resistance in series with it. The first option is laborious, and besides, there is not always free space for winding additional turns.

The resistance of the resistor ballast must be selected experimentally depending on the type of adapter. It is good to do this using a laboratory autotransformer (LATR) with a milliammeter in the load circuit. The value of the ballast resistance is selected so that the no-load current does not exceed 5-10 mA (the lower this current, the longer the transformer will last).

A resistor as a ballast is much better than a capacitor. First, there are no inrush currents that shorten the life of the capacitor. If the capacitor breaks down, the transformer will also fail. And the resistor in case of burnout behaves like a fuse. Secondly, the capacitor with the primary winding of the transformer forms an LC circuit. If its resonant frequency approaches 50 Hz, then the transformer is in serious danger.

The designs of Asian adapters are simplified to the limit: a transformer, four diodes (bridge) and one or two capacitors. The change in the output voltage is carried out by switching the taps from the secondary winding of the transformer. Do not be surprised that your receiver is very buzzing and "wheezing", and its sound is distorted. The easiest way to eliminate this drawback is to increase the capacitance of the filter capacitor. Usually, a 1000 uF capacitor is connected in parallel with the standard 4000 uF capacitor. Now the hum in the speaker is almost inaudible. Additional capacitors can be placed both in the adapter and in the receiver itself.

In order not to bother looking for small-sized capacitors, you can use a transistor ripple filter. Figure 1 shows options for such a filter.

The type of transistors and the ratings of the elements R1, C1 depend on the electrical modes. For low-power receivers like IB-200 R1 = 2...10 kOhm, and C1 = 50...500 uF. The filter is connected in parallel with the rectifier capacitor, and the receiver is connected to the output of the circuit (Fig. 1). A capacitor with a capacity of 20 ... 200 microfarads is connected in parallel with the output (not shown in the diagram). The three parts of the filter are easy to place in almost any adapter.

The circuits shown in Fig. 1b and Fig. 1c have even greater ripple suppression than the circuit in Fig. 1a. Here, the property of a field two-terminal network is used, which consists in a large difference in the conductivity of direct and alternating currents. These schemes are much more profitable than the scheme shown in Fig. 1a. In addition, these circuits have the property of limiting the maximum current in the load, the value of which cannot exceed IVT2 h21EVT1, where IVT2 is the current through the two-pole VT2 (available in reference books as the initial drain current).

Reducing the current in the load in these circuits is very simple. To do this, a resistor is included in the source circuit of the transistor VT2. Its resistance is selected experimentally, the larger it is, the less current in the load. These circuits allow you to reduce the capacitance of the filter capacitor. The circuits are also operable at high load currents. To do this, a composite transistor of the KT1A type with a large value of h827E is installed as VT21.

If the receiver needs a stable voltage, then the easiest way is to use microcircuit voltage stabilizers (CH), for example, KR142EN5A. It is also easy to reduce the voltage of this stabilizer (Fig. 2) by turning on the diodes VD1, VD2 in series. For the IB-202 receiver, you can use diodes D220, D223. Capacitor C3 is required.

If the input voltage of the rectifier is more than 15 V, then CH KR142EN8 is used and then a zener diode is switched on instead of diodes, for example, D815A (cathode to output 2 CH). The range of operating currents of powerful Zener diodes D815 is much wider than indicated in the reference books. The maximum current of 1,4 A is more than enough to work with CH KR142EN8.

In the circuits (Fig. 1), the zener diode can be connected in parallel with the capacitor C1 with the calculation Uout \u1d Ustab - UbeVT0,6, i.e. the output voltage will be 0,7 ... 2 V less than the stabilization voltage of the zener diode. It should be taken into account that the zener diode takes away part of the current VT302, so transistors of the KPXNUMX series must be installed in such CHs.

Our electrical network is full of a wide variety of interference. Because of them, it can be impossible to listen to the receiver, especially on the LW, MW bands. Therefore, on the side of the primary winding of the mains transformer, it does not hurt to install a low-pass filter.

The currents of the primary winding are small and resistors can be installed in the breaks in the network wire, for example, at an idle current of 10 mA, a voltage drop of only 100 V will occur on a 1 Ohm resistor. Therefore, you can safely put groups of resistors bridged by capacitors, as shown in Fig. 3.

Capacitors must be of high quality (with low tgδ, see [1]), for example, K73-17 for an operating voltage of 630 V (0,1-0,47 μF). It is even better to put K782 polypropylene capacitors, which have high reliability.

Such filters are used not only when powering receivers, but, for example, when powering an amplifier of a CD player [2]. At high currents in the transformer winding, the resistors are replaced with inductors of 100 ... 200 μH. The level of RF interference further reduces the capacitor C3 installed in the secondary winding. Its capacity should be an order of magnitude greater than C1 and C2.

Often there are adapters designed for a 100 ... 110 V network. They cannot be directly connected to a 220 V network, but the excess voltage can be extinguished using zener diodes included in the primary winding circuit (Fig. 4). In the circuit of Fig. 4, a, the zener diodes are connected in parallel, and in the circuit of Fig. 4, b - in series. The specified type of zener diode (KS620A) allows changing the current through it within 5...42 mA [3, 4].

For low-power equipment, this is quite suitable. In this case, the primary winding serves as a current limiter (ballast). Zener diodes must be selected in pairs according to the minimum spread of the stabilization voltage, since they have a spread of ± 15% [4]. The dissipated power is defined as P = UstI1, and at currents below 10 mA, heat sink is not needed. In a similar way, you can reduce the voltage on the secondary winding.

The considered options do not exhaust the variety of tricks with power supplies. For example, it is advantageous to turn on incandescent lamps instead of ballast resistors [5].

References:

1. Directory. Electrical Capacitors and Capacitor Units / Ed. G.S. Kuchinsky. - M.: Energoatomizdat, 1987.
2. Zyzyuk A.G. Buffer amplifier for CD player "Technics SL-PG670A" //Radioamator. - 2001. - No. 9, 10.
3. Directory. Semiconductor devices. Diodes, thyristors, optoelectronic devices / Ed. N.N. Goryunov. - M.: Energoatomizdat, 1984.
4. Directory. Semiconductor devices. rectifier diodes. Zener diodes. Thyristors / Ed. A.V. Golomedova. - M.: Radio and communication, 1989.
5. Zyzyuk A.G. Repair of power supplies for imported equipment//Radioamator. - 2000. - No. 12.

Author: A.G. Zyzyuk

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