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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Power supplies for MP3 player and game console. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Power Supplies Now many people use pocket MP3 players and other miniature electronics powered by a single "finger" or "disk" battery (voltage 1,5 V). Despite all the efficiency, one battery is rarely enough for an MP3 player for a day. You need to buy a new one, or use rechargeable batteries. If you use your MP3 player most of the time at home, during work or class, that is, in a place where there is a ripple power supply. As a result, an unstabilized voltage of 9 V is obtained at the output of the adapter (actually from 7,5 to 10 V). That's what the game console feeds on. In order to get a stable 1,6 V from this unstable voltage, we will need to make a stabilizer that will lower the voltage to 1,5 V and keep it stable. On fig. 2 shows a diagram of an already converted network adapter, then you can power the MP3 player from the outlet. But for this you need a special power supply (adapter). On sale now, 9 V adapters are most often found to power 8-bit TV game consoles like Dandy or Kanga. These set-top boxes are not very reliable and fail most often due to a broken connector into which game cartridges are inserted, or due to a break or break in the printed tracks coming from the set-top box microcircuit to this very connector. Usually, such set-top boxes are poorly repaired and, since the cost is relatively small, they buy a new one instead of a broken one, and the power supply (network adapter) remains. It is from such a 9 V network adapter that you can make a stabilized source for powering an MP3 player from the mains.
Schematic diagram of the network adapter "Dandy" usually looks like this. as shown in fig. 1.
T1 is a low power transformer. Its high-voltage winding (many turns of a thin wire) is supplied with voltage from the mains, and the reduced voltage from its low-voltage winding is fed to a bridge rectifier based on VD1-VD4 diodes. Capacitor C1 smoothes in which a stabilizer is already built. The stabilizer is made on the transistor VT1 according to the scheme of a parametric stabilizer with a current amplifier. Transistor VT1 works as a cascade - an emitter follower. Theoretically, in such a stage, the voltage at the base is equal to the voltage at the emitter, but the current at the emitter is greater, that is, the power is higher. In practice, the voltage at the emitter will be slightly lower than at the base. This is due to the fact that the emitter of the transistor is a pn junction, similar in properties to a diode. Therefore, some voltage drops on the emitter (like a forward voltage across a diode), so it turns out that the KT814 transistor in this circuit will have a voltage on the emitter that is about 0,6 V less than on the base. When stabilizers are made according to such schemes, voltage is usually supplied to the base from the zener diode. If we take into account that 0,6 V drops on the emitter, then we need a 1,5 + 0,6 = 2,1 V zener diode. There are no such zener diodes. There are stabistors, but they are also very rare on sale, and we need to make a circuit on available parts. For example, affordable KD522 diodes, they are found in almost all electronics, and are very freely available for sale. On one KD522 diode, a voltage of about 0,7 V drops in the forward direction. If you take three such diodes and turn them on in series, then you will get 0,7x3 = 2,1 V. A circuit of resistor R1 and three diodes KD522 forms a simple parametric voltage regulator of 2,1 V. This voltage is supplied to the base of the transistor VT1 And on its emitter it turns out 2,1-0,6 = 1,5 V, that is, just the same voltage , which we need to power the MP3 player. Capacitor C2 additionally suppresses ripples, and resistor R2 serves as an additional load for the transistor so that when the MP3 player is turned off the transistor does not remain without load, and when the adapter is turned off from the outlet, so that C2 is quickly discharged through R2. How to do all this practically primarily depends on the design of the network adapter being reworked. If there is a choice, it is better to take a larger adapter so that there is enough space in it to install the stabilizer circuit. If there is only a small adapter, and the stabilizer cannot be pushed into it, then you can make the stabilizer in a separate case, for example, in a matchbox or a film cassette. Then there will be one wire from the adapter to the stabilizer, and then another wire from the stabilizer to the MP3 player. But of course it's better when the whole scheme is "in one bottle". The stabilizer is soldered on a small board, shown in Figure 3. The tracks are shown when looking at the board from the side of the tracks. and details - from the side of details. Pay attention to the pinout details. The KT814 transistor has a radiator metal plate on one side of the case, and markings on the other. The wiring diagram shows exactly how the transistor should be located (solder it the other way around - and the circuit will not work, and the transistor can be ruined). Diodes KD522 are made in striped glass cases. A wide strip is closer to the cathode terminal (this is indicated on the wiring diagram). Capacitor C2 must also be soldered, observing the polarity. If this is a domestic capacitor of the K50-35 type, then there will be a "+" on its case near the positive terminal. but for imported capacitors, a minus is indicated by a wide strip.
The KT814 transistor has a screw hole. With this hole, the board is attached to the network adapter case - drill a hole in the adapter case and screw the transistor there with a suitable screw and nut, and the board will already be held on it. If you don’t have a suitable screw, it’s better to look carefully, since you can’t drill a hole in the transistor. When connecting the circuit to the rectifier of the network adapter, you must observe the polarity so as not to confuse the plus with the minus. The same applies to connecting to an MP3 player. A single finger-powered MP3 player does not have a connector for connecting an external power supply. Therefore, it will be necessary to make a model of the battery. You can take a thick pencil of suitable thickness and saw off a piece from it in length slightly shorter than the battery. Then squeeze the stylus out of it, clean the hole where the stylus was. Then screw on a short screw or self-tapping screw from both ends - they will be instead of contacts. Connect the wires from the power source to these screws. At the same time, do not confuse the polarity of the connection, and sign on a piece of wood where is plus and where is minus, so as not to confuse when installing an MP3 player in the battery compartment. Now, in order to power the MP3 player from the network, you need to remove the galvanic cell from it and insert this dummy there, observing the polarity. Then plug the adapter into a power outlet. You may also need to cut a groove in the MP3 player's battery compartment cover so that you can lead the wire through it, or you can simply leave the cover open. Author: Andreev S.
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