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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Alteration of network adapters in the SUP standard. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Power Supplies Products that are produced under the brand name "network adapter" are a low-voltage transformer power supply in the form of an enlarged mains plug with a DC output to the connector via a flexible cord. They come with a stabilized output voltage or without stabilization (these are simpler and cheaper), with or without battery charging cells, for one output voltage or several, and also differ in power, weight, design. Many electronic devices of small mass, but with limited autonomy (that is, with a significant current consumption from batteries or accumulators, for example, calculators and voice recorders, receivers and video cameras, etc.) are equipped with network adapters. This configuration increases the price of the product, dimensions and weight. Therefore, electronic devices of low cost are not supplied with network adapters, and adapters are sold on the market as separate products. I propose a simple alteration of the universal network adapter. It is desirable that it has a good load capacity (up to 1 A in current), multi-standard connectors and a polarity switch. The universal adapter of the FIRST type (Austrian production) with a power of 18 W and a maximum load current of up to 1 A meets these wishes most fully. It has the six most "popular" mains voltages in the range of 1,5 ... 12 V and is equipped with a multi-standard DC chip (a cross of four concentric plugs and a connector for the "Crown"), as well as a built-in switch for the polarity of the output voltage on the electrodes of the plugs. Such a system requires special attention when connecting powered devices, but is generally accepted. Figure 1 shows a schematic diagram of a typical adapter (thin lines indicate the original circuit).
The refinement is as follows: a switched channel is introduced according to the transistor switch circuit. When connector X2 is closed with a plug, voltage is switched on at output X1. Switch SA1 can change the polarity of the output voltage (as well as switch SA2 in the adapter circuit). Structurally, switches SA1 and SA2 are installed side by side on a standard printed circuit board (with turning SA2 and re-arranging the board section: remove the LED from the board, drill holes for both switches in the vacant section, and connect their outputs with flexible wires). LEDs (one regular, the second for an additional switch), together with 1 kΩ current-limiting resistors, are transferred to the volume above the transformer. Cords from X1 and X3 are released from the adapter from the side walls from below (we assume that the adapter is plugged into the socket with the switch panel down). Socket X2 of the GK-2 type input is fixed on the lower wall of the transformer volume. Transistor VT1 is a powerful integrated composite type KT825 (for currents up to 1 A at a control current of 20 mA, one transistor is enough). The transistor in the TO220 package must be installed on a small radiator (50 cm2) and placed in the volume of the case near the transformer. If the transistor is in a metal case, then it can be installed without a radiator on the upper wall of the transformer compartment (outside). At the same time, the terminals of the base and emitter enter the case by 4 mm, onto which the resistor R2 is soldered, and two M4 screws (a collector petal is placed under one of the nuts). Resistor R1 is placed in a PVC tube ("cambric") on the wire from the VT1 base to pin 1 of the X2 socket. Capacitor C1 is desirable to choose for reasons of suppression of possible emissions and amplified by the transistor VT1 pulsations, pickups and noise. It can be placed on the main board near the rectifier, while connecting the leads to the switch SA1 directly to the capacitor C1. It is also necessary to increase the capacitance of the standard capacitor C2 to at least 4000 microfarads. The KT825 transistor can be replaced by two, for example, a powerful KT818 or KT837 and a low-power KT502 or KT209, connected according to the composite transistor circuit. If the volume allows you to install a low voltage fuse holder for a current of 1-2 A, then it is advisable to install it. It is not worth introducing a voltage stabilizer into the adapter, since it is better to stabilize the voltage directly in the powered device (this is better for eliminating interference and interference). In connector X2, use a conductive plug SYUP-g (see "RA" 2/99) to turn on the channel with a key without external control. It is possible to introduce a switched channel for supplying DC power with remote control by closing the input to a common wire in many other power sources. If the device that needs to be remotely turned on has a built-in power supply, then the same key can be built directly into the device, and to control it, install a GK-2 input socket on the device case. This will enable internal control. The unswitched channel in the adapter modification described above is left to power some control devices with limited autonomy. In the practical use of such a switch (based on a network adapter) as part of a discrete automation complex built in the SUP standard (for example, when implementing an alarm clock with turning on a radio or tape recorder) using a clock of the "Bright" type (see "RA" 3/99, p.24), it will be turned on by the alarm for 1 min. In order to permanently turn on the controlled device by means of the proposed adapter by means of the proposed adapter, you should use a remote control with a latch (see "RA" 5/99, p. 38). To implement a shutdown mode (sleep timer, for example), a FET inverter must be connected between the latch remote control and the input and output switches of the power supply (see "PA" 5/99, p. 40). Thus, it is possible to build very complex systems and automation devices, subjecting the original products to minimal alteration. However, DC power switching is not always applicable (especially if the controlled device has a complex multi-voltage circuit power supply). Therefore, a power switch of alternating mains voltage is needed, which is also implemented on the basis of a network adapter, as a convenient design basis. The second adapter is subjected to a more complex alteration associated with a change in the function of the original product. From the adapter "Electronics D2-11" (included in the set of microcalculator "Electronics MK-60") we get a universal network triac AC switch (Fig. 2).
A distinctive feature of the resulting product is complete galvanic isolation from the AC mains and the original design (small dimensions and weight, connection to the control device by means of a SYuP-v plug on the cord without installing the GK-2 socket). I called such a switch a switch, because the mains voltage appears at the output X3 (socket Rн) only during the operation of the control circuit at the input X1. When reworking, we use the elements and details of the original adapter as much as possible (in Fig. 2 they are highlighted with thin lines), namely: a case with a mains plug, a rectifier (diodes and a capacitor), a transformer. In its original form, the network adapter "Electronics D2-11" has limited use, it has an output voltage of 3 V at a current of up to 50 mA (it can power a VHF receiver, but the player no longer "pulls"). So, we open the adapter and let's do the alteration. The body of the network adapter is an enlarged end plug with dimensions of 75x48x36 mm (without pins) and consists of two halves fastened with one self-tapping screw that tightens the halves of the body in the area of the pins. Mutually incoming hooks are made at the other end. The body halves are equal in volume and differ in counterparts (shoulders, thrust pins, bushings, etc.). The part into which the self-tapping screw is screwed, we will call the lower part or the mounting base, and in it we will perform the entire installation of the switch (Fig. 3, a). The other half, in which the head of the self-tapping screw is visible, will be called a cover and subjected to minimal refinement (basically, we will choose a semicircle for mounting the HL1 LED in the area where the halves are joined by jointly drilling the assembled case with a drill with a diameter of 5,2 mm for LEDs of the AL307, AL336 types).
Then we unscrew the self-tapping screw and remove the housing cover, while the transformer should remain on the base with the leads up, and the rectifier printed circuit board is soldered to the leads of the secondary winding (Fig. 3, b). Now you need to remove the printed circuit board from the transformer leads, using a soldering iron with solder suction or a medical needle with a sharpened cut, and clean the holes so that when assembling the board, it is easy to put on the transformer leads. The standard printed circuit board undergoes a slight refinement: we rearrange one of the bridge diodes, which stood along the board, across and get two or two diodes in parallel in order to move the capacitor C1 closer to the transformer and free up some space for installing the triac VS1. In the wiring diagram, we also use a standard cord, the standard plug of which is replaced with a SUP-v plug (see "RA" 2/99, p. 22). Capacitor C1 must be insulated (wrap the case with tape in several layers or use an imported one with case insulation and smaller dimensions). Now we will remove the extra parts: the KS136A zener diode and the 1,5 kΩ resistor and clean the holes. The third extra detail is the U-shaped cardboard, which was included in the cord attachment. In order to more securely fix the cord, install the HL1 LED and the VS1 triac (in the TO-220 package), you need to make an additional printed circuit board 25x40 mm in size (the main board has the same size). This board is shown in Fig. 3a (rear view). To improve the quality, I advise you to drill holes in the following sequence: a hole for the LED (mentioned above), mounting holes for the board with a diameter of 2,5 mm, first with a thin drill in the case, and then in the workpiece we drill to the specified diameter. We assemble an additional board with a case with screws 8 mm long, and spacers 1,3 mm thick must be installed between the board and the case (there must be a gap between the case and the board). We drill holes for the LED leads (1,2 mm in diameter) and a hole for passing the cord (4 mm in diameter) on the joint axis (Fig. 3, a rear view). The hole for mounting the triac VS1 (diameter 3,2 mm) is drilled last and under it we select the M3 screw with a low head (this screw should hide under the housing cover). During the described procedures, do not forget to check the position of the upper end of the additional board and, if necessary, file it so that when the standard board is installed, their joint is parallel to the case joint. On an additional board with nitro paint we apply: 1) in the center a rectangle for a triac 14 mm wide to the entire height of the board (when installing the triac, we solder a small copper radiator 0,5 mm thick and 25x25 mm in size with a bend on both sides); 2) around the mounting holes of the platform board 6x6 mm, on which M2,5 nuts must be soldered; 3) slightly higher, but not at the very top edge, two pads for the LED leads (the pads are spaced 5 mm from the holes for the leads to prevent the LED from overheating when soldering); 4) along the edges of the board (departing from the top edge of 3 mm) 4 contact pads 3x3 mm each for mounting circuit elements. After that, the board can be pickled. Fuse FU1 is installed in the compartment in the area of the pins of the mains plug (Fig. 3). We install a ceramic insert 15 mm long in a home-made holder, soldered onto a 10x20 mm board with contact pads at the edges (the board can be etched along with an additional one). We select an outlet for output X3. This is a two-socket appliance socket with a distance between the sockets of 19 mm and a mounting hole in the middle. I installed the outlet inside the case, but not all types of outlets allow this installation. In addition, it is advisable to assemble a circuit before installing the outlet to make sure that the outlet goes to the indicated place. Let's turn to the scheme of Fig.2. The triac switch consists of four main nodes: 1) the key node with optocoupler LED current stabilization is assembled on a transistor VT1 and resistors R1 and R2, to which an on indicator on the HL1 LED is added (the same node includes a control supply cord with a plug X1); 2) a low-voltage rectifier assembly assembled on adapter elements - diodes VD1 ... VD4, capacitor C1 and transformer T1; 3) a power switching unit on a thyristor VS1 (it includes a power plug X2, a fuse FU1, a socket X3, a resistor R3); 4) an AC switch assembly with galvanic isolation on an optocoupler U1 of the AOU-160 type. The designations of the optocoupler pins A, B, C, D are made to suggest options for replacing this node (if you could not get the optocoupler). In the first version, we replace the triac optocoupler with two popular thyristor optocouplers of the AOU-103V type, while we turn on the LEDs in series, and the thyristors in anti-parallel (Fig. 4, a).
In the second option, we use an optocoupler with a transistor output, add a current amplifier on a VT1 transistor, a resistor R1 and a diode bridge VD1-VD4 (Fig. 4, b). If optocouplers, in general, cannot be obtained, then this node can be implemented on an electromagnetic relay, best of all, a reed relay of the RES-55 type (Fig. 4, c). It is possible to use a KEM-2A reed switch by winding a winding with a resistance of at least 4 Ohm on the frame equal to the length of the reed switch and with a cheek height of 500 mm. Instead of an optocoupler with a triac, you can use a modern power optocoupler of the 5P19 series. The use of these options will require an increase in volume, while the X3 socket will have to be taken out of the case, and the standard board will have to be redone. As a result of the work done, a universal, very convenient and safe AC power switch is obtained. In conclusion, a few words about security. Circuitry and design provides for a number of measures to ensure protection against electric shock (full double galvanic isolation) and fire safety in case of overloads (fuse for current 2 A). However, the installation was carried out to a limited extent, and therefore special care and attention should be paid to the issues of insulation and the choice of materials and structural elements (optocouplers should only be used with an insulation voltage of more than 500 V). If there are doubts about the quality of products (for example, a transformer), then they should be checked in an electrical laboratory with a test voltage of 1500 V. The same should be done with the finished design (check the decoupling between the low-voltage and high-voltage parts). Remember that your life depends on it! Author: Yu.P.Sarazh
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