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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Power management for computer peripherals, 1200 watts. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Power Supplies Equipment connected to a personal computer can consume tens or even hundreds of watts of power from the AC mains in idle mode. In addition, if electrical equipment is unnecessarily connected to the AC mains for a long time, for example, while in standby mode, then the likelihood of damage increases. To automatically turn off the power of devices connected to the computer, you can assemble a simple design, the schematic diagram of which is shown in Fig. 1. The device is designed to connect loads with a total power of up to 1200 watts.
Depending on the connection method, the device can operate in two modes: 1 - power is always supplied to the loads if the mains voltage is applied to the computer itself;
The first mode of operation is provided due to the fact that if the computer is in standby, standby or sleep mode, then +5 V is usually present on the USB ports, which can be disabled in the BIOS settings of some computer motherboards. In the second mode, the control input should be connected to the computer's +5 V power line, which is usually not energized if the computer is not working. Power +5 V is applied to all red wires coming out of the desktop power supply. The second mode is difficult to implement for laptops and netbooks. The first mode of operation is most appropriate if this device will manage the power of various disk drives, the voltage of which is undesirable to turn off when the computer goes into standby mode. When a voltage of 5 V DC is received at the control input, the HL1 LED lights up and the contacts K1.1 of the electromagnetic relay close. This relay provides the necessary electrical isolation between the computer and the mains voltage of 220 V. For the same purpose and to increase the reliability of the device, other methods have been taken to additionally decouple the computer nodes from the 220 V network. For this purpose, the relay contacts are connected through series-connected resistors R1 - R4. These resistors significantly reduce the leakage current of the network - computer-human ground in the event of an insulation breakdown of the electromagnetic relay. In addition, the chance of damage to your computer in the event of a close lightning strike during a thunderstorm is greatly reduced. The following elements also increase the level of protection against adverse collisions in the power supply network: U1, R7, R9, R10, R11, R14, R15, C5, C6. In addition to protective functions, these radio elements perform other functions necessary for the operation of the respective nodes. When contacts K1.1 are closed, transistors VT1, VT2 open as a composite transistor according to the Darlington circuit. The use of a composite transistor allows you to increase the resistance of resistors R1 - R4. Capacitor C1 eliminates the sensitivity of this node to interference. When the transistors are open, the HL2 LED is on. as well as the LED of the triac optocoupler U1. The triac of the optocoupler opens at each half-wave of the mains voltage, along with it a powerful triac VS1 opens. The supply voltage is supplied to the load, which is indicated by a brightly lit two-crystal LED HL3. Resistors R10, R11 reduce the direct and pulse current through the phototriac, and also protect it in case of damage or open circuit of the triac and VS1 The node on transistors and optocoupler U1 is powered by a voltage of +33 V from a capacitor DC source, implemented on capacitors C5, C6 that quench excess power. The AC bridge rectifier is implemented on diodes VD2...VD5. Resistors R14, R15 reduce the surge current of the capacitor power supply. The ripple of the rectified voltage is smoothed out by the oxide capacitor C2. Zener diode VD1 limits the rectified voltage at a level of about 33 V. With open transistors VT1, VT2, the voltage across the plates of capacitor C2 drops to 24 V. Mains voltage 220 V AC to this device and the loads connected to it is supplied through fuses FU1, FU2 and LC noise filter C3L1C4. Varistors RU1, RU2 connected in parallel eliminate high-voltage impulse noise and protect connected loads from overvoltage. The device can be mounted on a 155x70 mm printed circuit board, a sketch of which is shown in fig. 2. All elements are placed on it, except for the L1 choke. On the left side of the board at the installation site of the electromagnetic relay, two air slots are made to reduce the likelihood of breakdowns; resistors of types CM, S2-23, S2-33, MLT, RPM with power indicated on the diagram. Varistors FNR-20K471 can be replaced by FNR-20K431, MYG20-471, MYG20-431. When installing varistors, it is necessary to provide for the protection of the structure from fire of their housing, for example, using asbestos paper or fiberglass.
The number of varistors connected in parallel can be increased. Capacitor C3 ceramic high-voltage K15-15 with a capacity of 2200 ... 10000 pF. Capacitors C4 ... C6 film type. K73-17, K73-24 or similar imports for an operating voltage of at least 250 V AC. Capacitor C1 of any type is small-sized, capacitor C2 is oxide K50-35, K50-68 or equivalent. Diodes. VA159 can be replaced with any of the series 1N4001...1N4007, UF4001... UF4007, KD105, KD209, KD243, KD247. Instead of the D816V zener diode, in this design, you can use D816B, 1N5362, 1N5363, 1N5364 or two KS509A, KS515A, 2S515A zener diodes connected in series. The RL50-YG413 and RL50-HY213 LEDs can be replaced with any general purpose continuous light without built-in resistors. The L-57SRCRD LED can be replaced by any of the L-57, L-937 series. In the absence of two-chip LEDs with back-to-back crystals, you can install a conventional LED by including it in the diagonal of a low-power diode bridge rectifier. The 2SC945 transistors can be replaced with any of the. BC547, SS9011, SS9014, 2SC1815, 2SC1845 or domestic from the KT3117, KT645, KT6114 series. Instead of the triac optocoupler S21ME3, you can use S21ME4, which contains a built-in "zero detector". Another low-power triac optocoupler is also suitable, the optosimistor of which is designed for an operating voltage of at least 400 V. Powerful triac. VT139-800E is designed for operating voltage up to 800 V, direct current 16 A, pulsed 140 A. Can be replaced by any similar series. VT139-600, VT139-800, VT145-600, VT145-800, VTA216-600, VTA216-800, or MAC320-A8. The triac is installed on a heat sink, the cooling surface area of which should be sufficient so that during long-term operation with the maximum load current, the temperature of the triac body does not exceed 60 ° C. The excess power of the triac is necessary so that the triac can withstand the pulsed charging current of the mains voltage filter capacitors of the connected loads. Inductor L1 is any two-winding with inductance of half-windings from 100 μH, the windings of which are designed for the maximum load current. You can use a ready-made two-winding inductor, for example, from a large-format copier, a powerful computer power supply, or make it yourself based on a ferrite core from an output line transformer of a kinescope TV or monitor. The core must be assembled with a non-magnetic gap of about 0,5 mm. In this case, for example, 15 turns of winding wire on the core from the transformer. TVS-90LTs5 will give an inductance of about 100 μH. The diameter of the copper winding wire is at least 1,2 mm. Fuses FU1, FU2 are set to 8 A based on the ability of the device to work together with a laser printer. If you do not intend to connect high current consumers of electricity to this device, you can install fuses with a lower current. The 65V-1 relay has a winding with a resistance of about 160 ohms, designed for an operating voltage of 5 V. It can be replaced by a GJ-SH-105LM, the coil of which is also designed for an operating voltage of 5 V. In the absence of such relays, common electromagnetic relays with a winding of 12 V can be used. 1215 V, eg RAS112, SDT-SS-2DM, G14R-12 In this case, the control input is connected to the computer's +XNUMX V voltage, eg using a standard four-pin "Molex" plug. The relays are not soldered into the holes of the printed circuit board, but are glued to it with polymer glue, the connections are made with short mounting wires. This is necessary to improve the safety of the device. Accurately assembled from serviceable radio components, the device starts working immediately and does not require adjustment. To check the operability as a source of control voltage, it is advisable to use not a computer, but a laboratory power supply. When operating the structure, it should be borne in mind that most of its elements (except for R6, VD6 and HL1) are energized by the AC mains. Author: Butov A.L.
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