Switching power supplies are widely used in modern electronic equipment. Readers are invited switching power supply 800 watts. As described previously, it is used in the field Converter transistors and transformer with the primary winding with the secondary output. First provides higher efficiency and reduced levels of high-frequency interference, and the second - half the current through transistors key and eliminates the need in the isolation transformer in the chains of their locks.
The drawback of this scheme solutions - high voltage on the primary halves winding, which requires the use of transistors with a corresponding valid voltage. However, unlike bridge Converter, in this case only two transistors instead of four, slightly simplifies the design and increases the efficiency of the device. The proposed UPS applied push-pull Converter with a transformer, the primary winding of which has an average output. He has high efficiency, low ripple and poorly radiates noise into the surrounding space. It is used to power two-channel omednennaja option of USC.
The UPS input voltage - 180...240 V, rated output voltage (at input 220V) - 2x50 b, maximum load capacity - 800 watts, working the frequency Converter is 90 kHz. Schematic diagram of the UPS shown in Fig. 4.47. As you can see, this Converter with external excitation. the output voltage. At the entrance of the device includes a high-pass filter C1, L1, C2 to prevent interference in the network. After mains voltage rectified by a diode bridge VD1...VD4, ripple smoothing capacitor C3. The rectified DC voltage (about 310 B) is used to power high-frequency transducer.
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The Converter is implemented on chips DD1 DD3.... Eats it from a separate stable source consisting of step-down transformer T1, rectifier VD5 and voltage regulator on transistors VT1, VT2 and the Zener diode VD6. On the elements of DD1.1, DD1.2 assembled the master oscillator generates pulses with a repetition rate of about 360 kHz. Followed by a frequency divider 4, performed on the triggers circuit DD2. Using elements DD3.1, DD3.2 creates additional delay between pulses. The pause is nothing but as a logic level 0 at the outputs of these elements, appearing in the presence of the logical 1 level at the output of the element DD1.2 and triggers DD2.1 and DD2.2. Voltage low level output DD3.1 (DD3.2) blocks DD1.3 (DD1.4) in the "closed" state (the output is a logic level 1). The duration of the pause equal to 1/3 of the pulse voltages on pins 1 DD3.1 and 13 DD3.2, which is enough for closing the switching transistor. From the outputs of the elements DD1.3 and DD1.4 finally formed the pulses arrive at the transistor keys (VT5, VT6), which through resistors R10, R11 powerful operate the gates field-effect transistors VT9, VT10 (see Fig. 4.48).
Pulses with direct and inverse outputs of the trigger DD2.2 go to the inputs devices, transistors VT3, VT4, VT7, VT8. Opening alternately, VT3 and VT7, VT4 and VT8 create conditions for rapid discharge of the input the capacitances of the switching transistors VT9, VT10, i.e. their quick closing. In the circuit transistor gates and VT9 VT10 included a relatively large resistors resistance R10 and R11. Together with the capacitance of the gates they form a lower filters frequencies, reducing the level of harmonics when the lid of the keys.
With the same purpose on entries...VD9 VD12, R16, R17, C12, C13. In stock chain transistor VT9, VT10 included the primary winding of transformer T2. Rectifiers the output voltage is made in a bridge circuit diodes VD13...VD20 that slightly reduces the efficiency of the device, but significantly (more than five times) reduces ripple on the output of the UPS. It is important to note that the shape of the oscillations, almost rectangular at maximum load smoothly into the close to sinusoidal while reducing the power to 10 to 20 watts, which positively affects the noise level supplied from this block of USC at low volume. Rectified voltage IV winding of transformer T2 is used to power fans.
The device incorporates capacitors K73-17 (C1, C2, C4), C50-17 (C3), MBM (C12, C13), K73-16 (C14...C21, C24, C25), C50-35 (...C5 C7), km (the rest). Instead specified in the scheme allowed the use of chips series C, K. Diodes D (VD1...VD4)interchangeable with any other, suitable for direct current of at least 5 A and reverse voltage not less than 350 (CDC, CDM, CDR, KDB, DB), or diode rectifier bridge with the same parameters, diodes KDA (VD13...VD20) - CDB, CDB, Zener DU (VD6) - DV. As can VT1 to use any transistors series CT, CT, as VT2...VT4 and VT5, VT6 - accordingly, any of the series KT315, CT, KT3102 and KT361, CT, CT, in place VT9, VT10 - KV, KE. Transistors CTR (VT7, VT8) substitutions are not recommended.
The transformer T1 - TC-10-1, or any other voltage secondary winding 11...13 V At a load current of at least 150 mA. The coil L1 line filter wound on ferrite (MNM) ring size CH,5x7 wire Sew-1-1.0 (2x25 of turns), the transformer T2 is glued together on three of the rings ferrite of the same brand, but the size Chg. Winding I contains 2x42 loop the PEV-2-1,0 (coil in two wires), winding II and III - to 7 turns (in five wires sew-2-0,8), winding IV - round 2 sew-2 and 0.8. Between windings lay three layers of insulation of PTFE tape.
The magnetic cores of the inductors L2, L3 ferrite (NS) rods 6 and length of 25 mm (the trimmers from armored core B). Coils contain 12 turns of PEV-1 to 1.5. The transistor VT9, VT10 is mounted on a heat sink with fans used to cool microprocessors Pentium ( similar nodes and 486 processors). Diodes VD13...VD20 fix on a heat sink with a surface area of about 200 cm2.
When installing the UPS should strive to ensure that all connections were possible in short, and in the power section to use the wire as possible section. UPS preferably enclosed in a metal shield and connect it to the output 0 output source, as shown in Fig. 4.49.
Common wire of the power part with the screen to connect should not. Since the UPS is not equipped with a protection device against short circuit and overload, the supply circuit must include fuses 10 A. In establishing described the UPS is almost not necessary. It is important to correctly to stateroute half of the primary winding of transformer T2. With proper details and no errors in mounting the unit begins to work immediately after you turn in network. If necessary, the frequency Converter adjusts the selection of the resistor R3. To improve the reliability of the UPS, it is desirable to operate with USC, which are provided through the blowing fan.
Author: A. P. Seman