Adjustable power supply with protection, 220 / 1,2-24 volts 2 amps. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Power Supplies
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Power supplies BP2-3 from calculators of the "Electronics" series are still used to power various radio equipment, modernized [1, 2] or become "semi-finished products" for more modern developments [3]. There are two main advantages of these blocks. Firstly, the large volume of the case, which allows you to place additional elements in it, and secondly, a high-quality step-down transformer with a low no-load current (a few milliamps).
The author "works" three similar blocks with different output voltages, redone at different times and according to different schemes. The power supply described below provides one of seven fixed voltages: 1,5, 3, 4,5, 5, 6, 7,5, or 9V.
Rice. 1 (click to enlarge)
At an output voltage of 9 V, the maximum output current is 300 mA (76% efficiency), at 1,5 V - 800 mA (34% efficiency). The ripple voltage does not exceed 5 mV.
These parameters are obtained through the use of voltage stabilization, first with a pulse, and then with a linear voltage regulator. The power supply circuit is shown in fig. 1. The primary winding of the network transformer is protected by a self-resetting fuse FU1 and a varistor RU1. A rectifier bridge VD2-VD1 is connected to the secondary winding through a self-healing fuse FU4. Capacitors C1, C2 and C4 suppress interference penetrating from the network or arising from the operation of the switching regulator of the power supply, capacitor C3 smoothes the ripple of the rectified voltage.
The switching regulator is assembled on a specialized AD1507-ADJ (DA1) chip. The switching circuit is standard, the inductor L1 is storage, capacitors C5 and C6 are smoothing. The output voltage is determined by the resistive voltage divider R1-R8 and the position of the XP2.1 jumper: Uout.imp = 1,23(1+RΣ/R5), where RΣ - the total resistance of the resistors between the FB input of the DA1 stabilizer and the "+" of the capacitor C5. Uout.imp exceeds the output voltage of the power supply by 1,2 ... 1,5 V, which ensures a relatively high efficiency of the linear stabilizer following it.
This voltage stabilizer is assembled according to the standard scheme on the KR142EN22 (DA2) microcircuit with a small allowable input-output voltage drop. The output voltage is determined by the resistive voltage divider R9-R16 and the position of the XP2.2 jumper: Uout.line = 1,25(1+RΣ/R11), where RΣ - the total resistance of the resistors between pin 2 of the DA2 stabilizer and the common wire.
In this case, one of the seven fixed voltages is set at the output, the values of which are indicated above. Switching the output voltage of the pulse and linear stabilizers occurs simultaneously, since the XP2.1 and XP2.2 jumpers are structurally combined. In the absence of jumpers, the output voltage of the power supply is 9 V, so the XS1.7 and XS2.7 sockets may seem redundant, but their presence makes the voltage switching more understandable and helps not to lose jumpers.
All elements except the transformer were removed from the main board of the power supply, and resettable fuses, a varistor, a capacitor C3, a DA2 microcircuit and next to it a capacitor C8 and a resistor R11 were installed. Some printed conductors are preserved, some of them are used for wiring AC voltage, common wire and positive voltage. These conductors are additionally "reinforced" with a single-core copper wire. The remaining elements are mounted on two breadboards. They are fixed on the main board with metal corners. On one board there are diodes VD1-VD4 and capacitors C1, C2 and C4 (Fig. 2), on the second - diode VD5, capacitors C5-C7, inductor L1, sockets XS1, XS2 and all resistors except R11 (Fig. 3).
Fig. 2
Resistors for surface mounting of size 0603 or 0805 are used. Capacitors C3 and C5 are aluminum oxide, C7 and C8 are tantalum oxide for surface mounting, the rest are K10-17.
Fig. 3
Inductor - RCH895NP-101K from Sumida, resettable fuses - FRV012-240F (FU1), FRX040-60F (FU2), varistor - SAS-431KD10. The KR142EN22A chip can be replaced with LT1084, AP1507-ADJ with AP1506-ADJ. Sockets XS1, XS2 - PBD-16 series, shortened to seven sockets in a row.
Fig. 4
The surface mount resistors and capacitor C7 are soldered on the pads between the pins of the sockets, as shown in fig. 4. Jumpers XP2.1, XP2.2 are made of PLS-4 plug. The pins are connected in pairs using a segment of the breadboard, which increases the strength of this part. From the soldering side, the pins are covered with a layer of hot-melt adhesive. Chip DA1 is mounted on a ribbed heat sink measuring 36x15x15 mm, cut from a heat sink removed from a faulty computer motherboard. A cooling aluminum plate measuring 2x36x13 mm is fixed on the DA1 chip. This plate from below has a "shelf" 3 mm wide and is additionally fixed to the main board with a screw for greater structural rigidity. To accurately set the output voltages of the stabilizers, resistors R5 and R11 are selected.
Fig. 5
The appearance of the power supply is shown in fig. 5.
Literature
- Alexandrov I. Refinement of block BP2-3. - Radio, 1991, No. 1, p. 71.
- Nizovtsev A. Refinement of the power supply unit BP2-3. - Radio, 2002, No. 7, p. 60.
- Butov A. Small-sized adjustable power supply. - Radio, 2012, No. 5, p. 55, 56.
Author: V. Nikulin
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