Simple laboratory power supply, 220/+-15 volts 1 amp. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Power Supplies
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As you know, to power the circuits on operational amplifiers, a bipolar stabilized power supply of ±15 V is required. It is desirable to have an adjustable power supply in the laboratory power supply with an output current of up to 1 A.
The circuit diagram of the power supply that meets these requirements is shown in Fig. 1.
(click to enlarge)
The voltage of 1 ... 14 V removed from the secondary winding of the transformer T15 is fed to a bridge rectifier assembled on diodes VD1 ... VD4. Capacitors C1, C2 of the filter provide smoothing of the ripple of the rectified voltage of positive and negative polarities. A bipolar voltage regulator based on a unipolar DA1 microcircuit with a stabilization voltage of 15 V is made according to the scheme given in [1].
To obtain a stabilized voltage of negative polarity, an operational amplifier DA2 and a transistor VT1 are used. Capacitor C3 is necessary to smooth low-frequency relaxation oscillations. It reduces the ripple of the output voltage of the negative arm of the power supply. Capacitor C4 is used to reduce the ripple of the positive shoulder. The regulated power supply from 0 to +13 V is assembled on DA3 according to the scheme borrowed from [1]. Since when the supply voltage is turned off, the voltage rises to +13 V at the output of the regulated power supply, the load is connected to this output through the SB1 toggle switch, with which the 0 ... +13 V circuit is opened before the power supply is turned off.
The design uses a transformer with a power of at least 36 W with a tap from the midpoint of the secondary winding with a voltage of 2 x (14 ... 15) V. For the transformer, you can use the USh 22x33 magnetic circuit. The primary winding contains 2000 turns of wire PEV-2 x 0,2 mm, the secondary - 130 turns of wire PEV-2 x 0,8 mm. The design uses diodes of the KD226 type, capacitors C1, C2 of the K50-35 type, even better - Taiwanese-made 4700 μF x 25V, capacitors C3-C5 of the K73-17, K73-9 type. Operational amplifier DA2 can be replaced by KR140UD708 or K140UD6, K140UD7. As a transistor VT1, you can use any powerful low-frequency p-n-p transistor.
Fixed resistors of the MLT-0,25 type, variable resistor - SPZ-4aM. Switch SB1 type P2K with latching in the pressed position, you can use the MT-1 toggle switch, but in this case it is installed outside the printed circuit board.
The main part of the power supply elements is placed on a printed circuit board measuring 100 x 55 mm from one-sided foil fiberglass 1,5 mm thick (Fig. 2).
Microcircuits DA1, DA3, transistor VT1 are each placed on its own ribbed radiator with an area of 30 ... 50 cm2.
References:
- Shcherbina A., Blagiy S., Ivanov V. Application of microcircuit stabilizers of series 142, K142, KR142 // Radio. - 1991. - No. 3. - P.47-51.
Author: O.V. Belousov
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