Simple laboratory power supply, 220/16,32 volts 0,5 amps. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Power Supplies
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When developing and setting up analog devices, a power supply with an output voltage of 8 ... 25 V, a load current of 0,3 ...
A power supply that meets these requirements is described below. Its output impedance is approximately 5 mΩ, the ripple voltage is no more than 1,2 mV. The device (Fig. 1) consists of a network transformer T1 with a bridge rectifier on diodes VD1 - VD4 and a compensation voltage regulator on transistors VT1, VT2 and op-amp DA1. The rectifier generates two voltages - 16 and 32 V.
With an output voltage not exceeding 12 ... 13 V (set by a variable resistor R2), 2 ... 2 V drops on the regulating transistor VT4. For the transistor VT1, this voltage is closing, so the current through it is small and the main load current flows through the diode VD5, i.e., the stabilizer is powered by 16 V.
If the output voltage is increased, the voltage drop across the transistor VT2 will decrease, which will lead to the opening of the transistor VT1. Now both transistors, VT1 and VT2, are included in the regulating element of the stabilizer. In this case, the stabilizer will be powered by a voltage of 32 V through the transistor VT1, the diode VD5 will be closed. In other words, transistor VT1 opens or closes depending on the voltage set at the output of the device.
Thus, the input voltage of the regulator automatically changes when the output voltage changes. As a result, the dissipated power on the regulating element is reduced and the efficiency of the stabilizer is increased. In addition, the use of field-effect transistors made it possible to simply solve the problem of protection against emergency overload, since the output current of the stabilizer when the output circuit is closed cannot exceed the initial drain current of the transistor VT2 (0,3 ... 0,4 A). For example, if at a voltage of 20 V the output circuit turns out to be closed, then this will lead, first of all, to closing the transistor VT1 and reducing the input voltage of the stabilizer to 16 V, and the current will be limited to the above value. In this case, the transistor will dissipate a power of 5 ... 6 W, and in this mode it can work for a long time.
Capacitors C3, C4 prevent possible self-excitation of the stabilizer.
The device can use OU K140UD7, K140UD8 (with any letter index), K140UD9, K140UD11, K140UD12, K553UD1; transistors. KP903A, KP903V (VT1, VT2), KP103M, KP103D (VT3), rectifier diode blocks. KTs402B - KTs402E [VD1-VD4), diodes KD209V, KD212B (VD5), zener diodes KS156A, KS162A, KS162B, KC168A VT6; Capacitors C1, C2-K50-12, K50-6; C3, C4 - CT, KLS, CM, BM; C5 - MBM, BM. Resistor R2 - SP-1, SPO-0,4, the rest - VS, MLT.
The mains transformer T1 must provide an alternating voltage of 10 ... 12 V at a current of 0,5 A on the winding II.
You can use unified transformers. TPP245-127/220-50, TPP251-127/220-50, TPP253-127/220-50, TNZO-127/220-50, TN32-127/220-50, etc.
All parts, except for the fuse FU1, the switch Q1 and the variable resistor R2, are mounted on a printed circuit board (Fig. 2) made of foil fiberglass with a thickness of 1,5 ... 2 mm.
The front panel is attached to the board with screws using a duralumin corner. The rear wall of the block is a ribbed heat sink; you can also use a plate with a thickness of 2,5 ... 3 mm with a useful scattering area of at least 100 cm2. The casing of the block is made of sheet duralumin with a thickness of about 0,7 mm. The casing consists of a pallet, in which a board with a front panel and a heat sink is fixed, and a U-shaped cover. Ventilation holes should be provided in the pan and lid.
The establishment of the unit consists in setting the limits for regulating the output voltage, for which resistors R1 and R3 are selected. It is desirable to control the output characteristics of the device for different voltage values. Graphs should have the form shown in Fig. XNUMX.
To indicate the inclusion of the block in series with the transistor VT3 (in the drain circuit), you can turn on the LED, for example, AL307B.
Author: I. Nechaev
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