Powerful laboratory transistorized power supply, 220/3-30 volts 2 amps. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Power Supplies

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The proposed power supply is made on transistors. It has a relatively simple circuit (Fig. 1), and the following Parameters:

• output voltage ......3...30 V;
• stabilization coefficient when the mains voltage changes from 200 to 240 V ....... 500;
• maximum load current ....... 2 A;
• temperature instability ....... 10 mV / ° C;
• ripple amplitude at I max ....... 2 mV;
• output impedance ....... 0,05 ohm.

Fig.1 (click to enlarge)

The main rectifier is assembled on diodes VD5-VD8, the voltage from which is supplied to the filter capacitor C2 and the regulating composite transistor VT2, VT4-VT6, connected according to the common collector circuit.

On transistors VT3, VT7, a feedback signal amplifier is made. Transistor VT7 is powered by the output voltage of the power supply. Resistor R9 is its load. The emitter voltage of the transistor VT7 is stabilized by the Zener diode VD17. As a result, the current of this transistor depends only on the base voltage, which can be changed by changing the voltage drop across the resistor R10 of the voltage divider R10, R12-R21. Any increase or decrease in the base current of the transistor VT7 leads to an increase or decrease in the collector current of the transistor VT3. In this case, the regulating element is locked or unlocked to a greater extent, respectively, reducing or increasing the output voltage of the power supply. By switching the resistors R13-R21 with the SA2.2 section of the SA2 switch, the output voltage of the unit is changed in steps of 3 V. The output voltage is smoothly regulated within each step using the resistor R12.

The auxiliary parametric stabilizer on the VD9 zener diode and the R1 resistor serves to power the VT3 transistor, the supply voltage of which is equal to the sum of the output voltage of the unit and the stabilization voltage of the VD9 zener diode. Resistor R3 is the load of transistor VT3.

Capacitor C4 eliminates self-excitation at high frequencies, capacitor C5 reduces the output voltage ripple. Diodes VD16, VD15 accelerate the discharge of the capacitor C6 and the capacitive load connected to the unit when the output voltage is set to a lower level.

On the transistor VT1, trinistor VS1 and relay K1, an overload protection device is made for the power supply. As soon as the voltage drop across the resistor R5, proportional to the load current, exceeds the voltage across the diode VD12, the transistor VT1 opens. Following it, the trinistor VS1 opens, shunting the base of the regulating transistor through the VD14 diode, and the current through the regulating element of the stabilizer is limited. At the same time, relay K1 is activated, with contacts K1.2 connecting the base of the regulating transistor to a common wire. Now the output current of the stabilizer is determined only by the leakage current of transistors VT2, VT4-VT6. Contacts K1.1 of relay K1 turn on the light H2 Overload. To return the stabilizer to its original mode, it must be turned off for a few seconds and turned on again. C3, resistor R2 and diode VD11.When the power supply is turned on, the capacitor is charged in two circuits: through resistor R2 and through resistor R3 and diode VD11.At the same time, the voltage at the base of the regulating transistor slowly increases following the voltage across capacitor C3 until the stabilization voltage is established.Then diode VD11 closes and capacitor C3 continues to charge through resistor R2. Diode VD11, closing, eliminates the effect of the capacitor on the operation of the stabilizer. Diode VD10 serves to accelerate the discharge of capacitor C3 when the power supply is turned off.

All elements of the power supply, except for the power transformer, powerful control transistors, switches SA1-SA3, fuse holders FU1, FU2, light bulbs H1, H2, pointer meter, output connectors and a smooth output voltage regulator, are placed on printed circuit boards (Fig. 2,3 ).

Ris.2

Ris.3

The location of the power supply units inside the case can be seen from Fig.4. The P210A transistors are mounted on a needle-shaped heatsink mounted at the back of the case and having an effective dissipation area of ​​about 600 cm2. Ventilation holes with a diameter of 8 mm are drilled in the bottom of the case at the place where the radiator is attached. The housing cover is fixed in such a way that an air gap of about 0,5 cm wide is maintained between it and the radiator. For better cooling of the control transistors, it is recommended to drill ventilation holes in the cover.

Ris.4

A power transformer is fixed in the center of the case, and next to it, on the right side, a P5A transistor is fixed on a 2,5x214 cm duralumin plate. The plate is insulated from the body with insulating bushings. The diodes KD202V of the main rectifier are mounted on duralumin plates screwed to the printed circuit board. The board is installed above the power transformer with the parts down.

The power transformer is made on a toroidal tape magnetic circuit OL 50-80/50. The primary winding contains 960 turns of wire PEV-2 0,51. Windings II and IV have output voltages of 32 and 6 V, respectively, with a voltage on the primary winding of 220 V. They contain 140 and 27 turns of wire PEV-2 0,31. Winding III is wound with PEV-2 1,2 wire and contains 10 sections: the lower one (according to the diagram) - 60, and the rest 11 turns each. The output voltages of the sections are respectively equal to 14 and 2,5 V. The power transformer can also be wound on another magnetic circuit, for example, on a rod from TVs UNT 47/59 and others. The primary winding of such a transformer is retained, and the secondary windings are rewound to obtain the above voltages.

In power supplies, instead of P210A transistors, transistors of the P216, P217, P4, GT806 series can be used. Instead of P214A transistors, any of the P213-P215 series. MP26B transistors can be replaced with any of the MP25, MP26 series, and P307V transistors with any of the P307 - P309, KT605 series. Diodes D223A can be replaced by diodes D223B, KD103A, KD105; KD202V diodes - any powerful diodes with a permissible current of at least 2 A. Instead of the D818A zener diode, you can use any other zener diode from this series. Instead of the trinistor KU101B, any of the KU101, KU102 series will do. As relay K1, a small-sized relay of the RES-9 type was used, passports: RS4.524.200, RS4.524.201, RS4.524.209, RS4.524.213.

The relays of these passports are designed for an operating voltage of 24 ... 27 V, but they begin to operate already at a voltage of 15 ... 16 V. When an overload of the power supply occurs (see Fig. 2), as already noted, the trinistor VS1 is unlocked, which limits stabilizer current to a small value. At the same time, the filter capacitor of the main rectifier (C2) is immediately recharged to approximately the amplitude value of the alternating voltage (with the lower position of the SA2.1 switch, this voltage is at least 20 V) and conditions are created for fast and reliable operation of the relay.

Switches SA2 - small-sized biscuit type 11P3NPM. In the second block, the contacts of the two sections of this switch are paralleled and are used to switch sections of the power transformer. When the power supply is on, the position of the switch SA2 should be changed at load currents not exceeding 0,2 ... turning it off. Variable resistors for smooth adjustment of the output voltage should be selected with the dependence of resistance on the angle of rotation of the type "A" engine and preferably wire. Miniature incandescent bulbs HCM-0,3 V-1 mA are used as signal lamps H2, H9.

Any pointer device can be used for a current of full deflection of the pointer up to 1 mA and a front part size of not more than 60X60 mm. In this case, it must be remembered that the inclusion of a shunt in the output circuit of the power supply increases its output impedance. The greater the current of the total deviation of the arrow of the device, the greater the resistance of the shunt (provided that the internal resistances of the devices are of the same order). To prevent the influence of the device on the output impedance of the power supply, the switch SA3 during operation should be set to measure voltage (upper position according to the diagram). In this case, the shunt of the device closes and is excluded from the output circuit.

The adjustment comes down to checking the correctness of the installation, selecting the resistors of the control stages to adjust the output voltage within the required limits, setting the protection operation current and selecting the resistances of the resistors Rsh and Rd for the pointer meter. Before tuning, a short wire jumper is soldered instead of a shunt.

When setting up the power supply, switch SA2 and the slider of resistor R12 are set to the position corresponding to the minimum output voltage (lower position according to the diagram). By selecting the resistor R21, a voltage of 2,7 ... 3 V is achieved at the output of the block. Then the slider of the resistor R12 is moved to the extreme right position (upper according to the diagram) and by selecting the resistor R10 the voltage at the output of the block is set to 6 - 6,5 V. Next move switch SA2 one position to the right and select resistor R20 so that the output voltage of the unit increases by 3 V. And so in order, each time switching switch SA2 one position to the right, resistors R19-R13 are selected until the final voltage is established at the output of the power supply 30 V. Resistor R12 for smooth adjustment of the output voltage, you can take a different value: from 300 to 680 ohms, however, approximately proportionally you need to change the resistance of resistors R10, R13-R20.

The protection operation is configured by selecting the resistor R5.

the additional resistor Rd and the shunt Rsh are selected by comparing the readings of the PA1 meter with the readings of an external measuring device. In this case, the external device must be as accurate as possible. As an additional resistor, you can use one or two series-connected resistors OMLT, MT for a dissipation power of at least 0,5 W. When selecting the resistor Rd, switch SA3 is switched to the "Voltage" position and a voltage of 30 V is set at the output of the power supply. An external device, not forgetting to switch it to measuring voltages, is connected to the output of the unit.

A piece of manganin or constantan wire with a diameter of 1 mm is used as a shunt. When setting up the shunt, switch SA3 is switched to the "current" position, and the power supply is turned on only after a piece of manganin wire is soldered instead of the previously installed jumper. Otherwise, the pointer meter PA1 may fail. In this case, the external device is connected in series with the load, which can be a 5 ... 10 Ohm resistor designed for a dissipation power of 10 ... 50 W. By changing the output voltage of the power supply, the load current is set to 2 ... 2,5 A and, by reducing or increasing the length of the manganin wire, the same readings of the PA1 meter are achieved. Before each operation to change the length of the shunt, do not forget to turn off the power supply.

See other articles Section Power Supplies.

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