Test station power supply. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Power Supplies
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For adjustment, control and testing of electronic circuits and, if necessary, recharging the batteries, a test station power supply is offered, consisting of two stabilized and one regulated channel.
The power supply is made using radio components from decommissioned monitors and computer power supplies. The power supply circuit (Fig. 1) consists of:
- input noise filter on transformer T1 and capacitors C1 ... C2;
- step-down transformer T2;
- rectifier VD1 with smoothing capacitor C3;
- two analog voltage stabilizers on DA1 and DA2 microcircuits (DA2 output voltage for recharging batteries with a voltage of 12 V is increased using the VD2 diode);
- electronic voltage regulator on a composite transistor VT1;
- circuits for protecting the power transistor from overloads and short circuits on the parallel stabilizer DA3.
(click to enlarge)
The stabilized voltage from the output of the DA2 chip is also used to power the voltage regulator circuits on the composite transistor VT1. The regulator transistor has a gain of at least 400 and an output current of more than 5 A, which eliminates the need for additional amplifying stages.
To protect VT1 from failure in the event of a short circuit in the load, the circuit has a feedback circuit from the load current sensor R8 to the VT1 base through a parallel stabilizer on the DA3 chip. Increasing the voltage on the sensor R8 leads to the opening of the parallel regulator DA3, which shunts the base of the transistor VT1 and limits its current. The setting of the current limit can be done with a resistor R7 Instead of a parallel stabilizer, you can install any low-power reverse conduction transistor. The output voltage indication is made on the green LED HL2. To reduce fluctuations in the output voltage, a large capacitor C6 is installed.
The device is assembled on a printed circuit board with dimensions of 72x51 mm (Fig. 2), which is placed in a case from a computer power supply.
Switch SA1 and fuse FU1, together with an ammeter and voltage regulator R3, are installed on the front wall of the case, the ammeter is mounted in the window after removing the fan. The voltmeter in the circuit is shown conditionally; any tester in the voltage measurement mode is suitable as it.
The RA1 ammeter is made on a measuring head of the M2003 type with a total deflection current of 100 μA. The RS1 shunt is made of 10 turns of 0,8 mm copper wire wound on a 0,8 mm mandrel. The shunt is calibrated by connecting the tester in series with the ammeter in the high current measurement mode.
A step-down transformer with a power of 120 ... 150 W is used industrial, such as TN-58 (59) or TPP-292 (293,294,303), with a total voltage of the secondary windings of 18 ... 24 V and an allowable current of 3 ... 5 A. In the diagram the pinout is not indicated, it can be performed based on the voltages of the secondary windings and their connections. The surge protector is taken ready - from a computer power supply.
Instead of a bridge rectifier VD1, you can use 4 diodes D213B or D304, D246. It is not necessary to install radiators on diodes. The electrolytic capacitor C3 in the circuit is taken for a voltage of 35 V to reduce leakage and possible overheating when the power supply is operating at high load currents.
Integral stabilizers DA1 and DA2 are fixed on a metal case through mica gaskets. Indication of the on state of the power supply is made on the LED HL1. Transistor VT1 is mounted on the case through a gasket with fastening on the outside of the radiator. Resistor R8 can be made of nichrome wire 01 mm and 50 mm long, wound on a resistor type MLT-2.
The power supply circuit does not require special adjustment. It is enough to connect a load in the form of a car light bulb (0 candles) to the output (16 ... 50 V) and set the desired output voltage with the R3 regulator. Resistor R7 is set to a position at which the voltage at the load stops rising when the slider of resistor R3 is turned.
Authors: V.Konovalov, A.Vanteev, Laboratory "Automation and Telemechanics", Irkutsk Center "Energy Saving Technologies", Irkutsk.
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