Transistor stabilizer with short circuit protection, 15-27 volts 3 amps. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Surge Protectors
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On fig. 3.6 shows a voltage regulator circuit with an output current of up to 3 A, which uses short circuit protection. With the help of a variable resistor R7, the voltage at the load can be changed in the range from 15 to 27 V, and with the help of a variable resistor R3, the protection operation current can be changed in the range from 0,15 to 3 A. The rated input voltage of this stabilizer is 30 V, the stabilization coefficient is not less than 300. The amplitude of the output voltage ripple is not more than 10 mV.
If the stabilizer does not work well at low load currents, you need to reduce the resistance of the voltage divider R6, R7, R8, or load the output of the stabilizer with a constant resistor, but this reduces its efficiency. Therefore, it is better to replace the transistor VT1 with another one with a lower gain value. If the stabilizer does not return to operating mode after an overload even when the load is off (this phenomenon is often observed at a low value of the set current of the protection operation, that is, at the maximum resistance of the resistor R3), it is necessary to reduce the resistance of the resistor R3, or briefly connect between the collector and the emitter of the transistor VT1 resistor with a resistance of 300 ... 510 Ohm.
Sometimes it is useful to include a constant resistor with a resistance of 2,2 ... 10 kOhm between the collector and emitter of this transistor. In this case, the stabilizer reliably returns to the operating mode, and the stabilization coefficient decreases slightly. Zener diode VD1 with direct connection pn junction reduces the temperature drift of the output voltage of the device. Resistor R4 increases the reliability of the stabilizer at elevated temperatures. The VT1 transistor is mounted on a radiator in the form of a duralumin plate measuring 100x100x5 mm. It should have as little initial current as possible (it is desirable to use a silicon transistor). The input voltage is supplied to the stabilizer from the rectifier in a single-phase bridge circuit, made on D304 diodes.
In conclusion, it should be noted that when the stabilizer output is overloaded, the full input voltage will be applied to the emitter-collector section of the regulating transistors.
Therefore, to improve the reliability of this circuit, the maximum allowable voltage of the transistors used must be at least 1,5 times higher than the effective value of the voltage of the secondary winding of the power transformer used in the rectifier.
Author: Semyan A.P.
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