ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Voltage stabilizer with overload protection, 13,8 volts 10 amps. Encyclopedia of radio electronics and electrical engineering Encyclopedia of radio electronics and electrical engineering / Surge Protectors The stabilizer provides a maximum load current of up to 10 amperes at a ripple voltage of less than 1 mV, an output impedance of 0,01 ohms. The stabilizer is assembled according to the bridge circuit in the output circuit, formed by resistors R4, R5, zener diodes D1, D2 and LED D3. The emitter junction of the transistor Q3, which controls the regulating compound transistor Q2, Q1, is included in the diagonal of the bridge. The composite transistor is connected according to the scheme with a common emitter. The output impedance of the terminal stage, which is higher compared to the emitter follower, is compensated in this circuit by the fact that the output stage has a high voltage gain, the latter significantly increasing the loop gain of the stabilizer circuit. Since the voltage at the base of the control transistor Q3 with respect to the positive wire is stabilized, changes in the output voltage are transmitted to the emitter junction of this transistor without attenuation by the divider. The maximum load current is set by resistor R4. The base current of transistor Q2 cannot exceed the value of the current flowing through resistor R4. Therefore, by selecting this resistor, you can set the required protection current. The stabilizer is also protected from short circuits in the load circuit. The short circuit current depends on the value of the starting current flowing through the resistor R2. This resistor is selected at the minimum load resistance for a stable start of the stabilizer. Such a system provides a reliable start of the stabilizer, and practically does not worsen the parameters, since in the operating mode the current through the resistor R2 closes through the low resistance of the open zener diode D2. The output resistance of the stabilizer is determined by the differential resistance of the zener diode D1 divided by the product of the gains of transistors Q1, Q2, Q3. The minimum drop across transistor Q1 is equal to the collector-emitter saturation voltage of this transistor (0,1 E 0,5 V depending on the load current). The voltage at the output of the stabilizer is determined by the total stabilization voltage of the zener diodes D1 and D2 minus the voltage drop at the emitter junction of the transistor Q3. Temperature changes in the voltage drop across LED D3 and Zener diode D1 compensate for temperature changes in the voltage drop across the emitter junction of transistor Q3. The TKN of the stabilizer as a whole is at the level of -0,1 mv/degree. To reduce the dependence of the protection threshold and short circuit current on temperature, the radiator of control transistors is selected with a margin of at least 1000 cm2 in terms of the effective heat dissipation area. Author: Valery Rezvyakov, UA3NBW See other articles Section Surge Protectors. Read and write useful comments on this article. Latest news of science and technology, new electronics: Artificial leather for touch emulation
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