Voltage stabilizer with overload protection, 10 amps. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Surge Protectors
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The stabilizer provides a maximum load current of up to 10 A at a ripple voltage of less than 1 mV, an output impedance of 0,01 Ohm. The stabilizer (Fig. 3.25) is assembled according to the bridge circuit in the output circuit, formed by resistors R4, R5, zener diodes VD1, VD2 and the HL1 LED. The emitter junction of the transistor VT4, which controls the regulating composite transistor VT1 ... VT3, 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 gain of the stabilizer circuit. Since the voltage at the base of the control transistor VT4 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 the transistor VT3 cannot exceed the value of the current flowing through the 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 R3. 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 R3 is closed through the low resistance of the open zener diode VD2. The minimum drop on transistors VT1, VT2 is equal to the collector-emitter saturation voltage of this transistor (0,1 ... 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 VD1 and VD2 minus the voltage drop at the emitter junction of the transistor VT4. Temperature changes in the voltage drop across the HL1 LED and the Zener diode VD1 are compensated with the temperature change in the voltage drop across the emitter junction of the transistor VT4.
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 effective heat dissipation area.
Author: Semyan A.P.
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