Smooth switching on of the load of the integrated voltage stabilizer
Encyclopedia of radio electronics and electrical engineering / Surge Protectors
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Integrated adjustable voltage stabilizers of the KR142, KR1157, KR1168 series and similar foreign ones are widely used in amateur radio practice. Using the possibility of changing the value of the stabilized voltage with the help of hinged elements, it is possible to ensure a smooth exit of such stabilizers to the operating mode. This turns out to be very useful for reducing overloads of the rectifier and the stabilizer itself, or reducing various kinds of noise (for example, clicks in the speakers) at the moment the equipment is turned on.
A typical stabilizer circuit is shown in the figure.
The capacitance of capacitors C1 and C2 corresponds to the standard inclusion of the microcircuit. The output voltage determines the resistive divider R1R2. Elements of an additional unit that provides smooth switching are drawn with dashed lines.
When the stabilizer is turned on, voltage appears at the output of the microcircuit. Since the capacitor C3 begins to charge, the transistor VT1 will be open and at the initial moment the output voltage will not exceed 2,4 V. As the capacitor charges, the transistor closes and the voltage on its collector increases. Consequently, the output voltage also increases. When the capacitor is charged, the output voltage will reach the set value. The transistor will completely close and will not affect the operation of the stabilizer.
After turning off the device, the capacitor C3 quickly discharges through the diodes VD1 and VD2, the resistive divider R1R2 and the load.
The output voltage rise time depends primarily on the capacitance of the capacitor C3 and the resistance of the resistor R4 and, to a lesser extent, on the current transfer coefficient of the transistor.
For comparison, the rise time of the output voltage of the stabilizer was measured. With an output voltage of 15 V, a load resistance of 15 ohms, and a capacitance of the rectifier and load filter capacitors of 4700 μF each, without the specified refinement, this time was approximately 30 ms. And after the introduction of an additional node - about 1,5 ... 2 s.
The allowable voltages of all capacitors and the transistor must correspond to the operating voltages in a particular voltage regulator.
In a similar way, it is possible to modify stabilizers based on other microcircuits, only for stabilizers included in the negative circuit, it is necessary to use a transistor of a different structure and change the polarity of the capacitors. In addition, such additional nodes can be introduced into the power supply with several output voltages in order to provide a certain sequence of supply voltages.
Author: I. Nechaev, Kursk
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