Voltage stabilizer, 11-20/9 volts 0,5 amps. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Surge Protectors
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This voltage stabilizer is very simple, but has very high parameters and is therefore suitable for powering a wide variety of radio equipment (Fig. 1.18).
With very good efficiency - the current it consumes in the absence of a load does not exceed 25 μA - it provides a load current of up to 0,5 A. The stabilization coefficient is about 500, the output resistance is 0,07 Ohm.
A distinctive feature of the stabilizer is the use of a powerful field-effect transistor in the control element and the operation of the control element in the microcurrent mode. In order to increase efficiency, the source of exemplary voltage is the reverse-biased emitter junction of the transistor VT3. The high input resistance of the field-effect transistor and the high resistance of the resistor R1 cause a large gain of the control element, and hence a high stabilization factor. The stabilizer is not afraid of closing the output circuit, since in this case the current through the transistor VT2, and hence the load current, will be limited by the initial drain current of the field-effect transistor.
Another important advantage is that with an increase in the temperature of the body of the regulating transistor, the slope of the characteristic and the initial drain current decrease, due to which, in the overload mode, overheating of the regulating transistor with an avalanche-like uncontrolled increase in its current, which is usual for a bipolar transistor, does not occur. The choice of field effect transistor VT2 determines the maximum possible load current.
The stabilizer starts automatically. At the moment of switching on, the transistor VT1 will be closed, so the input voltage will be supplied to the gate of the field-effect transistor, which ensures a reliable start of the stabilizer. The permissible drain-source voltage of the field effect transistor is 20 V, and for its normal operation a voltage of 2 ... 3 V is required, therefore the maximum output voltage of this stabilizer can be 15 ... 17 V. The minimum stabilization voltage is determined by the cutoff voltage of the field effect transistor and is equal to approximately 5 ... 7 V. To increase the output current, you can use the parallel connection of two or three field-effect transistors. In this case, transistors should be selected with close parameters in order to avoid uneven distribution of dissipated power on them, or a resistor with a resistance of 1 ... 2 Ohm should be included in the source circuit of each of them. To improve the quality of the output voltage and the stability of the stabilizer when working with a load of various nature, capacitors C1, C2 are provided.
In the stabilizer, instead of the KP903A transistor, you can use KP903B, KP903V. The regulating transistor should be installed on the heat sink. The KT3102B transistor can be replaced with KT3102V ... KT3102E, KT342B, KT342V; instead of KT315A, any of KT315B ... KT315Zh will do. With a load current of not more than 50 mA, the KP303G transistor can be used in the control element. When establishing, a VT3 transistor is selected with the required stabilization voltage. It can be replaced with a conventional zener diode and resistor R2 can be selected from the condition of providing the rated current through the zener diode. The efficiency of the stabilizer will, of course, worsen.
Author: A.Mironov
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