Voltage converter for powering the varicap. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Voltage converters, rectifiers, inverters
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The use of varicaps in low-voltage transistor equipment is often limited due to the need to use sources of increased stabilized voltage (about 40 V) to power them. A simple voltage stabilizer for a varicap (see figure) provides an output regulated stabilized voltage of 0..39 V. The device consumes a current of about 60 mA, the maximum load current is 12 mA.
On the logic elements D1.1-D1.3 of the D1 chip, a rectangular pulse generator with a repetition rate of about 90 kHz is assembled. A buffer cascade is made on element D1.4. Transistor V1 operates in key mode on an inductive load L1. At the moment the key is closed, self-induction EMF pulses appear on the collector of the transistor, which are rectified by the V2 diode and smoothed out by the capacitor C2.
The DC voltage is stabilized by the parametric stabilizer R2V3V4V5 and is supplied to the varicap through a voltage divider on a variable resistor R3. Capacitor C4 protects the varicap from the penetration of high frequency voltage into its power supply circuit.
Coil L1 is wound on two K10X6X3 rings of 600NN ferrite folded together. The winding consists of 200 turns of PEV-2 0,1 wire. The microcircuit is powered directly from a 12 V voltage source through a 270 Ohm limiting resistor (not shown in the diagram).
The converter must be carefully shielded and decoupled from the supply circuits, as it is a source of interference in a wide frequency range (up to several megahertz).
Editorial note. To protect the transistor and the microcircuit from possible overloads, a current-limiting resistor with a resistance of about 1 kOhm and a power of 0,25 W should be included in the base circuit of the transistor.
Author: S. Rotar, Chisinau; Publication: N. Bolshakov, rf.atnn.ru
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